Hydrotest Failure

Reply from engineering was to conduct integrity check on the line.

Can someone tell me the type of integrity check to done; and why?

They would have to be more specific, Can be anything. X-Ray, spectrograph. depends if they are going to look to see if the pipe was up to specs.....

Is it Code requirement?

Yes, for it to carry a stamp

Hi Guest

Are you sure that you have the correct test pressure? 150 Bar on a 10" pipe sounds extremely excessive although may be correct!

What factor of safety are you applying?

A coded welded joint will have a procedure that must be worked out by the responsible engineer and could be anything he deems suitable given ALL the variables including mill spec of pipe and connector, welding fill etc.

My guess is that it would need Crome Molly fill wire at least but don't quote me !

DP = 43 bar = 624 psi. TP should = 1.5 * DP = 64.5 bar = 936 psi. Actual TP = 150 bar = 2180 psi. Integrity check of pipeline not needed. New engineer needed.

I am afraid you may have damaged your pipe with this high test pressure. The only way to know is to perform NDT of all welds and check the calculations to see if the size and wall thickness of this pipe can theoretically take the pressure they had on it when the weld burst. If you find the test pressure to be appropriate and no damage to piping or welds from when the first test failed you would then do another hydro to confirm the systems integrity. I have seen in the past where contractors installed the pressure test temp. piping and it not be installed/welded at the same spec. as the pipe being tested. I think the reasoning was that it is only a one use temp. pipe spool that would be removed after testing so a shortcut could have possibly been made on the welding. I would start by examining the failed weld to see if it was up to par and figure out why it failed. If this 150 bar pressure was the appropriate test pressure required for your specification then it is evident that the weld was not done correctly or that sub par materials were used. I am curious about what wall thickness or schedule of the 10" pipe did the spec. call for in this application?

On re-reading your post, I saw that the weld failure was from the hydrotest header (of contractor and assumedly temporary structure) to the actual job (pipeline) weld and there were no failure in tha actual pipe-line.

The rest were consequential damage.

It is probable that the contractor has not carried out this one weld properly (assuming it to be temporary weld, of no consequence) and that has lead to failure. And due to this the engineering has asked for the pipeline integrity test.

This will depend on the extent of damage and assumedly no major damage has taken place first do a visual inspection of the whole thing.

Whenever you find a doubtful area ensure the integrity by LPI or other suitable method and especially concentrate on welds, bends etc wherever the pipeline was stressed. However your comment says that the damage has been on the pipe coating does it mean no significant damage to pipeline?

But most important check up whether your test pressure was OK? if you have tried to cross the safe limit corresponding to the pipe schedule then you have a problem and for that the contractor is not responsible.

api 5l pipe can not withstand 150 bar . i remember the hydrotest pressure is 1000psi i.e 70 bar. the design pressure of a pipe depends upon the od,thk, code allowable stress at a particular temperature and the joint efficiency factor. once the design pressure is decided (MAWP- max allow working pressure) then the hydrotest pr shall be 1.5 times design pressure.

for heavens sake please do not go beyond the national code requirement. this is unsafe.

in your case the hydrotest pressure should have been 70bar(1000 psi)

with best wishes

pkmohapatra

Apart from the application data you have provided (whether it is high or normal pressure in the joint) for your line, from welding /fabrication point of it, (a) It is not very clear whether the rupture has occurred on the weld or in the HAZ. (b) The thickness of the base metal , the type of consumable you have selected , parameters, procedure details may help to analyze the cause of failure. 1. It could also be due to lower tensile strength of the weld metal compared to base metal --but it could be ruled out as balance weld joints have not shown similar fault except this particular one in your Hydrostatic Pressure Testing. 2. Being a high pressure joint, we assume, you would have done 100 % Radiography of welded joints -- Hence please cross check the films once again for defects, repairs re-repairs done if any on the particular joint. 3. You can also conduct few more examinations like: (a) Metallographic (micro analysis)Tests on the weld and HAZ. This will reveal a true picture of the grain Microstructure /structural changes and reason for the failure and origin of the failure. (b) Hardness test on the weld and HAZ areas as this will help to substantiate the above point. (c) You can also conduct Chemical (Spectra Analysis) tests for Carbon and Manganese elements of base and Weld metal – you can collect the samples at the ruptured areas and this will also help us (irrespective of the Manufacture Certificates) to get the actual Chemistry in both, also determine the cause of rupture and change the Welding Procedure if required. Above tests are all part of Failure analysis and the results will give an indication to start with and then it is easy to pin point the cause of defect/failure and avoid in future welding / fabrication. Wishing you Good Luck. Sridhar.

The hydrostatic test pressure for pipes is

1.5xPxstress ratio (St/Sd) minimum, 90% yield stress maximum

Now, 150 bar test pressure for 43 bar design pressure is too high, however if this test pressure is less than 90% yield stress you are safe.

If this test pressure (150 bar) exceeds 90% yield stress, the pipes are useless and need to be scraped and you don't need to do any further test it is over.