Ring joint VS Spiral Wound Gasket class 2500 cycling and different flanges temperatures 1

[fers144]

Hello my friends!
I would like to know how ring joint are afected in cycling cases and situations where needed isolating results in different flanges temperatures.
Is there a tendency to replace ring joint gaskets with spiral wound gaskets for 2500 class?
Knowing there is loss of preload on the bolts because of plastic deformation on cycling temperature cases, I assume a similar cause affects gaskets and grooves having two flanges at different temperature.
I would like to know how temperatures, loads and deformations affect or not these two types of gaskets in these cases.


Thanks a lot!

 

[racookpe1978]

Not sure why you feel this particular problems specifically relates to nuclear issues, will the replacement be made in a nuclear-grade piping system at that pressure and temperature?

 

[fers144]

It is related to the primary piping system as a general rule for replacement.

 

[Duwe6]

IF both flanges and the bolting are all the same material, AND all under the same insulation, AND Start-ups use gradual warm-up, then the spiral-wound gaskets do not experience plastic deformation. On a Class 2500 system, that's too many IF's for me. Those flanges are massive, and the bolting area warms up much later than the gasket area.

Ring-Joint flanges make better engineering sense - the RTJ gasket can deform elasticaly and maintain a seal during temperature cycling. Plus, I've never been a fan of raised-face flanges and flat gaskets ['paper' or spiral-wound] in high-pressure systems. And Class 2500 is pretty much the definition of a high-pressure system.

 

[fers144]

OK, thanks, so 2500 class would not work fine with spiral wound gaskets ,
I would like to know also if in a lower pressure piping system (for example class 900, 300 and 150), would I have some advantage with spiral wound gaskets? I readed an article wich explained how plastic deformation occurred with ring joint gastkets after a temperature cycling (380ªC, 80bar) creating critical loss of bolt preload. It,s sensible to replace ring joint gaskets where there is lower pressure with spiral wound gaskets ? All this is concerned around the design for a new piping system. it,s not about a replacment on an existing pipe line.

Thanks a lot!!

 

[racookpe1978]

If the system works - no current leakage under current pressures and heatup rates - why replace the current flanges at all?

 

[davefitz]

I am not sure if the following are approved for use at nuclear plants, but there are advantages to using Belleville washers to prevent bolt overstrain during thermal cycling, and there is also much less thermal stress developed in a modern " compact flange" ( designed by calculation as per sect VIII) compared to a classic B16.5 flange ( whose geometry was developed circa 1927 by-eye).

"Whom the gods would destroy, they first make mad "

 

[ricklts]

fers144 and davefitz,

From my experience, a RTJ flanged joint will also see unequal expansion of the components (gasket-flange bodies-bolting) when exposed to thermal excursions. The RTJ gasket will be subject it's thermal expansion limits long before the flange begins to absorb sufficient heat to reach an upper equilibrium (thermal expansion is volumetric), and the bolting even more so. Therefore, the gasket will be subjected to additional plastic deformation due to this differential. This may result in leakage, especially after the joint returns to normal conditions.

The SWG will also be compressed more; the windings are small metal components, but they are supported somewhat by the filler materials and tend to 'rebound' better. Most PWR Steam Generators use SWG's throughout the Steam Generator systems.

Dave, most nuc's in the use have been using Bellville style washers in many applications. I don't remember any (it's been 12+ years since I was last in containment) in the primary side, but I'm sure they are there.

Good luck,
Rick