Welding Procedure SpecificationFrom Wikipedia, the free encyclopedia

Bend test coupons for welding procedure qualification.

A Welding Procedure Specification (WPS) is a formal written document describing welding procedures, which provides direction to the welder or welding operators for making sound and quality production welds as per the code requirements . The purpose of the document is to guide welders to the accepted procedures so that repeatable and trusted welding techniques are used. A WPS is developed for each material alloy and for each welding type used. Specific codes and/or engineering societies are often the driving force behind the development of a company's WPS. A WPS is supported by a Procedure Qualification Record (PQR or WPQR). A PQR is a record of a test weld performed and tested (more rigorously) to ensure that the procedure will produce a good weld. Individual welders are certified with a qualification test documented in a Welder Qualification Test Record (WQTR) that shows they have the understanding and demonstrated ability to work within the specified WPS.

Contents  [hide] 

1 Introduction 2 See also 3 References 4 List of standards

Introduction[edit]

The following are definitions for WPS and PQR found in various codes and standards:

According to the American Welding Society (AWS), a WPS provides in detail the required welding variables for specific application to assure repeatability by properly trainedwelders. The AWS defines welding PQR as a record of welding variables used to produce an acceptable test weldment and the results of tests conducted on the weldment to qualify a Welding Procedure Specification. For steel construction (civil engineering structures) AWS D1.1 is a widely used standard. It specifies either a pre-qualification option (chapter 3) or a qualification option (chapter 4) for approval of welding processes.[1]

The American Society of Mechanical Engineers (ASME) similarly defines a WPS as a written document that provides direction to the welder or welding operator for making production welds in accordance with Code requirements.[2] ASME also defines welding PQR as a record of variables recorded during the welding of the test coupon. The record also contains the test results of the tested specimens.

The Canadian Welding Bureau, through CSA Standards W47.1,[3] W47.2[4] and W186,[5] specifies both a WPS and a Welding Procedure Data Sheet (WPDS) to provide direction to the welding supervisor, welders and welding operators. The WPS provides general information on the welding process and material grouping being welded, while the WPDS provides specific welding variables/parameter/conditions for the specific weldment. All WPS and WPDS must be independently reviewed and accepted by the Canadian Welding Bureau prior to use. These CSA standards also define requirements for procedure qualification testing (PQT) to support the acceptance of the WPDS. A record of the procedure qualification test and the results must be documented on a procedure qualification record (PQR). All PQTs are independently witnessed by the Canadian Welding Bureau.

In Europe, the European Committee for Standardization (CEN) has adopted the ISO standards on welding procedure qualification (ISO 15607 to ISO 15614), which replaced the former European standard EN 288. EN ISO 15607 defines a WPS as "A document that has been qualified by one of the methods described in clause 6 and provides the required variables of the welding procedure to ensure repeatability during production welding". The same standard defines a Welding Procedure Qualification Record (WPQR) as "Record comprising all necessary data needed for qualification of a preliminary welding procedure specification".[6] In addition to the standard WPS qualification procedure specified in ISO 15614, the ISO 156xx series of standards provides also for alternative WPS approval methods. These include: Tested welding consumables (ISO 15610), Previous welding experience (ISO 15611), Standard welding procedure (ISO 15612) and Preproduction welding test (ISO 15613).

In the oil and gas pipeline sector, the American Petroleum Institute API 1104 standard is used almost exclusively worldwide. API 1104 accepts the definitions of the American Welding Society code AWS A3.0.[7]

WPS is of two types- Prequalified WPS(pWPS) & qualified WPS.

Procedure Qualification Record (PQR)

PQR's are not required if Standard Welding Procedures are used, see below for details.

This document contains details of the welding test, it must include details of all the parameters listed as variables in tables QW250 to QW265 for each process involved and all the destructive test results.

The relevant variables for each type of welding process are clearly defined in tables QW250 to QW265. The left hand column of each table defines the section and paragraph where each variable and its application to the table is explained in the code.

Welding Variables

Variables used in a welding procedure test are divided into 3 categories :-

Essential Variables Are variables that have a significant affect on the mechanical properties of a joint. They must not be changed except within the limits specified by this code. e.g. Material thickness range, Material Group etc.

Non-Essential Variables Are variables that have no significant affect on mechanical properties. They can be changed without re qualification of the PQR.

