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

 

[TGS4]

As you would probably expect, this is a topic that is current and starting to be well discussed. At the ASME PVP conference for the past couple of years, there have been some interesting papers presented on this topic. Check out the ASME electronic store at

http://store.asme.org/category.asp?...%5Fname=Pressure+Vessels+and+Piping%A0&Page=1

and I would recommend look at the last 3 PVP conferences.

BTW, MANY B16.5 flanges fail the Appendix 2 calculations - it's a well-known fact. However, they are successfully used everywhere. Also, you should check out ASME PCC-1, because even though your "allowable" bolt stress may be on the order of 25,000psi, it is recommended to stress them to 50,000psi (an even above). (Also see the notes in Div.1, Appendix S).

 

[saplanti]

TGS4,

Your reply does not address the problem that I described above. I am following the code rules and the bolts do not comply under the gasket seating condition when the spiral wound gasket used.

I have checked ASME PCC-1, it is not related the design, ASME VII Div 1 and Div 2 are the same concerning to the bolt calculation. I used the method given by these standards.

There are some papers about leakage and bolting in the ASME electronic store that you referred, however, the codes are the driving rules for the calculations and these papers do not address the problem above directly.

Thanks and regards,

Ibrahim Demir

 

[vesselfab]

B16.5 flanges often do not pass a full set of calculations when using gaskets with high seating factor, spiral wound.

However, the ASME Code Section VIII says that they are acceptable to use without calculations if you follow the pressure/temperature ratings in B16.5.

I am not really familiar with piping codes

Did that answer your question?

 

[TGS4]

splanti, you seek an answer to a question that has no answer. Perhaps the more appropriate response would be to question why you are asking the question in the first place. As vesselfab says, ASME B16.5 flanges are acceptable up to their rating pressure (note that there is no mention of what gasket is to be used...) in B31.3 and Section VIII application without additional calculations.

Frankly, I could care less about the code limits on bolt stress - because as indicated in Appendix S and PCC-1, I am going to apply an assembly bolt stress well in excess of that value anyway...

 

[saplanti]

I am using B31.3 for the piping design; Appx F-Precautionary Consideration recommends checking the flange connection and all the connection components although this appendix is not mandatory. Para 304.5 accepts ASME VIII Div1 Appx 2 calculation with the B31.3 allowable. This includes bolts.

I have checked ASME B16.5; Para 5.4.3 specifically talks about 150# flanges. Is says "It is recommended that only Annex C, Table C1, Group No.1 gaskets to be used for Class 150 flanged joints.". Group No.1 consists of two groups, Gasket Group No.1a and Gasket Group No 1b. The Gasket Group No 1b lists Spiral Wound and Corrugated jacketed gaskets and Group No 1a lists self energized gaskets, compressed sheets, polymers and elastomers. My suspicion is that Para 5.4.3 mistakenly writes Group No 1 instead of Group No 1a.
In this case my suspicion on the flange connection in my original post is correct. If the paragraph does not have any mistake, the para 5.4.3 needs to be reconsidered.

TGS4,

I believe m original post covers your second paragraph. I understand that we do apply a tensile stress lower than the yield stress, industry general is max about 0.6*Fy ( ASME VIII Div 1 Appx S has the formula for the recommended stress which is lower than this value ). However, during the bolting, bolts are working against the full gasket contact surface. In the code calculation of required bolt area by using allowable stress of bolts, the code asks for the effective gasket seating area. In my case the allowable bolt forced are significantly lower than the required force to compress the gasket in the effective bolt area. This is the dilemma not the stresses on the flange.

Thanks for your input.

Ibrahim Demir

 

[vesselfab]

yes, that is the standard results of calcs.

but, the flanges are deemed safe by codes, by industry, and by everyday practice.

Perhaps it is not really a bolt overstress problem as much as it is a conservative factor for gasket seating.

regardless, they are in use all over the world with spiral wound flanges.

why re-engineer the world?

maybe I have an over simplistic view of things. If it aint broke, don't fix it.

I do think that you will have a hard time convincing the world that the pressure temperature ratings of b16.5 need to be changed and that all the flanges in use are not adequate and should be changed.

 

[saplanti]

vesselfab,

I have done the analyses for flanges with class 150# and sizes DN150, DN200 and DN300 by using spiral wound gasket. Flange bolting with sizes DN150 and DN300 seems to be closely adequate, however the bolts of flanges with the size DN200 fail due to large gasket seating area and insufficient number of bolts in case spiral wound gasket is used.

I did not want to generalize the problem for all flange sizes with class 150#, and especially concentrated on DN200 flange bolting in my original post.
I would like to hear more about this size and class of flange from the experienced professionals in the industry.

I am just giving a warning about what I found about this particular size and class of flange connection. Do not get me wrong, I am not trying to convince one who is not related to the design and maintenance of flanges for the plants and not trying socializing on the forum without any reason. Therefore, I would expect a discussion with a convincing background.

Kind regards,

Ibrahim Demir

 

[TGS4]

saplanti - You appear to be missing the main message of several of the posters: many ASME B16.5 flanges (especially the ones that you are evaluating) do NOT pass the applicable Appendix 2 calculations. End of story. You're re-hashing old news.

But, like vesselfab says, B16.5 flanges have a very long successful history of acceptable use. The conclusion that I have drawn is that the calculations are inadequate - in fact the ASME Code committees are working on a new calculation methodology right now... Stay tuned.

 

[saplanti]

TGS4,

Are you refering copying EN 1591 into ASME as the new calculation methodology or something else based on the Taylor Forge Method?

Ibrahim Demir

 

[TGS4]

c) Neither. I haven't seen the latest proposal yet. I will be sure to "bleed" all over it...

