Inside diameter below of tolerance

[aatara]

Hello, Anyone could help me to find in what part of the code ASME explains the rules or requirements to increase the inside diameter of a 90º bend?

I have several 90º bends 30" SA234WPCW Sch XS. After a dimensional test, the inside diameter in some parts of the ends is below of the ANSI B16.25 tolerances (5 - 8 milimeters). The thickness is OK. The supplier recomend me a phisical process to increase the diameter (pushing a special tool into the end of the bend without thermal treatment). This process could produce a weakness in this part of the fitting?

Thanks in advance.

 

[panduru]

Increasing the ID does not necessarily help in strenghtening the member - so the code may not be relevant in the context.

On the other hand, any process that could potentially weaken a part may disqualify the whole equipment for acceptance under the code.

The solution may be to use a bend that satisfies both min ID and min thickness throughout its length.

 

[deanc]

If the part does not meet the requirements why use it at all? Part of your QC system is to qualify vendors. If they cannot provide what is ordered,replace them.

 

[SooCS]

I don't think there is any code governing the tolerance requirement for bending a pipe. You have to specify the requirement usually the max. ovalation, the max. thinning allowed. A special test tools, which simulates an inteligent pig to pass through is also specified.

 

[aatara]

Thank you for your answers. At first I need theses fittings urgently (sorry, they are elbows and not bends from a pipe) and I don´t have any time to wait for news elbows. I have to repairs this fitting and I need to know some requirements from the code to accept them.

 

[TD2K]

This may be a silly question but would the out of tolerance dimensions give you a problem when it was installed?

 

[aatara]

Thank TD2K for your interest.

The main problem is welding these elbows out of tolerance with pipe that respect the ANSI tolerance, then I have to repair the elbows (increasing the ID) or prepare the border of the pipe and the elbows in order to weld them in a good way. In the last case, the thickness of the wall would be reduce from the nominal to one thickness lower. Probably This lower thickness is enough to the inside design pressure, but I don´t know if the ASME say something about this case.

 

[bmoorthy]

If welding is your problem then there could be solution. since the size is 30" one can approach the joint from back side there by performing back chip and compensating the thickness variation as per UW 42 of ASME Sec VIII Div 1.

If the fittings are going to be welded to Pressure vessel or a heat exchanger(As an extension of Nozzle or as a Nozzle it self) designed to Sec VIII Div 1 then one can consider the usage as it is legally, since ASME does not address the Ovality of nozzles explicitly. In which case you may have to change the item tag from standard Elbow to Fabricated Bends.

If the fittings are part of plant piping, then plant piping code such as ANSI B 31.3 Etc would govern.

One could use ASME UF as guideline, where in there is provision to change the maximum allowable pressure if a forging has ovality beyond ASME limits. Although UF does not address standard fittings you may use it as convincing tool.

You may also justify the useage by sacrificing one fitting and perform Proof test to satisfy yourself for using the fitting. You may also try FEM annalysis.