Ch15 Nondestructive Inspections, Welding, And Heat Treatment

8/22/2019 Ch15 Nondestructive Inspections, Welding, And Heat Treatment

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CHAPTER 15

NONDESTRUCTIVE INSPECTIONS, WELDING,AND HEAT TREATMENT

Chapter Objective: Upon compl et i on of th is chapter, you wi l l have a basic

kn owledge of nondestru ctive inspection (NDI ) methods, wel di ng pr ocedu res andequi pment , and t he different form s of heat tr eatm ent.

In this chapter, we will discuss the basic principles

and procedures of nondestructive inspections, welding,

and the heat treat ment of meta ls . These three areas

require special training, and in the case of non-

destructive inspections and welding, they require

special certif ication prior to performing these two

functions. While not all AMs are required to become

NDI operators, aeronautical equipment welders, or have

the need to perform heat treatment of metal, there is theneed to be familiar with these procedures and how they

apply t o the AM ra te. The informat ion in these area s is

being presented in a broad nature. For a more detailed

discussion of these procedures, refer to the applicable

technical manuals.

NONDESTRUCTIVE INSPECTION

PROGRAM

Learning Objective: Eval uate the background

and personnel trai ni ng requir ed for th e NDI

program and the var ious ND I personnel

qual i f icat ions.

In t he han ds of a tra ined and experienced technician,

nondestruct ive inspection (NDI) methods al low

detection of f laws or defects in ma teria ls with a high

degree of accuracy and reliabil i ty. I t is important that

you become fully knowledgea ble of th e ca pabilit ies of

each NDI method, but i t is equally important that you

recognize the limitations of these methods. The non-

destructive inspection methods covered in this chapter

serve as tools of prevention, which allow defects to bedetected before they develop into serious failures.

During the inspection of aircraft, i t is essential that

faults are found and corrected before they reach

catastrophic proportions. In applicable areas, NDI can

provide 100-percent sampling with no affect upon the

use of the part or system being inspected. The effective

use of NDI will result in increased operational safety,

and in many instances, dramatically reduce maintenance

man-hour expenditures.

NDI is the practice of evaluating a part or sample of

material without impairing its future usefulness. The

methods used in naval aviation include, but are not

limited to, visual or optical, liquid penetrant, magnetic

part icle, eddy current, ultra sonic, a nd r adiographic. The

success in their use depends heavily upon intelligentapplication and discriminating interpretation of results.

NDi is performed only by qualified and currently

certif ied NDI personnel, and in a ccordance with NA

01-1A-16, Nondestructive I nspecti on M ethodsma nua l .

This is a general ma nua l covering the th eory a nd general

applications of the various methods of NDI.

The Aircraft Nondestructive Inspection School,

located at NATTC Memphis, Tennessee, provides NDI

technician training for both military and civil service

personnel. Ca reer designat ed (gra de E-4 and above)

Navy a viat ion str uctura l mecha nics (AMSs), Marine

Corps structural mechanics, and equivalent civil service

personnel are eligible for the course. In addition, NDI

operator training in liquid penetrant, magnetic particle,

and eddy current methods; refresher training; and

recertification of NDI technicians are provided by the

Na va l Avia tion D epot (NADEP ) a nd ACC /TYCOM

designated NDI specialists. Information pertaining to

curriculum, quota requests, obligated service require-

ments, and, where applicable, convening dates is

published in the NAVEDTRA 10500, Catalog of N avyTr aini ng Courses(CANTRAC). Requests for NADEP

tra ining an d aut horization for recertif ication of NDI

technicians wh o have been inactive in NDI for more

than 1 year must be made, via the chain of command, to

th e cogniza nt ACC /TYCOM. If t he request is a pproved,

th e ACC /TYCOM w ill advise w hich NADE P is to be

used.

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NDI PERSONNEL

Before candidates arc selected for NDI technician

or operator training, and annually thereafter , they are

required to have an eye examinat ion. Mil i tary and

civilian NDI personnel are identified as NDI specialists,

technicians, or as operators.

NDI Specialists

NDI specialists are authorized by the ACC to

provide tra ining a nd certificat ion/recertification of NDI

techn icians /opera tors. They a lso provide techn ical ND I

services.

NDI Technicians

N D I t e c h n i c i a n s a r e p e r s o n n e l w h o h a v e

successfully completed the NDI course (C-603-3191) at

Aircraft Nondestructive Inspection School at NATTC

Memphis, Tennessee. NDI technicians a re a ssigned

NE C 7225/MOS 6044, and th ey a re qu a lified an dcertified to perform liquid penetrant, magnetic particle,

eddy current, ultrasonic, and radiographic methods of

NDI. These personnel are normally assigned to IMAs.

NDI technicians with 3 or more years of experience and

wh o are currently certif ied a nd engaged in NDI on a

regular basis may be authorized by ACCs to train and

certify NDI operators for specific NDI applications. The

ACC may also waive the 3-year experience requirement

provided requests for this authorization are addressed to

th e ACC /TYCOM via t he appropria te w ing.

This request must include the technicians currentqualification, experience history, and the specific

techn ical directive/techn ical publicat ion-directed ND I

a pplica tions for wh ich operat or certif ication is t o be

provided. If approved, a copy of the ACC authorization

will be at ta ched to t he technicians NDI certif ica tion

record and ma inta ined with his/her individual NDI

record. Such a uthorizat ions rema in in effect only a s long

as the currency of certification and NDI experience is

maintained. Currently active NDI technicians require

reccertification every 3 years.

Early recertification is authorized and encouraged

to prevent expirat ion of certif ica tion during tours of

deployed duty. Current certification of NDI technicians

who are regularly engaged in all methods of NDI may

be extended by ACCs for up to 1 year if circumstances

warrant. NEC 7225 personnel who have been inactive

in ND I for 1 year or more require recertificat ion before

resuming active NDI technician status. Recertification

is provided by designated NADEPs or by ACC

designated and qualified NAESU Navy federal civilian

or military technical specialists.

NDI Operators

NDI operators are military personnel E-4 and

above, or civilian equivalent, who have successfully

completed training and are certified to perform specific

NDI tasks using one or more of the following methods:

l iquid penetra nt, eddy current, or ma gnetic par ticle. NDI

operat ors may be assigned an d used in IMAs to perform

specific publication-directed NDI tasks only when the

NDI workloa d exceeds the capa city of a ssigned NDI

technicians. E a ch ca se of NDI operat or use at I-level

maintenance must be authorized by the cognizant ACC.

Requests for such authorizations are made to the ACC

via the appropriate wing.

Basic NDI operator training is provided by

NADEPs and NDI specialists. When training is not

ava i lable, ACCs m ay aut horize the tra ining of NDI

operat ors by ND I technicians in specific liquid penetran tk it a p pl ica t i on s . N D I o p er a t or c er t i f i ca t i on /

recertification is provided by NDI specialists and NDI

technicians. Rccertification of NDI operators is required

a nnua lly. NDI operat ors at I -level activities must be

closely monitored by qualified NDI technicians and by

cogniza nt QARs/CD QARs. ND I operat ors ar e not

authorized to operate radiographic or ultrasonic

equipment. They may, however, be used to assist NDI

technicians operating that equipment.

NDI technicians and operators must use the NDI

method or methods for which they are certified at leasttwo times each month, as evidenced by entries on their

w ork r ecord (OP NAV 4790/140). This ca n be d one

either thr ough normal w orkload or practice applicat ions.

In those cases where the prescribed proficiency is not

maintained for 1 or more months, technicians or

operat ors can r egain proficiency by ma king pra ctice

applications under the supervision of a certified NDI

technician, who will provide recertification upon

determination of proficiency. Failure to maintain

proficiency for 6 months for NDI operators and 12

months for NDI technicians will require updated

training for recertification. NDI technicians who fail toma inta in proficiency for 3 years or more will require

complete retraining. In all cases exceeding 6 months for

operators and 12 months for technicians, authorization

for updated training or complete retraining is requested

from the cognizant ACC.

Activities th a t a re au th orized to certify/recertify

NDI technicians a nd operators must administer an

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Figure 15-1.-NDI Certification Record (OPNAV 4790/139).

appropriate written test on the NDI methods involved.

The NA 01-1A-16 manual is the source for test

questions. Personnel being certified or recertified will

also be required to demonstrate the ability to perform

NDI inspections as appropriate. The objective is to

provide sufficient testing of the candidate to ensure the

person is competent to conduct NDIs.

The effectiveness of the NDI program can be

e n h a n c e d t h r o u g h d e v e l o p m e n t o f n e w N D I

techniques/applications by efficient an d in ventive ND I

personnel. Useful new techniques, so developed, will be

submitted to the appropriate CFA for approvaI and

distribution to other f leet a ctivities. An informa tion

copy is submitted to the ACC NDI specialist.

