DESTRUCTIVE TESTING OF WELDS IN WPS_PQR PREPARATION

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DESTRUCTIVE TESTING OF WELDS IN WPS / PQR PREPARATION

Transcript of DESTRUCTIVE TESTING OF WELDS IN WPS_PQR PREPARATION

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DESTRUCTIVE TESTING

OF WELDS IN WPS / PQR PREPARATION

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WELDING PROCEDURE SPECIFICATION ( WPS ) – A

WPS is a written qualified welding procedure prepared

to provide direction for making production welds to

Code requirements. All the numerous welding process

variables are described in the WPS with sufficient detail

to permit reproduction of the weld and afford a clear

understanding of the parameters for performing the

production weld.

PROCEDURE QUALIFICATION RECORDS ( PQR ) – A

PQR is a record of the welding data used to weld the

test coupon and the results of testing the specimens cut

from the test coupon.

The purpose of the WPS and the PQR is to determine

that the weldment proposed for construction is capable

of having the required properties for its intended

application

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QUALIFICATION OF THE WPS

ASME IX – All ASME IX WPS must be qualified. The

basic steps in the qualification of a WPS based on

ASME IX are as follows

• Preparation of WPS.

• Welding of test coupon following all the variables

from the WPS.

• Testing of cut specimens from the test coupon.

• Evaluation of overall preparation, welding, testing,

and end results.

• Possible changes in procedure.

• Approval.

AWS D1.1 – The AWS D1.1 employs the concept of

prequalified weld joints. By following a number of well-

defined variables, the user of this Code does not have

to qualify the procedure. Instead, the values of the

specific variables are recorded. Qualification is

required only if any of these variables are changed

beyond their specified limits.

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REQUALIFICATION OF A QUALIFIED WPS

If a Fabricator that has a qualified WPS has to change

any essential variable at some later date, it is

necessary to requalify the WPS. This requalification

establishes that the revised WPS will produce

satisfactory results.

Such requalification tests are not required if there are

changes in non-essential variables. They are required,

however, if there are changes in essential variables

which will alter the properties of the resulting welds.

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TWO TYPES OF WPS:

GENERAL – Broad, general type that applies to all

welding processes of a given kind on a specific material.

SPECIFIC – Narrower, more definitive type, as when a

WPS has to be requalified to allow an essential variable

be changed .

ESSENTIAL / NON-ESSENTIAL VARIABLES

ESSENTIAL VARIABLES – Changes in some variables

are considered critical that will affect the mechanical

properties of the weldment and will require requalification

of the WPS.

NON-ESSENTIAL VARIABLES – Changes to other

variables will require that the WPS be rewritten to

recognize the change, but will not require requalification.

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ESSENTIAL VARIABLES

• Welding Process or Method of Application – A

change from the welding process or method of

application established in the procedure specification.

• Base Material – A change in base materials of two

different material groups.

• Diameters and Wall Thicknesses – The range of

outside diameters and wall thicknesses over which the

procedure is applicable shall be indentified.

• Joint Design – The specification shall include a

sketch or sketches of the joint that show the angle of

bevel, the size of the root face, and the root opening.

• Filler Metal and Number of Beads – The sizes and

classification number of the filler metal and the

minimum number and sequence of beads shall be

designated.

• Electrical Characteristics – The current and polarity

shall be designated, and the range of voltage and

amperage for each electrode, rod, or wire shall be

shown.

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• Time Between Passes – The maximum time between

the completion of the root bead and the start of the

second bead, as well as the maximum time between the

completion of the second bead and the start of the other

beads, shall be designated.

• Position – The specification shall designate roll or

position welding.

• Direction of Welding – The specification shall

designate whether the welding is to be performed in an

uphill or downhill direction.

• Pre- and Post-Heat Treatment – The methods,

temperature, temperature-control methods, and ambient

temperature range for the pre- and post-heat treatment

shall be specified.

• Shielding Gas and Flow Rate – The composition of

the shielding gas and the range of flow rates shall be

designated.

• Shielding Flux – The type of shielding flux shall be

designated.

• Speed of Travel – A change in the range for speed of

travel.

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DESTRUCTIVE TESTING, is used to describe an

evaluation process of a weld by a technique that of

necessity destroys the test specimen or destroys its

ability to function in its design application. They are

performed on sample weldments made with procedures

duplicating those used in the fabrication of the actual

welded structures.

The destructive testing techniques can be classified as

three general types: chemical, metallographic, and

mechanical.

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CHEMICAL TESTS – are conducted on the specimen to

determine its chemical composition.

METALLOGRAPHIC TESTS – are used to determine the

following:

• The soundness of welds.

