Cross country pipeline hydro test

[prashant pansare]

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

[lakshman kumar]

Hi,

Good morning to all,

 

1.      Because of safety parameters HT will be done after back filling – as the pipe passes in public areas also, and keeping the excavated sections to open up to HT is also risk, so there is no other option except to do HT after back filling.

2.      Leakage water will come to ground and we can identify – however in water pipe lines – some extent of leakage is acceptable for small leakages (as per CODE), and heavy leakages will be identified by water on the ground.

For oil& Gas, LPG, other services lines so many other options are their to detect(75% of the cases it will be identified in pigging only)

 

3.      Maximum length depends up on service of the line, geographical conditions, site conditions, elevation differences, water availability and disposal situation however maximum length restriction are their in respect codes ex ASME B 31.8 – for oil & gas 50KM is maximum – and this will be given in client spec also.

 

Thanks and Regards................?

Lakshman Kumar.B|Manager |Lanco Infratech Limited Plot No 1255 | Sanjeevani chowk | Mahanadi vihar | Cuttack 753004 Phone : + 91 671 2445033 | Mobile : +91 9937286851 |www.lancogroup.com Go Green|The future will thank you

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[bele...@gmail.com]

Dear Mr Kumar,

Would you please elaborate why 50 km is stipulated as the restriction according B31.8? Or did I get it wrong?

Correct me if I'm wrong, ASME B31.8 does not restrict the hydrotest length by number, does it?

Regards

[Lakshman Kumar B]

Hi,

 

Please note a small correction in my earlier mail…

As stated by you there is no restriction of length as per B31.8, - your statement and understanding is correct.

In one of my previous project we had a limitation of 50KM and the same I shared at here.

However in general doing 50KM at a single stretch is a big challenge and other parameters may not support too (particularly in INDIA)

If your project specs are permitting you can do the hydro test more than 50KM also, no code restrict’ s you…

 

Thanks & Regards,

Lakshman Kumar B,

+91 9440031459.

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[rajeev arora]

Section length also decide based on confirmation of pig manufacturer and pressure difference at high and low point or maximum and minimum

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[Dark_Horse]

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 !!!