Max Bolt Spacing Design 1

[Zimann]

I have looked through the ASME B&PV for this, but no luck.
I have a capscrewed metal-metal joint that has an outer diameter and inner diameter bolt circle with pressure applied between bc.

I am looking for a reference that relates the applied pressure, flange thickness and material, bolt size and pre-load, and bolt spacing to prevent deflection/leakage.

I have lots of info about stresses, but the SPACING aspect is confusing me.
Thanks in advance.

 

[proinwv2]

Zimann

My experience has shown that the flange and gasket calculations in ASME VIII gives very stiff and effective joints. They do include all metal joints. A stiff bolt joint is essential so that it never looses preloading.

You could do a FEA analysis on your design to determine deflections. I have not done a metal to metal joint so my thoughts are merely a starting point.

I'll be very interested to see the others comments on your question

Paul Ostand

http://www.ostand.com

 

[Zimann]

Thanks Paul -
Maybe question needs a little clarification for others -
This is a semi-circle component with OD, ID, and splitline bolts.
No sealant or gasket between component and the case it is fastened to.
ASME VIII MA 3, Art 3-3 Flanges with Ring Type Gaskets discusses required bolting, but I cannot find guidance that limits the separation/spacing of the bolting based on plate thickness. It tells you roughly how many bolts you will need based on tensile stress area.
Flange Rigidity in paragraph 3-395 - I may use it to "prove" that the design is "sufficiently rigid to control leakage" - but it has gasket factors in the calculation........and I'm not sure how to relate my case.
I also have to modify the ASME equations since they treat the flange as 360 degrees round - and I have a semi-circular shape.

 

[TGS4]

There isn't anything in the ASME B&PV Code that will help you - other than Section VIII, Division 1, U-2(g). Good luck!

 

[SnTMan]

Zimann, while not strictly applicable to your case you can find bolt spacing limits in Taylor Forge Bulletin "Modern Flange Design" (so modern its out of print) or TEMA.

Regards,

Mike

 

[Zimann]

Mike,
Taylor Forge "Modern Flange Design" Bulletin 502 contains the following:
"When the condition is encountered where a very few bolts will satisfy the requirements of safety but will result in bolt spacing so wide that leakage may occur, it is necessary to adjust the design either by increasing the flange thickness, increasing the number of bolts, or both. The effect that must be achieved is to permit the flange to apply sufficient loading on the gasket between bolt holes to provide a tight joint. It has been found that application of the following gives excellent results:
Bolt Spacing (Max) = 2a + 6t/(m+0.5) "
Where "a" is Nom Bolt Diameter, "t" is flange thickness, and "m" is the gasket factor. For soft flat iron or steel, basically, max spacing is 2 nominal diameters plus flange thickness.
This equation does not relate Applied Pressure, but I suppose that used in conjunction with calculations for required bolt loads (which do account for forces) it should be sufficient.
Thanks for heading me in the right direction.

 

[deanc]

http://www.hexagon.de/

Software....for sale. There are some free papers on this site.

 

[SnTMan]

Zimann, my TEMA 8th also uses the expression you stated for Bullletin 502, while my Bulletin 502, Edition VII also uses this expressions then goes on to state "It assumes proper load distribution when bolt spacing = 2a + t", which expression is also used in the calc sheets. A little more convenient sometimes since gasket factor is not involved.

Regards,

Mike

 

[proinwv2]

Again,it seems that FEA would be a good choice, the opportunity to write a paper....if you are a masochist.

Paul Ostand

http://www.ostand.com

 

[TGS4]

ostand - I know the perfect venue for that paper too -

http://www.asmeconferences.org/PVP07/

 

[arto]

For "homemade" flanges, it used to be "use pi spacing [3.14" between bolts]& you don't have to analyze it/ it won't leak" i.e. 10 bolts on a 10" BCD


Round it up to the nearest multiople of 4, then you can straddle centerlines. {i.e., go to 12 bolts for the 10" BCD}