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Project Engineer
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Join Date: Jul 2015
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Maximum Allowable Working Pressure.

07/16/2015 12:50 AM

Why we assign Maximum Allowable Working Pressure(MAWP), if already design pressure is mentioned and have value more than the operating pressure?
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lyn
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#1

Re: Maximum Allowable Working Pressure.

07/16/2015 1:55 AM

Ask the project engineer. If they don't know, you're in trouble.

What does the project specification say?
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Project Engineer
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#2
In reply to #1

Re: Maximum Allowable Working Pressure.

07/16/2015 4:37 AM

Actually, the question arose from the finalization of SOP regarding hydrotesting. If, MAWP of pressure vessel is not given then at which Test Pressure, we have to conduct hydrotest?
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Mikerho
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#3

Re: Maximum Allowable Working Pressure.

07/16/2015 4:48 AM

MAWP @ temp. is usually about 1/3 the design pressure @ temp.

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Project Engineer
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#4
In reply to #3

Re: Maximum Allowable Working Pressure.

07/16/2015 5:06 AM

Can you kindly provide the reference against the comment?
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simonsd
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#8
In reply to #3

Re: Maximum Allowable Working Pressure.

07/17/2015 12:25 AM

Umm are you sure about that Mikerho or was that meant to be 10/3

The big problem with these terms is that they are all used differently in different codes and companies and sometimes interchangeably.

My experience is that MAWP and Design Pressure are essentially the same just that one includes a component for static head. (Based on some quick googling I see ASME VIII quoted that MAWP is at the top tan line and Design Pressure includes the static head and is the number you use for the vessel wall thickness)

If you had a max working pressure I am not sure why you would want to have a design pressure at 3 x that value, that seems over designed.

Hydrotest pressures are 1.3 x Design Pressure (based on the company standards where I last worked which is one of the big contractors in London)

However you do raise the important factor that hydrotest pressures are usually at ambient and so they have to be corrected if the vessel is designed for high design temperature

So you need to check your local and project regulations for how they define these terms

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aurizon
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#5

Re: Maximum Allowable Working Pressure.

07/16/2015 6:01 AM

pressure vessel regulations

If you want to know why they have these regulations...

bang

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SHOCKHISCAN
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#6

Re: Maximum Allowable Working Pressure.

07/16/2015 9:35 AM

To minimize risk & liability not only from the design and manufacturing end but also at the owner/user end of the equipment use.

Design pressure is substantially higher than working pressure in order to account for unexpected pressure impulses, wall thickness degradation due to erosion/oxidation/wear, and operational control failure conditions that expose the vessel to higher-than-normal pressure.

If the MAWP is not designated the owner/operator could rightfully assume it is safe to operate the vessel continuously at design pressure value(s) which would put the vessel at-risk of failure.

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Project Engineer
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#10
In reply to #6

Re: Maximum Allowable Working Pressure.

07/19/2015 10:42 AM

Bravo dear...! Very well explained. Thumps up.
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PWSlack
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#7

Re: Maximum Allowable Working Pressure.

07/16/2015 1:02 PM
  • Design pressure is the maximum process condition that determine the structure of the equipment when built.
  • MAWP varies with time, and is determined by the statutory insurance examination at intervals. MAWP takes into account the condition of the equipment at the time of the inspection, and anticipates its deterioration in the period up to its next inspection to give a MAWP that will still ensure safety at that date, on the basis of the materials of construction of the equipment, its use, the wetting agent, and experience with other similar equipment elsewhere, which the designer would not be expected to have.
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Project Engineer
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#9

Re: Maximum Allowable Working Pressure.

07/19/2015 10:39 AM

Thanks to all the participants, specially to SHOCKHISCAN, whose comment is really up to the mark.
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aurizon (1); lyn (1); Mikerho (1); Project Engineer (4); PWSlack (1); SHOCKHISCAN (1); simonsd (1)

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