Hydro test pressure exeeds the set value 1

[shaff]

10" Sch 120 pipe is hydrotested at 165.45Barg pressure. The relief valve was set of 1.1 times this pressure (181.99Barg). However during test the pressure went upto 188 Barg. due to improper settings.
Will this raise in pressure (188Barg) have any impact on properties of pipe material? Has any permanent deformation set in? How do I justify this?
Any help is of great benefit.

Thanks.

 

[LittleInch]

What is material properties (SMYS), type, grade etc?? Which design code - B 31.3? From that you should be able to work out the pressure at the SMYS value based on Barlows formulae with design factor of 1.0.

Do you have a plot of volume of water injected vs pressure? (And if not why not?) If you plot volume (x axis) vs pressure (y axis) and it's still a straight line then you should be OK. If it flattens off ( unlikely) then you've strained the pipe, but you would need to look at it carefully.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[zdas04]

Up to SMYS, pressure changes are elastic and any (small) deformation will only be present while the pressure is applied. Above the yield point the deformations become permanent and change the performance of the metal. As LittleInch pointed out, you need to run the stress calcs and see if the overpressure took you past the yield point. If it did, you might still be OK since Barlow's formula is pretty conservative (I've had pipe sections in hilly country go to 105% of SMYS without actually yielding).

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"

 

[LittleInch]

You need to confirm what material it is, but just to see what we were looking at I did a quick calc based on pretty basic Carbon Steel and came out with a pressure of nearly 400 bar before you got to yield at normal ambient temperatures. Sch 120 is pretty thick pipe (21mm) and the effective design factor used in 31.3 allows a substantial margin over Hydro test pressure before anything goes wrong.

Still need to see what the material and what your design pressure and temp is to confirm, but I think you've almost certainly got away with it so long as you're using Carbon Steel.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[shaff]

Pipe Material : Carbon Steel

We checked the line list and found that the line is designed for 110 Barg pressure whereas the pipe class selected allows us to design for 138.8 Barg. This allows us to reach upto 208.2 Barg test pressure without bothering SMYS. A pressure of 188 Barg is well within this valve (208.2 Barg).

Thanks LittleInch for giving the idea of design pressure. Relieved to have gotten away with it without doing some complex analysis...

Shaff

 

[XL83NL]

Another (quick check) would be to determine if your line class/pipe spec (whatever you call it) is flange limited.

If so, you can up to 1.5 times the flange rating @ ambient Temp. without any problem for the hydro case. From your OP and replies, I cant make up if this is true.
138.8 bar(g) is a flange rating for a B16.5 grp 1.17 flange @ 200 C, and F12 Cl 2 or F5 are (low-alloy) carbon steels if Im not mistaken.

PS: carbon steel a MoC designation is too plain. Carbon steel comes in several specs (ASTM/EN) and a wide variety of grades. Be more specific next time.

 

[Gnoom]

You also normally still have some extra margin between the actual wall thickness chosen commercially and the sum of what you calculate that the wall thickness should be according yield tension, plus the specified corrosion allowance.
For instance, let's say I calculate for a CS pipe that I need for a 4" pipe a wall thickness of 5mm (based on standard tension calculation) and I add a corrosion allowance of 1,5mm to that. That brings me to 6,5mm. Schedule STD is 6mm, so I have to go up a level, which brings me to Schedule XS; 8,6mm. That gives you 2,1mm extra to play with. In you case you might have a similar situation.