Permissible out of roundness UG 80

[lcatg]

Hi,

As per UG 80(a)(1), difference between diameters shall not exceed 1% of nominal dia.then (a)(2) says when cross section passes through an opening or 1 ID of opening from center,difference may be increased to 2%. why this extra 1% is added and how does it make any difference? In what cases it is helpful)

Thanks.

 

[SnTMan]

lingeshgdvg, warpage due to removed material and welding usually occurs at openings (nozzles), particularly in larger openings. There is only so much that can be done during fabrication to prevent or minimize it.

The Code recognizes this per (a)(2).

Regards,

Mike

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

 

[MECH993]

Hi lingeshgdvg,

Permissible out of roundness in above stated case is not 2% of nominal dia of vessel as stated in query.

As per UG-80 (a) (2)
"When the cross section passes through an opening or within 1 I.D. of the opening measured from the center of the opening, the permissible difference in inside diameters given above may be increased by 2% of the inside diameter of the opening".

That means total permissible out of roundness for above case = 1% of nominal dia of vessel + 2% ID of opening.

& for second question regarding additional tolerance I agree with SnTman.

 

[lcatg]

Thanks SnTMan and yog993.

yes, only after submitting the question i realised that.