Welding essential variables

Essential Clause(s) Reference
Parent material groups 8.3.1, Table 5 & 6 ISO/TR 15608
Parent material thickness, Table 7 & 8
Diameter, for pipes 8.3.3
Branch angle 8.3.4, Fig. 4
Welding process 8.4.1 ISO 4063
Welding positions 8.4.2 ISO 6947
Weld Type 8.4.3
Product Type 8.4.3
Filler Material Classification 8.4.4 Table A.1
Type of Current and Polarity 8.4.6
Heat Input 8.4.7 EN 1011, ISO/TR 18491
Preheat Temperature 8.4.8
Inter-pass Temperature 8.4.9
Post-heat Temperature 8.4.10
Post Weld Heat treatment 8.4.11
Specific essential variables 8.5

Parent material groups

Material groups refer to ISO/TR 15608

Permanent backing material within the approval (sub-) group.

  • Permanent backing for steel group 1.2 may be use material group 1.1 or 1.2 are acceptable.

Test piece material in group 1, 2, 3 and 11 qualify the equal or lower specified minimum yield strength steels.

  • Group 1.2 qualify steels in group 1.1 and 1.2.

Test piece materials in groups 4, 5, 6, 8, 9 qualify steels in the same sub-group and any lower sub-group within the same group.

Test piece materials in group 7 and 10 qualify steels in the same sub-group.

  • Material group 10.1 qualify steels in group 10.1 only.

Parent material thickness


  • t: thickness of test piece
  • s: deposited weld metal thickness for each process (if qualified on a combined processes).
  • D: outside diameter of test piece.
  • a: nominal throat thickness

Range of qualification

Limits of parent material and deposited metal are shown in Table 7 and Table 8.

Dissimilar thickness parent material no limits on the thickest part, if parent metal qualified on thickness of 30 mm or greater.

A combined welding procedure qualification, deposited metal of each process shall be used on each range of qualification.

Eg. Test piece on pipe with deposited thickness of GTAW (3mm) and SMAW (10mm).

  • The max. deposited metal of GTAW process qualification will be 2xS* = 6 mm;*
  • The max. deposited metal of SMAW process qualification will be 2xS* = 20 mm.*
    Refer to Table 7.

Fillet weld qualified by butt weld test, the throat thickness range shall be based on the thickness of deposited weld metal. See foot note in Table 8.

Butt weld on plate qualify on pipe with OD > 500 mm or > 150 mm in the PC, PF rotated and PA rotated positions.

D is the dimension of the smaller side (hollow section or other than circular), is the OD for pipe of a butt weld or OD of branch pipe for branch connection.

Note a in Table 7: if you want to run PQR in butt weld T-joint, thickness should be above 8 mm (for UT) and range of qualification max. 12 mm.

Welding process

I recommend to make a test piece with single process. To cover all positions and level 2, you should be performed the test pieces at 2 different positions, see Section 8.4.2.

Welding position

To qualify for all positions, you should consider test piece position to cover highest/ lowest heat input:

  • Fix pipe position J-L045, PG, PJ.
  • Combination of 2 welding position such PF+PC.

Type of joint / weld.

See welding variable in Section 8.4.3.

Filler metal

manufacturer trade name should be considered in welding procedure if impact testing is required less than – 20 deg. C.

Heat input

Range of qualifications are +/- 25%.

Preheat and inter-pass temperature

  • A decrease more than 50 deg. C from the recorded preheating temperature.
  • A increase more than 50 deg. C from the recorded preheating temperature.

Heat treatment

  • Addition or deletion of PWHT is not permitted.

Request for services, here.



Leave a reply

Your email address will not be published. Required fields are marked *


Log in with your credentials

Forgot your details?