MDT B31.3 Piping & Warmup

[reichertc]

Hi folks,

Imagine that I have a 600# ASME B31.3 piping system with a minimum design temperature of -29°C. Now imagine that it is -35°C outside and the piping is also at that temp. If a person were to run low pressure steam through the pipe until the metal temperature reached -29°C, and then put the pipe into normal operation, would this be a violation of B31.3?

Same question, but now I have performed calculations for the Stress Ratio and applied the reduction in Figure 323.2.2B without doing impact testing?

Same question, but instead of actually performing the calculation, I use the arguement that with the low pressure steam, the Stress Ratio will be low enough that I can apply the reduction without performing the detailed calculations?

The goal here is, obviously, to avoid having to perform impact testing. This has been a point of contention between several different groups within my company for quite a while. I'd appreciate anyone's comments on the matter, especially if you are close to the committee members or have personal expereience. I'll probably be submitting a technical inquiry to ASME on the subject, but I don't expect a response in time for the project that I am working on...

Thanks in advance.

 

[LSThill]

Hi ASME B36_19M.pdf


What is the materil in the Piping Specification?

 

[reichertc]

Assume A106-B piping or any other material with a -20°F minimum temperature as listed in Table A-1.

 

[bjones1]

I am not a B31.3 expert, but way I see it; the code applies to "design conditions", however the design must be able to cover the full operational range of the material selected.

The code is not an operational or maintenance code - it is a "design" code. Your design temp as stated in your question is at the design limitation of A106 Gr.B material, not below it. If you are given a design point less than -29 C, you may have to impact test the base metal, HAZ, and weld metals during your weld procedure, but not the production welds.

If you run steam through your system at -35 C, I would consider the system to be operational at a point other than the min. allowable temp (as in table A-1) and the rules in Chapter III would apply.

If you want to avoid this issue, consider some way to keep the piping above the -29C temp at all times or select another type of piping material.

 

[bvi]

Answer to the first question, yes you would be in violation as you are operating it below the minimum design metal temperature.

Answer to the second, if you have shown that you can run it at the -35F metal temperature without requiring impact testing, because of the low stress condition, you would be in compliance and no impact testing would be required.

With respect to doing calculations are not, the code simply provides requirements based on stress ratio. How detailed the calcuations need to be to determine the stress ratio is not specified. If you can, for example, confidently determine that the stress ratio is, for example, less and 0.3, by judgement, that is not a violation of the code unless your judgement is wrong. Note that thermal expansion (and contraction) stresses are included in the stress ratio. If the system was erected at 70F and is presently at -35F, I would expect that there are thermal stresses to consider.

 

[LSThill]

Hi reichertc (Mechanical) and menber's

Note for your requirement 600# ASME B31.3 piping system (Full flange ratings per ASME B16.5, TABLE 2-1.1) A105 -20f Temperature.

Per Piping standards

Leonard@thill.biz

http://www.thill.biz

 

[niteattheopera]

Hi reichert

As our company is located in the frozen waste lands of Canada we are confronted with this problem constantly. A few items to consider

1. you can not simple base your MDMT on material spec alone and must also address the design thickness while establishing your allowable design MDMT

2. ASME B31.3 provides exemptions to impact testing as , as you have mentioned based on differential stress , therefore , always pressure test your systems at the maximum possible pressure allowed by the piping system components

3. Circulating warm product , steam or what have you to warm the piping material to -29 C prior to applying operating pressure is acceptable providing the circulating pressure does not exceed 103 kPa. Define of "operation" is when the operating pressure exceeds 103 kPa

hope this helps

 

[ganvis]

Hi reichertc,
We do come across similar situation in gas processing facilities during blowdown (gas cooling during depressurization due to Joule Thomson effect).
You are not violating ASME B31.3.
Firstly, for 600# rating (1480 psi) you are OK upto and including -20 deg F (-29 deg C).
For colder than -20 Deg F upto -31 deg F (-35 deg C), the pressure shall not exceed 0.88 times 1480 psi = 1302 psi (FIG 323.2.2B)
This means if you meet both the conditions you are OK and impact test is not required.
If your pipe wall is -31 deg F, you can't pressurize to the 1480 psig. You have to limit the pressure to 1302 psi till it warms up to -20 deg F and then the pressure can be 1480 psi.
The important thing to note is coincident pressure and temperature condition. No detailed calculation in your case is not required. All that you need is a simple Technical Note which states the above coincident pressure and temperature design conditions and the relevant B31.3 code para references.
In gas processing we get very cold temperatures -150 deg F and here in addition to pressure ratios, we have to perform stress anlysis to use the concession given in B31.3.
Your case is straight forward and simple logic will do!
Good luck!!