Permissible out of straightness

curiousguy · **Joined:** Sat May 09, 2009 7:29 pm **Posts:** 11

Can anybody tell me what ASME code says about linearity (or out of straightness) for vessels. I have searched through section VIII but havent been able to find anything like that, but im told it is defined. If some one can specify the exact article number or something it would be really helpful. Thanks.

dr.chris · **Posted:** Sun May 10, 2009 5:17 pm

curiousguy

ASME Section VIII Div.1 does not have any requirements for straightness tolerance. The Code only requires that the ovality tolerance or out-of-roundness tolerance of UG-80 be met. Fabrication tolerances such as straightness, nozzle locations, attachment locations, nozzle/flange alignments, etc. are usually provided by the Client or Owner.

dr. chris

curiousguy · **Joined:** Sat May 09, 2009 7:29 pm **Posts:** 11

dr.chris
Thanks for the reply...
Is there any code that defines such a variable? or is it always client dependent?

dr.chris · **Posted:** Mon May 11, 2009 7:16 pm

For ASME vessels, it is always client dependent. Clients may have their own standards for vessel tolerances or they use standards developed by Process Industry Practices (PIP). PIP VEFV1102-Vessel Tolerances requires that "Alignment of cylindrical shell sections shall be true and straight within 0.01" per foot of height from base line but shall not exceed 3/4"."

There are other codes, besides ASME, that defines straightness tolerance. EN 13345-4 is an example. Section 5.4.3 of EN 13445-4 requires that "the deviation from the longitudinal axis over the length of the cylindrical portion of the pressure vessel shall not exceed 0.5 % of the length of the shell."

curiousguy · **Joined:** Sat May 09, 2009 7:29 pm **Posts:** 11

Alright thanks a lot for the info dr.chris

curiousguy · **Joined:** Sat May 09, 2009 7:29 pm **Posts:** 11

dr.chris wrote:

Section 5.4.3 of EN 13445-4 requires that "the deviation from the longitudinal axis over the length of the cylindrical portion of the pressure vessel shall not exceed 0.5 % of the length of the shell."

Does "length of the shell" mean the length of the total shell assembly or length of the individual shell?

dr.chris · **Posted:** Tue May 12, 2009 7:25 pm

total shell assembly

curiousguy · **Joined:** Sat May 09, 2009 7:29 pm **Posts:** 11

we have a 20 metre long reactor so according to EN 13445-4 would that mean linearity of upto 200 mm is allowed? :shock:

or is there some kind of fixed upper limit?

dr.chris · **Posted:** Thu May 14, 2009 10:45 pm

0.5% x 20000 mm = 100 mm. Yeah that's way too much. I have not really worked on a EN 13445 vessel. There should be an upper limit specified in EN 13445-4.

Most of the vessels I've worked on are designed to ASME Section VIII Div. 1. As I have said before, straightness tolerance is set by the Client or Owner. Most of the Clients I've worked with requires a 3/4" (19.05 mm) maximum deviation. Sometimes if the vessel is over 100 ft. or 30 meters, a 1" (25.4 mm) maximum deviation is allowed by them.

curiousguy · **Joined:** Sat May 09, 2009 7:29 pm **Posts:** 11

Thanks for all the info dr.chris. I ll look into it...

Permissible out of straightness

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