Welding Procedure Specifications (ASME IX)

​​​​Welding procedure specification (WPS)

A WPS is a written qualified welding procedure prepared to provide direction for making production welds to Code requirements. The WPS or other documents may be used to provide direction to the welder or welding operator to assure compliance with the Code requirements. It contains all the necessary parameters such as joint details, base metals, filler metals, positions, preheat, PWHT, gas, electrical characteristic, technique etc. (including ranges). These parameters are known as WELDING VARIABLES (QG-105 & QW-250).

Essential Variables QG-105.1 & QW-251.2, QW-401.1

 A change in essential variable is considered to affect the mechanical properties of the weldment and shall require requalification of the WPS. Hence, the WPS must be required qualification, if any the essential variable is changed.

Supplementary Essential Variables QG-105.3 & QW-251.2, QW-401.3

A change in the supplementary essential variable will affect the toughness properties of the joint, heat-affected zone, or base material. Hence supplementary essential variables become additional essential variables in situations where procedure qualification requires toughness testing. When procedure qualification does not require the addition of toughness testing, supplementary essential variables are not applicable.

Nonessential Variables QG-105.3 & QW-251.3, QW-401.4

Nonessential variables are those in which a change can be made without requalification of the existing WPS, since it is not considered to affect the mechanical properties of the joint. Though a change in the nonessential variable doesn't require requalification of the WPS but still it should be properly addressed in the welding procedure specification (WPS).

These variables listed in tables QW-252 through QW-266 are subdivided into the variables of article IV - welding data. Each welding process is a separate table containing the list of all variables.

Steps to be prepared a pWPS and PQR

Knowledge and understand the specifications

Firstly, we need to identify the welding process, application, and understanding the specification. The WPS must be described all variables in the table QW-252 through 269, which welding process is selected to apply. Each table has detailed the limitation of welding variably by the symbol ">, <, +, -, etc.", it easy to understand and found explanations at the subdivided variables (QW-400), for example, welding process is SMAW, refer to Table QW-253, para. QW-402.1 mentioned " change Groove design", nonessential variable, so, we go to para. QW-402.1 means "A change in the type of groove (V-groove, U-groove, single-bevel, double-bevel, etc.).". 

Material, tools and equipment 

All materials, tools, equipment to be used  the test, I recommend to prepare in a checking list for monitoring such as:

Welding machine, tool for inspectionmulti-amps, welding gauges, tape/square steel, weld purge monitoring (for stainless steel), flashlight, temperature device, etc. are in good condition and calibrated.

Base material and welding consumables: available MTCs, must be reviewed and verified compliance with material specification, chemical composition, mechanical properties, NDE, actual dimension, type of inspection certificate (recommended 3.1 or 3.2), etc.

  • In case of PQR subject to hardness survey complying with NACE MR0175, the hardness values stated in MTC must be within range allowance, This purpose to minimize hardness value at HAZ areas. For carbon steel accordance to NACE MR0175 part 2, stainless steel accordance to NACE MR0175 part 3.
  • In case of running PQR compliance with Classification Rules, or for classification project, the welding manufacturer / welding consumables must be approved and classified by International Classification Society.
  • Test coupon preparations are either select plate or pipe for qualification.
  • If qualification on pipe and CVN test, I suggest to set up at 6G position. In case of qualification on pipe OD. less than 100mm, 2 test coupons must be prepared.
  • If qualification on plate must be enough long of test coupon for testing.
  • If any combination procedure, thickness subject to test at latest 13 mm and over.

Welders, who conduct the test coupon, must assign a skilled welder.

Official running the test coupon

PQR shall be recorded as actual values, true records. It may need a third party to witness and endorse document.

Sequences to be checked during test

Before welding

Position: properly tack welding.
Welding machine: calibrated and ready for using.
PQR template: ready for recording.
Welding consumable: had baked and dry out.
Skilled welder: available with ID for checking by Thirdpaty (if any).
Inspection tool: certified and ready for using
Fit-up inspection: as per pWPS.
Preheat temperature: minimum preheat temperature check and crosscheck by Tempilsik, read more "temperature measurement".

During welding

Welding parameter: such as voltage, amperage, current & polarity, travel speed, time, gas, backing gas, follow rate within range allowed in pWPS.
Material: filler metal on each process, gas compositions (%).
Weld bead: check thickness of weld metal deposit, run out length within range allowed in pWPS.
Cleaning each weld pass/layer: properly clean by brushing, grinding.
Priority, root layer must be carefully inspected full weldment, any imperfections of lack of root fusion, incomplete penetration, burnout, etc, are cause of rejection.
Rest layers continue deposition as per welding parameter within the pWPS.

After welding

Visual inspection after welding, to make sure no crack, complete penetration and complete fusion of base metal and weld metal. After successful welding, test coupon is subjected to non-destructive test and destructive test.

Based on the proposed WPS, test coupon is prepared, and the coupon is welded as per the values (or range) provided in the pWPS. All the real time data (observed during the welding of test coupon) are recorded.

