cement lined pipe repair

[piiengineers]

Dear Experts,
We have a sea water cooling water nework piping and due to lining failure the line is leaking frequently at small bore tapping points like vent,pressure gauge as well as sleeve portions(field butt joint). What is the best practice in repairing leaky sea water cement lining piping especially at small bore take-off area. We are using SS316L piping for small bore connection(3/4" dia). I would like to know the repair methodology currently adoped in repairing the cement lined pipes and metallurgy of small bore piping. If someone have the repair procedure and other details please send the same to my personal id: piiengineers@yahoo.co.in

with advance thanks,

[ben]

As obvious, restoring cement lining is only possible by taking the piping offline. But you would be interested in knowing about an online solution. Before I suggest you any would you like to explain about the exact location of leakage. Its from the weld joint of small bore fittings or from the base metal also?
ASME PCC-2 describes about many repair option for general wall thining of pipes or equipment. You must give a look to Table 1 of ASME PCC-2 and see for the applicable option.

[mechcolor]

Do you need the re-lining procedure or a temporary one as an online mitigation?

[ashfaqanwer]

Take a look at the RepairShop a free software recently released by thePetroStreet on code compliant repair options as listed in AME PCC-2. It would provide you with the available option for online or offline rectification.
http://www.thepetrostreet.com/forums/vi ... f=23&t=294

Hope this would help you in suggesting some repair options for many other problems also.

[arcpro]

Cement lining near off-take points requires special care. Here are the two main points need to be considered:
1. Near the off-take points, the cement lining must be tapered off to the pipe ID.
2. Off-takes must be having a stub-in connection with full penetration groove with the pipe thickness in order to avoid the thickness of CS pipe exposed to the service.

At butt joints of piping following practice may be followed:
1. The bevelled ends of the cement lined pipes shall be thoroughly cleaned and lining shall be removed over 20 mm at either sides of the joint.
2. After the welding has been completed, a hand-applied mortar shall be used to finish the cement lining on the inside surface of the steel pipe at the location of the field weld.
3. The sides of the existing cement lining shall be sealed with a priming coat consisting of one part of a multi-purpose adhesive, based on synthetic resin, and one part of potable water (this mix will act as a bonding agent). After the priming coat stays for some 20 minutes, the ready mixed mortar shall be applied.
4. Manufacturer's specifications shall be followed for adhesive and mortar mixing.
5. The hand applied mortar shall be finished by means of a trowel and shall be brushed flush after which a curing compound shall be applied.

If you have sleeve type joints also in the piping with fillet welds on the piping, do let me know so that I may provide you an appropriate solution for that also.

[piiengineers]

Thanks to all for the feedback. I seek solution for the exisiting line which is in service for more than 20 years. Due to lower diamter (1" vent/drain point,PG Take-off point)cement lining could not be carried out at take-off location and hence SS316L material was chosen for the fittings. Overperiod of time severe corrosion was noticed at these weld/HAZ location resulting in frequent leaks. I seek solutions for the following:-
1)Is there any better metallurgy to comabt sea water corrosion for small bore take-off in place of SS316L without cement lining
2)What is the best on-line repair methodology for (patch repair or composite wrapping)corroded portion of cement lined pipe?
3)Is there any fast scanning method available to(other than conventional UT,RT)detect cement lining failure/corrosion at these location(especially small bore points and other sleeve joint-field butt joint)

regards,

[mechcolor]

Now your questions are much clear.

1) SS 316L suffers pitting in sea water although it's OK with deaerated sea water. You have to be very careful in your inspections during shutdowns / Outages. What I recommend is to try SS 904L small bore piping which would be costing you about two times SS 316L but surely have a better pitting resistance.

2) You can go for either of the two as both are applicable as an online rectification. Patch repair is an easy to go approach but would effect cement lined piping whereas non-metallic composite repair requires rigorous qualification.

3) Not in my knowledge other than UT.

[arcpro]

1) SS 316L normally does not pose much of problems which you are facing. The leaking area as told by you is the weld and HAZ area which indicates that pitting starts from the base metal where cement lining is damaged and pipe ID is exposed. Weld and HAZ then becomes the leakage path. If you find this as the man reason, just adopt the right lining practices as I mentioned in my previous post.
Otherwise, if you find SS 316L not fit for your case, I would recommend you to replace it with 90/10 Cu-Ni Alloy. It has provided excellent results in general corrosion, deposit attacks, chlorination, crevice corrosion and other related problems of sea water.

2) You can use reinforcing sleeve, welded box clamp also in addition to patch working or composite repair.

3) Since your locations are tricky ones so no NDT would help. However, general wall thinning can be measured where cement lining has been damaged. Automated UT technique T-scan can quickly scan for the thickness of the piping. An effective technique but would not be helpful for your specific case of leakage from small bore off-takes.

[piiengineers]

If we replace the SS316L with 70-30 Cu-Ni will there be any corrosion problem in dissimilar weld portion? Any user experience with 70-30 Cu-Ni dissimilar welding with Carbon Steel if so which is the best electrode to use.

regards,

[arcpro]

You would not be facing any corrosion problem at the weld joints between 70/30 Cu-Ni alloy and the carbon steel material. Suggested welding procedure is as under:
1. First pass with GTAW using ERNiCu-7 AWS A5.14
2. Remaining passes with SMAW using E-NiCu-6
Notes:
a. If possible, carbon steel side may be overlaid / buttered with ERNi-1 or ERNiCu-7
b. 70/30 Cu-Ni alloy may face dilution due to iron content but suggested welding consumables reduce suspected dilution