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Hydrostatic Test Pressure -Press. Vessels & Piping


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#1 ankur2061

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Posted 10 August 2010 - 09:32 AM

Dear All,

Hydrotest pressure value has always been confused between equipment & piping. However the pressure vessle code as per ASME Section VIII, Div. 1 & the process piping code as per ASME B31.3 give different values of hydrotest.

ASME Sec. VIII, Div.1 (pressure vessel code) specifies hydrotest pressure as follows:

P = Design Pressure X 1.3 X (Stress Value of the metal at test temperature / Stress Value of the metal at design temperature)

ASME B31.3 (process piping code) specifies hydrotest pressure as follows:

P = Design Pressure X 1.5 X (Stress Value of the metal at test temperature / Stress Value of the metal at design temperature)

I have attached the relevant portions of both the codes for clarity.

This should help in clearing any doubts.

Regards,
Ankur.
.

Attached Files



#2 Toor

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Posted 10 August 2010 - 01:10 PM

Dear Ankur,

we can use these standards for old vessels also or these standards for new vessels.

Thanks
Toor

#3 ankur2061

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Posted 11 August 2010 - 11:13 AM

Dear Toor,

As the hydrotest pressure also takes into account the metal stress values, the stress values for old used vessels will be lower compared to new vessels. An adequacy check for the used vessel strength will be required to be done using NDT techniques such as random radiography, dye penetration test, ultrasonic test or any other before determining the design pressure or MAWP of the used vessel.

Since it is obvious that the design pressure or MAWP of an old used vessel will be lower it goes without saying that the hydrotest pressure will be lower compared to a new vessel.

Regards,
Ankur.

#4 benabed

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Posted 12 August 2010 - 12:02 PM

Dear Ankur

i am working in an old LPG plant and we are preparing for the next turnaround where all the vessels will undergo a hydrotest pressue. This plant is 38 years old so i am afraid that some vessel especially columns will colapse during the water filling. MY question is how to proceed in such a delicate situation. please help

Regards,
Benabed

#5 Zauberberg

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Posted 12 August 2010 - 12:16 PM

The vessels definitely should not collapse if proper Inspection/Maintenance program has been applied over the last 38 years, or at least during the last several years. You should be having inspection and testing reports for various periods, since those must have been done for sure - that is a compulsory item and it is defined by the law (inspection and hydrotesting of pressure vessels is normally done after each 5 years maximum). If any unusual thing was observed during previous inspections, such as: the requirement for vessel re-rating, or any sort of structural damage, the results were captured in the subsequent testing reports.

As a conclusion - no need for panicking, just contact your Maintenance Department and look for the inspection records.

#6 ankur2061

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Posted 12 August 2010 - 12:18 PM

Benabed,

You can try the following:

1. Hire a material testing specialist

2. Get all your tanks and vessels tested by the specialist and based on the testing derate the MAWP or Design Pressure of the old vessels/tanks.

3. Use the derated MAWP or Design Pressure values for performing the hydrotest of the tanks/vessels.

Hope this helps.

Regards,
Ankur.

#7 benabed

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Posted 12 August 2010 - 12:43 PM

Dear Zauberberg,

the hydrotest pressure in my contry is done each 10 years also i have to point out that all the vessel have been re-rated as a consequence of the plant ageing.

thank you


benabed

#8 ASH25320

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Posted 09 October 2010 - 12:06 PM

Dear Ankur,

What Are the issues to be considered if one has to go for a pneumatic test for an entire loop of plant?

#9 ankur2061

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Posted 09 October 2010 - 12:18 PM

ASH25320,

Have a look at the following post on pneumatic testing which should answer your question:

http://www.cheresour...h__1#entry24211

Regards,
Ankur

#10 kkala

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Posted 10 October 2010 - 02:38 AM

Thanks for the useful information concerning hydrostatic tests. Over here Process is not directly involved, yet following notes (applied as local standard practice mainly on refineries) may be of interest (correction of stress variation due to temperature is not considered for simplicity, but is applicable in practice).
1. Vessels, exchangers, big basket filters and relevant equipment were hydraulically tested at 1.5 X design pressure (DP) before ca 2006, according to ASME code in force at that time. Then code new requirements lowered test pressure to 1.3 X DP (hence the rule of 2/3 for exchangers became rule of 10/13).
2. Existing equipment is hydraulically tested according to the code it complies with; i.e. test pressure for an old vessel (hydraulically tested now) is 1.5 X DP.
3. Depending on Client's decision, new equipment in an old unit may be specified (in requisition) to be hydraulically tested at 1.5 X DP for uniformity. Apparently it is simpler to have same test pressure for old & new equipment & piping.
4. Pneumatic tests have not been heard of, most probably due to the risk of compressed gas (usually air) explained by Ankur (and also read in other publications as well). I conclude they are limited as much as possible.

Can I place a question? Every 5 years (max) vessels should be hydraulically tested as a normal practice (post by Zauberberg, 12-Aug-2010) . What about piping?

Edited by kkala, 10 October 2010 - 03:03 AM.


#11 ankur2061

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Posted 10 October 2010 - 09:02 AM

Kostas,

A few reasons piping need not be tested in a 5 year interval or any other interval.:

1. Piping or sections of pipe is easier and cheaper to replace then a vessel / tank during a maintenance turnaround.

2. Pipe stress values for a given schedule (wall thickness) are much higher then for a vessel made of steel plates with a comparable thickness.

3. In most cases the difference in cost of testing the piping and replacing is very less and hence replacement is a more economically attractive option.

Regards,
Ankur.




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