Leakage from Cross Country Piping (CS - ERW Type)

[Nabeel Ahmed Qureshi]

We have faced two leakages from an 8'' cross country Efflunent line & both leakages have occured from piping weld seam. UT readings of piping metal show very little thickness loss but why these seam welds are failing? Request to share how we can ensure the integrity of entire piping seam welds (Line length is approximately-3Km). Your valuable inputs would be a great help.The line is of Carbon steel (ERW type)

Regards
NAQ

[ashfaqanwer]

To start with, you must check the documentation provided by the supplier for compliance of required weld inspection and hydrostatic testing. Check the design conditions against which ERW pipe was selected. What's the thickness of piping? Was a complete hydrostatic test was done for the assembled line? Any findings?

[mechcolor]

Against which design code the piping was designed? ASME B31.8?

[Nabeel Ahmed Qureshi]

Dear Mechcolor,

The line is approximately 25 years old & was designed as per B-31.8. At the time of line laying all the checks & pre-requisits as laid in code were satisfied. The intent of asking this question is, if the issues in weld seams are due to aging of pipeline & if it is then how i can have the health evaluation done for this line? What about using LRUT?

[mechcolor]

Is there any problem in circumferential seams also? Or you have this problem only in longitudinal seams?
LRUT is good for screening only. You cannot have exact inspection readings out of that. It has its limitations like 5% loss of cross sectional area. For a pipe diameter of 300 mm and having 10 mm thickness you would be having 100% wall loss in 50 mm of circumference equivalent to 0.5 mm uniform thickness loss.
The way forward for you in my opinion is to start with LRUT but keep your inspectors' team equipped with TOFD also which may provide you with actual flaw sizing over those areas highlighted as problematic by LRUT.

[Nabeel Ahmed Qureshi]

Dear MechColor,
Todate we did not notice any issue in circumferencial seam. This problem is only in the longitudinal seam welds.
Really appreciate your response but would it not be enough to get the screening done thru LRUT & have the qualitative idea about overall condition of pipeline as severe, Medium & moderate defects & on that basis take a decision of pipe replacement (if more than 50% defects are of severe nature) or you advise on doing TOFD & spending much cost on a Water Line?

[Nabeel Ahmed Qureshi]

Dear Mechcolor,

Our pipe has 8'' Dia & has a thickness of about 4.5mm. Do you recommend to do LRUT on a pipe with these specs?
Any limitations of the technique on the above dimensions & any considerations to be kept in mind during performing the LRUT test?

[mechcolor]

Dimensions are OK to qualify for LRUT but for your case of burried piping there are several challenges:
1. In case of LRUT inspection of buried piping, attenuation occurs to a larger extent especially due to soil and presence of bituminous coating which in most of the cases is present.
2. Attenuation leads to lesser inspection length and with one inspection at exposed location you may be able to screen about 20-25 meters of piping length.
3. Contact with soil leads to difficulty in data analysis.
It is strongly recommended that only experienced personnel must report the results of LRUT for buried piping.

I would mention again that LRUT will screen and then you have to use any exact thickness measurement / flaw sizing technique to be sure of actual thickness. If not TOFD, manual UT has to aid LRUT results to make the right decision. Screening is enough in certain situation but normally, you have to narrow down your finding and to come up with right repair procedure.

I hope it would help.

[Nabeel Ahmed Qureshi]

Dear Mechcolor,
Many thanks for providing the details & shall be done accordingly as explained by you.

Regards
NAQ