NDI CERTIFICATION RECORD

This form (fig.15-1) prov ides a record o f

certification. The original copy goes to the individual,

with one copy ea ch to qua lity a ssura nce/an alysis

(QA/A) a nd t he d ivision officer. All certified ND I

personnel must initiate and maintain individual records

of NDI performed.

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NDI TECHNICIAN/OPERATOR

WORK RECORD

This form (fig. 15-2) is used to record a nd verify

NDI performed. Entries will be verif ied by the

individuals work center supervisor, or, if the work

center super visor perform s th e NDI , by QA/A.

Personnel doing repetitive NDI, such as eddy current on

aircraft wheels, may record weekly entries, as indicated

on the sample entry in figu re 15-2. Upon tra nsfer, NDI

work records a re carr ied by t he individua l to his/her next

command.

NDI PROGRAM RESPONSIBIL ITIE S

NDI is of vital concern at all levels of mainte-

nance, and all operational and support commandersshould direct their efforts toward its proper use. NDI

is used in the maintenance of Navy aircraf t and

aircraft systems wherever contributions to safety,

reliability, QA, performance, or economy can be

realized. The following text discusses the various

commands and their responsibilities pertaining to the

NDI program.

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Figure 15-2.-NDI Technician/Operator Work Record (OPNAV 4790/140).


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Naval Air Systems Command

The Naval Air Systems Command (NAVAIR) has

cognizance over the NDI program. They are responsible

for managing a program of research, development,

tra ining, and applicat ion of NDI techniques and

equipment. NAVAIRINST 13070.1A assigns the

responsibility for nondestructive testing and inspection

within NAVAIR. NAVAIR is responsible for the

following:

1. Coordinate and issue information on NDI within

naval aviation, other services, and industry, as

appropriate

2. Ensure appropriate application of NDI at all

levels of maintenance

3. Procure NDI equipment to support an effective

program

4. Procure NDI technical publications, and ensure

the updating of such publications as newer techniquesand applications are developed

5. Establish the necessary standards and specif i-

cations for NDI

6. Monitor, evaluate, and standardize the NADEPs

NDI program

7. Provide NDI training for the NADEPs, as

requested

8. Assign an NDI program coordinator to be

responsible for managing implementation of the

application and training elements

Aircraft Controlling Custodians

Aircraf t control l ing custodians (ACCs) are

responsible for the following:

1. Monitoring the NDI program in activities under

their cognizance

2. Advising on availability and location of NDI

t raining

3. Maintaining liaison with NAVAIR, NADOC,

N a v a l Av i a t i o n M a i n t e n a n c e O f f i c e ( N AM O ) ,

NADEP s, and f leet a ctivities on NDI mat ters

4. Ensuring that NDI laboratories, equipment, and

personnel are audited as required

5. Designating NDI specialists as required

6. Designating an NDI program manager

Intermediate Maintenance Activities

Intermediate maintenance activities (IMAs) are

responsible for the following:

1 . Ensur ing compl iance wi th qua l i f i ca t ion

requirements and safety precautions

2. En suring industr ia l ra d iat ion safety require-

ments are strictly enforced in accordance with the

Radi ological Af fair s Support Program (RASP)ma nua l ,NAVSEA S0420-AA-RAD-010.

3. Using available NDI equipment fully, and

developing new procedures and applications, as far as

practical, to provide labor, material, and cost savings.

4. Maint aining a n adequ at e number of certif ied

a nd proficient ND I technicia n a t a ll times to provide

NDI services to supported organizations and transient

aircraf t .

5. Ensuring the material condition of NDI

equipment and the laboratory is continuously ready for

use (RFU). This includes availability of consumable

i tems.

6. Establ ishing and maintaining a continuing

training program within the NDI work center to allow

NDI technicians to remain up to date with newly

developed NDI techniques and applications.

7. Establishing and maintaining l iaison with the

cognizant ACC NDI spec ia l i s t , and reques t ing

assistance via the chain of command on all NDI

problems.

8. Providing and maintaining industrial X-rayfilm processing facilities, both ashore and afloat.

9. Providing scheduled and unscheduled NDI

support to O-level activities, as required.

10. Maint a ining liaison with ship/sta tion radia tion

officer.

Quality Assurance/Analysis

Quality assura nce/an alysis

for the following:

(QA/A) is r esp ons ibl e

1. Monitoring compliance with NDI personnel

qua lifica tions, cert ifica tion/recertificat ion requ ire-

ments, safety precautions, and instructions.

2. Monitoring the organizations NDI training

program t o ensure it is current a nd comprehensive.

Special empha sis should be pla ced on th ose area s of

NDI tha t a re accomplished by personnel other t han those

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a s s i g n e d N a v y e n l i s t e d c l a s s i f i c a t i o n ( N E C )

7225/milit a ry occupa tiona l specialt y (MOS) 6044.

Organizational Maintenance Activities

O-levels responsibilities areas follows:

1. Request NDI I-level support as required.

2. Obtain IMA NDI services in all situations where

NDI results are suspicious.

3 . H a v e a n N DI t e c h n i c i a n v e r i f y d e f e c t s

discovered by an NDI operator, whenever possible.

4. Inform th e IMA, in adva nce, of scheduled NDI

requirements. Include these requirements in the monthly

maintenance plan.

5. O-level NDI technicians maybe assigned to the

supporting IMA, as necessary, to maintain their

proficiency and to augment IMAs NDI capabilities.

NDI INSPECTION METHODS

The various NDI methods serve as tools of

prevention that allow defects to be detected before they

develop into serious or hazardous failures. With the NDI

methods, a trained and experienced technician can

detect flaws or defects with a high degree of accuracy

a nd reliability. I t is importa nt t ha t you become fully

knowledgeable of the capabilities of each method. It is

equally importa nt tha t you recognize the l imita tions of

the methods. Some of the defects found by NDI include

corrosion, leaks, pitt ing, hea t/str ess cracks, a nd

discontinuity of metals. The following paragraphs will

give a brief synopsis of the various NDI inspections. For

further information on NDI procedures, you should

consult the N ondestru ctive I nspections M anu al,

NA-01-1A-16, or t he a ppropriat e inspection ma nua l

perta ining to the type of a ircraf t or part tha t is to be

inspected by an NDI method.

Magnetic Particle Inspection

Magnetic particle inspection is a rapid, non-

destructive means of detecting discontinuities in parts

made of magnetic materials. If the part is made from an

alloy that contains a high percentage of iron and can be

magnetized, i t is in a class of metals called ferro-

magnetic, and it can be inspected by this method. If the

part is made of mat erial tha t is nonmagnetic, i t cannot

be inspected by this method. The ma gnetic part icle

inspection method will detect surface discontinuities,

including those that are too fine to be seen with the naked

eye, those that lie slightly below the surface, and, when

special equipment is used, the more deeply seated

discontinuities.

The inspection process consists of inducing a

magnetic f ield into a part and applying magnetic

part icles, in liquid suspension or dry powder, t o the

surface being inspected. When the magnetic field is

interrupted by a discontinuity, some of the field is forced

out into the air above the discontinuity, forming a

leaka ge field. The leaka ge field will be str onger an d

more concentrated the closer the discontinuity is to thesurface. The presence of a discontinuity is detected by

the ferroma gnetic part icles applied over t he surfa ce.

Some of these part icles will be gathered a nd held by t he

leakage field. This magnetically held collection of

particles forms an outline of the discontinuity and

indicates its location, size, and shape.

Electric current is used to create or induce magnetic

fields in magnetic materials. The magnetic lines of force

are always aligned at right angles (90) to the direction

of the current flow. The direction of the magnetic field

can be altered, and it is controlled by the direction of the

magnetizing current. The arrangement of the currentpaths is used to induce the magnetic lines of force so that

they intercept and a re as near a s possible at right angles

to the discontinuity.

The magnetic field must be in a favorable direction

to produce indications. When the flux lines are oriented

in a direction parallel to a discontinuity, the indication

will be weak or lacking. The best results are obtained

when t he f lux l ines are in a direction a t r ight angles to

the discontinuity. I f a discontinuity is to produce a

leakage f ie ld and a readab le magnet ic par t i c le

indication, the discontinuity must intercept the flux lines

of force at some angle. When an electrical magnetizing

current is used, the best indications are produced when

the pat h of the ma gnetizing current is f lowing pa rallel

to the discontinuity, because t he ma gnetic flux lines a re

always at an angle of 90 to the flow of the magnetizing

current. The two types of magnetizing methods used are

circular and longitudinal.

CIRCULAR MAGNETIZATION. -Circular

magnetization is used for the detection of radial

discontinuities around edges of holes or openings in

parts. It is also used for the detection of longitudinal

discontinuities, which lie in the same direction as the

current f low either in a part or in a part that a central

conductor passes through.

