Bellows - Type Expansion Joint Failure 3

[chazjr]

Has anyone had any experience with bellows-type expansion joint failure due to stress corrosion cracking caused by Chloride. Material of construction is 304 SS. Fluid is 125psig steam. Related questions:
1) Is 304SS a suitable material for steam service
2) Is Inconel 625 a suitable matl for steam service.
3) Is there a protocol for hydro testing such joints (prior to startup).
4) Does it make a difference (in terms of preventing corrosive attack) whether the joint is placed in horizontal or vertical position?

 

[StressGuy]

I'll leave the definitive answer on the material selection to some of our other experts. Although, if chlorides are in your stream, SS is probably a bad idea. I should think that 625 would be plenty good, and 617 probably as well - there's a 617LCF (Low Cycle Fatigue) that was developed primarily for use in metal bellows expansion joints.

As far as testing goes, that would be covered by ASME B31.3 Appendix X.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.

 

[monkeydog]

Ok I will add to StressGuy's comments. By personal experience I can tell you if you have chlorides in your steam/water you will have corrosion and cracking.

 

[hokie96]

I've had some fairly significant experience with chloride SSC in 600 psig and 125 psig steam service. If this expansion joint is the one (or one of a few) austenitic stainless steel components in your steam system, the metallurgy upgrade you propose may be the appropriate path. Inconel 625 should perform very reliably in steam service.

However, if your system is anything like those I've experienced, you may have a large number of austenitic components throughout your system (check control valve trim, boiler tubes, safety valve trim, any vessel internals, strainers, intrument components, etc.) If you have a large system with many austenitic components, upgrading your way out of the problem may not be a cost effective choice.

Do you know what is causing the chloride contamination of your steam system? Can you isolate the contaminate? In dealing with large steam systems, I've typically worked to isolate the contaminate, rather than attempt to upgrade all of the austenitic components. Upgrades were limited to components with very high consequences of failure. Once the contaminate is isolated, you may have a couple "residual" failures, but generally, the system (if blowndown properly) will clean itself up fairly quickly. We continue to operate today with a large number of austenitic components in our steam systems.

One final thought: Depending on the component, downgrading the metallurgy can also be effective. Ferritic stainless steel components (valve trim, traps, rotating equipment) faired very well when exposed to chloride contamination in our steam system.

 

[metaltrade]

twice both on the metal bellows of a heat exhcnager. both in horizontal position. the first failure is not service related but rather induced by invironment. the other is service related but at a lower temp. Both exchnager were repaired using a split bellows. On both occasion, we did not upgrade the material. on the first exhanger an in-kind replacmcnet was impleemnted and then we jsut apply a suitable coating.we did a forensic exam of the feed on the other, find the source of the chloride and then add a scruber. this was a couple of years ago.