The ball tank nozzle flange bolts have been changed from alloy steel to stainless steel
Thread Content
A 600-cubic-meter oxygen storage tank made of 07MnCrMoVR material, with a design pressure of 3.5 MPa and an operating pressure of 2.5 MPa; the bolt specifications for the connection flanges are M39, and according to the design drawings, the bolts should be made of 35CrMoA material ； Rust often forms during use, which hinders disassembly; the using unit has replaced the bolts and nuts with stainless steel ones. Is the actual strength of these components sufficient to meet safety requirements? (They have been in use for 5 years now without any issues observed.)
This requires change management; it cannot be changed casually
It should be possible; ASME regulations specify that the bolts used for the nozzle flanges must have a stress level of at least SA193-B8 CL2.
Rusting is likely caused by the external environment. This cannot be achieved simply by replacing the material; it must have the same strength, and relevant approval for the changes is required. For reference
It should work fine when in use. Once an accident occurs, the problem becomes serious, and a design change is required
To even dare to change it by oneself – that’s too bold