Hydrotesting without exposing an Underground Line

[Nabeel Ahmed Qureshi]

Can some one tell me that is it possible to hydrotest a long length (say 5Km)underground line without exposing it? If it is possible then what is the procedure? What would be the method to identify if any leakage exists? Any code/standard reference would be a great help.
Thanx
NAQ

[mechcolor]

What's line service? Test pressure?

[ashfaqanwer]

See this thread:
viewtopic.php?f=11&t=138
In order to differentiate that there is a leakage or not, it is good to have pressure-volume calculations which would help you in defining whether this pressure change is due to temperature difference or there is any leakage. And if there is a leakage, tracer gas methods may be utilized. See this http://www.freepatentsonline.com/5046353.pdf

[Ahsin]

Tracer gas?? AAnr pls give me more details about it.

[Ahsin]

http://www.freepatentsonline.com/5046353.pdf... Useful link btw

[qaisarabbas]

I am Reverting back to Nabeel's query about the procedure for hydtrotesting of underground piping and code/standard basis.

Basically, hydrotesting without exposing is a ususal practice for cross country gas / water lines. Following construction codes & api standard give the guidelines on the subject matter:

API RP 1110 : Pressure Testing of Liquid Petroleum Pipelines
ASME B31.4 : Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids
ASME B31.8 : Gas Transmission and Distribution Piping Systems

Stepwise procedure is mentioned as:

1. Cleaning thru compressed air to remove welding slag, sand and construction bedris
2. Propoer insulation & backfilling to minimize ambient effects like wind, rain & sunlight during hydrotesting
3. Installation of all hydrotesting instruments (pipe surface temperature recorders, soil temperature recorder, pressure gauges, dead weights, temporary filling piping, etc) prior to water filling
4. Carrying out following six distinct hydrotesting phases w.r.t. time:
- Water Filling (6~5 hrs in daytime)
- Temperature Satablization (starting from daytime to overnight holding for 12 hrs @ 50% of hydrotest pressure)
- Pressurization (@ 50 kpa/min to 100% of hydrotesting pressure while monitoring Pressure-Volume Plots)
- Strength Test (holding at hydrotesting pressure for 4 hrs in daytime)
- Leak Test (holding at 110% of Max. Operating Pressure for 4 hrs in daytime)
- Depressurization (reduing pressure @ 50 kPa/ min followed by de-watering)

5. Leak detection thru visual inspection of backfilled area, analying PV plots & Trece Gas method (as mentioned by Ashafaq)

Regards - Qaisar

[ashfaqanwer]

Qaisar: What do you say about pressure-temperature recorder? Is that mentioned in any of the standards you mentioned?
Ahsin: I will share about tracer gas leak detection method soon.

[Inspectengr]

What about piping designed as per B 31.3 and length is 180 meter approximately... underground...

Should we have to perform day night test cycle here as well or we can give ok after 1~2 hours test (if pressure does not drop)
Hope to hear from any body soon.

[arcpro]

You would not be finding any thing evry clearly written any where in the code. The essence of performing hydrostatic test is to be sure that there is no leakage in the piping. In order to meet the same, ASME B31.3 directly asks for a complete visual examination of the piping and requires a minimum staying time of 10 minutes. This is the case with above ground piping or with underground piping which is exposed during hydrostatic test.

Now talking about the hydrostatic test for buried / unexposed underground piping, it is not possible to perform a visual examination / walk through of the whole piping therefore, in order to clear all the doubts about any leakage, the test must be extended up to 24 hours (or 12 hours at least) with pressure-temperature recorder so that there must be a strong documentary record / evidence also for all the observations (pressure - temperature variations).

[ashfaqanwer]

Inspectengr,
I agree with arcpro, in case underground pipeline has been backfilled due to safety concerns or other, and visual check of all the weld joints is not practical, test time shall be at least 24 hours with automatic pressure-temperature recorder installed.

Discussed at this link once: http://forums.thepetrostreet.com/viewto ... f=11&t=138