CVN Test Temperature for API 5L B31.4 pipe 1

[IFRs]

For API 5L pipe X42 to X60 used for both an above and below ground B31.4 pipeline facility being purchased to PSL-2 what should the CVN test temperature be specified as? I am not an expert in such things but had expected the design temperature of minus 20 F but find plus 32 F on the drawings. I need help understanding the logic before I parade my ignorance to the EOR. Many thanks in advance...

 

[SJones]

The standard API Spec 5L Charpy test temperature is 0 deg C. The minimum design temperature should be set by process and mechanical engineers and need not be below 0 deg C to incur Charpy testing.

Steve Jones
Materials & Corrosion Engineer

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

 

[IFRs]

So if the project is in an area of the country where the lowest one-day mean temperature is -15 degrees it is still OK to do the CVN at +32? Can you help me understand the rational? For instance for above ground storage tanks the CVN temperature is the design metal temperature which is based on the lowest one-day mean temperature.

 

[IFRs]

I understand that for the underground portion, the pipe will never see temperatures low enough to be of concern and the same could be said for above ground portions that are normally full but what about the pig traps that are empty possibly for long periods and then get sudden pressure? If they cooled off to ambient ( say -20 ) is there a concern that they may fail when the pig and pressure come?

 

[SJones]

Setting the Charpy test temperature against the minimum design temperature is another question. At first sight, given the quoted environmental conditions, a minimum design temperature of 0 deg C does seem inappropriate. B31.4 stipulates the Charpy test temperature relative to the lowest expected metal temperature and API Spec 5L states that other Charpy test temperatures can be agreed.

Steve Jones
Materials & Corrosion Engineer

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

 

[IFRs]

And therein lies the problem. Neither of the codes gives guidance on determining the CVT temperature if different than 0 deg C. The 49 CFR 195 paragraph 102 is similarly silent. I'm wondering if the materials that are generally used are sufficiently resistant to brittle fracture that for the continental USA there is no need to change from 0 deg C. Perhaps the industry simply does not need to be worried about this and I am barking up the wrong tree.

 

[stanweld]

The need for impact testing is not based on the lowest ambient temperature conditions. The temperature is based on the minimum metal temperature at a design load. If the pig launchers/receivers are envisioned to (designed) and will operate at -20 F at a pressure of 72% of the base materials' SMYS, it behoves you to purchase the base materials impact tested at -20 F or below. If this is not the case, or the design condition is low; e.g., < 50% of the SMYS at -20F, there is really no need to do so if the longitudinal welds are suitably examined. This is an Engineering decision.

 

[BigInch]

B31.4 (2009, 24 Mar 2010) Charpter III Materials 423.2.3 Steel
"The test temperature shall be the lower of (32F-0C) or the LOWEST expected metal temperature during service, having regard to past recorded temperature data and possible effects of lower air and ground temperatures."

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[IFRs]

Thank you sir. I looked all over and missed this.

 

[BigInch]

You are welcome. Thank you for the "

"

Like I tell all the engineers here, start on page one and read until you've finished. Next time you'll remember where you saw it.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[SJones]

I said it first!

Steve Jones
Materials & Corrosion Engineer

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

 

[BigInch]

It was the way you said it. I figured, if I didn't understand your answer, the OP didn't either, so best way to explain it was to quote the code. In, "relative to the lowest expected metal temperature", relative could mean virtually any relationship, whereas "=" leaves no doubt as to what that relationship is.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[SJones]

There's still the issue with the minimum design temperature though.

Steve Jones
Materials & Corrosion Engineer

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

 

[BigInch]

I don't see any issue, other than that design temperature looks wrong, but that is not issue to the question regarding CVN test temperature. That problem I believe is solved.

The Design temperature above is probably set on one process high temperature, that often being the high annual ambient temperature for pipeline work, however we all should know there is a temperature range that is often more important than some nominal high, especially for pipeline work that is exposed to winter temperatures. And for pipeline work in B31.4, any design temperature(s) between -20F and +250F are not expected to have significant implications. The low limit design temperature here should probably have been specified as -15F, within the -20F range, but IFR figured that part of the problem out.

What the code says about temperature is,

"401.2.3.7 Temperature Effects. The design temperature is the metal temperature expected in normal operation. It is not necessary to vary the design stress for metal temperatures between −20°F (−30°C) and 250°F (120°C). However, some of the materials conforming to specifications approved for use under this Code may not have properties suitable for the lower portion of the temperature band covered by this Code. Attention should be given to the low temperature properties of the materials used for facilities to be exposed to unusually low ground temperatures, low atmospheric temperatures, or transient operating conditions. The design temperature should be established considering temperature variations resulting from pressure changes and extreme ambient temperatures.

