ASME Edition 2017 - Note no. 8 - UW-13.1 - skirt length - query 1

[RAJPT89]

for one of my vessels, which is having a seamless shell of 14.27 mm thickness (NPS 12 diameter) attached by Dish Ends of 14 (nom) / 12 (min.) on both sides. We have provided skirt length of 32 mm.

Note 8 of Fig. UW-13.1 seems very confusing, and what i conclude is, skirt length 3 times th (need not exceed 38 mm) is required for th greater than 1.25 only. For th less or equal to 1.25 ts, skirt length shall be sufficient for required taper only.

Please let me know your thoughts on this.

Thanks in advance,

Rajput

 

[SnTMan]

Appears to me Note 8 does not apply to your case, where the head is thinner than the shell. Instead Notes 6 and 7 apply. See sketches (j) and (k). Your required length of taper looks to me to be not more than 3 x (14.7-12) = 8.1 mm.

Regards,

Mike

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

 

[RAJPT89]

Taper would not be required as thickness difference is only 0.27 mm.

Sketch (j) & (k) looks like there is no any skirt!, also as per UG-32(k) integral skirt is not required.

Note (8) is applicable to all cases.

Thanks Mike.

Rajput.

 

[SnTMan]

RAJPT89, agreed no taper required in your case.

I gotta admit after closer reading I am having trouble parsing Note 8, although I still believe it only applies to the case where the head is thicker than the shell. It would seem to say that when th <= 1.25 ts the minimum skirt length from the previous sentence (th apparently > 1.25 ts) is not required, only enough to provide the required taper. Apparently this ratio inherently meets the limits on the centerline mismatch, 1/2(th - ts) & UW-33. My best guess

Agreed, sketches (j) & (k) show no skirt and none required as you say. Presumably, the taper is made of weld metal, or an unusual head detail, thicker at the periphery.

In practice I think elliptical and torispherical heads would normally be supplied with a skirt and the taper formed from weld metal, unless the shell has sufficient excess thicknes to accomodate it. A spherical head may normally have no skirt and the taper presumably formed from weld metal.

Regards,

Mike






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