Hydrostatic Test of Piping With Vessel as a System 1

[purnawan]

Hi guys,
My company currently have a project, Ammonia Urea Plant Project.

The contractor is preparing the hydrotest plan for piping system, he would like to carry out the hydrotest of piping system together with the connected static equipment to expedite the progress, which s allowed by the specification of ASME B31.3, Hydrostatic Test of Piping With Vessel as a System. We herein paste this spec as below:

(b) Where the test pressure of the piping exceeds the vessel test pressure, and it is not considered practicable to isolate the piping from the vessel, the piping and the vessel may be tested together at the vessel test pressure, provided the owner approves and the vessel test pressure is not less than 77% of the piping test pressure calculated in accordance with para. 345.4.2(b)

As per above spec, he would like to test the piping and vessel together at the minimum 77% of the piping test pressure where the test pressure of the piping exceeds the vessel test pressure. Note: All vessel had already tested at their pressure test.

Before we approve his proposal,
A. What are some things we should consider?
B. The limitation 77% minimum test pressure, is applicable for overall fluid service category?

Thanks
Rudy

 

[KoachCSR]

What are the test pressures involved (of the vessel, and of the piping)? Have you confirmed that the vessel test pressure is within 77% of the piping test pressure?

77% is merely the lowest threshold at which it is acceptable to test the system to the vessel test pressure -- it does not mean that you can test the system to 77% of the piping test pressure regardless of the vessel test pressure. The code plainly states that the system would be tested "at the vessel test pressure" if that 77% threshold is met.

Also, consider the design function and critically of the system - would a reduced hydrostatic test introduce any risk into the start-up of the system?

 

[mk3223]

As per above spec, he would like to test the piping and vessel together at the minimum 77% of the piping test pressure where the test pressure of the piping exceeds the vessel test pressure. Note: All vessel had already tested at their pressure test.

It isn't right the "system" test pressure exceeds the vessel test pressure.

IMO, since the vessel has been tested, there is no sense to test it again. And, if the flanged nozzle is available for the piping isolation, the piping should be tested separately at 1.5x of the design pressure, instead of the 77% of the 1.5x design pressure (i.e. ~1.15x design pressure).

 

[KoachCSR]

I missed the part which stated the vessel(s) had already been tested. I agree with mk3223 in that testing the piping separately is more sensible given that.

 

[purnawan]

thanks for your response guys

As additional information, because the amount of piping system is very much then if the piping test alone, amounted to more than 1000 packages. If some test piping package with vessel as a system, it can be reduced in number.

Also, because the design pressure is more than 200 kg/cm2, the vessel nozzle connection is welded instead of the flange

 

[KoachCSR]

Provided the piping hasn't already been installed at the nozzles, that section can be pre-fabricated and hydro-tested prior to being installed, with the appropriate NDE performed to qualify the nozzle weld.

Also, if your piping design pressure is over 200 kg/cm^2 (over 2,800 psi), your vessel design pressures would need to be over about 2,100 psi to take advantage of that test method.

 

[mk3223]

IMO, it may be easier to test a small system at one time, instead of the vessel with many pipings. Also, to consider if extra work of cleaning or drying the vessel is required.