Design Minimum temperature per ASME B31.3

[engr2GW]

Hi all,

B31.3 says "In establishing design temperatures, consider at least
the fluid temperatures, ambient temperatures, solar
radiation, heating or cooling medium temperatures, and
the applicable provisions of paras. 301.3.2, 301.3.3, and
301.3.4."

my question are:
1. Does anyone have any idea/experience on how to determine DMT?

2. If I'm considering ambient temp. and there's a chance of having -30F for one or two days in a particular state, does that mean that my DMT can be as low as that?

3. Is DMT the same as minimum design metal temperature (MDMT)?

4. because if the DMT has a chance of being below -20F, then it appears that A106 grade B may not be a suitable material for flow line for oil and gas well sites and separation piping and gathering above ground.

5. Is it uncommon to have a low temp material like A333 instead of A106 grade B for line pipes and flow lines here in the US.

6. Is it common or allowable to have ambient fall below DMT for a few days due to extreme weather or should DMT always be below...

7. What about the fact that the flow stream is always warmer, usually 60F to over 100F, except for hydrates or freezing due to sharp pressure drops

I have looked at historical weather and found that most of the US states have seen less than -20F...any material, DMT recommendation?

Thanks for your help.

As much as possible, do it right the first time...

 

[SNORGY]

It is the lowest *metal* (pipe wall) temperature that will be experienced coincident with highest *pressure* (when in operation). You can take credit for process fluid temperature as well as heat tracing and insulation to avoid A-333-6, etc.

Study ASME Section VIII Division 1 UCS-66 and ASME B31.3 323.2.2 for other credits that can be taken to demonstrate suitability of A-106-B. It isn't often that you cannot use it.

Regards,

SNORGY.

 

[SJones]

That might be the pressure vessel definition of MDMT, but it is not the piping definition of DMT. It is simply "the lowest expected service temperature". Your flow stream might 'always be warmer' when it is flowing, but what if it is shut in? And yes, shut in is a service condition before we start a debate. The failure mode will be brittle fracture resulting in a full bore rupture; what will be the consequences? Is A333 Gr 6 so expensive as to justify its avoidance?

Steve Jones
Materials & Corrosion Engineer

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

 

[engr2GW]

It is definitely more expensive that 106 B, but is it a common material for use in regular oil and gas production flow lines in service where the only source of sub zero temperatures are only weather conditions?
Also, questions 1,2,4,6...

Thanks

As much as possible, do it right the first time...

 

[SJones]

You can make A106 work to at least -48 deg C if you can confidently use Figure 323.2.2B and get the weld metal and HAZ through a Charpy test. As to whether A333 is a common flowline material, I can't say.

Steve Jones
Materials & Corrosion Engineer

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

 

[engr2GW]

Thanks,
first of all, the stress ratio of A106B is well above 0.3
secondly, when you say get the weld metal and HAZ through charpy, do you mean each material or just the WPS, because since it's not a low temp material by material spec, they don't come with charpy when ordered and each one from each mfg have a different heat number, does that mean that a new charpy will be done for every one ordered?

Thank you.

As much as possible, do it right the first time...

 

[SJones]

since it's not a low temp material by material, they don't come with charpy

Precisely. That's why you would have to take a flyer if you want to take the material down to a lower temperature for a high stress ratio. Will you get the required Charpy energy in the HAZ when you have no idea of what the parent material toughness was? That's when most give up and get the A333 - saves a whole lot of bother.

Steve Jones
Materials & Corrosion Engineer

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