Group 1.3 Material in a Group 1.1 Pressure Class 1

[Angsi2]

Enviroment: Offshore Facility (Hydrocarbon Gas/Crude Processing)
Design Code: B31.3

I have tried several places and have not got a straight answer. This is the question.

I have a carbon steel 150# class for which the associated Piping Materials Class Specification design conditions are rated for the flange material per B16.5, Group 1.1.

Assuming the piping system is already installed and I need to change out a valve in there due to some corrosion failure. The substitute valve body is material is to A352 LCB (for whatever reason this is the only one material available), per Material Group 1.3 (which has a lower P&T).

1st Question: Can I proceed to use the LCB valve material as long as the valve design pressure (P&T) is above the maximum anticipated service conditions #AND# the system relief pressure/over pressure protection is set lower than valve P&T?


Please refer to Para 301.2.1 (a), (b), (c) and (d) of B31.3. I have got various answers. I need some good advise from a serious specialist.

Thanks in advance.

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301.2.1 General

(a) The design pressure of each component in a piping

system shall be not less than the pressure at the most

severe condition of coincident internal or external pressure

and temperature (minimum or maximum) expected

during service, except as provided in para. 302.2.4.

(b) The most severe condition is that which results

in the greatest required component thickness and the

highest component rating.

(c) When more than one set of pressure-temperature

conditions exist for a piping system, the conditions governing

the rating of components conforming to listed

standards may differ from the conditions governing the

rating of components designed in accordance with

para. 304.

(d) When a pipe is separated into individualized

pressure-containing chambers (including jacketed piping,

blanks, etc.), the partition wall shall be designed

on the basis of the most severe coincident temperature

(minimum or maximum) and differential pressure

between the adjoining chambers expected during service,

except as provided in para. 302.2.4.
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[rneill]

Providing the system is protected at a pressure lower than or equal to the design pressure / MAWP of the lowest rated component in the system, there is no problem with Code (B31.3) compliance.

The problem occurs when you use the lower rated component in a system and DO NOT provide protection at that lower pressure.

Having said this, depending on your local regulations, there may be some paperwork required. For example, in my jurisdiction we have to register our pressure piping systems with the regulatory authority and when we do that we specify an official design pressure. If we wanted to use a lower rated component, we would have to update our line lists and officially reduce the specified design pressure for that line.

 

[JLSeagull]

Others know B31.3. We often have stainless steel instrumentation flanges at a higher flange rating in a lower piping class and PSV settings for carbon steel. You might consider LCB in Class 300 with a spec break of specialty item noted for the connection. Revising the line specification for another material group might be better.