Welding procedure for weld a sleeve on internally coated pipe ?

[khalodee123]

Hi Gents,

I would appreciate if you can provide me a Welding procedure for weld a sleeve on internally coated pipe?

Externally corrosion was found on our line 16" dia. CS pipe and if we weld a sleeve on the pipe, the coating will be damaged.

Thanks

 

[Metalguy]

How thick is the pipe wall? Can you run cold water thru it when you weld?

If the pipe is still strong enough, maybe you can coat/protect the OD from further corrosion.

 

[khalodee123]

The line is 0.625 inch thick. The line is on-stream operated under 2100 psig. The line is strong enough since the corrosion depth is only .08 in. but the minimum thickness is .535 and the current t is .54 which is approaching the Tm

 

[Metalguy]

If you're that close to min. wall, I don't think you should attempt welding it under that kind of pressure. This repair should be easy under no/low pressure. If you have to wait a while to depress. it, I'd coat the low areas and wait it out.

 

[robert2]

I am assuming that the corrosion is on the OD of the pipe as you don't want to damage the internal lining.

At 0.625 in. thick, you are likely not going to heat up the internal pipe surface sufficiently to damage the coating when installing a sleeve to the OD as long as there is some flow in the pipe. The penetration does depend on the product characteristics and flowrate at the time of welding, as with the process used for welding and the electrode type. The pipeline industry has had years of experience with this type of repair and it is done quite routinely for repair of metal loss and damage.

You should look at ASME B31G or API 579 to determine if the corroded area can simply be cleaned and recoated, or whether a repair is needed.