*For original article with graphics click the PDF link attached below.
GE Cross-Over Toroid Bellows Replacements Protect the turbine with identical OEM designs
Beware of substitutions
Think twice, no think three times before allowing your original GE cross-over toroid expansion joint to be replaced by a different bellows design.
Many GE cross-over expansion joints have a toroid bellows profile, and some users get sold that the more common U-profile will be an adequate in-kind replacement. Don’t believe it.
Toroid bellows are a great design, getting their name from the circular shape of their profile.
It is true that a U-profile bellows can be designed to take the same pressure, temperature, and movements as a toroid, but that’s not the full story.
Design aside, the real reason not to change profiles is proven successful operational history of the part AND the turbine it was designed to protect.
Significant design differences Three reasons to stay with the original Toroid profile : Spring Rate. Often the redesigned U-profile bellows has a higher spring rate – that’s bad long-term for the turbine. Even if the replacement bellows can be designed with a lower spring load, any such change can result in unexpected bellows harmonic behavior – in short, it might vibrate differently and fail way too soon.
Corrosion. Most folks attempting to build an aftermarket bellows don’t know that the GE toroid bellows are vacuum annealed after forming. Don’t ask me how I know this. Annealing improves resistance to stress corrosion cracking in the material.
Pressure rating. Toroid bellows have burst pressures far in excess of U-profile bellows. That may be overkill but is just extra insurance.
Legal disclaimer We are not GE; as if you didn’t already know that. If you are a GE lawyer and are reading this article please understand we do not have your proprietary stuff and promise to scream and run if anyone ever tries to give it to us.
To end users – we’ve been around, built lots of these parts, and that’s all we’re saying.
The Bottom Line
U-profile bellows are not evil and do have their place – just not on your GE turbine that was designed to go with a toroid bellows cross-over.