B31.4 Charpy Impact Requirement Interpretation 1

[Patty Cakes]

I'm working on NGL pipelines and pump stations (B31.4) and have had several discussions on the interpretation of the Charpy impact test requirements in section 423.2.3. The code states "Steel pipe designed to be operated at a hoop stress of more than 20% SMYS shall be impact tested in accordance with the procedures of API 5L, PSL 2, or ASTM A333. The test temperature shall be the lower of 32 deg F or the lowest expected metal temperature during service, having regard to past recorded temperature data and possible effects of lower air and ground temperatures." Our facilities are in west Texas along the 5 deg F isothermal line from API 650 and operate above 20% SMYS. Our engineering contractors are insisting that all above ground API 5L pipe be Charpy impact tested to at least 5 deg F because the pipes could get that cold with cold weather. The fluid in our line is never below 60 deg F. My interpretation of the code is that it has to be impacted tested to the lowest expected metal temperature during operation. The only way our pipes get to 5 degrees F is if they are not in service, so the Charpy requirement doesn't apply. Looking for the communities input on how this is meant to be interpreted.

 

[EdStainless]

So is your interpretation that they should be impact tested at 32F?
That looks to be the only alternative.

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P.E. Metallurgy, consulting work welcomed

 

[georgeverghese]

What do you mean by NGL ?
If it is mostly C5plus, then 32degF may be okay.
If it contains significant amounts of propane, temperatures at the depressuring line tee off could get as low -30 to -40degC < -22degF
If propane content is low, but C4 content is significant, then temperatures could be as low as -10degC = 14degF during the depressure routine for this pipeline at this tee off.

And you have to include a margin to get to the lower design temp which would be also be the impact test temp.

Process design documents and simulation models with the engineering contractor would show how they got to 5degF. Ask them for it.

 

[SJones]

Apart from the good points above, a pressurised shut-in is a “service condition” is it not?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[Patty Cakes]

Ed - Correct, my interpretation is that the pipe should be Charpy impact tested to 32 F.

George - This is Y-grade so ~40% C2, ~30% C3, and the remainder is C4+. Our drain lines where we de-pressure are good for -50F to account for JT.

Steve - On our pump suction/discharge lines we keep the isolation valves open when the pump is not in service and prevent backflow with a check valve. The only time we are shut in is when operations is onsite to blowdown a line to perform maintenance, otherwise the liquid is still connected to the main headers even if it's not flowing. The only spot I could see a pressurized shut-in for an extended period would be at our pig traps. We operate with dry traps, if a valve were leaking the trap could fill up with liquid, pressurize, and sit stagnant until noticed by operations.

 

[SJones]

Thanks for the info. The key question is from George: what minimum design temperature is being set for the equipment?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[georgeverghese]

So, if the pipeline is not flowing for operational reasons and under full pressure, you've got 5degF even before you begin to depressure if there were to be a subsequent emergency or even a planned maintenance depressure. So lower design temp ought be much lower than 5degF, given you've got quite a bit of C2 and C3 in this NGL.
Am not a pipeline person : what is Y grade ? Is this good for -50degF if it is capable of passing impact testing at -50degF ? In any case, 5degF = -20degC, so I dont see how API 5L is going to reliably pass impact test at -20degC.
Think there are sufficient grounds to query and challenge the contractor for this 5degF lower design temp / charpy test requirement.
If you have -50degF on the drain line, then the same will apply at the main line tee off to this drain line.

 

[1503-44]

George, Y grade is only half the answer. Y-52, Y-60, Y-70 grades define yield strength in 1000s of psi according yo MSS SP-44. No temperature range is specified therein.

Charpy should probably be speced at whatever the min blowdown temperature will be.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[SJones]

From the above, “Y-grade” seems to be some classification of fluid composition.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[r6155]

More info: diameter, thickness......?

Regards

 

[1503-44]

The OP did not mention anything but "Y" in conjunction with flange specifications, so I did assume he is referring to the MSS spec, in which "Y" is the designator for the yield stress number x 1000psi which follows, but that is only my assumption, until he says something specific about that.

The MSS spec does not distinguish between, or specify any fluid restrictions. It is a mfgr spec only, basic material and dimensions for sizes and grades not specifically included in the ASME B16 flange, pipe and fittings series, which are generally published only up to 24" diameters.

Work I have done in the same area we generally used lowest blowdown temperature. However if the flange, fitting or pipe in a certain area will not experience blowdown temps, the lowest in-service temperature could be used. Just do not get the stuff mixed up with other flanges that have had Charpy tests at different temperatures. It's better to set ONE temperature range for the whole job, irregardless of specific locations, to simplify changes in line numbers, temperature and pressure ratings on one criteria. Materials have a way all their own of getting easily mixed up and potentially used in the wrong place. But it would be conceivable to have one temp range for all pipeline parts and another for all compressor station parts, as generally its two different job numbers and contractors and archives that are maintained separately anyway. Unless the compressor Station might also experience the same temperature when their blowdown gets activated at the same BD temperature.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[akpipelineengr]

Y grade is raw NGL plant liquids.

[URL unfurl="true"]https://www.linkedin.com/pulse/what-y-grade-ngl-jack-babcock/[/url]

 

[1503-44]

Thanks. Never seen it called y-grade before.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

API 5L should be good for-20C. Not onerous.

It's difficult to say that low temp and high pressure can never occur, even once in the systems life time.

You don't want your pipe to get brittle at low temps which can be experienced due to weather.

And I'd never heard of Y grade NGLs before either....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Okay, so Y grade NGL is essentially bottoms product from demethanizer deC1. Knee jerk reaction from process engineer familiar with cold blowdown simulations would be -20degC lower design temp simply wont do, given the C2 and C3 content.

 

[1503-44]

-20C looks good to me.

With all the high vapor pressure products being produced lately, marketing gimmicks must follow.
So, which are the W, X and Z grades?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."