Low Design Temp for Piping 3

[Krausen]

I'm in the process of writing oil & gas facility piping specs for cold weather regions in ND & MN. My question has to do with API/ASME's treatment pipe & fittings with design temperatures below -20 F. I know many of their specs address higher temperatures, but often they seem to be capped to -20 F on the low end. For example, flange connections under ASME B16.5 only have pressure class ratings down to -20 F for their materials.

How does a guy write a piping spec if his minimum design temp is -35 F?

Thank you in advance.

 

[BigInch]

I'm currently working with some liquid ammonia and polypropylene pipelines, temp -33 to -47F.
Toughness against brittle failure is the important parameter. I found this introductory article helpful.

http://www.pipelineandgasjournal.com/selection-pipe-material-low-temperature-service-0?page=show

You might be able to adopt some of these too,

http://www.talisman-energy.com/uplo...nical_specifications_for_piping_materials.pdf

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

 

[europipe]

Nice word: adopt

 

[BigInch]

Agree. & BTW those are not from the ammonia & polypropylene project I'm working on.

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

 

[racookpe1978]

I don't know the inside details of the material listed in that spec, but most of the brittle failure criteria research started coming from the WWII failures of the then-new welding and steel failures at low temperatures. Ships cracking, tanks failing, trucks in Russia failing, pipes failing, etc.

Since the common low-alloy steels and welding at that time were only good down to -20 (or so they thought, because that's what they had experienced) they wrote spec's down that far for the most susceptible alloys. Written another way, most steel and welds they knew were good down to about -20, but stuff started failing below that temperature.

 

[rconner]

An uncle of mine lived in the area of Grand Forks and spent much of his career outside working as a lineman in ND and Northern MN for Northern States Power. While I also have some experience kind of up close and personal off and on over many years with the cold and other conditions in this particular area, I believe with the even wilder and woolier conditions of many decades ago he was a tougher man than I will ever be (though I guess I thus do have some appreciation for your conditions.)

I suspect however long before the disaster nearly a hundred years ago with the Titanic and less popularized eventual events also with Liberty Ships, I think many or most folks basically realized that a whole lot of things get some brittle with cold! I guess about the only thing I would add is planned or unplanned release of pressurized gas through leaks or whatever other breeches from vessels or pipelines, and "decompressive cooling" or "decompression" thereby, can reportedly result in localized spots on pipelines or other containers of even more intense cold (that is some lower than whatever the ambient is). Per some authorities there has been historical concern or knowledge that under certain circumstances this can result in enhanced embrittlement,and more dramatic effects than just small leakage even in pipelines. While at least some former grades of otherwise rather formidable steel are known some subject to effects from the cold, I believe that on weaker plastics and elastomers etc. it can be expected to be even more dramatic.

You have been given some helpful references. I suspect virtually all of us were exposed in some extent to the various "gas laws" (in introductory physics classes etc.), and many more of us even in more specialized at least small pipe and tubing applications as we watch or feel what goes on under our car hoods or our home heat exchanging systems. While the good reference the Big one provided above did at least mention, "However, the general guidance in such case should be to look at the product properties, risk analysis, PRODUCT LEAKAGE" , and will a reduction in pressure at a certain point reduce the temperature to what is considered a low-temperature range." - I supplied the caps) there is apparently not a whole lot of detailed guidance out there concerning such phenomena in larger pipelines. While one reason for this is likely good or better performance in this regard of modern steel pipes, another reason is the detailed analysis of such effects is no doubt quite complicated, involving a rather hairy juxtaposition of hydraulic engineering, thermodynamics, and mechanics of materials that in whole is perhaps straining the ken of most common folk.

 

[TD2K]

Where we have needed a lower than -20F design temperature, I've seen the piping materials changed from your standard carbon steels to low temperature carbon steels, A-333 I think is what we used and it was good to -50F. Similar material for fittings.

 

[BigInch]

A333 is what we're proposing for the ammonia & polypropylene lines. I thought I mentioned that, but alas.. not until now.

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

 

[moltenmetal]

This is an area of confusion frequently. Lines subject to operation at temperatures below -20 F during defined operational conditions are easy: you spec materials suitable for those low temperatures. But lines which are being used in environments where AMBIENT temperatures often fall below -20 F are another matter entirely. Does it make sense to design water lines with design metal temperatures below -20 F? I've seen people try to do that. I also am aware that in northern Alberta, almost all of the structural steel used is NOT low temperature steel- it's just thicker sections of ordinary structural steel grades.

 

[BigInch]

Agree. For cold temperatures, in Minnesota, ND and Montana, I've speced CS with impact testing at -20F, everywhere, including above ground station piping, launchers and receivers.

