PJP Welding vs. CJP Welding

Please don't double-post, Guest. I just removed your second thread on this same subject. Also, please be patient with the user community. I'm sure you need an answer as soon as possible, but double-posting won't help.

Everything happens <...as soon as possible...>; this term actually means "low priority".

My comments are as under : -

1. To install steel pipes for water pumping stations and transmission pipeline , complete (full) joint penetration welding only should be used.

2. Rather than resorting to chip off the cement lining from pipe ends, such pipes are always left unlined for a portion of 4 to 5 inch length on either end. After CJP the unlined portion is covered with mortar suitably.

3 Since internal cement lining after welding is not an efficient process, extra care need to be exercised during this work rather than leaving it to unskilled manpower and good results can definitely be obtained.

4. Partial joint penetraion will anyway damage the cement lining due to differential expansion and should not be adopted. It will deceive you as you will feel lining is intact and actually it is not.

5. PJP can provide us with the required pressure rate for the pipes but here we are more worried about corrosion on bare or exposed pipe surface.

6. DONOT GO FOR PJP.

7. Small dia. pipes upto say 14 inch ID, internal REPAIRING OF THE CEMENT LNINING cannot be easily practiced. Such pipes shall be joined by alternate methods.

Few things are not clear.

Why it is required to remove 5" of cement lining for welding.

What is the size of the pipes.

There can not any difference of coating removal, whether it is CJP or PJP

We have done welding of 100 kms. length - 10, 12 inch dia. pipes for burying it in the (Bombay high off shore project) sea bed.

All the pipes were having only 2 inch non coated area both inside and outside. once welding was over, radiography was done, clearance obtained, only top (outer side) was coated immediately and as the barge moves, it gets buried continuously.

We have not done any coating inside since ID of the pipe is lower. I think this is the basic concept.

Again, all the joints are of 100% CJP type and if any repair like , LF, LP, Porosity was noticed, the repair work was carried then and there and re-radio graphed prior to approval.

The entire process of welding including stringer, fillers and cap pass takes 15 minutes and repairs if any with in 10 minutes time and radiography exposure is for 4 minutes and developing within (wet films only) 2-3 minutes. .

You can imagine the magnitude of the work and tight time schedule.

The point here is you have to use expert welders, spl. quick setting cement for that nature of work.

SRIDHAR ,

It was a mistake , the chippoff length is 2" not 5".

But , why we have to chipp off the internal cement lining for PJP , if penetration of wedling is not required for the full wall thickness , usually we do't chipp off the cement lining for PJP ??

Use the full penetration weld. Repair the chiped parts with whatever Belzona recomends. If you can't get to the chipped area for repair then chain weld the butted-chamfered pipes without chipping and join the pipes with a filet-welded oversleeve that is as thick as the pipe and as long as the pipe diameter.

Thanks for the correction. If you have full lining inside the pipe for PJP, then during the welding operation the cement and other ingredients will melt off due to high minute-temperature of the arc, (say 5,000 to 6,000 deg C) and the smoke generated will affect the root side (corrosion) and also thickness of the weld within the both edges through porosity and slag if not LF.

Even if over-sleeves are used, then, the sleeve length can not be less than 4 inches or so, making it much more cumbersome (more chipping of cement) for the life of the joint.

Generally CJP gives more strength (as U said correctly) compared to PJP which has anywhere between 40 to 60 % of the original strength of the joint.

PJP is recommended for structural joints, automobile sub assemblies and not for pressure piping.

Sridhar.