This document provides guidance on the application of Mechanical Stress Relieving (MSR) as an alternative to Post Weld Heat Treatment (PWHT) for Type C tanks. Welded structures naturally develop tensile residual stresses along the weld, and PWHT has traditionally been the primary method for stress relief. Where PWHT is difficult to perform, the IGC Code may allow MSR by pressurizing during hydrostatic testing.
The Guidance Note summarises the minimum expectations for an MSR procedure, covering scope and applicability, preparation and set up, loading and conditioning methodology, instrumentation and monitoring and acceptance criteria.
This guidance is intended for shipyards and manufacturers responsible for the fabrication and approval of Type C tanks. Applicants are required to submit a detailed for LR review, and the proposed methodology shall be agreed with LR prior to conducting MSR.