Wall thickness according API5L 1

[robb4]

Dear all,

I'm designing a 32'' gas pipeline and according specification of my client I've to choose wall thickness according API5L 2004.

The problem is that wall thickness I've calculated (39.1mm) is above the maximum wall thickness reported on standard (31.8).

As far as you know, is it possible to go above this limit of 31.8 (is the same for all OD from 10" 3/4 to 80")? Is it a manufacturing limit?

If not can you advice any standard / RP or something else I can use to choose wall thickness (and I can advice to my client too)?

Just for sake of clarity, I cannot change the grade of material (API 5L X65).

Thank you for help.

 

[BigInch]

An alarm should be going off in your head when you get a result that isn't included in the tables!

Basically can use any wall thickness you can get a mill to manufacturer to your specification. That said, there are other factors to consider. You probably do not have the best diameter for your flowrate. Rethink the diameter selection!

The problem with that 39mm wall thickness will come during construction when you have to pay for long weld times and stress relieve every welded joint. If you have a long pipeline, this wall thickness is something you probably don't want to be using, as I'm sure your client won't want to pay the extras that goes with that.

I would suggest that you increase the diameter and lower the pressure to something that gives you a reasonable wall thickness.





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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[robb4]

Thank you Big Inch

Unfortunately I cannot decrease pressure because I need that one for other reasons, but if there are major problems with these thickness we can change the grade material and go to X70 or X80.

Considering that our design temperature are -10°C and 80°C do you think it's possible to go with this grade without other problems?

The pipeline is gas one for sweet service with a content of water.

 

[BigInch]

Yes. I would have suggested a higher grade material, but you said that you could not change that. You should try to find a wall thickness of 20mm, 3/4", or less. Be carefull to consider the possibility of welding quality implications for materials > 80X. Welding is of course possible these days, but those may still be problematic in some areas of the world.

The 80C hi temperature will be no problem for the pipe, as it is less than 120C. Lo temp of -10C should not present a problem either. Some companies require notch toughness testing, but usually only when temp is going lower than -20 C.

Watch the temperature limit of coatings that you might want to use. Many coatings start going soft over 120F and many are not suitable at all for use at or above 80C.



**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JT100]

I have a similiar question here, apologise for hijacking thread, I found some of this usefull though and thought it may be relevant.

Can DNV codes be used against ASTM-A-106 materials? I've had a look in the codes and cannot find anything definitive, F101 lists the API material requirements but nothing specifically regading these. I have been using ASME 31.8 VIII but was looking to find a way to use and increased hoop stress design factor, and I see F101 quotes a value of 96% for hydrotest. Thanks.

 

[SJones]

F101 is a submarine pipeline code and A106 will NOT be sufficient to comply. It requires a tightened application of ISO 3183.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[JT100]

Thanks Steve, I thought that may be the case.