TIG weld of boiler feed water line

Date 07-08-2004 12:25

Dear sir
when we weld on boiler feed water and other accesory pipe of boiler with TIG and use filler rod ER-70S then we observe porosity in root pass and finally we do welding with SMAW (E-6010 & E-7018) for solving this problem.I dont know that why produce this porosity in root pass of TIG because we clean the surface and not exist any oil or moisture .
The material of pipe is carbon steel
Would you please explain the reason of it ?

best regards
A.A.Sharif

By pipewelder_1999 (****)

Date 07-08-2004 12:41

Have you removed the scale from inside the pipe. This may be very tightly adhering and cannot be removed with a flapper wheel. A grinder should be used.

If the pipe is clean, verify the torch shielding gas is ARGON and that no leaks exist. If the torch isa flex head, verify that the rubber does not have any cracks that may open up if the torch head is moved. If that is OK then verify the flow rate is not so high that air is drawn into the weld. Smaller Gas cups require less gas flow.

Some 70S-x compositions may not be suitable for the steel you are welding on. The suffix -2 -3 -6 etc all have slightly different purposes. This may be a contributing factor.

Verify that no internal draft exists in the pipe. This can often cause shielding gas be removed too quickly.

Thats all I can think of.

Have a nice day
Gerald

By wrangler97 (*)

Date 07-16-2004 02:10

depending on position your torch angle can play a part, try and be sure you are maintaining the proper torch angler especially coming on the top of a 5g