Equipment with Metric Flanges.

[kepharda]

I am trying to design some pipework and a customer has specified 2 explosion safety valves that originated in Europe. The piping spec calls for class 150 flanges, but the bolt hole diameter of these 2 safety valves is 11 5/8" and 24 7/16" respectively, so a standard ANSI bolt pattern is not going to work. Any suggestions?

Am I going to have to resort to getting metric flanges?

thanks, Dave

 

[RossABQ]

What little metric work I have done (in China and the Far East) they call their stuff metric, but the dimensions are identical to ANSI. Are the dimensions you give of the bolt circles? How does the number of bolts compare?

 

[kepharda]

Yes the bolt hole diameters of the larger flange is
24-7/16" and an ANSI bolt hole dia is 25"

for the smaller flange the bolt hole dia is 11-5/8" and an ANSI flange is 11-3/4"

I am considering just giving details so the contractor can fab a custom flange with the right bolt hole dia., but with the inside bore to fit NPS pipe.

-dave

 

[RossABQ]

Just to be clear, "bolt hole diameters" means the diameters of the bolts, not the bolt circle. Obviously the bolts are not 24" and 11" diameter.

I would suspect a dimensioning error; conversion from mm to inches. Did you do the conversion, or did they?

 

[katmar]

The dimensions you give agree with the British Standards. The smaller flange with the bolt circle dia that you gave as 11-5/8" is probably a BS4504 PN10 200mm (8") flange that actually has a PCD of 295 mm. The larger flange is probably a BS4504 PN10 500mm (20") flange with a PCD of 620 mm.

Here in South Africa we are faced with these mixed specs all the time. Fortunately, the pipe dimensions are the same for the US and BS specs so your flange bore will be correct. If you can get an undrilled ANSI flange and drill it according to the required PCD you should be fine, but you may have to get its compliance to your code checked.

Check the bolt hole size as well. It should be OK for the small flange because they should be 7/8" for ANSI and 22 mm for BS. This is less than 1/100" difference. However, on the 20" flange the BS spec calls for 26 mm holes which is approximately 1-1/32" while ANSI calls for 1-1/4". The numbers of bolts are the same at 8 and 20 respectively.

As an aside - you can do this with larger flanges, but with flanges of 3" and less the BS flanges have significantly larger PCD's than the ANSI 150 flanges so you would probably not have enough metal outside the ANSI PCD to drill to the BS PCD and still be safe.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com