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Maximum Allowable Operating Pressure

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BFZHA

Mechanical
Oct 29, 2009
33
Hi;

Please, can you explain me what's a Maximum Allowable Operation Pressure for ball valves since I haven't find this parameter in API 6D and ASME B16.34.

Thanks.
 
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Maximum allowable operating pressure can be stated or are normally given or described for:

a) single components as: vessels, instruments, valves and pipelines and pipeline components etc.

b) complete constructions assembeled as: vessels with equipment, process constructions with pipelines, instruments vesssels and valves etc.

Maximum allowable working pressure is the maximum pressure that regularily during the process can occur as a normal part of the process, or continously permanently be present during the process. It can thus never (of course) be above the normal allowed operating pressure for the given designed pressure class (allowed pressure related to the temperature) for the valve or component.

For robust components as ball-valves, the allowed maximum working pressure, certified and allowed from the factory, is normally equal to the pressure given by the pressure class.

That seat thightness and body normally are tested above pressures for the pressure class, do not indicate that mawp is allowed to be set above the pressure class limit.

For the total design with other components the mawp can be set a bit lower than the pressure class as a safety limit.

Some norms (EN (European - equal for different European countries) for vessels among others) describe how different pressure limits are to be understood, and allowed variations.



 
Note that there is a provision in ASME B16.34 that says soft seated valves need not be rated to the pressure class assigned to the valve but if they are not rated for the full pressure class value then the manufacturer needs to note the lower maximum pressure rating on the nameplate.

Some ball valves do come with cold working pressures lower than the class rating whereas some have full flange rating. However, at elevated temperatures, soft seated valves will almost certainly have lower than full class rating.
 


rneill,

thank you for your additional, and necessary, detailed remarks on how to read and understand the classification according to class society and manufacturer and temperature in combination.

I could have been even more specific:
Note that if you on the one hand have a mawp for your assembeled process equipment, then each of your components must under all process conditions (fluid, temperature pressure etc) have a total construction (sealing, flanges, classification, constructional details, emission, etc) that conforms to and allow the given pressure.


 
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