Circular magnetization derives i ts name from the

fact that a circular magnetic f ield always surrounds a

conductor, such as a wire or a bar carrying an electric

current (fig. 15-3). The direction of the magnetic lines

of force (magnetic field) is always at right angles to the

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Figure 15-3.-Magnetic field surrounding an electrical conductor.

Figure 15-4.-Magnetic field in part used as a conductor.

Figure 15-5.-Creating a circular magnetic field in a part.

direction of the ma gnetizing current. An easy w ay to

remember the direction of magnetic lines of force

around a conductor is to imagine tha t you a re grasping

the conductor w ith your han d so tha t t he extended thumb

points parallel to the electric current flow. The fingers

then point in the direction of the magnetic lines of force.

Conversely, if the fingers point in th e direction of current

flow, the extended thumb points in the direction of the

magnetic lines of force.

Since a magnetic part is in effect a large conductor,

electric current passing through this part creates a

magnetic f ield in the same manner as wi th a small

conductor (fig. 15-4). The magnetic lines of force are at

right angles to the direction of the current as before. This

type of magnetization is called circular magnetization

because the lines of force, which represent the direction

of the magnetic field, are circular within the part.

To creat e or induce a circular f ield in a part wit hstat ionar y magnetic part icle inspection equipment, the

part is clamped between the contact plates and current

is passed th rough the part , as indicat ed in figure 15-5.

This sets up a circular magnetic field in the part that

creates poles on either side of any crack or discontinuity

tha t runs para llel to th e length of the part . The poles will

at tra ct magnetic particles , forming a n indicat ion of the

discontinuity.

Figure 15-6.-Using a central conductor to circularly magnetize acylinder.

Figure l5-7.-Using a central conductor to circularly magnetizeringlike parts.

Figure 15-8.-Magnetic field in a part placed in a coil.

On parts that are hollow or tubelike, the inside

surfaces are as important to inspect as the outside. Whensuch parts are circularly magnetized by passing the

magnetizing current through the pa rt, t he magnetic field

on the inside surface is negligible. Since there is a

magnetic field surrounding the conductor of an electric

current, it is possible to induce a satisfactory magnetic

f ield by placing the part on a copper bar or other

conductor. This situation is illustrated in figures 15-6

a nd 15-7. Pa ssing current th rough the ba r induces a

magnetic field on both the inside and outside surfaces.

LONGITUDINAL MAGNETIZATION. -Lon-gitudinal magnetization is used for the detection of

circumferential discontinuities, which lie in a direction

transverse to or at approximately right angles to a parts

a xis. Electric current is used to creat e a longitudina l

magnetic field in a piece of magnetic material. When a

part of magnetic material is placed inside a coil , as

shown in figure 15-8, the magnetic lines of force created

by the magnetizing current concentrate themselves in

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Figure 15-9.-Coil creates a longitudinal field to show crack ina part.

the part and induce a longitudinal magnetic f ield.

Inspection of a cylindrical part with longitudinal

magnetism is shown in figure 15-9. If there is a

transverse discontinuity in the part, such as that in the

illustration, small magnetic poles are formed on either

side of the crack. These poles will attract magnetic

part icles, forming a n indication of the discontinuit y.

Compare figure 15-9 with figure 15-5, and note tha t in

both cases a magnetic field has been induced in the part

tha t is a t right a ngles to the defect. This is the most

desirable condition for a reliable inspection.

ALTERNATING CURRENT. -The us e of alt er-

na ting current (ac) in ma gnetic part icle inspection is

recommended only for the detect ion of surface

discontinui t ies , which comprise the majori ty of

service-induced defects. F a tigu e an d st ress corrosion

cracks are examples of cracks usually open to the

surfa ce. Alterna ting current, w hich must be single pha se

when used directly for magnetizing purposes, is taken

from commercial power lines or portable power sources,

an d is usua lly 50 or 60 hertz.

DIRECT CURRENT. -Dir ect current (dc) ma g-

netizes the entire cross section more or less uniformly

in the case of longitudinal magnetization. Magnetic

fields produced by direct current penetrate deeper into

apart than fields produced by alternating current, which

makes it possible to detect subsurface discontinuities.

Generally, direct current is used with wet magnetic

particle methods. In the presence of dc fields, dry

powder particles behave as though they were immobile,

tending to remain wherever they happen to land on the

sur face of a par t . This is in contra st to w hat happens with

dry powder particles in the presence of ac fields. In these

fields, the par ticles have mobility on a surface due to the

pulsating character of the fields. Particle mobility aids

considerably the formation of particle accumulations

(indications) at discontinuities.

PARTICLES AND METHODS OF APPLI-

CATION. -The particles used in magnetic particle

testing are made of magnetic materials, usually

combinations of iron and iron oxides, that have a high

permeabili ty and low retentivity. Particles that have

high permeability are easily magnetized by and attracted

to the low-level leakage fields at discontinuities. Low

retentivity is r equired to prevent the pa rticles from being

permanently magnetized. Strongly retentive particles

tend to cling together and to any magnetic surface,resulting in r educed part icle mobility an d increased

background accumulation.

Particles are very small and are various sizes. Each

magnetic particle formulation always contains a range

of sizes and shapes to produce optimum results for the

intended use. The sma llest part icles are m ore easily

attracted to and held by the low-level leakage fields at

very fine discontinuitics; larger part icles can more easily

bridge across coarse discontinuities, where the leakage

f ields are usually stronger. Elongated particles are

included, particularly in the case of dry powders,because these rod-shaped part ic les easi ly a l ign

themselves w ith leakage fields not sha rply defined, such

a s th ose that occur over subsurfa ce discontinuit ies.

Global-shaped particles are included to aid in the

mobility and uniform dispersion of particles on a

surface.

Magnetic particles may be applied as a dry powder,

or wet, by using either water or a high flash point

petroleum distil late as a liquid vehicle carrier. Dry

powder is a vaila ble in various colors, so the u ser can

select the color that contrasts best with the color of the

surface upon which it is used. Colors for use with

ordinary visible light are red, grey, black, or yellow.

Red- and black-colored particles are available for use in

wet baths with ordinary light, and yellow-green

fluorescent particles for use with a black light.

Fluorescent pa rticles a re widely used in w et ba ths, since

the bright f luorescent indicat ions produced at

discontinuities are readily seen against the dark

backgrounds that exist in black light inspection areas.

Radiographic Inspection

Ra diogra phic is a nondestructive inspection method

tha t u ses a source of X-ra ys t o detect d iscontinuities in

materials and assembly components. Radiation is

projected through the item to be tested, and the results

are captured on film. Radiography may be used on

metallic, nonmetallic, and combination metallic/

nonmetallic materials and assemblies without access to

the interior. However, defects must be correctly aligned

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Figure 15-10.-Diagram of radiographic exposure.

an d oriented with respect t o penetra t ing ra ys to be

reliably detected. Radiography is one of the most

expensive and least sensitive methods for crack

detection. It should only be used to detect fla ws tha t a re

not accessible or favorabl y oriented for use by other test

methods.

The extent of recorded informationupon the following three prime factors:

1. The composition of the material.

is dependent

2. The product of the density and the thickness of

the material .

3. The energy of the X-rays, which is incident upon

the material. Material discontinuities cause an apparent

change in these characteristics, and thus make

themselves detectable.

Figure 15-10 is a diagram of radiographic exposure

showing the elements of the system. Radiation passes

through the object and produces an invisible or latent

image in the film. When processed, the film becomes a

radiograph or shadow picture of the object. Since more

radiation passes through the object where the section is

thin or where there is a space or void, the corresponding

a rea on t he film is da rker. The ra diogra ph is read or

interpreted by comparing it w ith t he known nat ure of the

object.

RADIOGRAPHIC INTERPRETATION. -The

usefulness of the information obtained from the

radiographic process depends upon the intelligent

interpretation of the derived image. To successfully

interpret the radiograph, the radiographic interpreter

must ha ve a w orking knowledge of the component or

materia l and be able to relate the images to theconditions likely to occur. Specifications are used to

spell out the discontinuities that maybe considered

detrimental t o the function of the part an d the a ccepta ble

magnitudes of the discontinuities. It is the duty of the

film interpreter to recognize the various discontinuities,

their magnitudes, and be capable of relating them to the

particular specification required. The responsibility and

capability of the radiographic interpreter cannot be

overemphas ized . Of ten , many human l ives and

investments of millions of dollars are depending on the

judgement of the radiographic interpreter.

RADIATION HAZARD. -Radiation from X-ray

units is destr uctive to living tissue. I t is un iversa lly

recognized that in the use of such equipment, adequate

protection must be provided to personnel. Personnel

must keep outside the primary X-ray beam at all times.

