SUGGESTION TO DETERMINE HYDRO TEST PRESSURE 2

[RajVas]

A 50KM LENGTH OF 10" DIA(WALL THICKNESS 7.8MM,C.S., ASTM A53 GR.B) OIL EXPORT PIPELINE IS REPAIRED WITH REPLACEMENTS OF SECTION OF PIPES WHICH ARE LESS THAN 3MM THICKNESS. OPERATING PRESSURE OF THE LINE IS 200 PSI. HYDROSTATIC TEST IS PLANNED.IS IT ADVISABLE TO PRESSURISE UPTO 600 PSI? WHAT IS THE SUGGESTED HYDRO TEST PRESSURE?

 

[BigInch]

How much less than 3mm is a rather critical detail you did not tell us.

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[RajVas]

ORIGINAL PIPE WALL THICKNESS IS 7.8MM. PIPE SECTIONS WALL THICKNESS 3 AND LESS THAN 3MM WERE REPLACED

 

[BigInch]

Yes, but what was the minimum wall thickness used?

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[vpl]

RajVas, Were there sections that were 3mm or less replaced with new material having wall thickness of 7.8 mm? Or were sections of the pipe where the new material has a thickness of less than 3mm?

This distinction makes a large difference.

Also, please consider using both upper and lower case keys. It makes it easier for others to read. Thanks

Patricia Lougheed

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[RajVas]

Thanx vpl for the tips.

Old pipes of < 3mm thickness were replaced with pipes of 7.8mm thickness. Please note old pipe sections of thickness between 3mm and 7.8mm were not attended.

 

[BigInch]

You need to check your particular code, however
in accordance with B31.4 Liquid Pipeine Code,
and using a design factor of 0.72,
AND

IF YOU HAVE AT LEAST 1.5 mm wall thickness,

Using a test factor of 1.25 x Operating Pressure,

You could test at 1.25 x 200 Operating Pressure = 250 psig minimum test pressure.

Theoretical yield pressure of 1.5 mm x Grade B, is 329 psig, so DO NOT test to 600 psig.

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[vpl]

Big Inch,

It appears that RajVas' minimum pipe wall is 3mm (as everything below was replaced.)

Patricia Lougheed

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[BigInch]

Patricia & Raj,

It may be so, but it doesn't matter anyway because of the desired 200 psig operating pressure. 1.5 mm will permit an operating pressure of 200, as long as Raj tests to 250 (min) psig. Therefore, and in any other case, even those with wall thicknesses above 1.5 mm, there is no point going over the minimum required test pressure of 250 psig (according to B31.4) any more than you have to. A 250 psig min test is all that is needed to permit operating to 200 psig.

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[RajVas]

BigInch,

Could you please tell me what is the test pressure & suggested operating pressure for the 3mm thickness trunk pipeline according to B31.4?

 

[jte]

Raj-

Are you implying that you (electrical) are making decisions for hydrotesting piping for which you do not have access to the appropriate code? How much money is at stake here and how much does a copy of B31.4 cost? Buy the code and have a mechanical engineer within your organization study it...

jt

 

[RajVas]

Nothing is implied; the forum is used for what it is meant for

 

[RossABQ]

We won't design any medium voltage distribution systems, if you won't design or specify piping systems. Deal?!

 

[BigInch]

Code: B31.4

Pipe: 10.75 O.D. x 3 mm w.t. (0.118")
ASTM A53 Gr B, Yield Stress = 35000 psi

Permits a Maximum Operating Pressure of 553 psig
IF it is tested to AT LEAST 692 psig for 4 hours.

MAOP is defined as Minimum Test Pressure / 1.25
so if you hold a minimum test pressure lower than 692,
you would have to divide the actual minimum test pressure by 1.25 to determine your actual MAOP.

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[Cockroach]

BigInch is bang on here boys. Correct specification and geometery of pipeline. I concurr with 1.25 MOP minimum, except would add that 1.50 MOP would be the absolute highest test pressure.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[BigInch]

Ken, I think the 1.5 test factor isn't B31.4, but is defined as the max in B31.3 and also in B31.8, where its use depends on the B31.8 area classes.

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