Weld Procedure Qualification for a New Steel Grade
A fabrication shop is introducing welding on a new steel grade, S690QL, for a pressure vessel. The existing Welding Procedure Specification (WPS) is qualified for S355 steel. The shop's welding coordinator proposes using the same WPS with a slight increase in heat input, arguing that the higher strength of S690QL compensates for any differences. The vessel will operate at -40°C and must meet Charpy V-notch toughness of 27 J minimum. The client requires full compliance with ISO 3834-2. The coordinator has scheduled the first production weld for next week, but no new procedure qualification test (PQT) has been performed.
1. What are the key requirements for qualifying a WPS for S690QL according to ISO 3834-2 and related standards?
Read the worked answer
According to ISO 3834-2, the manufacturer must qualify welding procedures in accordance with ISO 15614-1 or other applicable standards. For S690QL, a new PQT is required because the existing WPS is qualified for S355, which is a different material group. Key requirements include: (1) Material group: S690QL belongs to a higher strength group (e.g., ISO 15608 group 3.2 or similar), so the existing WPS cannot be extended without testing. (2) Welding consumables: must be suitable for the higher strength and toughness; often matching consumables are used. (3) Preheat and interpass temperature: must be controlled to avoid cracking; typically higher preheat may be needed. (4) Heat input: must be within a range that ensures mechanical properties, especially toughness at -40°C. (5) Post-weld heat treatment (PWHT): may be required depending on thickness and application; if PWHT is used, the PQT must include it. (6) Testing: the PQT must include tensile, bend, impact (Charpy V-notch at -40°C), and hardness tests, as per ISO 15614-1. The impact test is critical to verify the 27 J minimum at -40°C. (7) Qualification range: the PQT will qualify a range of thicknesses and heat inputs; the WPS must be within that range. (8) Documentation: the PQT must be recorded in a Welding Procedure Qualification Record (WPQR) and approved by an examiner. The coordinator's proposal to use the existing WPS without PQT is non-compliant.
2. What immediate actions should the welding coordinator take to ensure compliance before production welding?
Read the worked answer
The coordinator must halt production welding until a suitable WPS is qualified. Immediate actions: (1) Develop a preliminary WPS for S690QL based on material data and welding consumable recommendations, considering preheat, heat input, and PWHT. (2) Arrange for a PQT according to ISO 15614-1, including all required tests, especially impact toughness at -40°C. (3) Ensure the test weld is performed by a qualified welder using the proposed procedure. (4) Select a qualified test laboratory or in-house facility for mechanical testing. (5) Document the PQT results in a WPQR and have it reviewed by an authorized examiner. (6) Update the WPS based on the WPQR and obtain client approval if required. (7) Communicate the delay to the client and adjust the schedule. (8) Verify that all other ISO 3834-2 requirements (e.g., welder qualification, equipment, inspection) are met for the new material. The coordinator should also consider whether any additional testing (e.g., hardness, macro) is needed for the application.