The procedure for making a butt weld is as follows:
1. Machine the pipe ends for the butt-welding joint.
2. Clean the pipe ends, valve joint, and the inside of the valve socket with a degreasing agent to remove oil, grease, or other foreign materials.
3. Align by means of fixtures, and tack weld in place.
4. Make certain the valve is in the open position before applying heat. The valve bonnet should be hand-tight to prevent distortion or damage to the threads. Nonmetallic discs should be removed before applying heat.
5. The valve and pipe should be supported during the welding process and must not be strained while cooling.
6. Preheat the welding area 400°F to 500°F .
7. Depending on the welding method used (gas, arc, and so on), a butt weld is normally completed in two to four passes. The first pass should have complete joint penetration and be flush with the internal bore of the pipe. Make sure the first pass is clean and free from cracks before proceeding with the second pass. The second pass should blend smoothly with the base metal and be flush with the external diameter. Avoid excessive heat because this can cause distortion and possible malfunctioning of the valve.
8. Use a wire brush and a clean cloth to remove discoloration.
