Section 7 Tolerance of ASME B16.5

[mechengineer]

It does not mention what kind of method of manufacturing flange to be suitable for the tolerance in section 7 of B16.5. I think it may be for the worst case, like casting and forging rather than machining. But there are a lot of flange drawing that show the tolerance as per section 7 of B16.5 for the machining flange. It is too big. I think that for the dimensions without the tolerance shown in the drawing shall be as per the General Tolerance of DIN ISO 2768 which is a common practice in machining industry.

 

[The Obturator]

In what way are the tolerances in ASME B16.5 too big? Flanges aren't precision machined components.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[XL83NL]

Why not simply provide your case to the B16 committee and ask them to revise the standard?

Huub
- You never get what you expect, you only get what you inspect.

 

[mechengineer]

XL83NL-Thanks for advice. i will.

 

[SnTMan]

Tight tolerances are a poor substitute for good design.

Lets be very careful about tightening tolerances...

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[bcd]

Yes, B16.5 tolerances are based on the least accurate manufacturing method. Indication of alternate possible manufacturing methods can be seen throughout the standard. For example, in Table 1A list of material specifications. In 7.4, where the flange thickness is applicable to as-forged, as-cast, spot-faced or back-faced (machined).

So tolerances are set to accommodate the least accurate production method. Why would you ever require tighter tolerances? The flange meets the standard and will perform to the standard pressure-temperature limits with the wider tolerances. Those looser tolerances may save you some day if a machinist makes a mistake and cuts-off a little too much material.