Flange Connection DN200-150# with Spiral Wound Gasket - Gasket Seating 1

[saplanti]

Dear contributors,

I would like to find out what is your opinion on the flange connection with the specific size, ASME B16.5 - DN200-150#, using spiral wound gasket and material pairs A105/A193B7 or A182F5/A193B16. The given flange and bolt material pairs are very common in the industry and the piping design code is ASME B31.3.

In the flange connections we investigate the compliance of flange and bolt stresses with allowable in accordance with ASME Sect VIII Div 1 under the operating and gasket seating conditions.

When I investigate the flange connection with operating condition with the external loads, the flange and bolt stresses are adequate. However, under the gasket seating condition (which requires large gasket seating stress) the bolt stresses are larger than the allowable although the flange stresses are adequate.

I did the calculation by a spreadsheet and the Flange Analysis option of Caesar II, in both cases the results are the same. The required bolt area is always greater than the available.

In the calculation, the effective gasket seating area is considered for the bolt calculation rather than the full seating area. Bolts are checked with allowable stress at the ambient temperature against the gasket seating force. I come up with around a ratio of 0.72 which is the allowable forces of bolts to the force introduced by the gasket seating for this size of flange connection.

Is there any source I can reach that explains the background of using effective gasket area and the allowable stress of the bolts in the flange calculations?
Why do not we consider the full gasket seating area for gasket (instead of effective area) and 0.6 times the yield stress of the bolts at ambient temperature?

I have done similar calculation with other sizes and the ratio of allowable forces to the gasket seating force is around 0.97 and accepted adequate. But DN200-150# flange connection with spiral wound gasket looks very suspicious.

Have you been experienced this kind of problem with spiral wound gasket?
By considering the piping code B31.3, would you accept the connection adequate from your experience?

I would like to hear from you and thanks in advance.

Ibrahim Demir

 

[saplanti]

jte,

My answer is yes, I am concerned about the bolt failure under the gasket seating condition specifically for flanges sized DN200-150# with spiral wound gasket.

You are saying the calculation method is old. In that case, can you refer the most current calculation method especially for the bolt calculation? Can you refer me a spiral wound gasket provider is going to ask gasket seating pressure that is a lot less than the code gives?

The current code reduces the gasket seating area to the reduced effective area ( around 1/3- 1/2 of the real seating area ) with the code gasket seating pressure. The allowable bolt force is suppose to overcome this load.
Are you saying that the most current calculation method (not the current code rule) does not require the bolt strength under the gasket seating condition?

The flanges with size DN200-150# has large effective seating area and the connection contains 8 - 3/4" bolts. The number of bolts or total bolt area is not sufficient to overcome the seating force (considering the effective area) using bolt allowable stress/force. I keep writing the same thing, but my expectation is from the experts to refer the most current calculation method instead of writing that this is the industry practice.
Please not that I am not refering the other flange sizes and classes or gaskets.

Vesselfab,

I believe that you are not using the spiral wound gaskets for the tests. This is my conclusion from your answers.
If you use the compressed fibre gaskets you do not have the problem that I am discussing in this post.

Regards,

Ibrahim Demir

 

[Gator]

saplanti, by "compressed fibre gaskets", are you referring to asbestos? That stuff is dangerous, cancerous and deadly if you snort it intentionally.

I've always wondered why it was replaced - was asbestosis common amongst field workers or factory workers? My understanding is that the risk is only when loose fibres are airborne in large concentration, perhaps I'm wrong.

 

[saplanti]

Gator,

Compressed Asbestos Fiber gaskets were banned in the piping a long time ago for most of the applications and probably you may not be able to find one if you need it.

There are some more compressed fiber gaskets that do not include asbestos. I attached the Flexitallic catalog for information.

Ibrahim Demir

 

[vesselfab]

saplanti,
I am not to bright, but I would not interject a statement that was not germane to the conversation. And I do know the difference between a spiral wound gasket and a compressed synthetic fiber gasket. I test using spiral wound gaskets as a standard operating procedure. Why would you assume otherwise?

 

[jte]

splanati-

Since you didn't directly respond to the question about actual failures, I'll assume that the answer is that you are not aware of any specific failures of bolting in these flanges.

'nuff said.

jt

 

[saplanti]

Guys,

Please do not get me wrong. I am a design engineer. I am not investigating an accident or a failure at the moment.

My job is to make sure the system is working under all the conditions that the codes and the customer specification require as minimum and consider the possibilities of the failure modes. This is my job and one may think that I may be overdoing it. My lifetime experience confirms that the "Murphy Rule" always works. I do not have to wait for the accidents happen to prevent it.

Most of the applications were generalised in the codes to cover all the conditions and they are based on the many theorical and practical experience that supported by the researches. Time to time the code rules can be tightened or loosen in accordance with the problems that raised by the industry engineers or costly accidents etc.

When I see a problem that does not satisfy the current code rules I have to raise the question until I find the answer. Finding the satisfying answer is important for everybody including myself in this forum or somewher else. However, I do not believe the subjective discussions (Vesselguy, I am not targeting you with these words. However, I was not satisfied with your answers. Of course however your inputs are still valuable for me.) can solve any problems other than hurting each other.

I gusss the misunderstanding ends here, and I thank you for your patience in my post.

I wish you all Merry Chrismas and a Happy New Year.

Ibrahim Demir

 

[vesselfab]

splanti you said

""When I see a problem that does not satisfy the current code rules I have to raise the question until I find the answer""

what I and everyone else was trying to tell you was...

it does satisfy the current code rules.
there was never a question of that.

except from you.

hopefully you will find better answers

 

[saplanti]

To All,

I was looking for "EN 13445 Unfired pressure vessels - Background to the rules in Part 3 Design" and found it in the following address:

http://www.unm.fr/fr/general/en13445/Background to Design rules_Issue 2.pdf

It gives plenty information on the flange connection for methods used, their weaknesses and improvements. Pages 25-27 and 99-117 give plenty information on the Appendix G ( EN 1591 ) approach. I suggest the interested parties to read the pages above.

In case of other approaches available to the flange connections I would like hear about them.

Kind regards,

Ibrahim Demir

 

[saplanti]

This is onother one with a different sealing approach in the flange connections;

http://www.standard.no/pronorm-3/data/f/0/02/42/5_10704_0/L-005r1.pdf

Kind regards,

Ibrahim Demir

 

[saplanti]

The following is an API paper "Design of Compact Flange Joint" with different sealing approach;

http://committees.api.org/standards/ecs/sc17/docs/deesigncfj.pdf

Kind regards,

Ibrahm Demir