[MW:26000] Re: Cross country pipeline hydro test

Dear Querist,

1) Why hydro test is carried out after covering / back filling the complete pipeline?

Logic :  If it is left exposed or open, then heat transfer during the night will be fast & pressure drop due to temperature drop will also be high, which migh result in failure of hydro-test record.  

2) In case of seepage, we' ll get pressure drop on gauges,but how to detect the location of leak?

Logic : If the pressure continuously drops, then you may have to cancel the hydro-test, put some color dye in the hydro-test water & pump it again, open up the backfilled portion at strategic locations, repressurise it, if it is truly leaking, then one should see wetted colored soil.   The other case is when temperature drops, pump & increase the pressure to test pressure & hold it, repeat the same for 24 or 48 hrs., if it truly leaks in pipeline, then the defective portion should SWELL in size & one must get higher pressure drop compared to previous one, within the same calculated / observed time.  (this is also called Mechanical Strength Testing which is for 24 hours & can be extended based on field findings, before actual hydroo-test pressure hold starts - practiced by SHELL).    If it does not, then possible there may be some entrapped air,  do the air volume calculations again.    

3) What is the maximum length of pipeline that can be hydro tested at a time?

Logic : There is no set maximum limit specified by the code or standard or specification.  Considering the soil condition - rocky section, black cotton soil or red murram or lose desert sand,  the temperature drop in the pipeline during night time will be different, which the TPI or Consultant will reject the hydro-test on some pretext or so.  Refer to above Point No.2 & the involved logic,  pipeline length of 15-20 kms is good & easier to handle in case of any pressure drop.  Longer sections of say 45-50 kms, will create hassles to you - go back to involved logic in above Point No. 2.  Conclusion :  It is site conditions & situations, topography or terrain, accordingly decide.  Consider maximum piepline section length limit as 25 kms, as the best option.  Further, when running the gauge pig & any imperfections in the received gauge pig, then corresponding investigation will also kill your good work.  So better choose smaller sections & breath maximum oxygen during the pressure holding period,  can go to sleep at right time !!!

On Sunday, October 16, 2011 at 5:34:39 PM UTC+4, prashant pansare wrote:

Dear All,

In Cross country pipeline

1) Why hydro test is carried out after covering / back filling the complete pipeline?

2) In case of seepage, we' ll get pressure drop on gauges,but how to detect the location of leak?

3) What is the maximum length of pipeline that can be hydro tested at a time?

Thanx & Regds,

PSP

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