Root causes regarding widespread cracking in tee fittings

Tee fittings stamped as A-/SA-234, designed to ASME B16.9, and installed in ASME BPVC Section I or ASME B31.1 piping systems are experiencing widespread damage in the tee crotch position, and the main or branch outlet weld heat affected zone (HAZ) aligned with the crotch position. Damage is documented as leaks, cracks, or ‘undetectable’ creep damage that is later documented in post-mortem laboratory examinations. At the tee crotch positions, complications have been well-documented which include vee-profiles on the inside diameter surface, and subcritical post-weld heat treated weld repairs to variable through-wall extent. Such observations are believed to be a result of the variability in the forming process(es) necessary to produce the tee fitting. To date, there is no trend with the system (main steam or hot reheat) or size (10-inch to 32-inch outside diameter tees have experienced leaks) or material (Grade 22, 91, 92 and X20 are affected). The systemic nature of the problem brings to light the need for comprehensive solutions which address integrated life management concepts, implement informed material correlations for improved design requirements, properly database metallurgical and non-destructive evaluation findings, and take this body of information forward to enhance the relevant codes and standards governing the affected product form(s) and system(s).