In any case, the objective should be to avoid installation of pipelines in depths with temperatures below freezing. It is relatively easy to do in most regions, as freeze temperatures rarely extend below 2 meters, even in the coldest regions. In permafrost, buried pipelines should be installed below the permanently frozen zones, or if not possible, be placed above the soil on elevated pipe supports. That practice is prevalent everywhere except in Russia, where the pipelines seem to be just placed anywhere for the most part. Lots of them are popping out of the ground, being jacked up by ice lenses freezing below.

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

 

[rmw]

If the design is to ASME B31.1, below -20F the bolting has to change from B7 to A320 L(x).

To Krausen:

Are you going to pump something at -20 or lower, or just design piping that won't fall down below -20 if the heat trace fails? If the former, then chech the fluid properties before doing your design.

rmw

 

[dcasto]

I hate to answer a question with one, but I have many. Polypropylene is a solid, how is it pumped. So if you design a pipeline to the fluids boiling point when the pressure is relieved to atmosphere, how could we afford to lay an ethylene. Line with a not of -125f?

I have blow down ethylene and dug in frozen ground near Houston to getting the line it's not an issue.

 

[BigInch]

Thanks dcasto, you are correct, there is no "poly", just propylene (butane)

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

 

[anglisk]

Krausen,

If the line is determined to be designed for temperatures less than -20F, proven notch toughness (at -50F if this is the design) of the materials of construction (if your case, probably carbon steel) is required, as well as the weld procedures used to join the materials together. This would include material specifications such as A350-LF2, A333-6 and A516-70.

 

[Krausen]

I appreciate all the help from this forum, especially BigInch for his willingness to share a sample spec with everyone. Definitely some good feedback from all sorts of folks here.

rmw - I will look into 31.3's requirement for low temp bolting. Thanks for mentioning. Currently I'm just using the A193 B7 stud bolts, as the client has their own mandatory spec for these. I may need to pursue a variance to this, if necessary. Interestingly enough, I noticed the sample spec from BigInch called for A193 B7 stud bolts for both regular temp & low temp crude oil service (my spec is geared for a light sweet crude line).

And yes, the liquid crude oil will be pumped through the piping at a lower design temp of -35 F. This design temp will only hold true for the above ground segments that will not be housed in a heated building and will not be electrically heat-traced or insulated. The bulk of the piping will be buried to depths near the bottom of the frost zone and thus insulated from ambient air conditions.

moltenmetal - Interesting you mention that regular carbon steel is commonly used in Northern Alberta. The client in this case is from Northern Alberta (Edmonton), and to my knowledge they appear to be comfortable with regular carbon steel for all the piping designs I've seen. I'm just not sure if I'm comfortable spec-ing out regular CS for my piping design yet!

As many have mentioned though, it seems the critical parameter is Charpy testing. So long as the CS remains ductile enough, there shouldn't be issues.

Thanks again.

 

[BigInch]

CS is common all over the northern US. If the client has had good experience with it farther north, I wouldn't push anything else at him.

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

 

[curtis2004]

Krausen,
It is true that in Northern Alberta "regular" CS can be acceptable. But don't forget operational conditions, indoor/outdoor location affect greatly design temperature.
When you move below -20F next border condition is -50F. You not only change you piping material to A333, but also change flange, fittings, valve bodies (grade LCB or LCC) - everything should change.
Regards,
Curtis

 

[Krausen]

Curtis,
The question you've asked is the one I've been struggling with as well. The more I research, the more I'm leaning to go all low temp CS components. CS flanges, fittings, & valve bodies will all be spec-ed out as low temp CS with proven Charpy test values at a temp of -50 F. The absorbed impact energy values will vary depending on the component. In addition, I'm inclined to use A320 stud bolts for flange connections in lieu of the good ol' A193s. Per ASME B16.5, both of these bolt materials are considered high-strength, which I prefer to use regardless if the flange connection is Class 150, 300, or 600.

As for pipe material, we're subjected to API 5L line pipe (PSL 2). I believe custom Charpy tests can be specified for this line pipe, so as of this moment I'm not sure about how much A333 pipe I'll be dealing with. I'm hesitating in this area, as the latest API 5L spec has merged with the international ISO spec and has been a nightmare to read.

 

[stanweld]

Krausen,
Is it truly possible for your crude to reach -35 F without it clogging the line? If the crude is readily pumpable at that temperature and you are sure that the crude will be at that temperature, choose the low temp piping recommended above per ASME B31.3. If not truly possble, select the standard materials acceptable at -20 F.

 

[BigInch]

Before you go out and demand that your client must have A333 ... and the cost associated with it, you might want to ... have an informal discussion with him about low temperature materials ... over a cup of coffee .. or something.

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