Large diameter gasket types ?
Large diameter gasket types ?
(OP)
We have the requirement for a 42" diameter overhead line from a 50m high vacuum tower. Our required piping materials specification only goes up to 36" and needs to be expanded to 42". We use graphite reinforced stainless steel flat ring gaskets normally in this material spec. Someone has raised the question of wouldn't a graphite/stainless steel spiral wound gasket, with inner and outer ring, be better in this application. AS i have no experience in lines of this size, can anyone advise ?





RE: Large diameter gasket types ?
Can you give a little more information on the existing flange and gasket like is this an envelope type or something else. You will get a more informative answer with more information.
Is the flange a standard type or calculated type?
What standard?
Are you having trouble with existing gasket on 36" flange?
RE: Large diameter gasket types ?
RE: Large diameter gasket types ?
It was in our standards that a spiral wound gasket was not to be used in conjunction with a Class 150 flange of any description.
RE: Large diameter gasket types ?
RE: Large diameter gasket types ?
1) There is a recognised problem with 150# joints and spiral wound gaskets, in that the required bolt stresses needed to fully compress the gasket can be excessive. Some gasket manufacturers have developed a specific low-stress range of spiral wound gaskets to overcone this potential problem. Consult with your proposed gasket manufacturer prior to purchase.
2) 150# gaskets of this sort can be mechanically unstable during assembly and sometimes have tendency for the windings to fall away from the inner/outer rings before the flanges can be brought together. Careful handling is essential. Once the windings have separated, throw the gasket away and use a new one (expensive at 42").
You proposal of using a stainless steel reinforced graphite ring gasket looks fine to me and is used extensively by my company.
RE: Large diameter gasket types ?
A spiral wound would at least be in one piece so easier to handle, but as already mentioned it can “spring” apart if handled roughly. On this flange I would not worry about the available bolting unless you are using B8 bolts which have a relatively low yield. Generally it is the ½”-24” class 150 range that are a little under-bolted, especially 3” and 8” N.B. – the 42” series A has enough bolting to achieve a decent level of initial and operating stress on the standard ASME B 16.20 size gasket.
If you are worried about the possibility of springing the windings during handling, then a kammprofile type made to the same dimensions as the spiral might be a better option.
RE: Large diameter gasket types ?
It had been my experience that decent or just adequate bolting is not viable for real world operations. We have tested every type and style of spiral wound gasket both in the laboratory and field and have never been able to get the Class 125 flanges with spiral wound gaskets to perform satisfactorily even with a lot of tender loving care. I agree that everything calculates outs but operations never seem to operate by the rules agreed on.
Another problem is if you have a proliferation of types and styles of gaskets you are asking for trouble with today’s maintenance and management schemes.
A note on the installation of spiral wound gaskets. Never allow any type tape to be used on the gasket especially in the radial direction. We had a very expensive incident occur when a mechanic put 3 pieces of green fabric tape on 24" gasket to hold it togather and in place while they moved a blind flange into place. After a few hours operation at 650 F at 70 psig a small leak was noticed and within a couple of hours a second leak on the same flange was noted. By the time I arrived there were three leaks about 60 degrees apart. We had to shut the equipment down and the lost of this piece of equipment resulted in the loss of additional equipment with a maintenance bill of over $200,000. Examination of the gasket revealed 3, barley discernible, radial depressions across the spirals exactly 2" wide, the tape width.
RE: Large diameter gasket types ?
RE: Large diameter gasket types ?
jt
RE: Large diameter gasket types ?
Please excuse my error as it was Class 150 instead of Class 125.
Not getting off of my soapbox I will have to admit that properly designed, selected, and installed spiral wound gaskets will work very well if used in a some what steady state piping system. It is probably just that we have nothing that doesn't cycle, shake, wiggle, or run very long.
One additional point to be made for using heavier flanges is that the metal spirals alone can seal if someone uses a gasket with the wrong filler. It has happened to us several times where a graphite filled gasket was substituted for a ceramic filled gasket in NOX service at 1200 F.
We do also use the all metal gasket in a couple of styles, with and with out graphite. One problem we have had with the graphonic style on SS at high temperature is that we sometimes get a pronounced embossing of the flange face. This has resulted in having to make a skin cut on one set of flanges to clear it up.
A lot of people may be aware of this but I'll mention it anyway. A long long time ago we were having trouble with centering (2) 72" dia 1/2" wide metal gaskets on high temperature heat exchanger flanges. Since we used set-in studs on the inside flange I welded 4 thin (0.020) tabs on the gasket edge that would allow it to properly hang on the set-in studs. The gaskets are now purchased with the tabs.