You're in the middle of a four week outage and find out that the bellows on the steam turbine cross-over expansion joint is leaking. The standard option is to ship it to a qualified expansion joint manufacturer who will replace the bellows and retest. Unfortunately the current expedited lead time is 3 weeks - a full week beyond the outage which does not even include ippe's Shelf dryer another 3 days of reinstallation.
Plan ahead now so that this unpleasant experience doesn't happen to you.
Buying time with a cartridge bellows
A large time consumer in refurbishing a cross-over is manufacturing the 2-ply testable alloy 625 bellows. The bellows manufacturing can't be started until the whole unit is disassembled and measured. That's because unknown past modifications could have occurred to the cross-over which could potentially cause the bellows to be scraped and lead to an even longer delay.
The image above shows a common OEM cross-over expansion joint (rhymes with 'resting house').
(The original article can be viewed with diagrams and graphics at the website noted below)
The only option that allows for the bellows to be manufactured ahead of time is a cartridge bellows, that is a steam turbine generator bellows welded to pipe ends.
This solves the problem of fitting the bellows to a pipe that may be out of round or have a length difference. The old bellows is cut off with a section of pipe and the cartridge bellows is welded back in.
Here's the really good part - the cartridge can be installed and the unit retested within a one week window. The welding can also be performed by plant personnel; that provides more outage options. The key is that the cartridge needs to be ordered in advance of the outage.
Yes, this means ordering a part that may or may not be needed for the upcoming outage. True, but if the existing cross-over expansion joint is over 20+ years it is living on borrowed time and having a replacement cartridge in the warehouse is the right move to make. Another plus is the cost savings of avoiding expedite charges. Both bellows should be replaced at the same time.
Most cross-over units have 2-ply testable bellows which can be used to determine leaks while on-line (see The Bellows Bottom Line, 'Maintaining 2-ply testable bellows' - Sept '08).
The bottom Line
If you have an old cross-over, have the covers removed and take a convolution count the next time the turbine is down (even easier if drawing are available). With that information the cartridge bellows can be put on order so that your replacement options are pre-planned.