Impact test for welding procedure qualification
This article will guide to prepare the test coupon and additional test coupon for previously qualified PQR, combine welding procedure according to ASME BPVC Section IX.
When WPS are required impact test?
There are almost required in the project specification or you also find in design code, the testing requirement, material requisition requirement, piping material or piping shop fabrication, or mentioned in construction drawing (as red highlight).
Test procedure and apparatus as specified in the specification or conform to the requirement in ASTM A370.
Examples for design code ASME B31.3
- Mid-carbon steel are required the CVN when the minimum design temperature MDT lower than -29 deg.C.
- Low temperature carbon steel and high strength material shall require CVN test at -46 deg.C.
- Duplex materials require Charpy V-notch impact testing at -46 deg. C. Acceptance criteria per NORSOK M-630.
Supplementary Essential Variables are in addition to the essential variables for each welding process. Read more QG-105, QW-250, QW-401.1.
Let review with us for SMAW welding process as table QW-253 - supplementary essential.
QW-403.5: change group number as material grouped in table QW-422.
QW-403.6: T limits toughness,
Base metal limits qualification shall a thickness of test coupon T or 16mm, whichever is less. Almost procedure missing this article. Below photo is detailed of T qualification and T limits the CVN test that should detail in the WPS.
Note: "T" means base metal thickness, "t" means deposit weld metal thickness.
QW-404.7: Change diameter of electrode > 6mm.
The manual process is most use electrode of dia 3.2 mm, 4.0 mm. So, It is not essential variable with us.
QW-404.12: change classification of welding electrode.
Any change in the designated classification as moiture-resistant (E7018R to E7018), diffusible hydrogen level (E7018 H4 to H16), classification required toughness to another (E7108 to E7018-1).
QW-405.2: Change position.
QW-406.3: Increase interpass temperature > 55 deg. C as recorded in PQR.
Most projects specified IP max. 150 deg C for stainless steel, 250 deg. C for mid-carbon steel, high strength low alloy steel depend on type material application.
QW-407.2: Change PWHT (T & T range).
QW-409.1: Incease heat input or in volume of weld metal deposit per unit length, for each process records in the PQR
QW-409.4: Change current and polarity.
Any change from DC to AC or EN to EP and vice versa.
QW-410.9: Change multi to single pass per side.
Multi-pass per site as limited in QW-409.1 ( Heat Input). So, you can't deposit one weld bead with electrode 3.2/4.0 mm per side except a small fillet weld.
The previously PQR qualification without impact test?
> The additional test coupon shall prepare enough long for testing, all essential variables using the same welding procedure. and then apply new supplementary essential vasiables.
The previously PQR qualification including impact test, but one or more supplementary essential variable is changed?
> The additional test coupon shall prepare enough long for testing, all essential variables using the same welding procedure. If a previously qualified weld procedure has satisfactory toughness values in the weld metal , then it is necessary only to test toughness specimens from the heat-affected zone when such are required.
Read more: QW-401.1.
Test specimens and test results
Number of test specimens: as per specification or 3 specimens for weldment, and 3 specimens for HAZ, and 3 specimens for base metal.
Preparation of sample: please find out ASTM A370, figure - 11 (a) for standard full specimens, and figure - 11 (b) for standard subsize specimens.
In case of base metal thickness of test coupon greater than 25mm or combined 2 welding process in a PQR, the test specimens should note the specimen preparation for the cap bead and root bead.
Test results: minimum required CVN test values as ASME B31.3 Table 323.3.5
In case of base metal thickness less than standard specimens, as known a subsize specimens, reduction temperature must be noted as ASME B31.3 Table 323.3.4.
Don't miss record "LATERAL EXPANSION" for P-nos 6,7,8 or specified UTS > 656 MPa as highlight in red in the table 323.3.5
The PQR may need to note such as duplex stainless steel or stainless steel was qualified on pipe NPS 2" Sch 10S.
When selection of welding procedure specification for bidding or construction, It is one of way to save cost for your company. Any mistake will effect the WPS and qualification.
So, you don't ignore some below important note.
- Change base metal group number,
- T limits,
- Change welding consumable classification,
- Heat input,
- Power characteristic,