Hydrotest Question
Hydrotest Question
(OP)
Hi All,
Can across a situation yesterday and I am still unclear on the details.
Had a 150# piping system with a design pressure of 1770 kPA. Now that would make the minimum hydrotest pressure 2655 kPa. The Client actually had the hydrotest pressure set at 2948 kPa which I was fine with. However they later requested the hydrotest pressure be increased to the ANSI maximum allowable non-shock pressure for a 150# flange rating of 3105 kPa (450 psi), as per the following table: http://www.engineeringtoolbox.com/ansi-flanges-pre...
Their reasons for the change is they like to make the hydrotest the maximum allowable in case the design pressure is change down the road, that way they don't have to re-test the pipe if the design pressure is increased.
I see several problems with this: The inspector will always want to see the test pressure during the hydrotest indicating equal to or above the stated hydrotest pressure, which means there is a danger of exceeding the maximum allowable non-shock pressure during the test. Also, if you were testing a vessel, or even a large vertical run of pipe, the additional hystrostatic pressure from the water used during the hydrotest could further exceed the maximum allowable pressure.
I think you are allowed to exceed your hydrotest pressure by 15%?
But can you exceed the maximum allowable non-shock pressure AT ALL? And if you do do you have to perform stress calculations to ensure the pipe has not been over-stressed?
Can anyone help me out on this one. Is it okay to have your hydrotest at the maximum allowable non-shock pressure as indicated by ANSI?
Thanks Much,
JABoomer
Can across a situation yesterday and I am still unclear on the details.
Had a 150# piping system with a design pressure of 1770 kPA. Now that would make the minimum hydrotest pressure 2655 kPa. The Client actually had the hydrotest pressure set at 2948 kPa which I was fine with. However they later requested the hydrotest pressure be increased to the ANSI maximum allowable non-shock pressure for a 150# flange rating of 3105 kPa (450 psi), as per the following table: http://www.engineeringtoolbox.com/ansi-flanges-pre...
Their reasons for the change is they like to make the hydrotest the maximum allowable in case the design pressure is change down the road, that way they don't have to re-test the pipe if the design pressure is increased.
I see several problems with this: The inspector will always want to see the test pressure during the hydrotest indicating equal to or above the stated hydrotest pressure, which means there is a danger of exceeding the maximum allowable non-shock pressure during the test. Also, if you were testing a vessel, or even a large vertical run of pipe, the additional hystrostatic pressure from the water used during the hydrotest could further exceed the maximum allowable pressure.
I think you are allowed to exceed your hydrotest pressure by 15%?
But can you exceed the maximum allowable non-shock pressure AT ALL? And if you do do you have to perform stress calculations to ensure the pipe has not been over-stressed?
Can anyone help me out on this one. Is it okay to have your hydrotest at the maximum allowable non-shock pressure as indicated by ANSI?
Thanks Much,
JABoomer





RE: Hydrotest Question
2) Not knowing your MoC, it hard to tell if the test pressure should be 2655 kPa(g).
Okay, so you're using 1.2 materials. From B16.5:2013, I get 1.5 x 19.6 bar(g) = 2970 kPa(g), which should be rounded to 30 bar(g) (3000 kPa(g)) as per B16.5 para 2.6.
Sounds like they want to have a flange limited spec.
Based on?
In the end, the system's test pressure should not exceed 90% of the yield of any component in the system (again, assuming it's B31.3 piping).
RE: Hydrotest Question
I prefer them - with an RT/UT rate of 5%, poor [or bad] quality welds can slip through. Any weld that passes Full Flange is just fine for use. I'd rather get my bad news today, in the fab shop, rather than next year while attemption to make product and $$ in a plant.
RE: Hydrotest Question
The root of your issue, and that of your client is IMO tied up in your first sentence - "Had a 150# piping system with a design pressure of 1770 kPA" No, you have a piping system with a design pressure of 17.7 barg which happens to have #150 flanges welded on it. That is the crucial difference. Your piping system has a design pressure for a reason - I don't know what that is, though my guess is that this is the de-rated pressure at a higher temperature in which case you are allowed in B 31.3 to test at a higher pressure to take account of that.
However, and this is where I don't agree with XL83NL, many systems have non flange rated design pressures and the piping and other fittings are designed to that design pressure. Therefore to blindly go to the maximum flange rating without actually doing any checks is dangerous and not good practice. If you look at a line list in any decent sized plant, you will find a large variety of design pressures for piping systems with identical flanges.
To be honest at #150, you are unlikely to run into serious trouble unless your design pressure is below 15bar, but for higher rated systems you could easily have a design pressure of 25bar and pipe sized accordingly, but #300 flanges with a max CWP of 50 bar. Now that would / could be lethal.
B 31.3 states a min of 1.5 x Design pressure (highest point) and no more than yield stress at the maximum (345.4.2.(c ), so yes, you need to perform checks to ensure that the yield stress on the piping is not exceeded. Any connected equipment / fitting with a lower design pressure limits the design pressure and pressure test.
Your clients desire to test to a higher pressure is understandable, but needs to be done properly otherwise you will eventually overstress something - the worst case being that you don't quite reach UTS, but you have seriously work hardened some piece of pipework or fitting which could then fail catastrophically. As said above, the higher the flange rating, the higher the difference might be between the design pressure of a bit of pipe and the max working pressure of the flange that just happens to be welded to it.
Also I don't know where you get the "maximum allowable non shock pressure". what the figure you quote is 1.5 times the highest working pressure as a test pressure. This is not the same as the maximum allowable working pressure which is what your phrase implies.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Hydrotest Question
http://www.engineeringtoolbox.com/ansi-flanges-pre...
Are they no the maximum allowable hydrotest pressures for each ANSI pressure rating class?
RE: Hydrotest Question
Though my experience is limited, I guess yours and mines are different then. The specs Ive seen, most of em are flange limited.
RE: Hydrotest Question
Also maybe I missed it before, but testing vessels is different to testing pipe systems. Vessels are custom designed and cannot just be raised in MWP just because it has a certain class of flange on it.
XL83NL - Yes may piping specs and lines are limited by the flange rating, but my point was that simply because a pipe has a flange welded to it, the design pressure of the pipe and other things attached to it cannot be assumed to the same max pressure that the flange can withstand.
At #150, the full rating is fairly common, but at #300 and above, designing the pipe and all the fittings to the max flange rating when you don't need it for the process is just a waste of metal in the vague chance that one day in the future maybe you would want to operate that piece of pipe at a higher pressure.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Hydrotest Question
Right again, spot on side note!
RE: Hydrotest Question