Low Temp Materials

[Krausen]

In designing to the US pipeline transportation code (ASME B31.4) I've been tasked with a minimum design temperature of -35 F. Has anyone run into any issues with the fact this code was only intended to apply down to -20 F minimum temperature? While this is probably fine for most of the country, there are regions where the minimum ambient design temp can be much lower (e.g. AK, MN, WI, ND)

Also, for low temp-rated "high yield" fittings, can anyone explain the key differences between ASTM A860 & ASMT A420 material? Both material types are impact tested to at least -50 F (or lower) and both types can be "high yield" (yield strengths above 35 ksi). For example, can a Y52 fitting be spec-ed out to either? Is one material type more costly than the other?

Thank you in advance

 

[BigInch]

I have used ASME B31.4 to design liquid ammonia pipelines to a similar low temperature. Materials (ASTM A333 pipe) was speced to be tested at -40F.

By the way, CFR 49 part 195 is the legal design requirement in the US for liquid pipelines. The CFR references the 2006 edition of ASME B31.4, not the latest edition. The CFR has no temperature limitation. It requires that suitable materials be chosen for the temperature environment.

 

[weldstan]

Minimum ambient temperature may or may not be taken into consideration. Most pipelines are buried and will not achieve a temp of -35 F. What is the minimum temperature of the fluid during operation? What is your fluid? API 5LX-60 and higher yield alloy steels can be obtained with impact toughness at -35f - but do you really need it?.

 

[SJones]

The difference between A420 and A860 could be deduced from the scopes: one is for piping and pressure vessels, the other is for oil and gas pipelines. That won't stop you using A420, but A860 is more tuned towards pipelines. You might find that you get some "mildly aggravating hoop jumping" owing to A860 not being listed in Table 423.1-1.

Steve Jones
Corrosion Management Consultant

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

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

 

[Krausen]

SJones - you nailed down the cause for confusion here. B31.4 explicitly lists A420 in their Material Standards table (Table 423.1-1) but mentions nothing of A860. Wonder why? Thank you for mentioning the scopes ... on further inspection, a careful reading does point to A860 fittings being intended for transmission systems as opposed to "pressure piping" stated in A420.

weldstan - low temp piping materials are needed. Client required for this crude oil system. Buried piping would never reach this temperature, but aboveground pipeline facility piping can. During normal steady operation, the aboveground process piping would obviously not get this low. But during line shutdowns or even aboveground "dead leg" lines (piping not carrying steady flow) during normal operation have had skin temperatures recorded at these low temps.

BigInch - thanks for pointing out that the latest CFR 49, 195 only recognizes the 2006 edition of B31.4. That's always an interesting dynamic. While CFR no has temperature limitation, B31.4 appears to be intended to apply down to only -20 F. Client is requiring compliance to B31.4 (as recognized by CFR 49, 195 in the US).

 

[BigInch]

B31.4 was and is intended to apply down to -20F, but nothing excludes it's use at lower temperatures. As design codes cannot and do not apply to all situations, use engineering intelligence and experience in addition to the code's minimum requirements whenever outside stated ranges. There should be no issues in using B31.4 at lower temperatures as long as proper materials are selected. ASTM A333 is an excellent steel for use at your -35F design temperature. Specify your test temperature on the purchase requisitions, inquires and specification's data sheets (if you will have specs) for the pipe and fittings.

 

[SJones]

B31.4, 423.1 (b) is worded loosely enough to assist your leap through the hoop on behalf of A860.

Steve Jones
Corrosion Management Consultant

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

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

 

[BigInch]

I'm not sure of fracture toughness properties of the A860 at low temperatures. In lieu of doing further research on that, perhaps you should check with suppliers of those fittings to see how low they are willing to go with the test temperature.

 

[SJones]

40 Joules average at -46 deg C for A860 versus 17 Joules average at -45 deg C for A420 - a pretty normal pipeline versus piping comparison.

Steve Jones
Corrosion Management Consultant

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

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