• The distribution of nonmetallic inclusions in the

weld.

• The number of weld passes.

• The metallurgical structure in the weld and fusion

zone.

• The extent and metallurgical structure of the heat-

affected zone.

• The location and depth of penetration of the weld.

MECHANICAL TESTS – are used to determine weld

strength.

• Tensile Strength.

• Impact Strength.

• Bend Tests.

• Hardness Tests.

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UNIVERSAL TESTING MACHINE

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TENSILE-TESTED SPECIMEN

Standard – 70,000 psi minimum.

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GUIDED BEND TEST JIG

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SIDE-BEND TESTED SPECIMEN

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VARIOUS BEND-TESTED SPECIMENS

– Side Bend Double-V Groove – Face Bend

– Side Bend Single V-Groove – Root Bend

Acceptance Criteria – One rounded indication maximum

of 2.5 mm.

Any appearance of crack is rejectable.

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IMPACT TESTING MACHINE

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IMPACT TESTING MACHINE

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ANVIL FOR HOLDING IMPACT TESTING SPECIMEN

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IMPACT TESTING SPECIMEN

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IMPACT TESTED SPECIMEN

Standard Impact Values – 47 joules minimum.

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Carbon Steels, at lower temperatures, exhibit coarse-grained

structures, and are more brittle. Carbon Steels, at higher

temperatures, have finer-grain structures, and give higher

Impact Values.

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Hardness is the property of a material that enables it to

resist plastic deformation, usually by penetration. However,

the term hardness may also refer to resistance to bending,

scratching, abrasion or cutting.

The Brinell Hardness Test method consists of indenting

the test material with a 10 mm diameter hardened steel

or carbide ball subjected to a load of 3000 kg.

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The Rockwell Hardness Test method consists of

indenting the test material with a diamond cone or

hardened steel ball indenter. The indenter is forced

into the test material under a preliminary minor load,

usually 10 kgf. When equilibrium has been reached,

an indicating device, which follows the movements of

the indenter and so responds to changes in depth of

penetration of the indenter is set to a datum position.

While the preliminary minor load is still applied an

additional major load is applied with resulting increase

in penetration. When equilibrium has again been reach,

the additional major load is removed but the preliminary

minor load is still maintained. Removal of the additional

major load allows a partial recovery, so reducing the depth

of penetration. The permanent increase in depth of

penetration, resulting from the application and removal

of the additional major load is used to calculate the

Rockwell Hardness Number.

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The Vickers Hardness Test method consists of indenting

the test material with a diamond indenter, in the form of a

right pyramid with a square base and an angle of 136 degrees

between opposite faces subjected to a load of 1 to 100 kgf.

The full load is normally applied for 10 to 15 seconds. The

two diagonals of the indentation left in the surface of the

material after removal of the load are measured using a

microscope and their average calculated. The area of the

sloping surface of the indentation is calculated. The

Vickers Hardness is the quotient obtained by dividing the

kgf load by the square mm area of indentation.

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BRINELL ROCKWELL VICKERS

HARDNESS HARDNESS HARDNESS

TESTERS TESTERS TESTERS

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DIFFERENT INDENTORS FOR DIFFERENT

HARDNESS VALUES.

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VICKERS HARDNESS TESTER INDENTATION ON

TEST SPECIMEN.

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PREPARING A METALLOGRAPHIC SPECIMEN

FOR MICROSTRUCTURE ANALYSIS

• Cut a section of the test specimen for

macro / microstructure analysis.

• Grind the specimen in successively finer silicon

Carbide abrasive grits of 120 / 320 / 600 / 1200.

• Polish the finely ground specimen on napped

polishing cloths in, first, colloidal chromium oxide

suspension, then, in colloidal aluminum oxide

suspension.

• Dip the buffed specimen in a 3% nitric acid solution.

• The specimen is now ready to be viewed under a

metallographic microscope.

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METALLOGRAPHIC MICROSCOPE WITH DIGITAL

CAMERA

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MACROSCOPIC EXAMINATION

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MICROSCOPIC EXAMINATION AT 25 X MAGNIFICATION

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THE ATOMIC ABSORPTION SPECTROMETER TECHNIQUE

TYPICALLY USES A FLAME TO ATOMIZE THE METAL

SAMPLE. A BEAM OF LIGHT PASSES THROUGH THIS

FLAME, ABSORBING A SET OF QUANTITY OF ENERGY

( LIGHT OF A GIVEN WAVELENGTH ). EACH WAVELENGTH

IN THE SERIES IS SPECIFIC TO ONLY ONE

PARTICULAR ELEMENT.

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