ASME B31.3 2018 - Minimum impact test exemption temperature reduction

[charles_ac]

In ASME B31.3 revision 2018, for the minimum impact test exemption temperature reduction, the code establishes 3 conditions for the use of applicable requirements:
(1) The piping is not in Elevated Temperature Fluid Service.
(2) Local stresses caused by shock loading, thermal bowing, and differential expansion between dissimilar metals (e.g., austenitic welded to ferritic) are less than
10% of the basic allowable stresses at the condition under consideration.
(3) The piping is safeguarded from maintenance loads, e.g., using a valve wheel wrench on a small bore
valve.
Could someone explain in a practical way what item (3) really means? What does the code refer to as "maintenance loads"? So how about using "a valve wheel wrench on a small bore"? What relationship does item (3) have with brittle fracture?
I would greatly appreciate anyone who can help.
Thanks

 

[GD2]

OP,
First explain, how will you open a stuck 1/2" drain valve on a cold line?

 

[charles_ac]

First explain, how will you open a stuck 1/2" drain valve on a cold line?

I think this is not the issue. We are not necessarily talking about cryogenic systems. In cryogenic systems, the valves must be equipped with an extended bonnet and positioned in such a way as to allow their operation. My case is a flare line, which is not cryogenic.

 

[GD2]

OP,
Low temperature doesn't mean it has to be cryogenic.
What is the MDMT of your flare line? Did you figure out if an impact test required from Fig 323.2.2A?

Or is it only the study at this time you are trying to understand the Code?

Before you come back with the answer, one needs to be careful when applying impact load to a cold component. Typically, plant operators don't carry wheel wrench to open/close a stuck valve. They will usually use a normal wrench and most likely a hammer. This causes an impact load on the valve. There had been many instances when the valve comes off from the pipe creating an incident.

this happens because at low temperature material loses ductility and becomes more brittle.

What the Code is saying is one should take precautionary/preventive measures before further applying the temperature allowed by Fig 323.2.2B/Table 323.2.2B.

 

[charles_ac]

I'm trying just to understand the Code. MDMT=-45 C (Not cryogenic).

Thanks,

 

[akpipelineengr]

I interpret condition 3 to require action to prevent impact loading, if you are going to take credit for that reduction. That may mean removing small bore valves from the system or taking administrative action (like car seals) to prevent impact loading at cold temperatures, as well as guarding or insulating pipework to prevent impacts from tools, etc.

Most operators I've worked with would interpret a flare system to be subject to impact loading that would prevent the use of this exception simply due to the nature of flare systems. Flare services are unpredictable and subject to significant dynamic physical and thermal loads, and require a conservative design approach.

 

[charles_ac]

I actually agree with your observation. In my case, we have a repair to be carried out on the piping with the installation of a part that must enclose a screwed clamp. We had external corrosion in the pipe caused by bird droppings that caused leakage into the atmosphere (believe me, it's true). The welding will be done in operation and I was just trying to understand whether a welding procedure based on the API 1104 standard would be sufficient (which does not require impact testing) or if, in this case, ASME B31.3 requires impact testing. Remembering that the stress level in the piping is very low and, therefore, the stress ratio is less than 0.3. This is an important point to consider when we are talking about flare lines.

 

[GD2]

OP,
You are all over the place. Why bring API 1104 with ASME B31.3? API 1104 is meant for Pipelines and Facilities (pumping/compressor Stations), whereas ASME B31.3 is for processing facilities and follows ASME Sec IX.
So, first thing first. Keep your steer and focus straight on what you want.
Impact test requirements comes from the Code, not by welding procedures.
Read Table 323.2.2 of ASME B31.3 and determine if a weld impact test is required. Acceptance criteria is also given in the Code.
Once you have determined, follow ASME PCC-2 for the repair. PCC-2 provides different options for repair and see which one best fits for you.
Remember, you plan to do an on-stream on a live flammable gas line. I suggest, you stand first in the line while doing the repair.
What can I say more than this?