WPS AND PQR

 A Welding Procedure Specification (WPS)

It 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.

Within the WPS a number of essential variables are identified. These essential variables are those features of the procedure that, if changed outside a range of approval, will result in an unacceptable change in the mechanical properties or defect level of the weld, invalidating the WPS and making re-approval necessary.

It lists the pre-and post-weld operations including heat treatments,machining, grinding and dressing of the weld alsodetails of  the welding variables and the run sequence; and may specify the acceptance criteria and inspection methods.

 The purpose of the WPS is to ensure that acceptance criteria can be met consistently, including mechanical properties and defectlevels. It is also useful in enforcing quality control procedures, in standardisingon welding methods, production times and costs and in controlling production schedules. Its prime purpose, however, is to give the welder clear,unequivocal instructions on how a weld is to be made. 



 EN ISO 15609-1 (formally EN 288 Part 2)  European Standard For Welding Procedure Specifications
  

EN ISO 15609 Defines the contents of a Welding Procedure Specification in the form of a list of information that should be recorded.  For some applications it may be necessary to supplement or reduce the list. For example only in the case of a procedure requiring heat input control would there be a necessity to quote travel speed or run-out length for manual processes.

 ASME IX  American Boiler and Pressure Vessel Code 

QW 250 Lists the variables for each welding process, all the variables stated should be addressed.  The range permitted by the WPS is dictated by the PQR or PQR’s used to qualify it. 

     Common to all Processes        .

• Procedure number
• Process type
• Consumable Size, Type and full Codification.
• Consumable Baking Requirement if applicable
• Parent material grade and spec.
• Thickness range.
• Plate or Pipe, Diameter range
• Welding Position
• Joint Fit Up, Preparation, Cleaning, Dimensions etc.
• Backing Strip, Back Gouging information. 
• Pre-Heat (Min Temp and Method)
• Interpass If Required (Maximum Temperature recorded )
• Post Weld Heat Treatment. If Required (Time and Temp)
• Welding Technique (weaving,max run width etc.)
• Arc Energy Limits should be stated if impact tests are required or if the material being welded is sensitive to heat input.      

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. 

PQR ( PROCEDURE QUALIFICATION RECORD) 

PQR's are not required if Standard Welding Procedures are used.

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.

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.