Radiat ion produces chan ges in a l l matt er tha t i t

passes t hrough. This is a lso true of living tissue. When

the radiation strikes the molecules of the body, the effect

may be no more tha n t o dislodge a few electrons; but a n

excess of these changes could cause irreparable harm.When a complex organism is exposed to radiation, the

degree of damage, if any, depends on which of its body

cells have been changed. The more vital parts are in the

center of the body; therefore, the more penetrating

radia tion is likely to be the more harmful in these area s.

The skin usually absorbs most of the radiation;

therefore, it reacts earliest to radiation.

If t he w hole body is exposed t o a very la rge dose of

radia tion, it could result in death. I n general , the type

and severity of the pathological effects of radiation

depend on the amount of radiation received at one time

and the percentage of the total body exposed. The

smaller doses of radiation may cause blood and

intestina l disorders in a short period of time. The more

delayed effects are leukemia an d cancer. Skin dam age

an d loss of hair a re a lso possible results of exposure to

radiat ion.

15-9


10/46

Figure 15-11.-Coupting of search unit to test part for transmissionof ultrasonic energy.

Ultrasonic Inspection

The term ultrasonicmeans vibrations or sound

wa ves whose f requencies ar e great er tha n th ose that

affect the human ear (greater than about 20,000 cycles

per second).

Ultrasonic inspection is a method of inspection that

uses these sound waves. The ultrasonic vibrations are

generated by applying high-frequency electrical pulses

to a transducer element contained within a search unit.

The transducer element transforms the electrical energy

into ultrasonic energy. The transducer element can also

receive ultra sonic energy an d t ran sform it into electrical

energy. Ultrasonic energy is transmitted between the

search unit a nd th e test part through a coupling medium,

such as oil, as shown in figu re 15-11, for the purpose of

excluding the air interface between the transducer and

the test part. The ultrasonic vibrations are transmitted

into and t hrough the part. When the beam st rikes the fa r

surface of the part or strikes the boundary of a defect,

the beam reflects back towards t he tra nsducer, tra velsthrough the couplant, and enters the transducer, where

it is converted back into electrical energy. Then the

information is displayed on a cathode-ray tube (CRT,)

screen.

Ult ra sonic inspections can be separa ted into tw o

basic categories-contact inspection and immersion

inspection. In th e conta ct method, the sear ch unit is

placed directly on the test part surface by using a thin

film of couplant, such as oil, to transmit sound into the

test part . In th e immersion method, the test part is

immersed in a f luid, usua lly wa ter, a nd the sound istransmit ted through the water to the test part

(fig. 15- 12). The immersion-type method is used to

inspect materials while they are immersed in a suitable

liquid, such as water or oil. This method proves more

satisfactory than contact testing for irregular-shaped

surfa ces. Imm ersion inspection a lso permits use of a

wider range of testing frequencies. The three general

Figure 15-12.-Immersion method.

methods of contact inspections are straight-beam,

angle-beam, and the surface-wave method.

STRAIGHT BEAM. -The straight-beam method is

used to detect discontinuities parallel to the test surface,

a nd is genera lly used on ma ter ial 1/2 inch t hick or

great er. Most st ra ight-beam met hods are applied by

using the pulse-echo technique (transmitting and

receiving search unit or units placed on the same

sur f ace) . Cer ta in appl ica t ions use the through-

tra nsmission method (transmitt ing search unit placed on

one surface, and receiving search un it placed on t he

opposite surface). In the through-transmission method,

discontinuities block the passage of sound. This results

in a reduction of the received signal (fig. 15-13). With

this method, echoes from t he discontinuit ies ar e not

shown on the CRT. Therefore, depth information on the

discontinuities is not determined. Typical discontinuity

examples are laminations, corrosion, and cracks.

ANGLE BEAM. -Angle-beam met hods a re usedextensively for field NDI, and can provide for inspection

of area s w ith complex geometry or limited a ccess. This

is because angle beams can travel through a material by

bouncing from surface to surface. Useful inspection

information can be obtained at great distances from the

search unit. Angle-beam inspections are particularly

applicable to inspections around fastener holes,

15-10


11/46

Figure 15-13.-Through-transmission inspection.

Figure 15-14.-Angle-beam inspection.

Figure 15-15.-Surface-wave inspection.

inspection of cylindrical components, examination of

skins for cracks, and inspection of welds. Figure 15-14

shows typical angle-beam inspections.

SURFACE WAVE. -The surface-wave methodprojects a beam of vibrations that travel along the

surface and just below the surface of the mat erial. When

surface waves are used to inspect painted surfaces, you

should exercise caution during set up and interpretation

due to the possibility of surface reflection from scratches

and breaks in the painted surface. Surface-wave

inspections can be used in many field NDI applications

Figure 15-16.-Generation of eddy currents in various part con-figurations.

involving surface cracks or s l ightly subsurface

discontinuities. On smooth surfaces, sound energy can

travel long distances with little energy loss. Surface

waves travel around curved corners, and they reflect at

sha rp edges. Rough sur faces or liquid on the surfa ce

at tenua te surface waves so the area in front of the search

unit must be kept clear of couplant. Figure 15-15 shows

a typical surface-wave inspection.

Eddy Current Inspection

Eddy currents are electrical currents induced in a

conductor of electricity by reaction with a magnetic

field. The eddy currents a re circular in na ture, a nd t heir

paths are oriented perpendicular to the direction of theapplied magnetic field. In general, during eddy current

test ing, th e vary ing ma gnetic field(s) is/a re generat ed by

an alternating electrical current (ac) flowing through a

coil of wire positioned immediately adjacent to the

conductor , around the conductor , or wi thin the

conductor. Figure 15-16 shows eddy currents flowing in

various configurations.

15-11


12/46

Figure 15-17.-Basic coil configurations.

COILS AND PROBES. -Eddy current coils and

probes consist of one or more coils of wire designed to

introduce a varying magnetic f ield into a part to

determine the effects of test variables on this magnetic

field. Generation of the magnetic field results from an

alternating current f lowing through the coil . A

fundamental consideration in selecting an eddy current

probe or test coil is its intended use. A small diameter

probe or narrow encircling coil will provide increased

resolution of small defects. A larger probe or widerencircling coil will provide better averaging of bulk

properties.

TEST COIL CONFIGURATIONS. - E d d y

current probes and coils can be classified into three

types: surface probes, encircling coils, and inside

(bobbin-type) coils. Figure 15-17 shows sketches of the

general configuration of each type of coil or probe.

Figure 15-18 shows photographs of typical surface

probes used for eddy current testing. Most eddy current

testing in the field is concerned with surface coils

(probes). The sur face probe is used on pla tes, sh eets, a nd

irregular-shaped parts. An inside coil may be used on

tubes, pipes, or other par ts t ha t a re accessible to the

inside. The inside coil should nearly fill the part opening

in order to provide good test sensitivity. The use of

inside coils is restricted by bends or nonuniform

diameters. Encircling coils-are used primarily for

Figure 15-18.-Typical eddy current test probes.

15-12


13/46

Figure 15-19.-Basic penetrant process.

inspecting rods, tubes, cylinders, or wire. With the

encircling or inside coils, the entire circumference of the

specimen is evaluated at one time. Consequently, the

exact location of defects cannot be defined. The surface

coil has the ability to better define the exact location of

discontinuities.

Dye Penetrant Inspection

The dye penetrant inspection is a s imple,

inexpensive, and reliable nondestructive inspectionmethod for detecting discontinuities tha t a re open t o the

surface of the item to be inspected. It can be used on

metals and other nonporous materia ls that are not

attacked by penetrant materials. With the proper

technique, it will detect a wide va riety of discontinuities,

ranging in size from those readily visible down to

microscopic level, as long as the discontinuities are open

to the surface and are sufficiently free of foreign

material . Figure 15-19 shows the basic principles of the

penetrant inspection process. A penetrating liquid,

which contains dyes, is applied to the surface of a clean

part to be inspected. The penetrant is a llowed t o remain

on the surfa ce of th e part for a period of time t o permit

it to enter and fill any openings or discontinuities. After

a suitable dwell period, the penetrant is removed from

the parts surface. You must exercise care to prevent

removal of the penetrant that is contained in the

discontinuities. A material called developer is then

applied. The developer aids in dr a wing a ny t ra pped

penetra nt from t he discontinuities and improves the

visibility of any indications. For more information

concerning the dye penetra nt inspection, consult the

Nondestructive I nspection Methods Man ual , NAVAIR

01-lA-16.

WELDING

Learning Objective: Recognize the qualif i-cati ons and r ecer ti fi cati on pr ocess to become

a cert i f i ed welder.