All in all, you hardly would expect to have any problem with toughness of API 5L X42 to 60 until you reach -40F. Below -20F, I have called for additional notch toughness, but above -20F, I do not recall ever having specifyied any additional requirements for API 5L pipe.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[SJones]

Having a wrong minimum design temperature is not a minor issue. Stating that 'Charpy test temperature is relative to minimum expected metal temperature' highlights the fact that neither B31.4 nor API are accounting for the thickness of the pipe compared to the Charpy test piece. In essence, thicker pipe could require a lowered test temperature, below the minimum expected metal temperature, as seen in other pipeline design codes.

Steve Jones
Materials & Corrosion Engineer

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

 

[BigInch]

I did not say having the wrong design temperature was a minor issue. I said, being that the proper CVN temperature is established at the minimum service temperature, that the design temperature was not, or no longer, relavent to the question asked.

B31.4 and API 5L are accounting for the pipe properties. In the same paragraph 401.2.3.7 it says, "However, some of the materials conforming to specifications approved for use under this Code may not have properties suitable for the lower portion of the temperature band covered by this Code."

401.2.3.7 cautions the engineer against against selection of materials of improper wall thickness, toughness, yield strength, operating press & temperature and decompression.

Not having full details of the project here makes it difficult to say anything else with any authority, other than what was said already, however
1.) Liquid line - relatively lesser danger of fracture propagation
2.) H2 & S exposure - probably not
3.) Toughness requirement is largely, if not totally, to limit fracture propagation, which will be limited in a launcher zone.
4.) -15 F @ launcher is not a great fracture propagation risk due to 1.) the fracture could only go one way, 2) number of fittings and valves in the zone.
5.) Being that the number of CNV samples from a heat is probably more important to guaranteeing toughness of a long pipeline, temperature almost becomes a parameter of lesser import to number of tests/heat.
6.) Reaching -15 in an underground pipeline when it is probably the air temperature he's talking about - probably not.
7.) IFRs has the proper temperature now regardless of what design temperature is stated.
8.) Design temp is stated at +32, which actually might not be wrong. It may be only IFRs idea of what temperature is possible there.
9.) It is API 5L PSL-2, which does have some CNV and DWT requirements, as opposed to A106.

If I had give a general opinion about all of this, it would be that there is a lot more important things to worry about on that project besides the CNV temperature, which has at this time, probably got a correct, or conservative test temperature.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[SJones]

Sorry, but the Charpy testing required is for fracture initiation. The DWTT is for fracture propagation and is unlikely to be called up for a liquid line, but that's not really the issue. Process safety considerations would surely lead to not wanting a fracture at all, let alone a propagating one. If I had to give an opinion, IFRs needs to get a definitive minimum design temperature and ascertain that sufficient Charpy energy is being specified at a correct test temperature.

Steve Jones
Materials & Corrosion Engineer

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

 

[BigInch]

Fine. I got the tests backwards. Still irrelavent to the question. According to what he said, he apparently has the proper test temperature now. I assume he is smart enough to realize that there might be a problem with the design temperature, because he has already noted that fact himself. If he thinks he needs to persue that further, I don't think he needs us to tell him to do it, but if he calls you, pick up the phone.

According to my experience designing pipelines as far north as Hibbing MN., constructed with above ground launchers and receivers, design temp to -20F, possibly actual temperatures much lower, API 5L, X42-60, Charpy tests at -15 are sufficient [full stop]. I'm happy.


"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek

 

[SJones]

You are easily pleased.

Steve Jones
Materials & Corrosion Engineer

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

 

[BigInch]

Quite the contrary. Everything you are worried about in this thread is based on a total supposition on your part.

Launcher barrels must be the most unlikely point on a pipeline to experience trouble related to material failure. Generally shop fabricated under very good quality control procedures. In gas lines, the design factor is normally highest in a launcher/compressor station zone. Not to mention that they are normally isolated at zero pressure.

My problem is that I don't believe special conditions should be imposed just for fun, especially when ALL indicators point to just about the lowest possible risk category imaginable. Can you identify JUST ONE specific incidence where a launcher barrel ever inititated a toughness related failure.

"People will work for you with blood and sweat and tears if they work for what they believe in......" - Simon Sinek