Open Discussion Forum Question 1

1. Please review the case histories in the DeMethanizer of an Ethylene Plant regarding studs / bolts failure along with best inspection practices / methods being followed for flanges / studs in cryogenic service? Ethylene Producer - 30 June 2003

Comment from Texas Ethylene Producer - 21 July 2003

We have not really seen a bolt failure problem in that area. Only problems I've seen have been related to leaks during initial cool down and the need for tightening flanges and connections during that time.

They could be having bolt failure problems due to over tightening them. Two possible ways to address that situation if that is what is happening. Aside from making sure that gaskets and bolts are adequate for the cold service, can use a hydrotorque machine to make sure things aren't over torqued or possibly use stainless Belleville washers for routine chronic leakers particularly on exchanger heads.

Standard pipe flanges aren't typically torqued with a wrench and it could be slightly over torqued when hot which could lead to high bolt stresses when things cool off.