Welding is the most pra ctical of the ma ny meta l

joining processes available to aircraft manufacturers.

The welded joint offers rigidity, simplicity, low weight,

high strength, and low-cost production equipment.

Consequently, welding has been universally adopted in

the building of all types of aircraft . Many structural

parts, as well as nonstructural parts, are joined by some

form of welding, and the repair of these many parts is

an indispensable part of aircraft maintenance.

QUALIFICATIONS OF WELDERS

For advancement, you should be familiar with the

operation of welding equipment and materials. You

should also be able to perform simple welding, brazing,

soldering, and cutting operations on ferrous and

nonferrous metals.

To weld on aircraft structural parts, you must be a

certified welder. To be certified as an aircraft welder,

you must pass a qualif ication test conducted in the

presence of a Navy inspector. Passing this test entitles

you to a certificate signed by the inspector attesting that

you are capable of welding the class of ma terial a nd type

of weld indicated on the certificate.

Naval aviation depots have training programs for

the benefit of those desiring to qualify as aircraft

welders, and they have facilities for testing.

15-13


14/46

RECERTIFICATION OF WELDERS

Only currently certified aeronautical welders may

weld on aeronautical equipment. Initial certification is

attained by satisfactory completion of Navy training

cour se(s) N -701-0007 a nd /or N-701-0009, a s

applicable. Certif ication can also be obtained by

documented satisfactory completion of equivalent

tra ining in accordance with Aeronauti cal an d Support

Equ ipm ent Weld i ng Manu a l , NA 01-1A-34, a ndsatisfactory completion of recertif ication testing. I f

proficiency is maintained, the recertification interval for

IMA-level aeronautical equipment welders is 3 years.

M a i n t a i n i n g p r o f i c i e n c y r e q u i r e s d o c u m e n t e d

frequency of use, as specified in NA 01-1A-34. Failure

to maintain proficiency in any group(s) of metals will

termina te current certifica tion in t ha t/those group(s).

Recertification is normally accomplished by locally

producing acceptable test welds and submitting those

welds to the nearest authorized welding examination

and evalua t ion facil ity . Exa minat ion a nd evaluat ion

facilities must complete required testing of test weldspecimens and provide test results and recertification

documentation, as appropriate, to the affected welders

command within 30 days of the test weld(s) receipt.

Detailed procedures for obtaining test plates,

produc t ion and submiss ion o f tes t welds , and

documentation are contained in NA 01-1A-34.

TYCOMs/ACCs m a y exten d curren t certificat ion of

welders for a maximum of 90 days in cases where test

w e l d s h a v e b e e n s u b m i t t e d b u t r e s u l t s a n d

recertification documentation have not been received

from the cognizant examination and evaluation facility.

Welders w hose test specimens fa il to meet minimum

requirements a re allowed one retest. This retest w ill

require submission of a double set of test welds of the

failed group(s) of metal(s) to the same examination and

evaluat ion faci l i ty that fa i led the test welds f i rs t

submitted. Welding examination and evaluation

facilities will forward double sets of test plates to the

f a i led welder s command concurrent ly w i th the

notif ication of failure. Retest test welds must be

completed and submitted within 30 days of receipt of

notification of failure of first test weld(s). Failure of any

retest test welds to meet minimum requirements will

require the welder to satisfactorily complete the Navy

t ra in ing cours es N-701-0008/N-701-0010, as a ppli-

cable, to recertify.

Aeronautical equipment welders may weld only on

equipment, components , and items ma nufactured from

the group of metals for which they are currently certified

and for which weld repairs are authorized by applicable

technical publications or directives. Groups of metals

Figure 15-20.-Welding Certification NAVAIR 13100/1).

for which separate and distinct certification is required

are specified in NA 01-1A-34. Separate certification is

also required for oxyfuel brazing process.

NA 01-1A-34 contains additional information and

guida nce relat ive to qua lifica tion, certificat ion/recertifi-

cation, and employment of aeronautical equipment

welders. It is, however, a general series technical ma nual

intended t o be used in conjunction w ith the OP NAV

4790.2E an d wit h specific ma int ena nce/repa ir/overha ul

ma nua ls/engineering documen ts. I n ca ses of conflict

bet w een N A 01-1A-34 an d t he OP NAV 4790.2E

regar ding certif icat ion/ recertif icat ion policy, the

OPNAV 4790.2E takes precedence.

QA/A is responsible for monit oring a erona ut ical

equipm ent w elder certifica tion/recertificat ion. Refer to

the OPNAV 4790.2E for specifics.

A Welding Certificate (Operators Card), NAVAIR13100/1, will be issu ed for ea ch ma ter ia l cat egory in

which the welder is qualified. The welding certificate

will be filled out, dated, and signed by an authorized

representat ive of a n examina tion facili ty. Figure 15-20

provides a sam ple of th e welding certif icat e. Figures

15-21 a nd 15-22 show a sample Welding Examination

Record (NAVAIR 13100/2) a nd i ns t ru ction s.

15-14


15/46

Figure 15-21.-Welding Examination Record (NAVAIR 13100/2) (front).

15-15


16/46

Figure15-22.-Welding Examination Record (NAVAIR 13100/2) (back).

15-16


17/46

Figure 15-23.-Portable oxyacetylene welding and cutting equipment.

OXYACETYLENE WELDING

Oxyacetylene welding is a gas welding process. A

coalescence or bond is produced by heating with a gas

f lame or f lames obtained from the combustion of

acetylene with oxygen, with or without the application

of pressure, and with or without the use of filler metal.

A welding torch is used to mix the gases in the proper

proportions and t o direct the f lame a gainst t he parts t o

be welded. The molten edges of the parts then literally

flow togeth er a nd, a fter cooling, form one solid piece.

Usua lly, it is necessary to add extra mat erial to the joint.

The correct ma teria l in rod form is dipped in a nd fuses

with the puddle of molten meta l from t he parent meta l

pa r t s .

Acetylene is w idely used as the combustible ga s

because of its high flame temperature when mixed witho x y g e n . T h e t e m p e r a t u r e , w h i c h r a n g e s f r o m

approximately 5,700 to 6,300F, is so far above the

melting point of all commercial metals that it provides

a means for the rapid, localized melting essential in

welding. The oxyacetylene flame is also used in cutting

ferrous metals. The oxyacetylene welding and cutting

methods are widely used by all types of maintenance

activities because t he flame is easy to regulate, the ga ses

may be produced inexpensively, and the equipment can

be transported easily and safely.

Oxyacetylene Welding Equipment

The equipment used for oxyacetylene welding

consists of a source of oxygen a nd a source of a cetylene

from a portable or stationary outfit. The portable outfit

consists of an oxygen cylinder and an acetylene cylinder

with at ta ched valves , regulat ors, gauges, and hoses

(fig. 15-23). This equipment may be temporarily

secured on the floor or mounted on a two-wheel, welded,

steel truck equipped with a platform that will support

two large size cylinders. The cylinders are secured by

chains a tt ached to the tru ck fra me. A meta l toolbox,

welded to the frame, provides storage for torches, tips,

gloves, fluxes, goggles, and necessary wrenches.

Stationary equipment is installed where welding

operations are conducted in a fixed location. The

acetylene and oxygen are piped to several welding

stations from a central supply. Master regulators are

used to control the f low of gas a nd ma intain a consta nt

pressure at ea ch stat ion.

OXYGEN. -Oxygen is a colorless, tasteless, odor-

less gas tha t is s l ightly heavier t han air . Oxygen is

15-17


18/46

nonflammable, but it will support combustion when

combined with other gases. This means that i t a ids in

burning, and this burning gives off considerable heat an d

light. In its free state, oxygen is one of the most common

elements. The atmosphere is made up of approximately

21 part s of oxygen a nd 78 par ts of nitrogen, with the

remainder being rare gases. It is the presence of oxygen

in the a ir tha t causes rust ing of ferrous meta ls , the

discoloration of copper, and corrosion of aluminum.

This action is known as oxidation.Oxygen is obtained commercially either by the

liquid air process or by the electrolytic process. In the

liquid air process, air is compressed and cooled to a point

where the gases become a liquid. As the temperature of

the liquid a ir is raised, nitrogen in a ga seous form is

given off first, since its boiling point is lower than that

of liquid oxygen. These gases, having been separated,

are further purified and compressed into cylinders for

use.

In the electrolytic process, wa ter is broken down

into hydrogen and oxygen by the passage of an electric

current through it. The oxygen collects at the positiveterminal and the hydrogen at the negat ive terminal . Each

of the gases is then collected and compressed into

cylinders for use.

