Definition of Max Operating Condition

Yep. The usual reference is a document called the Process Description. It is written by the Process Engineer responsible for the process in question.

Maximum Allowable Working Pressure (MAWP) (at a given temperature) is defined in pressure vessel codes. I don't think the other terms have standard definitions. (And hence may not have any references, either.)

So which one is the higher , the MAWP, design pressure or the maximum operating pressure

MAWP.

...because MAWP is a function of the age of the equipment, and will be determined by the Engineer/Surveyor from the company responsible for providing burst indemnity insurance cover at the facility. If the vessel is life-expired, it doesn't matter what its design pressure is if its MAWP is zero.

MAWP >= design pressure >= maximum operating pressure. Though the "=" is unusual, there's normally a margin.

Codemaster is correct, but elaboration is needed

The MAWP is used to calculate the minimum wall thickness for tanks, pressure vessels and piping. The MAWP is defined in the ASME pressure vessel code, but it is determined by the component specifyer.

It is assumed that the person specifying the equipment understands how it operates and the maximum conditions (temperature and pressure) that it will sustain during its operating life. However, freqently, MBAs become invloved in the design process and screw things up.

There is no code or standard to specify these margins.....it is a matter of engineering policy....Sorry Banu...

My experience has been a reasonable margin on pressure is 10% or a minimum of 30 to 50 psig.

So a tank with a maximum expected operating pressure of 150 psig would have a MAWP of 200 psig specified to the fabricator. Hydrotest pressure would be 1.5*200 or 300 psig ( this depends on the code)

With a vessel designed to operate at 1500 psig the MAWP would be 1650 psig

Code required relief devices are to be set at the MAWP !

Similarly, design temperature should be 50 to 75 degrees(F) above maximum expected conditions

These are approximate margins, higher or lower ones can be justified depending on the process and the way that the equipment is operated.

Thanks to you all for the valuable input/reply