hole on the slag ??

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our process is Submerged Arc Welding. we are using recycled flux with the parent flux in the ratio of 1:3; we see the hole on the slag that causes the concavity on the weld cap that should be repair.would you please guide me what should we do to prevent of this occurring.
Reply:Most effective way is to use run off tabs and run the weld bead off the joint onto the tab.  If you must stop on the joint you will have to stop the travel and hold in one location to increase buildup before shutting off feed and current.  How long you stop travel and what current you finish off with will be an unknown.  You will have to do some experimenting.
Reply:thank U Dear lotechman, but u must know that our production is Spiral Pipe and its continues, the defect occurs during the process, we have no place to use run off tabs.u can see the weld seam from attachment Attached Images
Reply:There are several manuals available online.   http://www.lincolnelectric.com/asset...ature/C550.pdfhttp://www.millerwelds.com/pdf/Submerged.pdfWhen I encountered pin holes or porosity the most common factor was small amounts of oil.  Do not use air operated grinders near the plate being welded.  In another case after chasing the problem for months it was large and ugly tack welds that the operators had put in to hold the assembly in position.  The Sub Arc would not melt through these tack welds and made pinholes in the weld.  I have not tried it but I am told that tack welds made with flux cored welding wire can create problems.   Also another very remote factor can be the flux that is ground too fine and prevents gassing.  The too small particles prevent the gasses from leaving the weld pool.   Keep notes on settings and only change one thing at a time.  In the case of the bad tack welds I was told that it was bad Chinese steel,  cutting oil, bad flux, bad wire, bad machine.   I marked the assembly with soapstone at the tacks and at locations I didn't like before the welding then looked at the finished weld.  All the pin holes were at the tack weld locations.  It was bad operators    You should inspect the plate edges before welding and mark things you are not sure about then look for pinholes after.