OXYGEN CYLINDERS. -A typical oxygen

cylinder (fig. 15-24) is made of s teel and has a capacity

of 220 cubic feet at a pressure of 2,000 psi and a

temperature of 70F. Each oxygen cylinder has a

high-pressure outlet valve located at the top of the

cylinder, a removable metal cap for the protection of the

outlet valve during shipment or storage, and a low

melting point safety fuse plug and disk. All oxygen

cylinders are painted green for identification. Technical

oxygen cylinders are solid green, while breathing

oxygen cylinders are green with a white ba nd a round the

top.

CAUTION

Oxygen should never be brought in contact

with oil or grease. In the presence of pure

oxygen, these substances become highly

combustible. Oxygen hose and valve fittings

should never be oiled or greased or handled

with oily or greasy hands. Even grease spots

on clothing may flare up or explode if struck

by a stream of oxygen.

PRESSURE REGULATORS. -The gases

compressed in oxygen a nd a cetylene cylinders a re a t

pressures too high for oxyacetylene welding. Regulators

Figure 15-24.-Typical oxygen cylinder.

are necessary to reduce pressure and control the flow of

gases from the cylinders. Most regulators in use ar e

either th e single-sta ge or the t wo-sta ge type. Single-

stage regulators reduce the pressure of the gas in one

step; two-stage regulators do the same job in two steps

or stages. Generally, less adjustment is necessary when

two-stage regulators are used.

Figure 15-25 shows a typical single-stage regulator.

The regulator mechanism consists of a nozzle through

which the high-pressure gases pass, a valve seat to close

off the nozzle, and balancing springs. These are all

enclosed in a suitable housing. Pressure gauges are

provided to indicate t he pressure in t he cylinder or

pipeline (inlet), as well as the working pressure (outlet).

The inlet pressure gauge, used to record cylinder

pressures, is a high-pressure gauge and is graduated

from 0 to 3,000 psi. The outlet pressure gauge, used to

record working pressures, is a low-pressure gauge and

is graduated from 0 to 500 psi.

In the oxygen regulator, the oxygen enters through

the high-pressure inlet connection and passes through a

glass wool f i l ter that removes dust and dirt . Turn the

adjusting screw in, to the right, to allow the oxygen to

pass from the high-pressure chamber to the low-

pressure chamber of the regulat or, thr ough the regulator

outlet, a nd thr ough th e hose to the torch at the pressure

shown on the working pressure gauge. Changes in this

pressure may be made at will , s imply by adjusting the

15-18


19/46

Figure 15-25.-Single-stage oxygen regulator.

handle until the desired pressure is registered. Turning is that the total pressure decrease takes place in two steps

the adjust ing screw to the r ight INCREASES the instead of one. On t he high-pressure side, th e pressure

working pressure; turning it to the left DECREASES the is reduced from cylinder pressure to intermediate

working pressure. pressure. On the low-pressure side, the pressure is

The operation of the two-stage regulator is similar reduced

in principle to the single-stage regulator. The difference pressure .

15-19

from intermediate pressure to working

Because of the two-stage pressure control, the


20/46

Figure 15-26.-Two-stage regulator.

working pressure is held constant, and pressure

adjustment during welding operat ions is n ot required. A

two-stage regulator is shown in figure 15-26.The a cetylene regula tor controls and reduces t he

acetylene pressure f rom a ny s t anda rd cyl inder tha t

contains pressures up to 500 psi. It is of the same general

design as the oxygen regulator, but it will not withstand

such high pressures. The high-pressure gauge, on the

inlet side of the regulator, is graduated from 0 to 500 psi.

The low-pressure gauge, on the outlet side of the

regulator, is graduated from 0 to 30 psi. Acetylene

should not be used at pressures exceeding 15 psi.

ACETYLENE. -Acetylene is a fuel gas made up ofcarbon a nd hydrogen. I t is ma nufactured by th e chem-

ical reaction between calcium carbide, a gray stonelike

substance, and w at er in a generat ing unit . Acetylene is

colorless, but it has a distinctive odor that can be easily

detected.

Mixtures of acetylene and air that contain from 2 to

80 percent of acety lene by volume will explode w hen

ignited. However, with suitable welding equipment and

proper precautions, acetylene can be safely burned with

oxygen for welding and cutting purposes. When burned

with oxygen, acetylene produces a very hot flame thathas a temperature between 5,700F and 6,300F.

ACETYLENE CYLINDERS. -Acetylene stored

in a free stat e under pressure greater t han 15 psi can be

made to break down by heat or shock and possibly

explode. Under pressure of 29.4 psi, acetylene becomes

self-explosive, and a slight shock will cause it to explode

spontaneously. However, when dissolved in acetone, it

Figure 15-27.-Acetylene cylinder.

can be compressed into cylinders at pressures up to 250

psi.

The acetylene cylinder (fig. 15-27) is f i l led with

porous materials, such as balsa wood, charcoal, and

shredded asbestos, to decrease the size of the open

spaces in the cylinder. Acetone, a colorless, flammable

l iquid, is added u nt il about 40 percent of the porous

ma teria l is f i lled. The fil ler a cts as a lar ge sponge to

absorb the acetone, which, in turn, absorbs the

acetylene. In this process, the volume of the a cetoneincreases as it absorbs the acetylene, while acetylene,

being a gas, decreases in volume. The acetylene

cylinders are equipped with safety plugs, which have a

sma ll hole through t he center. This hole is filled with a

metal alloy, which melts at approximately 212F or

releases at 500 psi. When a cylinder is overheated, the

plug will melt and permit the acetylene to escape before

a dangerous pressure can build up. The plug hole is too

small to permit a flame to burn back into the cylinder if

the escaping acetylene should become ignited.

WELDING TORCHES. -The oxyacetylenewelding torch is used to mix oxygen and acetylene gas

in t he proper proportions, and to control the volume of

these gases burned at the w elding tip. The torch ha s tw o

needle valves, one for adjusting the flow of acetylene

and the other for adjusting the flow of oxygen. In

addition, there are two tubes, one for oxygen and the

other for acetylene; a mixing head; inlet nipples for the

attachment of hoses; a tip; and a handle. The tubes and

15-20


21/46

Figure 15-28.-Mixing head for injector-type welding torch.

Figure 15-29.-Equal pressure welding torch.

handle are made of seamless hard brass, copper-nickel to dra w in the required a mount of acetylene. This is

a lloy, st ainless st eel, or other n oncorrosive meta ls of accomplished by the design of the mixer in the torch,

adequate strength. which operates on the injector principle. The welding

There are two types of welding torchesthe tips may or may not have separate injectors designed

low-pressure or injector type and the equal-pressure integrally with each tip.

type. In the low-pressure or injector type (fig. 15-28), The equa l pressure t orch (fig. 15-29) is designed to

the acetylene pressure is less than 1 psi. A jet of operate with equal pressures for

high-pressure oxygen is used to produce a suction effect acetylene. The pressure ranges from

15-21

the oxygen and

1 to 15 psi. This


22/46

torch has certain advantages over the low-pressure type

beca use the flame can be more readily adjusted, and

since equal pressures are used for each gas, the torch is

less susceptible to flash backs.

The welding tips are made of hard, drawn,

electrolytic copper or 95-percent copper and 5-percent

tellurium. They are made in various styles and types,

some havin g a one-piece tip either w ith a single orifice

or a number of orifices, and others with two or more tips

attached to one mixing head. The diameters of the tiporifices differ to control the quantit y of heat and the type

of flame. These tip sizes are designated by numbers that

are arranged according to the individual manufacturers

system. In general, the smaller the number, the smaller

the tip orifice.

No matter what type or size tip you select, the tip

must be kept clean. Quite often the orifice becomes

clogged with slag. When this happens, the flame will not

burn properly. Inspect the tip before you use it. If the

passage is obstructed, you can clear it with wire tip

cleaners of the proper diameter, or with soft copper wire.

Tips should not be cleaned w ith ma chinists drills orother sharp instruments. These devices may enlarge or

scratch the tip opening and greatly reduce the efficiency

of the torch tip.

HOSE. The hose used to make the connection

between the torch and the regulators is strong,

nonporous, l ight, and flexible to make the torch

movements easy. I t is made to withstand high internal

pressures, a nd the rubber used in its ma nufa cture is

chemically treated to remove sulfur to avoid the danger

of spontaneous combustion.

The oxygen hose is GREEN, and the acetylene hose

is RED. The hose is a rubber tube with braided or

wrapped cotton or rayon reinforcements and a rubber

covering. The hoses have connections at each end so

they can be connected to their respective regulator outlet

an d t orch inlet connections. To prevent a dan gerous

interchange of acetylene and oxygen hoses, all threaded

fittings used for the acetylene hookup are left-handed

threads, and all threaded fittings for oxygen hookup are

right-handed th reads. The hoses ar e obta inable as a

single hose for each gas or with the hoses bonded

together a long t heir length under a common outer r ubberjacket. This type prevents the hose from kinking or

becoming entangled during the welding operation.