Supplementary Variables Are variables that have an affect on the impact properties of a joint. They are classed as Non-Essential if impact testing is not required

All variables listed as essential, non-essential or supplementary should be addressed on both the WPS and the PQR. If any of the variables do not apply to the particular application then they should be specified as not applicable.

Joint Configuration Either plate or pipe can be used for the test piece (plate approves pipe and vice versa ref. QW211), any welding position approves all positions providing no impact tests are required ref. tables QW250 to QW265 and any joint geometry approves all geometry's, e.g. single V, double V, U prep, backed or unbacked.

A butt or groove weld approves branch and fillet welds but not the converse, ref. QW202. Non pressure retaining fillet welds in pipe or plate can be tested but they must be double sided if plate and at least the dimensions illustrated in QW462.4a, ref. QW202.2c. Pressure retaining branch welds must be qualified by groove (butt) welds.

Material Grouping Materials are assigned P numbers in QW420; a test in one P number approves all materials listed under that P number, except where impact tests are required then approval is restricted to materials listed in the group number within the P number. Other P number groupings are permissible ref. QW424.1 for details. Ref QW 424.1 for further details.

It is normally permissible if the material is not listed in QW422 to assign it to a P number which lists materials with the same metallurgical and mechanical properties although this is not in strict conformance with the code. Typically

BS1501 151 430A low carbon steel could be regarded as P1 and stainless steels such as 316, 304 as P8.

Note P5, 9 & 10 are divided into sub groups eg 5A,5B etc., Treat each sub group like a separate P Number

Dissimilar materials are acceptable providing they are compatible. For example P1 to P8, but this does not cover P1 to P1 or P8 to P8.

Note S numbers are for pipework to B31, a P number covers an S number but not the converse

Consumables The ASME code uses its own specifications for consumables SFA. which is almost identical to the AWS specification.

NOTE A change in consumable is only permissible providing it has the same F number and A number (if applicable) as the P.Q.R..  

Thickness Limits Thickness limits Groove welds. See QW451 for precise details.

When Impact tests are required the minimum thickness approved is restricted.  See QW403.6

More than one PQR may be required to qualify dissimilar thickness

The thickness little 't' of deposited weld metal for each process involved is approved from 0 to 2xt except:-

MIG/MAG (GMAW/FCAW) dip transfer weld of deposited thickness less than ½" approves maximum thickness of 1.1 x t only Ref: QW255 (QW403.10)

If any Pass in a single or multipass weld > ½" then the thickness approval equals  1.1xT

Dissimilar Thickness QW202.4:- The thicker and thinner part must be qualified, Except P8 and P4X the thinner part can be qualified if no Impacts and test coupon > 6mm thick.

Thickness limits for fillet welds as per QW462.4a or QW462.4d qualify all fillet weld sizes on all base material thicknesses and all diameters in one test.

Testing Requirements (Ref QW 463 for location of specimens)

Unlike EN288 there is no requirement for any non-destructive testing such as radiography or MPI/DPI, although I would recommend radiography for butt welds.

The testing requirement for groove welds are as follows:-

Two Transverse tensile tests (QW150).

Two Root bends and Two face bends unless the plate thickness exceeds 3/8" then 4 side bends are required. All bend tests should be done to QW160 using the correct former ref. QW466 to an angle of 180 degrees. Longitudinal (all weld) bend tests are not recommended unless the base/weld materials differ markedly in bending properties.  See QW 466 for exceptions and precise details.

The testing requirement for fillet welds on plate is 5 macro sections only, for Pipe fillet welds 4 macro sections. No fracture test required.

Welding Procedure Specifications (WPS)

This document details the practical application of the Procedure Qualification Record (PQR). It should contain enough information to give direction to the welder and should address all variables associated with the welding process defined in QW250 including non essential and supplementary.

A WPS can combine welding processes from other PQR's but all the relevant variables must be addressed including parent metal thickness. There is an exception to this rule for root runs from PQR's that are greater than 1.5 inches thick (38.1mm), see code for details.

Standard Welding Procedures Specifications   (SWP's)  Standard welding procedures listed in annex E of ASME IX can be purchased

from the 'American Welding Society' and used without qualifying a PQR.  Section V of ASME IX gives details of essential variables and restrictions.  A successful welder performance qualification must be carried out to demonstrate the SWP's before a manufacturer can use it. 

Brief Introduction Procedure Qualification Record (PQR) Welding Performance Qualification (WPQ) ASME definitions for welding processes, consumables and welding

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