Gasket Leakage Due to Thermal Fluctuation
Gasket Leakage Due to Thermal Fluctuation
(OP)
We will appreciate views and advice from colleagues on a problem being faced by us at one of our plants. The description is as follows:
In a heat-exchanger, we have a stainless steel jacketted gasket of graphite. The temperature of the heat exchanger swings between 250-300C at a frequency of around twice a month. Normally, it stays around 300C. The service is steam in the shell and cooling water in the tube. The shell is of carbon steel while tubes are of stainless steel 304.
We have been facing frequent leak at the gasket at the interfact of channel head cover and the shell. When we install the gasket, we tight the bolts and face no leakage when the exchanger is taken in service. However, after a 3-4 months, we face leakage. We perform hot-bolting and leak stops. However, it proves to be a temporary as leaks again starts and further tightening does not stop the leak.
Can some one guide us the probable cause of gasket leak and are there any other gasket other than stainless steel which can help resolve the proble. Feedback and advice will be greatly appreciated.
MetCorr
In a heat-exchanger, we have a stainless steel jacketted gasket of graphite. The temperature of the heat exchanger swings between 250-300C at a frequency of around twice a month. Normally, it stays around 300C. The service is steam in the shell and cooling water in the tube. The shell is of carbon steel while tubes are of stainless steel 304.
We have been facing frequent leak at the gasket at the interfact of channel head cover and the shell. When we install the gasket, we tight the bolts and face no leakage when the exchanger is taken in service. However, after a 3-4 months, we face leakage. We perform hot-bolting and leak stops. However, it proves to be a temporary as leaks again starts and further tightening does not stop the leak.
Can some one guide us the probable cause of gasket leak and are there any other gasket other than stainless steel which can help resolve the proble. Feedback and advice will be greatly appreciated.
MetCorr





RE: Gasket Leakage Due to Thermal Fluctuation
If you arrive to the conclusion that the flange is not thick enough, then we'll look for options to increase the thickness, within the Code requirements, without altering the original scope and design...
cheers,
gr2vessels
RE: Gasket Leakage Due to Thermal Fluctuation
Gasket creep, perhaps?
Although there may have been sufficent load applied to prevent leakage for the first few months, creep may have resulted in bolt load-loss.
Assuming that the designer had put in enough meat into his specified load to compensate for future load loss, it may be moot if the initial tightening procedure resulted in lower preload than desired. Were the studs on this joint simply "torqued". If so, what steps were taken to ensure that the required loads were actually achieved?
Ciao,
HevïGuy
www.heviitech.com
RE: Gasket Leakage Due to Thermal Fluctuation
Some questions.
Was this the original gasket by design.
What is the flange and bolt material?
What is the size of the gasket?
No more than you are cycling at your temperatures you shouldn't be having a problem.
We cycle numerous 24" to 30" flanges between 20C and 285C around twelve times a day using a graphite filled flexatallic gasket.
RE: Gasket Leakage Due to Thermal Fluctuation
1. This gasket is origional gasket by design.
2. The bolts are of B7 and flange is carbon steel overlayed with Stainless Steel.
3. The gasket diamter is around 700 mm.
MetCorr
RE: Gasket Leakage Due to Thermal Fluctuation
Metcorr:
Of course, it's very important to review the design. However don't get hung-up on this to the detriment of other major variable: Procedure.
The poor gasket is often the first to be pinned with the blame when something goes awry. Concurrent to your design analysis make sure that you review the actual assembly procedure.
Ciao,
HevïGuy
www.heviitech.com
RE: Gasket Leakage Due to Thermal Fluctuation
If all else is OK, you might also look at adding belleville washers to help retain bolt load, if the thermal cycling is causing the problem. This may require longer studs.
These can be tough to solve, and may require several attempts. Good luck.
Mike
RE: Gasket Leakage Due to Thermal Fluctuation
MetCorr
RE: Gasket Leakage Due to Thermal Fluctuation
1. Large diameter flanges are more difficult to machine flat than small. Check the mating faces to determine of they remain flat individually and parallel to one another. The repeated dis-assembly and re-assembly of this unit may have resulted in less than stellar mating surfaces.
2. The flange load on the gasket must be evenly applied, either by tightening the bolts in a crossing pattern over several passes until the proper bolt stress is achieved.
3. Metal jacket gaskets are a typical product used in this application, however some PTFE composites have become popular in chemical applications where temperatures are in line (500-550F)
4. Do not use a graphonics or graphite laminate material in this application. The use of graphite is limited by its tendency to facilitate pitting corrosion in some stainless steels, and to promote galvanic corrosion between dissimilar metals (due to its electrical conductivity).
RE: Gasket Leakage Due to Thermal Fluctuation
Being on the same page, I think that mkkessel had meant to add: "...or by simultaneous bolt tensioning (or a high percentage thereof)"
Ciao,
HevïGuy
www.heviitech.com
RE: Gasket Leakage Due to Thermal Fluctuation
This style of gasket (with graphite facing) is very common in shell and tube exchangers, however you need to satisfy yourself that you do not create other problems down the road.
Please let us know how this all works out.
Regards,
Mike
RE: Gasket Leakage Due to Thermal Fluctuation
Graphonics are also available with a PTFE facing, again keeping in mind limitations on your operating temps. Along the same lines if the gasket is strictly an ID X OD design, the ultimate in sealing technology would be a KAMM-Profile gasket. There is a large initial expense, but the core is reusable and facings relatively inexpensive. Normally considered the ultimate "gasket" problem solver.
RE: Gasket Leakage Due to Thermal Fluctuation
Regards,
Mike