sub-arch problems

admin

any suggestions? We continually are experiencing gas pockets and hydrotest leaks from visually sound welds with the sub-arch. we have researched all the data and adjusted every parameter there is. We even have had several lincoln reps come out and they could not figure it out. We are welding .250 SA-36 with a back weld inside of flux core first and a hard wire hot pass on the out side. MTR"s on the steel check out. Amps are 400-450 and volts are 30-35. Travel speed is good. Go figure
Reply:Hello chil, there are likely a number of items that you may wish to include in your description of your problem that might help others on the forum to help with analyzing your problem. Type of filler wire, type of flux, new flux or re-used, age and condition of flux, storage conditions for flux, was back-welding with the dual-shield process performed by a back-hand or forehand method, was solid wire welding of hot-pass performed after back gouging or grinding to sound metal of back-weld? I mentioned the weld progression of the dual-shield welding due to a propensity of slag entrapment and reduced penetration to the root of a joint for a fore-hand welding progression. This could possibly cause trapped slags to be liquified and attempt to reach the surface of subsequent welding passes but not completely float out and leave pockets or pores. Most dual-shield fluxes are designed to freeze quickly so they might be prone to being sluggish in making it through the sub-arc puddle before it freezes if you are hoping to gain 100% penetration by using the dual-shield layer as a "backing". I believe the bottom line here would be for you to include a more complete description of your welding processes and how you are incorporating them, including joint preparation and set-up, as well as all of the various parameters and progressions for each process. Look forward to the additional details and others input for you here. Best regards, Allanaevald
Reply:Hi Chil!I agree with aevald.  In order to help you out there needs to be some more info, and photo's always are a great help.   The porosity can come from a variety of sorts, but it must be fairly bad if you are not only failing RT, but hydrotest as well. The pratice of using a backing weld and then sub-arcing from the other side is a fairly common one.   This said, you have to make sure that there is a proper welding procedure in place and it is being followed.  Happy Thanksgiving!
Reply:Number 1 - Your voltage is way too high for DCEP SAW. Recommend 26 to 28V max for the amps you are using.Excessive voltage will contribute to porosity, however the main reason for porosity is hydrogen release during solidification. Your flux should be baked to remove any moisture and joint should be free of any contamination. SAW not passing hydrotest requirements is indicative of major weld quality issues.