Custom Flange Design and Gasket Requirement

[wailunwu]

From PV Elite, gasket material m and y values are required to determine the bolt area.

1) Can custom flange be designed to appendix 2 asme sec VIII div 1 without knowing the gasket (m and y values)? The flange thickness and number of bolts seem to have an effect on this.

2) For standard flanges, are they designed to any reference gasket (reference m and y values)?

Thanks.

 

[racookpe1978]

?

It is the other way around. Custom gaskets are seldom made (and are very, very expensive!) but can be ordered.

Standard gaskets are made by the tens of thousands to fit and work with standard gaskets, standard bolting patterns and standard bolts to allow for a specific temperature, pressure, metal and fluid combination needed.

 

[SnTMan]

wailunwu, it is the other way around, under Appendix 2 gasket m, y values affect the required bolt area, which in turn affects flange thickness. You can get kind of a lower bound by setting m = y = 0. Useless to attempt a flange design without knowledge of the gasket though.

Standard flanges such as B16.5 are wholly different animals and do not use Appendix 2 methods, at least explicitly. Not to say you can't run a standard flange under Appendix 2, but it may or may not make.

Regards,

Mike

 

[wailunwu]

@SnTMan

1) To reiterate, since gasket m and y values affect flanges in appendix 2, Appendix 2 cannot be used without knowing gasket information? Please correct me if I am wrong. The reason is because client sometimes do not specify gasket requirement and ask us to design custom flange.

2) Do gasket m and y values affect standard B16.5 flanges? In order words, is there a restriction on what gasket (m and y values) can be used for standard B16.5 flanges? I am not able to find the restriction on the gasket m and y values for the standard flanges.

 

[SnTMan]

wailunwu, 1) yes. Often as a designer, you have to chose the gasket.

2) B16.5 does not use m, y values for establishing the flange ratings. Gasket types are somewhat restricted by bolting strength. Recommend you get a copy of B16.5 for your reference, as it is not really possible to go into all details in a forum.

As well, recommend you study Appendix 2, to better understand the design process.

Regards,

Mike

 

[JStephen]

"Custom gaskets are seldom made (and are very, very expensive!) but can be ordered."

That depends on the gasket. Gaskets that can be cut from sheet-gasket materials are readily available, with prices varying depending on the material cost. So a rubber-type flat gasket in custom sizes is no problem, something like a spiral-wound gasket would be a different issue.

 

[SnTMan]

Well, actually a wide variety of custom gaskets for heat exchangers are readily available. Double jacketed, spiral wound, corrugated metal, grooved metal, flat metal, with and without facings, non-metallic, all with and without pass ribs. Yes, prices do vary. But they are no problem to get.

Larger manufacturers will generally have applications engineers on staff to assist with selection and design. Smaller shops, not so much.

Regards,

Mike

 

[marty007]

Just to thrown in one more detail. You asked if the m and y values have any impact on B16.5 flanges.

B16.5 recommends that certain hard to seal gaskets should not be used with 150# flanges. There is a table somewhere in the back that lists which ones should / should not be used.

 

[gasketguru]

Selecting the gasket is traditionally the starting point for a custom flange design given the vessel diameter and operating conditions. Sadly the m and y factors are a weakness and are not a good indicator of actual gasket behaviour and performance. They are little more than an “engineering opinion” and there is no good valid test to determine them.

Indeed in the Taylor-Forge / ASME method the concept of effective width means you calculate on a less than actual contact width and often under-calculate the load, which leads to things like Appendix S which allow you to thrash the bolts up a bit more if need be… Consequently most bolt workers aim at 40-50% bolt yield or more on-site, compared to say 25,000 psi as the typical design stress of the good old B7 bolt…. The required bolt load from other design codes such as the old DIN 2505 or EN1591 (which is at least based on gasket load-leak and creep data), or even the PVRC method would all usually give greater loads than m & y.

The custom gasket is probably not as expensive as some might think, though is often badly specified and over-looked until it is then also badly installed at the wrong load. At this point you develop a leak and the plant then spends thousands on leak repair clamps, and tries to investigate why it leaked and tries different gasket types from several manufacturers in an attempt to resolve it…. Make sure that you balance the actual gasket stress requirements against what the flange and bolts can give, and beware things like thermal differential growth between flange and bolts etc - EN1591 at least accounts for this where ASME does not.

 

[SnTMan]

gasketguru, I'm guessing you've heard this about gaskets: "It's a commodity until it fails, then it's an engineered product"

Regards,

Mike

 

[gasketguru]

SnTMan - perhaps I was getting a little cynical after a long day yesterday, but in the last 30 years I've fixed so many leaking joints where they have been under-designed, used the cheapest gasket possible, which has been fitted badly where the user has been overly optimistic about things like bolt friction vs. torque, then when it leaks they spend a fortune on a clamp and blame the gasket... I've tried making things idiot proof, but they always manage to send me a better idiot!...

 

[SnTMan]

Yeh, I've probably BEEN one of those idiots at sometime...