Hydrostatic test of vessel

You should be careful about some points of design and specifications of pressure vessels.

One thing is the design pressure. It's based on the material choice, work cycle, and expected life of the vessel. Another thing is the static pressure test.

Static pressure tests are done in pressures up to two times the working pressure. It is intended to test the integrity of the vessel itself, welds, connections, remaining wall material, and is intended to be a destructive test if the vessel is not within specs. It assures another period of 5 years or so of work without collapsing.

If your pressure inside the vessel has changed to a higher value than the vessel was designed to work with, I recommend you to go back to the vessel specs and control sheets, check the material stress specs against the new requirements, and see if it fits to the standard. Or, hire a consulting to do it for you, including material analysis and life expectation with the new load.

If your working to ASME sec. VIII, you should not be building anything without an authorized inspector (AI) The AI is a person who is fully up to date on all the ASME sec. VIII and is hired and paid for by your insurance company. There are no insurancance companies in the United States that will cover any pressure vessel that was not build to ASME sec. VIII and verified by an AI.

The AI will over see the design, sign off on the material, the thickness, and the process. Each piece of material must be tracable back to the foundry with material certs, and kept on file at your company and copies sent to ASME here in the US before you can ship your product.

You should NOT be using this forum for requesting answers to questions such as this, there are much more legal issues at hand and your company has too much at risk.

Get a copy of the code, if you don't have an AI ON SITE, stop and contact your customer and insurance company and get one. Remember, the US has a very dim view on pressure vessels being build to ASME sec. VIII. There must be a stamp on the vessel from your AI before it will be allowed to be installed in the US.

According to ASME Code, Sec. VIII, Div.1 :

1. The hydrostatic pressure, P_h = 1.3 P x (S_{at amb. temp.}/S_{at design temp.}) ,where

P = Design Pressure or Max. Allowable Working Pressure, MAWP (not operating pressure)

S_{at amb. temp.}= Allowable Tensile Strength of material at ambient temp. (test temp.)

S_{at design. temp.}= Allowable Tensile Strength of material at design temp.

2. That hydrostatic pressure must be measured at the highest point on the vessel.

3. It is not allowed to raise the hydrostatic pressure to avoid over stressing the vessel beyond the yield. Therefore, a stress analysis shall be carried out at hydrostatic to check that the stresses arised due to hydrostaic (and weight of vessel itself) are still at the allowable limits per code.

Thanks Mr. Abdel,

But please clarify me that can i pass the vessel or boiler drum if its hydro pressure get raise then it is required? that how much tolerance is allowed?

Dear Amitnaqpal

A vessel designer must calculate the stresses due to hydrostatic pressure, and satisfys himself that the stresses still in elastic portion of Stress-Strain Curve of material (yield). The AI have to check that calculations.

How can we calculate these stresses manually?any formulas?

Why hydrostatis pressure is 1.3 times greater than Design Pressure?? Why not greater than that??

And another point to be considered is the NBIC is any company modified the pressure vessel the use R stamp, because all pressure vessel that was repaired or altered (modified) shall be notified to the NBIC for registred and not to lossed the record this is for the assurance company.

The rules are very simple; ck the tag on the vessel and refer to ASME Boiler and Pressure vessel specs ,also recommend looking at condition of vessel and last NDT results, some vessels that have been in use have been subjected to H2S and other forms of hydrogen degradation ;dgideonapl@myway.com

If in hydrotesting of vessel ,my opearting preesure is 10 bar and design pressure is 18 bar, pls. let me know should I test it at 10*2 = 20 bar ( twice the opearing pressure) or 1.3 * 18=23.4 bar( 1.3 times of the design pressure), which one will be more correct procedure.

I have a different question about hydrotest of vessel and piping attached to it. I want to know what are the limits for hydrotest pressure if piping is welded to the vessel nozzle? Do we have any code references if any?