Non-destructive test

Volumetric NDE shall not require in procedure qualification, but we may subject RT or UT and make sure that no defects are presented of porosity, lack of fusion, slag inclusions etc. These defects may adverse to mechanical tests.

The acceptance criteria are according with QW-191.1.2 for RT examination or QW-191.2.3 & QW-191.2.4 for UT examination.

RT/UT report shall be recorded in PQR form and Welder Qualification Certificate.

Recommend NDE subcontractors has qualified DNV-GL approval service supplier.

Destructive test

Lab test must qualified ISO 17025 as instruction in topic "Mechanical and Chemical Laboratory qualified an ISO 17025".

Test specimens required in QW-202


QW-150 Tension test: 2 samples (either transverse or longitudinal).
Acceptance criteria: Based on a minimum specified tensile of base metal, and matching strength of welding consumable. The tensile strength of joint/specimens shall not less than:

  • The minimum specified tensile strength of base metal, or
  • The minimum specified tensile strength of the weaker of the two, if base metal of different tensile strength are used, or,
  • If the specimens breaks in the base metal outside of weld, the tensile strength shall not less than 95% of the minimum specified tensile strength of the base metal.

QW-160 Guided-bend test: 4 samples (4 - side bends or 2 face bends; 2 root bends).

Acceptance criteria: no open discontinuity in the weld ir HAZ exceeding 3mm.


QW-170 Toughness test (CVN): 9 samples (base metal, HAZ, weld metal),

Acceptance criteria: lower temperature and absorbed values as specified in contracting project or code application.

Hardness test and Macro test: 01 sample, it should subject to test on your PQR, It may conduct on the same specimens.

Acceptance criteria: hardness test for procedure qualification to comply with NACE MR0175 shall be subject to hardness survey as specified in NACE MR0175 part 2, para. 7.3.

Read more: Hardness Test Survey for Procedure

Chemical analysis: stainless steel, alloy should conduct the test, especial type of low carbon content such as type 316/316L, 304/304L, Duplex, Inconel, Monel, Hastelloy, etc.

Summary and development WPS

Supporting document for endorse PQR, WPS, Welder performance qualification include MTC (base metal & weld metal), actual PQR recorded, Official PQR, Lab test report, NDE report, official WPS(s).

Format WPS, PQR may be use a suggested format form QW-482, QW-483. We are recommended a development WPS/PQR format to meet QW-250 and  contents of WPS QW-200.1 that are listed out all variables for each welding process in the table QW-252 to QW-266.

In case of combination welding process, we can insert a row for its variable, if other welding process is not application “denote – n/a”.

Read more: sample WPSs and PQRs. and Welding Performance Qualification.

Difference between PQR and WPS?


True value of the actual variables used during the welding of the test coupon.


Range qualification based on PQR records and variables in each welding process.

Significant articles in ASME section IX

Article I   Welding General Requirements
QW-150 Tension Tests
QW-153 Acceptance Criteria-Tension Tests
QW-160 Guided-Bend Tests
QW-163 Acceptance Criteria-Guided Bend Tests
QW-170 Notch-Toughness Tests
QW-180 Fillet-Weld Tests
QW-182 Fracture Tests
QW-183 Macro Examination-Procedure Specimens
QW-191 Volumetric NDE (RT & UT)

Article II Welding Procedure Qualifications
QW-200 General
QW-210 Preparation of Test Coupon
QW-214 Corrosion-Resistant Weld Metal Overlay
QW-216 Hard-Facing Weld Metal Overlay
QW-250 Welding Variables

Article IV Welding Data
QW-400 Variables
QW-402 Joints
QW-403 Base Metal
QW-404 Filler Metal
QW-405 Position
QW-406 Preheat
QW-407 Post Weld Heat Treatment
QW-408 Gas
QW-409 Electrical Characteristics
QW-410 Technique
QW-420 Base Metal Groupings

QW-252 through QW-269Welding Variables Procedure Specifications
QW-422 Grouping of Base Metals for Qualification
QW-430 F‐Numbers
QW-432 Grouping of Electrodes and Welding Rods for Qualification
QW-440 Weld Metal Chemical Composition
QW-442 A-Numbers Classification of Ferrous Weld Metal Analysis for Procedure Qualification
QW-450 Specimens
QW-451.1Groove-Weld Tension Tests and Transverse-Bend Test
QW-451.2Groove-Weld Tension Tests and Longitudinal-Bend Test
QW-461 Positions
QW-462 Test Specimen
QW-470 Etching — Processes and Reagents

Article V Standard Welding Procedure Specifications (SWPSs)

Reference standards

ASME II Part A – Ferrous Material Specification
ASME II Part B – Non-ferrous Material Specification
ASME II Part C – Specification for Welding Rods, Electrodes, Filler Metals
ASME V Non-destructive Test
ASME B2.1 Standard Welding Procedure Specification

Nguyen Duy Bien

Enjoy learning and researching, reading book. Knowledge welding inspection painting inspection.

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