LIGHTERS. -A flint lighter is provided for igniting

th e torch. The light er consist of a file-sha ped piece of

steel, usually recessed in a cuplike device, and a piece

of f l int that can be drawn across the steel, which

produces the sparks required to light the torch.

WARNING

Matches should never be used to ignite a

torch; their length requires bringing the

hand too close to the tip to ignite the gas.

Accumulated gas may envelope the hand

and, when ignited, cause a severe burn.

GOGGLES. -Welding goggles are fitted with

colored lenses to keep out hea t a nd light ra ys a nd to

protect the eyes from sparks and molten metal.

Regard less of th e sha de of lens used, goggles should be

protected by a clear cover glass. The welding operator

should select the shade or density of color that is best

suited for his/her pa rticula r w ork. The desired lens is th e

darkest shade that will show a clear definition of the

work without eyestrain. Goggles should fit closely

around the eyes, and should be worn at all times during

welding and cutting operations. Special goggles, using

standard lenses, are available for use with spectacles.

WELDING (FILLER) RODS. -The use of the

proper type of f i l ler rod is very important in

oxyacetylene welding operations. This material not only

adds reinforcement to the weld area, but also adds

desired properties to the finished weld. By selecting the

proper type of rod, either tensile strength or ductility can

be secured in a weld. Similarly, rods can be selected that

will help retain the desired amount of corrosion

resistance. In some cases, a suitable rod with a lower

melting point will eliminate possible cracks from

expansion and contraction.Welding rods are c lassi f ied as ferrous and

nonferrous. The ferrous rods include carbon and alloy

steel rods as w ell as cast iron rods. Nonferrous rods

include brazing and bronze rods, aluminum and

aluminum alloy rods, magnesium and magnesium alloy

rods, copper rods, and silver rods. The diameter of the

rod used is governed by the thickness of the metals being

joined. If the rod is to small, it w ill not conduct h eat aw ay

from the puddle rapidly enough, a nd a burned weld will

result. A rod tha t is t o large w ill chill the puddle. As in

selecting the proper size welding torch tip, experience

will ena ble the welder to select th e proper diamet erwelding rod.

Welding Flames

The weld ing f l ame i s c l ass i f ied as neutra l ,

carburizing, or oxidizing. Each type of flame has its own

special function The opera tor can a djust th e torch to

produce the type of flame best suited for the job at hand.

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The neutral flame, in which a balanced mixture of

oxygen and acetylene is burned, is used for most

welding opera tions. The oxidizing fla me, in wh ich an

excess of oxygen is burned, is used for welding bronze

or fusing brass and bronze. The carburizing flame, in

wh ich a n excess of acetylene is burned, is used when

welding nickel alloys.

NEUTRAL FLAME. -The neutral flame does not

alter the composition of the base metal to any greatextent; t herefore, i t is t he f lame best suited for most

metals. The neutral f lame burns at approximately

5,850 F. A ba lan ced mixtur e of one volume of oxygen

and one volume of acetylene is supplied from the torch

when the flame is adjusted to neutral.

The neutral flame is divided into two distinct zones.

The inner zone consists of a white, clearly defined,

roun d, s mooth cone, 1/1 6 to 3/4 inch in lengt h. The out er

zone, made up of completely burned oxygen and

acetylene, is blue with a purple tinge at the point and

edges.

A neutral f lame melts metal without changing itsproperties, and it leaves the metal clear and clean. If the

mixture of oxygen and acetylene is correct, the neutral

flame allows the molten metal to flow smoothly, and few

sparks are produced when welding most metals.

CARBURIZING FLAME. -The carburizing

flame, produced by burning an excess of acetylene, may

be recognized by its three distinct colors. There is a

bluish-white inner core, a white intermediate cone, and

a light-blue outer flame. It may be recognized also by

the fea ther at the t ip of the inn er cone. The degree of

carburization can be judged by the length of the feather.

OXIDIZING FLAME. -The oxidizing flame is

produced by burning a n excess of oxygen. I t ha s t he

general appearance of the neutral flame, but the inner

cone is shorter, slightly pointed, a nd ha s a purplish t inge.

This flame burns with a hissing sound. When welding

ferrous metals, you can recognize an oxidizing flame by

the numerous sparks that are thrown off as the metal

melts and by the foam that forms on the surface.

FLAME ADJ USTMENT. -To adjust the flame,

light t he torch by opening t he torch acetylene valve

one-fourth to one-half turn. With only the acetylene

valve open, the flame will be yellow in color and give

off smoke and soot.

Now open the torch oxygen valve slowly. The flame

will gradually change in color from yellow to blue, and

it will show the characteristics of the excess acetylene

flame described earlier.

With most torches, there will be a slight excess of

a cetylene when t he oxygen and a cetylene valves are

wide open and the recommended pressures are being

used. Now close the acetylene valve on the torch slowly.

You w ill notice tha t t he secondary cone gets sma ller

until i t fina lly disappear s completely. J ust a t t his point

of complete disappearance, the neutral flame is formed.

To see th e effect of an excess of oxygen, close the

acet ylene valve still further. A change will be noted,

although it is by no means as sharply defined as thatbetween the neutral and excess acetylene flames. The

entire flame w ill decrease in size, and t he inner cone will

become much less sharply defined.

B ecau se of the diff iculty in ma king a distinction

between the excess oxygen and neutral f lames, an

adjustment of the flame to neutral should alwa ys be

made from the excess acetylene side. Always adjust the

f lame first so that i t shows the secondary cone

chara cteristic of excess acetylene; then, increase t he

flow of oxygen until this secondary cone just disappears.

During a ctual welding operat ions, where a n eutral

flame is essential, the flame should be checkedoccasionally to make certain it is neutral. This is

accomplished by momentarily withdrawing the torch

from the work and increasing the amount of acetylene

until a distinctive feathery edge appears on the inner

cone. Then, slowly decrease the amount of acetylene

until a well-defined cone, characteristic of the neutral

flame, is formed.

With each size of tip, a neutral, oxidizing, or

carburizing flame can be obtained. It is also possible to

obtain a harsh or soft f lame by increasing or

decreasing the pressure of both gases.

For most regulator settings, the gases are expelledfrom the torch tip at a relatively high velocity, and the

f lame is called har sh. For some work it is desirable

to have a soft or low-velocity flame without a reduc-

tion in thermal output. This maybe achieved by using a

larger tip and closing the needle valves until the neutral

flame is quiet a nd stea dy. It is especially desirable to use

a soft flame when welding aluminum, to avoid blowing

holes in the metal when the puddle is formed.

BACKFIRE AND FLASHBACK. -Improper

handling of the torch may cause the flame to backfire

or, in very rare cases, to flashback. A backfire is amomentary backward flow of the gases at the torch tip,

causing the flame to go out. Sometimes the flame may

immediately come on a ga in, but a ba ckfire is alw a ys

accompanied by a snapping or popping noise. A backfire

may be caused by touching the tip a gainst t he work, by

overheating the tip, by operating the torch at other than

recommended pressures, by a loose tip or head, or by

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Figure 15-30.-Welding light gauge metals.

dirt or slag in th e end of the t ip. A backfire is ra rely

dangerous, but t he molten metal ma y be splat tered when

the flame pops.

A flashback is the burning of the gases with in the

torch, and it is dangerous. It is usually caused by loose

connections, improper pressures, or overheating of the

torch. A shrill hissing or squealing noise accompanies a

f l ashback; and unless the gases a re turned o f f

immediately, the flame may burn back through the hose

and regulat ors and cause great dama ge. The cause of a

flashback should always be determined, and the trouble

remedied before relighting the torch.

Fundamental Welding Techniques

The composition, thickness, shape, and position of

the metal to be welded govern the techniques to be used.

The fundamental techniques that apply to different

thicknesses, shapes, and positions of the m eta l to be

welded are discussed in the following paragraphs.

HOLDING THE TORCH. -The proper method to

use in holding the torch depends upon the thickness of

the metal being welded. For light gauge metal, hold the

torch as shown in figure 15-30, with the hose draped

over the w rist. For hea vier w ork, hold the torch as shown

in figure 15-31.

Figure 15-31.-Welding heavy plate.

Hold the torch so that the tip is in line with the joint

to be welded, and inclined betw een 30 a nd 60 from

the perpendicular. The exact angle depends upon the

type of weld to be made, the amount of preheating

necessa ry, a nd th e thickness a nd ty pe of meta l. The

thicker the metal, the more vertical the torch must be for

proper heat penetration. The white cone of the flame

should be held a bout 1/8 inch from t he sur fa ce of th e

base metal.

If the torch is held in the correct position, a small

puddle of molten metal will form. The puddle should be

composed of equal parts of the two pieces being welded.

