Alteration in Bolt holes of 3-1/2" Blind Class 900 raised faceflange

[juanon]

Hi

A class 3-1/2" 900 RF Blind flange has some interference when mounted on the boiler opening due to misalignment of the stud holes. This is due to incorrect drilling of the stud holes on the boiler face at an angle which has a few bent studs installed ( off by 1/16&quot. While installing the blind flange interference was observed which led to some threads being damaged on the studs.

A suggestion was made to increase the bolt hole dia by 1/16" ( 0.06&quot.

B16.5-1998 section 7 provide tolerances.

The Bolt Circle dia is not effected
centre to centre adjacent bolts is not effected
Eccentricity between BCD and machined face diameter is met (0.06&quot


My questions:
a) Is this acceptable?
a) Is their any code provision to do this ?
b) Does this repair /alteration is common in that case can you refer to any code case :

I searched 16.5 could not find one any interpretation

any help is much appreciated

juanon

 

[chicopee]

first do an analysis of the force exerted on the bolts and determine if you have much greater strength then is necessary. If that is the case than increasing the holes by 1/16" should be OK. Also check with the National Board of Fired and Unfired Pressure Vessels for their opinion. This organization is in the Webb.