Dimension of gasket & flange 1

[PAN]

Normally I use stud bolt A193-B7 size 3/4" for ANSI flange size 6" Class 300.

In one of our projects, the outer ring of spiral wound gasket has diameter 250.8 mm. The distance between center of bolt holes is 270 mm. The case is blind flange of a nozzle. The above dimension seems no problem for installation. But, the gasket cannot be installed in this flange. We have to grind the edge of outer ring to install the gasket.

I understand that bolt hole diameter may be the cause of problem. However, I don't know the tolerance of hole diameter.

- Should we grind the outer ring for gasket installation?
- Can we say that the flange or gasket is deviated from standard dimension?

Please comment.

 

[unclesyd]

Your problem isn't that uncommon in industry. We had to deal with the same spiral wound gasket ring OD problem over the years by notching it out to fit inside the bolts. There were a lot of cases where the gasket was mechanically deformed by the flanges due to slight interference during make up. This is more of a problem on the higher class flanges because of the extra bolting you can put a pretty severe wrinkle in gasket and not realize it. Fortunately you find most of this when you break the flange and not through a leak.

There was one particular manufacturer than was very good at this, especially on the larger flange sizes. When one prominent manufacturer moved his operation offshore his gaskets went to hell, to the point even though they were our standard we had to change vendors. We even made 3 point measuring jigs for our most popular sizes used on class 2500 flanges. We found the problem especially true on gaskets with inner rings, of which most of ours were. You would call the manufacturer and the next batch would be right on the money.

I don’t' know where the problem lies but after a couple of phone calls its is still around. A maintenance mechanic says they still have the problem periodically and a tech at a local supply company measured two different manufacturer"s 6" 300 gaskets and there is approximately a 1/16" difference in the ODs'.

Given the tolerances on the flanges and evidently the tolerance on the gaskets I think we have a stacking problem.

 

[anotherpipeguy]

You may want to check for things like "DIN", ANSI, etc.

 

[PAN]

anotherpipeguy,

Thanks for your comment. I have checked with the mill certificate. Both flange and gasket are conformed to ASME/ANSI standard.