After the puddle appears, begin the movement of the tip

in a semicircular or circular motion. This movement

assures an even distribution of heat on both pieces of

metal. The speed and motion of the torch are learned

only by pra ctice and experience.

FOREHAND WELDING. -Forehand (also called

puddle welding or ripple welding) is the oldest

method of welding. The rod is kept ahead of the tip in

the direction in which the weld is being made. Point t he

flame in the direction of the weld, an d hold the tip at an

an gle of about 45 t o 60 t o the plates (fig. 15-32). This

position of the flame preheats the edges you are welding

just ahead of the molten puddle. By moving the tip and

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Figure 15-32.-Forehand welding.

Figure 15-33.-Backhand welding.

welding rod ba ck and forth in opposite semicircular

paths, you bala nce the heat to melt t he end of the rod and

the side walls of the joint into a uniformly distributed

molten puddle. As the flame passes the rod, it melts off

a short length of the rod and adds it to the puddle. The

motion of the torch distributes the molten metal evenly

to both edges of the joint and to the molten puddle. This

method is used in welding most of the lighter tubing and

sheet met a ls up to 1/8 inch th ick becaus e it permits bet ter

control of a small puddle and results in a smoother weld.

The forehand technique is not the best method for

welding heavy metals.

BACKHAND WELDING. -In this method thetorch tip precedes the rod in the direction of welding,

and the flame is pointed back at the molten puddle and

the completed weld. The end of the rod is placed

between the torch tip and the molten puddle. The

welding tip should ma ke an a ngle of about 45 t o 60

with the plates or joint being welded (fig. 15-33).

Less motion is required in

tha n in t he forehand method.

the backhand method

I f you use a s traight

Figure 15-34.-Four basic welding positions.

welding rod, it should be rota ted so tha t t he end will roll

from side to side and melt off evenly. You may also bend

the rod and, when welding, move the rod and torch back

and forth at a rapid rate. I f you are ma king a large weld,

you should move the rod so as to make complete circles

in the molten puddle. The torch is moved back and forth

across the weld while it is advanced slowly and

uniformly in the direction of the weld. Youll find the

backhand method best for welding material more than

1/8 inch th ick. You can use a na rrower V a t th e joint

than is possible in forehand welding. An included angle

of 60 is a sufficient angle of bevel to get a good joint.

It doesnt take as much welding rod or puddling for the

backhand method as it does for the forehand method.

By using the backhand technique on heavier

material , i t is possible to obtain increased welding

speeds, better control of the lar ger puddle, and more

complete fusion at the root of the weld. Further, by using

a r educing flame with t he backhand t echnique, a sma ller

amount of base metal is melted while welding a joint.

Backhand welding is seldom used on sheet metal

because the increased heat generated in this method islikely to cause overheating and burning. When welding

steel with a ba ckhand technique and a reducing f lam e,

the absorption of carbon by a thin surface layer of metal

reduces the melting point of the st eel. This speeds up t he

welding operation.

WEL DING POSITIONS.-The four basic welding

positions are shown in figure 15-34. Also shown are four

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Figure 15-35.-Types of welded joints.

commonly used joints. Notice that the corner joint and

butt joint are classified as groove welds, while the tee

and lap joints are classified as fillet welds.

Welding is always done in the f lat position

whenever possible. The puddle is much easier to control,

and the welder can work longer periods without tiring.

Quite often it is necessary to weld in the overhead,

vertical, or horizontal position in equipment repair.

The flat position is used when the material is to be

laid flat or almost flat and welded on the topside. The

welding torch is pointed downward toward the work.

This weld may be made by either the forehand or

backhand technique.

The overhead position is used when the material is

to be welded on the underside, with the torch pointed

upward toward the work. In welding overhead, you can

keep the puddle from sagging if you do not permit it to

get too large or assume the form of a large drop. The rod

is used t o contr ol the molten pu ddle. You should n ot

permit the volume of flame to exceed that required to

obtain a good fusion of the base metal with the filler rod.

Less heat is required in an overhead weld because the

heat natural ly r ises .

The horizontal position is used when the line of the

weld runs h orizonta l across a piece of work, and t he

torch is directed at the ma terial in a horizontal or near

horizontal position. The weld is made from right to left

across the plate (for the right-hand welder). The flame

is inclined upwar d at an a ngle of 45 to 65, a nd the weld

is made with a normal forehan d technique. Adding the

rod to the top of the puddle will prevent the molten metal

from sagging to the lower edge of the bead. If the puddle

is to have the greatest possible cohesion, it should not

be allowed to get too hot.

In a vertical w eld, the pressure exerted by the t orch

flame must be relied upon to a great extent to support

th e puddle. I t is import an t t o keep the puddle from

becoming too hot, a nd to prevent th e hot meta l from

running out of the puddle onto the finished weld. It may

be necessary to remove the flame from the puddle for

an instant to prevent overheating, and then return it to

the puddle. Vertical welds are begun at the bottom, and

the puddle is carried upward with a forehand motion.

The t ip should be inclined from 45 to 60, t he exa ctangle depending upon the desired balance between

correct penetration and control of the puddle. The rod is

added from t he top and in f ront of the f lame with a

normal forehand technique.

Welded J oints

The properties of a welded joint depend partly on

the correct preparation of the edges being welded. All

mill sca le, rust oxides, and other impurities must be

removed from t he joint edges or sur faces to prevent t heirinclusion in the w eld meta l. You should prepare th e

edges to permit fusion without excessive melting, and

you should take care to keep to a minimum the heat loss

due to radiation into the base metal from the weld. A

properly prepared joint will give a minimum of

expansion on heating and a minimum of contraction on

cooling.

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Figure 15-36.-Butt joints in light sections.

Figure 15-37.-Butt joints in heavy sections.

The preparation of the metal for welding is

governed by the form, thickness, kind of metal, the load

that the weld will be required to support, and the

available means for preparing the edges to be joined.

The five basic types of welded joints a rc the but t,

tee joints, lap, edge, and corner. (See figure 15-35.)

BUTT J OINTS. -A but t joint is ma de by placing

two pieces of material edge to edge so there is no

overlapping, and then welding them together. Plain,

square butt joints used for butt welding thin sheet metal

are shown in figure 15-36. Butt joints for thicker metals,

wit h several types of edge prepara tion, are shown in

figure 15-37. These edges can be prepared by flame

cutting, shearing, f lame grooving, machining, or

grinding.

P la te t hickn esses of 3/8 to 1/2 inch ca n be w elded

by using the single-V or single-U joints, as shown in

views A and C of figure 15-37. The edges of hea vier

sections should be prepared as shown in views B and D

of f igure 15-37. The s ingle-U groove i s more

satisfactory and requires less f i l ler metal than the

single-V groove when welding heavy sections and when

welding in deep sections. The double-V groove joint

requires a pproximat ely one-ha lf the a mount of f il ler

metal used to produce the single-V groove joint for the

same plate thickness. In general, butt joints prepared

from both sides permit easier welding, produce less

distortion, an d ensure better w eld qua lities in heavy

sections than joints prepared from one side only.

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Figure 15-38.-Tee joint-single pass fillet weld.

TEE J OINTS. -Tee joints are used to weld two

plates or sect ions whose surfaces are located

approximately 90 to each other at the joint. A plain tee

joint welded from both sides is shown in figure 15-38.

The included angle of bevel in the preparation of tee

joints is approximately half that required for butt joints.

Other edge prepara tions used in tee joints a re shown

in figure 15-39. A plain tee joint, which requires no

preparation other than cleaning the end of the vertical

plate, and the surface of the horizontal plate is shown in

view A of figure 15-39. The single-beveled joint (view

B of fig. 15-39) is used in pla tes a nd sect ions up t o 1/2

inch thick. The double-bevel joint (view C of fig. 15-39)

is used on heavy plates that can be welded from both

sides. The sin gle-J joint (view D of fig. 15-39) is used

for welding plat es tha t a re 1 inch thick or hea vier where

weldin g is d one from one sid e. The double-J joint (view

E of fig. 15-39) is used for w elding very hea vy plat es

from both sides.

You must take care to ensure penetration into the

root of the weld. This penetration is promoted by root

openings between the ends of the vertical members and

the horizontal surfaces.

LAP J OINTS. -La p joints a re used t o join t wo

overlapping members. A single lap joint, where welding

must be done from one side, is shown in view A of figure

15-40. The double lap joint is welded on both sides and

develops the full strength of the welded members (view

B of fig. 15-40). An offset lap joint (view C of fig. 15-40)

is used where tw o overlapping plat es must be joi

Ch15 Nondestructive Inspections, Welding, And Heat Treatment

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Transcript of Ch15 Nondestructive Inspections, Welding, And Heat Treatment