Dear Sir,

Many welded joints and/or weld assembly consist of Low alloy steels (LAS) are used in “as-welded” condition or under “Stress-relieved condition” or post weld heat treated condition to minimize the  residual stresses developed in the weld joints that developed during the heating and cooling cycle  . Under this treatment, the weldment is heated to a temperature below the transformation temperature, approximately 730°C for C-Mn ferritic steels, and held at this temperature for a  prolonged time, followed by uniform cooling.  Stress relieving is often used to reduce distortion and to control dimensional stability and tolerances.

Many welded assembly require precise dimensional control are often stress relieved after welding. PWHT is also done to prevent stress corrosion cracking (SCC) and/or to avoid higher hardness and brittle microstructure  in weld metal and HAZ.

Hence, the choice of an electrode is depending upon the service condition requirements.

Accordingly, many matching filer metals / electrodes for low steels are classified under the following AWS Specification-

AWS A5.5/A5.5M:  Specification for Low-Alloy Steel Electrodes for Shielded Metal Arc Welding

AWS A5.23/A5.23 M:  Specification for Low-Alloy Steel Electrodes and Fluxes for Submerged Arc Welding

AWS A5.28/A5.28 M:  Specification for Low-Alloy Steel Electrodes and Rods for Gas Shielded Arc Welding

AWS A5.29/A5.29 M:  Specification for Low-Alloy Steel Electrodes and Rods for Flux Cored Arc Welding

Regarding the AWS classification code to identify whether the particular selected electrode if used for joining low alloy steel material is suitable for the “as-welded” (AW) or “stress-relieved condition” (PWHT) requirement. There are various alphabetical and alphanumeric suffix given followed by electrode designation that indicates the suitable temperature for post weld heat treatment.

For example, AWS A5.5/5.5M specification for LAS electrodes for SMAW process designates following AWS classification suffix.

AWS
Classification Suffix		PWHT Temp (°C)
A1 620
B1690
B2 / B2 L690
B3 / B3L690
Etc….

For example, E8016-B2, SMAW electrode for matching Cr-Mo low alloy steel should be tested under PWHT condition. In which B2 indicates 690° C temperature for PWHT process.  Holding time usually 1 inch per hour thickness thumb rule. It is also to be noted that these suffix are also indicating the chemical composition of the electrodes as under

Electrode SuffixChemical CompositionType
A1
0.5% MoC-Mo Steel electrode
B1
0.5% Mo – 0.5% CrCr-Mo Steel electrode
B2
0.5% Mo – 1.25% CrCr-Mo Steel electrode
B3
1.0 % Mo – 2.25% CrCr-Mo Steel electrode
B4
0.5% Mo – 2.0 % CrCr-Mo Steel electrode
C1
2.5 % NiNi Steel electrode
C2
3.5 % NiNi Steel electrode
D1
0.3 % Mo -1.5% MnMn-Mo Steel electrode
D20.3 % Mo -1.75% MnMn-Mo Steel electrode
Etc.

It is to be noted that PWHT temperature guidelines are varying from type of electrodes (SMAW, SAW, GMAW or FCAW) so it is necessary to refer the concern AWS electrode specification.

Secondly, these PWHT temperature guidelines are for testing electrodes only , for production weld- joint procedure qualification, PWHT temperature may vary.

The testing of electrode under AW or PWHT condition is also depending on the agreement between purchaser and supplier.

One can refer the ASME BPVC SEC II Part C following Tables for the required AWS electrode specification

–Chemical Composition Requirements for Undiluted Weld Metal

–Tension Test Requirements (Which also classifies testing of electrode as AW or PWHT)

–Charpy V-Notch Impact Requirements

–Preheat, Interpass, and Postweld Heat Treatment Temperatures (as per Electrode Suffix)

In conclusion, If PWHT is to be conducted, the final weld properties should be evaluated. As we all know that PWHT also reduces the weld metal strength by 15-20 % depending on selected PWHT parameters so CVN properties of the weld metal after PWHT should also be evaluated. Secondly, while selecting the electrode / filler metal, care should be taken that it is classified under the PWHT test condition. The influence of the PWHT cycle on the weld metal, heat-affected zone and base metal properties also need to be evaluated.

Hope, this information will be helpful to you.

Reference:-

AWS A5.5/A5.5M:  Specification for Low-Alloy Steel Electrodes forShielded Metal Arc Welding

AWS A5.23/A5.23 M:  Specification for Low-Alloy Steel Electrodes and Fluxes for Submerged Arc Welding

AWS A5.28/A5.28 M:  Specification for Low-Alloy Steel Electrodes and Rods for Gas Shielded Arc Welding

AWS A5.29/A5.29 M:  Specification for Low-Alloy Steel Electrodes and Rods for Flux Cored Arc Welding

ASME BPVC SEC II  Part C Specifications for Welding Rods,Electrodes, and Filler Metals