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.