I recently dealt with a situation where a feeder tube had broken and washed the header. The header repair area was very jagged and required a substantial amount of material to be removed in order to make the area accessible/suitable for welding. The Material was carbon steel which required a preheat of 200 degrees F due to it's thickness, and it also required PWHT of 1100/1200 for 1 hour. My questions are: is it necessary to preheat prior to gouging?, and after gouging is it necesssary to grind the material prior to welding?
In my opinion and having qualified WPS's do so the gouged surface if carbon steel (If properly couged) has no detrimental effects of the tensile and bend properties of weld metal. There are very few deposits and the remaining metal receives very little heat.
I have performed repairs to steam drums in which cracks were removed by AAC and no preheat was required( for the gouging). If your the engineer then "a little preheat can't hurt". If your the welder then things get a little hot.
If there is a need to prehet for gouging then there is probably a need to preheat for grinding.
The welding on CS requires preheating depending upon the thickness, welding process restraint etc.
Good Day
Gerald Austin
Weldinginspectionsvcs.com
Usually if you are just cleaning up the surface the air blows all of the molten base metal away and removes most of the heat. The base metal does not really get very hot and therefore there should be no metallurgical changes in the base metal. I would only preheat if the gouging is being performed in cold weather. I would say that if the base metal is above 70 degrees F then you would have no problem.
The slag left behind on the base metal after gouging will cause serious porosity in subsequent welding unless completely removed by some means.
Regarding the question of preheat prior to arc gouging: the only references I'm aware of in Sect. I are PW-29.2 and PW-38.2. PW-29.2 states that when thermal cutting is used, the effect on mechanical and metallurgical properties of the base metal should be taken into consideration. PW-38.2 warns against introducing harmful material or processes while performing preheat prior to welding or thermal cutting. I can find no references to preheat prior to thermal cutting in the NBIC. If anyone knows otherwise,or has additional information, I'm all ears. That said, all our WPS's require meeting minimum welding preheat prior to arc gouging.
By -
Date 08-12-2001 19:05
When ACA gouging, you are melting the base metal. This means that the temperature in the "HAZ" of the gouge reaches the same temperatures as when you weld. When you then use the air to remove the molten metal, you are effectively quenching the high temperature HAZ. You will therefore have hardened regions around the area being gouged. Due to the repetative heating and cooling nature of the ACA gouging operation, this HAZ will be very narrow.
In addition, because you are not adding any filler that could potentially introduce hydrogen into the HAZ, hydrogen cracking is not such an issue. (Unless your material has already been contaminated with hydrogen.)
The bottom line is that you should seldom experience problems when ACA gouging, even without pre-heat. You should however remove the slag, carbon deposits and hardened areas by grinding, after ACA gouging. Any additional hardened areas remaining will typically be melted away during subsequent welding operations.
Hope this helps.
Regards
Niekie Jooste
Sasolburg - South Africa
I just found this web sight, that is why I'm responding to this so long after it was posted. Check AWS C5.3 (Recommended Practices for ...Gouging and Cutting). In section 4 there is a statement that says: "Note: where preheat is required for welding, similar preheat should be used for gouging. I accidently found this out when the company I work for put together an arc gouge training program at the request of a client. Now it's a standard instruction for activity planning when arc gouging will be performed on material that will remain in service. Charles Hall
