Bigpond Clarifications are needed on your failure in expansion bellow and expander. Have you seen in metallurgical analysis : Knife line attack which is seen in nitric acid service in HAZ of bellow. For a new solution annealed S.S 316 where is the question of work hardening effect seen by you? Is it possible that you have over work hardened the expander and a work hardened S.S 316 L would be susceptible to knife line attack (SCC) in nitric acid service at this temp ( 200 deg cent) You could try multi-ply expansion bellow instead of single V/U/omega design bellows type. Multi-ply expansion bellows can take more work hardening and also may not fail as often as you experience even with use of S.S 316 L. Hope this helps C.V.Srinivasan Nishi Engineers Pvt Ltd India March 10, 2009 E-mail: nishi@vsnl.com >Hi, >We have an expansion bellow which is made in SS 316 >(including convulsions) installed in expander of Nitric acid >plant. The medium is 96% N2, 3% O2 and less than 0.005% Nox >at 200 Deg C. There was a weld crack on the bellow to end >connections within 8 months of plant operation, the crack >also extends to the expansion bellow. I would like to if SS >316L is a suitable material for >1. Expansion bellows in general as this gest work hardens >fast compared to inconel and likes. >2. For Nox gases (though its is availalbe at less than 0.005 >percent) > >If anyone has experienced similar problems and would like to >share. > >regards >regards