Back gouging in welding

When welding on thick plate or pipe, it is often impossible for the welder to get 100% penetration without some type of groove being used. The groove may be cut into just one of the plates or pipes or both. On some plates it can be cut both inside and outside of the joint. The groove may be ground, flame cut, gouged, sawed, or machined on the edge of the plate before or after the assembly.

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Bevels and V-grooves are best if they are cut before the parts are assembled. J-grooves and U-grooves can be cut either before or after assembly. The lap joint is seldom prepared with a groove because little or no strength can be gained by grooving this joint.

For most welding processes, plates that are thicker than 3/8 in. (10 mm) may be grooved on both the inside and outside of the joint. Plate in the flat position is usually grooved on only one side unless it can be repositioned or it is required to be welded on both sides. Tee joints in a thick plate are easier to weld and will have less distortion if they are grooved on both sides.

Sometimes plates are either grooved and welded or just welded on one side and then back-gouged and welded. Back gouging is a process of cutting a groove in the back side of a joint that has been welded. Back gouging can ensure 100% joint fusion at the root and remove discontinuities of the root pass.

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This process can also remove the root pass metal if the properties of the metal are not desirable to the finished weld. After back gouging, the groove is then welded.

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Heavy plate and pipe sections requiring preparations are often used in products manufactured under a code or standard. The American Welding Society (AWS), American Society of Mechanical Engineers (ASME), and American Bureau of Ships are a few of the agencies that issue codes and specifications. The AWS D1.1 and the ASME Boiler and Pressure Vessel (BPV) Section IX standards will be used in this chapter as the standards for multiple pass groove welds that will be tested. The groove depth and angle are determined by the plate or pipe thickness and process. See Groove Design & Bevel Preparation

 

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