Valves - MAWP 2

[Angsi2]

A fundamental question (the 1st question):

- Take for example I have a 150# line class and I need a valve in there. Will I be correct in assuming that a 150# class valve will automatically be suitable for it?

The reason I am asking is valves have their own MAWPs I believe (which is slightly less then the flange P&T)and therefore won't it then be appropriate to look at the line process design conditions and review the suitability of the valve MAMP for the application. However, the valve casing maybe suitable for the full P&T.

Second question:

I have cladded valve (CS + 316L) in a Duplex Stainless Steel (DSS) 300# class. Naturally, the full P&T of the corresponding clad valve will be somewhat lower that the 300# DSS. Is this Ok as long as the process design conditions are met? But please note that the valve casing will not be able to withstand the full P&T of the DSS class.

Any help/input/insight will be much appreciated. Thanks in advance.

 

[BigInch]

No. Always specify ALL requirements, including the service duty, the pressure, the temperature and the fluid characteristics and be sure to include as many other special attributes that the valve must have and any other special conditions that the valve will be required to meet. You should do that in the valve specification and data sheets that you will attach to the bid documents or the purchase requisition.

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"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[JLSeagull]

Be sure to check the tables in B31.34 (if applicable) and B16.5 for the body and flange materials. Most design pressure assuptions apply to carbon steel. Higher alloys are rated for lower pressure and temperature within the same ASME flange class.

 

[unclesyd]

If you have an ASME Class 150 system, an unmodified/unaltered valve that is marked Class 150 will use the ASME pressure-temperature tables for that particular material. In your case where you have altered the valve generally it will have to be retested to pressure required for the base material plus any special requirements.

Here are two articles written by Greg Johnson, president of United Valve that underscore the information posted by BigInch and JLSeagull.

http://www.unitedvalve.com/art-valve_standards.htm

http://www.unitedvalve.com/art-valve_testing.htm

Here is need to know list to specify a valve even if you think a plain vanilla will do.

http://www.vma.org/?SpecifyingChecklist

Also you might want to contact United Valve for information on old valves.

http://www.unitedvalve.com/valve_res_library.htm

For pressure temperature values here is a starting point from Forged Components.

Go to the technical information section on the home page

http://www.forgedcomponents.com/

All the information laying around doesn't absolve one the need to have a copy of the applicable codes and standards that cover one's specific applications.

 

[rneill]

Ditto on the prior posts but I'll touch on one aspect of it which is that B16.34 permits soft seated valves to have an MAWP less than the rating that the flanges would otherwise have.

in other words, the normal valve ratings published in B16.34 which are based on the flanges may not apply to a soft seated valve; in these valves the manufacturer is allowed to design them and stamp them for less than the flange rating.

 

[Angsi2]

rneill and everyone,

Thanks, almost close to the answer I was looking for. I'll try to rephrase the question again for better clarity this time:

I have 300# piping class in Duplex Stainless Steel. The design conditions for this piping class is based on the P&T of the duplex flange in accodrance with B16.5. For economic reasons, I would like to use clad (cs+316L cladding) material for a 10" valve in the above piping class. But I am also aware for 300# CS Flange Pressure Temperature ratings per B16.5 will be somewhat slightly lower compared to a duplex material. So:

1. Is it OK to use this clad valve in the duplex 300# class

- OR -

2. Is there an absolute necessity to de-rate the entire duplex stainless steel 300# design conditions (flange P&T) to match the corresponding carbon steel class in order to meet uniform design conditions throught the piping system?

Any input will be appreciated.


Thanks.

 

[unclesyd]

Your selection of components for a piping are based on the actual process design conditions. Once these conditions are established you pick components that meet the design criteria and in the case of the flanges you might be able to use a Class 150 as far as P&T are concerned but you deem that the allowables for a Class 150 flanges are too close to design conditions and decide to go with Class 300 flanges, slightly over designed but this is absolutely OK. If your valve has Class 150 flanges it will still meet the process design conditions, only it doesn't have the added warm fuzzy feeling you have with the Class 300 flanges in the line pipe. The only problem that may come is the makeup with the line flanges. 10" Class 150 will not make up to a 10" Class 300. Again you are OK if Class 150 flanges are adequate for process design conditions you can use Class 150 flanges at this point.

The same is true with pipe schedules. If you have a system where Sch 5 SS pipe is adequate for design conditions you might want to use Sch 10 to alleviate fabrication, handling and support problems with the Sch 5 pipe.

We have a very large process area where we use Class 300 SS flanges in lieu of Class 150 SS flanges that are OK as far as process design conditions are concern. This change was made due to concerns with gasket leaks that were evident on startup with the as built Class 150 flanges.

 

[rneill]

As long as the CS valve has a pressure temperature rating in excess of that actually required by your anticipated operating conditions (considering any margins required by the applicable code), then there is no reason that you have to maintain the full rating of the duplex components throughout the entire system.

However, once you use a component with a lower rating, the system must be derated. The system rating can not be higher than the lowest rated component used within it. This means that any pressure relief devices that might be in use to protect this system, would need to be set based upon this lower rating and you would list this lower rating as the design condition in your documentation (e.g., project line lists).