API 650 Atmospheric Tank - Shell Nozzle Pipe vs. Plate 1

[amats42]

I was wondering if anyone knew the reason behind API 650 e12 Paragraph 4.5.2 which prohibits the use welded pipe for shell nozzles (though it does allow ASTM A671 electric-fusion-welded).

I recently had a tank vendor attempt to use API 5L pipe for a large bore pipe nozzle (since they specified seamless which they cannot get at these diameters) and it seems API 650 prohibits this. I'm not sure I understand why having the tank vendor roll and weld plate is a better design than an approved pipe spec such as API 5L.

I searched through the API 650 inquiries and only found confirmation that ASTM A671 pipe is the only approved welded pipe.

4.5.2 Unless ASTM A671 pipe is used (electric-fusion-welded pipe) (see 4.5.3), material for shell nozzles and shell manhole necks shall be seamless pipe, seamless forging, or plate material as specified in 4.2.10.1. When shell materials are Group IV, IVA, V, or VI, seamless pipe shall comply with ASTM A106, Grade B; ASTM A524; ASTM A333M/A333, Grade 6; or ASTM A334M/A334, Grade 6.

 

[Dhurjati Sen]

Dear amats42,

Actually the reason was to prohibit use of ERW pipes and the one your vendor is intending to fabricate all because of quality control issues.

If there is a leak in that welded portion of the pipe, you need to drain the entire contents of the tank, make everything hydrocarbon / gas free in order to obtain a hot job permit to carry out repair.

You can easily procure welded piping with multiple specs like API 5L PSL 2 / ASTM A 671.

Even seamless large bore piping is available now-a-days.

If nothing is possible, then fabricate the pipe as per the vedor's suggestion, carry out 100% RT of the weld joint. Also carry out UT of the plate before rolling to ensure there is no lamination.

Regards.



DHURJATI SEN
Kolkata, India

 

[amats42]

Thank you for the response, Dhurjati Sen.

Looking through API 650 I do not see a requirement for 100% RT on the seam. I agree that it would be wise to RT, but the vendor is stating the NDE will be per code.

I am under the impression that the shell nozzle should be fabricated in the same manner as a 36" manway.

Best Regards

 

[Dhurjati Sen]

Dear amats42,

If vendor insists on following the code reg. NDE, you don't deviate from the code and insist on seamless pipe as per API 650.

He would surely fall in line, if he wants to stay in business.

Regards.

DHURJATI SEN
Kolkata, India

 

[IFRs]

Section 8.1.1 specifically says RT is not required for rolled plate used for nozzle necks.
Why can rolled plate be used for nozzle necks and not pipe? The answer is not found in the standard. If you want to know or ask if 5L pipe can be used for nozzle necks, send in an inquiry.

 

[amats42]

Thank you, all.

I agree that the code does not require RT on rolled plate and perhaps an inquiry is the only route. I figured I would ask to see if anyone had experience or other sources that might discuss.

There was a previous inquiry that confirmed 5L pipe is not allowed, but no answer as to why.