I am a big fan of the EN-1591 procedure, but frankly it is excessively complex for your average engineer (I managed to incorporate the entire calculation into a 30+ page MathCAD worksheet...).

 

[saplanti]

TGS4,

I do not have EN1591 however I have EN 13445. Do you think it will satisfy the full requirements of EN1591 if I follow EN13445 rules for flange calculation?

I do not have a spreadsheet for EN13445 yet but I am thinking about creating one because of the problems I am having in ASME codes for flanges. I saw a spreadsheet from a website that I can not remember now, it was accessible to calculate flanges freely, however it was not working properly at that time.
To create a new one requires material properties that applicable, probably standard flange sizes in both ASME and EN standards with an option of flanges with special dimensions. The problem side is the application of ASME materials in EN flange calculation. Probably most of the properties that given by EN material standards and flange calculation are not defined by ASME material standards. Mixing the standards for calculation will end up with a disaster.

It does not look encuraging at the moment, but it is good to have another code spreadsheet, at least to compare the approaches.

Thanks for the input.

Ibrahim Demir

 

[TGS4]

EN-1591 and EN-13445 are two very different beasts w.r.t. flange design and analysis. You'll have to look at EN-1591 to see for yourself.

 

[saplanti]

EN13445-Annex G gives Alternative Design Rules for Flanges and Gasketed Flange Connections that are based on prEN1591 and Annex G is normative. These are the alternative rules to in Clauses 11 and 12. The main purpose is to ensure structural integrity and leak tightness for an assembly compricing two flanges bolts and a gasket.

This annex is based on pr EN 1591, Flanges and their Joints-Design Rules for gasketed circular flange connections. To ensure consistent presentation within the standard many editorial changes, e.g. numbering the equations, figures and sub-clauses, have been made from the text in pr EN1591.

These are the wording from Annex G, and I understand that EN1591 has been reflected in EN13445-AnnexG in the exact concept.

Ibrahim Demir

 

[vesselfab]

i hydrostatic tested a vessel today. on it were several 8"150# rf flanges. Test was carried out at 428 psig at ambient temps using 0.175" nom thick .125" compressed spiral wound gaskets t-304 ss/flexible graphite. test was held for several hours waiting for AI and user inspector. Actual pressure crept up to the 435 range. No leaks were present flanges performed well as they usually do. I have not heard or seen problems with these flanges. I can only assume that when we design new flanges per appendix 2, the code uses a higher gasket seating stress factor than is actually present.

It has been this way for years, and if the code, were to make the mistake as you listed...."My suspicion is that Para 5.4.3 mistakenly writes Group No 1 instead of Group No 1a."......I really think it would have been noticed by now.

In any event, good luck with you quest.

 

[saplanti]

Vesselfab,

You did not mention the bolt material used at the test and the load you applied on the bolts. If you can provide those I can probably come up with an idea about the connection in the test.

In the most applications, the bolts for testing are replaced by the new set of bolts for each flange connection due to overstreching.

I question the bolts because the bolts are important elements of the flange connections to keep the structural integrity and prevent leakage. In the processes that flange connections are not avoidable and the system may contain toxic gases, liquidified pressurised gases, high temperature steam etc that leak may be very important and hazardous.

You are saying that the code calculation is conservative for seating stress factor. Can you explain why gasket manufacturers do give the same seating stress in their catalogs?

I guess EN 1591 came up with a bit different approach to flange connection for design and I also would like to hear from the professionals experienced on EN1591 on the same issue.

Regards,

Ibrahim Demir

 

[vesselfab]

b7 studs 2h nuts
the same studs are shop stock and have been used over and over many times with no problems.
I would assume the flange manufacturers use the same values because they are the values listed by the ASME code.

 

[saplanti]

The second pharagraph of my last post was suppose to be the following:

"In the most applications, the bolts for testing are replaced by the new set of bolts for service conditions on each flange connections due to excessive overstreching in the test."

You may use the same bolts for several testing if you can control the tension on the bolts. Without a proper control it is inappropriate to use them. It may be unfortunate if they fail during the test. ASME PCC-1 gives all the conditions for the bolt tightening and I hope you comply with them.

Additionally, I do not say that you never can use the bolts used in the test for service condition. The bolt tightening procedure by checking the elastic deformation has to be written properly and applied properly to be able to use them in the service. In case the bolt goes into the plastic deformation the bolts future is questionable.

Regards,

Ibrahim Demir

 

[jte]

saplanti / Ibrahim-

You seem to be very concerned about the likelyhood of structural failure of the flange bolts. Industry experience would say otherwise: It is unusual for bolts to fail. Yes, some do fail, but the ones I've seen have something unusual about them - corroded, fatigue service, wrong material. Flanges tend to fail by losing containment thru excessive flange deformation (usually elastic) rather than by physically breaking either the flange or the bolts. Probably the most spectacular "flange" failure I've seen was when perhaps 100 bolts broke on some rather large equipment with body flanges. This equipment, which normally operates under inches of water, was exposed to a rapid and severe pressure increase due to an unenlightened startup procedure...

As stated in previous responses, the issue you raise as far as calculation methods go is old news. So, what are you after? Are you aware of a bolt failure which was attributed to overtorquing the nuts? If so, please let us know more details about that specific event.


vesselfab-

Out of curiosity, do you typically torque the flange studs for your vessel hydro's? I'd wager not. Yet, as would be expected, you've presumably experienced a low rate of flange leakage and probably virtually no bolt failures...

jt

 

[vesselfab]

jt

NOPE on torque
VERY VERY LOW
NO FAILURE