Rationale

In para. 1. Scope, A234/A234M-25 states “These fittings are for use in pressure piping and in pressure vessel fabrication for service at moderate and elevated temperatures.” This ballot is to revise A234/A234M to address inconsistencies and general concerns associated with elevated temperature use of fittings made from creep strength enhanced ferritic (CSEF) steels. CSEF steels are typically used for high temperature applications in the time-dependent regime where creep damage is a concern. Discontinuities affecting long term performance of CSEF steels may emerge over time from sites which may be considered as 'injurious defects'. Not explicitly defined, injurious defects may represent different levels of damage for different steels. Those defects which may be tolerated by less complex steels may act as initiation sites for future creep accumulation in CSEF steels. Creep accumulation alone is very difficult to detect with traditional NDE methods as it may be present sub-surface or even mid wall. Once damage is extensive enough for voids to ‘link-up’, it often appears ‘suddenly’ as cracks or crack-like features. Included in proposed revisions is the information necessary to enhance requirements for CSEF steels to improve the performance expected of fittings operating in the time-dependent regime. Changes include the addition of a 'CSEF' definition, a cautionary statement related to unique CSEF material characteristics, and additional wording to address specific CSEF material behavior. When exposed to long term high temperatures, current rules for weld repair, consumable chemical composition, heat treatment etc. may not result in a CSEF product that is fit for purpose. Changes are shown in the applicable paragraphs.