American Welding Society Forum
Sprinkler systems (for fire control in buildings) 1" threaded sockets welded over holes drilled every few feet in 4" pipe using GMAW, 70S6 wire 0.045" dia, argon/CO2 shielding gas.
Leaks at toes of weld when hydraulically tested with water @ 200 psi.
ASTM A135 is described as electric-resistance-welded steel pipe. Grade A contains 0.25% C, 0.95% Mn, 0.035% S and P.
Grade B contains 0.30% C, 1.2% Mn, 0.035% S and P.
Depending on which formula I use, Carbon Equivalent is from 0.41 to as much as 0.6 for Grade B. Some of the pipes are painted and some are coated with a 'varnish' like material.
My best guess is that hydrogen from the coating, along with the hardness of the HAZ is causing underbead cracks at the toes of the weld.The pipe wall and the fitting are only about 1/8" thick, no preheat is used.
Any suggestions for weld procedure would be appreciated.
Several things pop up flags in your message. It's been my experience that the weld application as you described could/can initiate cracking, but please consider these points also.
First, in order to achieve complete fusion with SC, GMAW, it's imparative that all surface coatings/contaminates be removed (bright metal) to at least 1" away from the weld area. Secondly, you're using .045" wire on a relatively small diameter fitting. The larger diameter can cause the welder to have difficulty controling his puddle (fusion to the base metal) especially at the start/stop interface as well as only allow a single pass application. Which in itself, a single-pass application is less then desireable for a leak proof system.
If you want to find out what's really happening at the failure site, I would advise removing the portion of weld that's adjacent to the leak (flush with the wall) and perform a PT test. See if it's a crack through the wall or is it LOF.
I AGREE WITH THE FLAGS , CLEAN THE METAL AND BECAUSE THE MATERIAL IS THIN TRY AND MINIMIZE THE HEAT INPUT AND USE A SMALLER DIAMETER WIRE. IF YOU HAVE ANY SCRAP WELDS TRY AND MAKE A CROSS SECTION CUT AND YOU SHOULD BE ABLE TO TELL IF IT IS LACK OF FUSION OR INCOMPLETE PENETRATION.
MY "GUT " FEELING IS A COLD LAP (LACK OF FUSION INTO BASE MATERIAL). WIRE SIZE TO LARGE FOR THAT ASSEMBLY? ELECTRODE ANGLE(WIRE) AS IT RELATES TO THE TOE THAT HAS THE DEFECT?
ARE THE 1" FITTINGS CAST OR MALLEABLE (MACHINABLE)? IF CAST A LOW HYDROGEN PROCESS IS PROBABLY MANDITORY! HAVE YOU TRIED A DIFFERENT PROCESS? (GTAW OR SMAW). DEFINITELY A FOOL PROOF PROCESS IS TWO PASS E6010 FOLLOWED BY E7018 BUT TIME CONSUMING.
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