Method of arc welding root pass
A method for root pass welding steel plate and pipe is provided that uses pulse arc welding having a current pulse waveform exhibiting a low constant background current and fixed frequency. The welding process may be performed without a backer or backing material.
1. A method for pulse arc welding a root pass of a butt weld joint, comprising:
providing first and second joint members with first and second facing edges tapered to form an included angle;
positioning the first and second facing edges to define a channel;
moving only a single electrode within the channel;
applying current that passes between the single electrode and the first and second facing edges to form a complete root pass between the first and second facing edges from a single side of the first and second joint members, the root pass forming a weld bead along a bottom surface opposite the first and second facing edges, and being formed exclusively by the single electrode and between the first and second facing edges without a weld bead supporting medium;
said current having a waveform comprising a constant background current level and fixed frequency current pulses, wherein a stable background current level is about 5 amps to about 40 amps, and the waveform is configured to produce a stable focused arc that penetrates a root pass area of the first and second facing edges.
2. The method of claim 1 wherein the joint comprises a plate or pipe joint and is formed between edges that are in the range of about one-eighth inch thick to about two inches thick or greater.
3. The method of claim 1 wherein each of the first and second facing edges is tapered to a knife edge.
4. The method of claim 1 wherein the root pass is welded using a GMAW-Pulse process in a generally horizontal position.
5. The method of claim 1 wherein the single electrode has a diameter in the range of about 0.02 inch to about 0.07 inch.
6. The method of claim 1 comprising the step of performing a fill welding process after the root pass weld is formed wherein the fill welding process is performed using a submerged arc welding process, GMAW fill welding process or flux core fill welding process.
7. The method of claim 6 wherein said fill welding process is performed during but delayed from the root pass welding process.
8. The method of claim 1 wherein each of the first and second facing edges comprises a land.
9. The method of claim 1 wherein front ends of the first and second facing edges are separated by a gap of up to about ⅛ inch prior to welding.
10. The method of claim 1 wherein the first and second facing edges are in contact with each other prior to welding.
11. The method of claim 1 wherein the frequency of the fixed frequency-current pulses is in the range of about 60 Hz to about 300 Hz.
12. The method of claim 1 wherein the first and second facing edges are tapered to an included angle of about 3 degrees to about 80 degrees.
13. The method of claim 1 wherein the welding process is performed with moving the electrode at a travel speed in the general range of about 5 inches per minute to about 25 inches per minute.
14. The method of claim 1 wherein the welding process is performed with a wire feed speed in the general range of about 300 inches per minute to about 600 inches per minute for a 0.045 inch electrode wire.
15. The method of claim 1 wherein the electrode is oriented at a push angle of about 0 degrees to about 40 degrees.
16. The method of claim 1 wherein the welding process is performed at a stick out distance of about ⅜ inch to about 1½ inches.
17. The method of claim 1 wherein said current comprises an average value DC voltage in the range of about 16 volts DC to about 25 volts DC.
18. A method for pulse arc welding a root pass of a butt weld joint, comprising:
providing first and second joint members with first and second facing edges tapered to form an included angle;
positioning the first and second facing edges to define a channel;
moving only a single electrode within the channel;
applying current that passes between the single electrode and the first and second facing edges to form a complete root pass between the first and second facing edges from a single side of the first and second joint members, the root pass forming a weld bead along a bottom surface opposite the first and second facing edges, and being formed exclusively by the single electrode and between the first and second facing edges without a weld bead supporting medium;
said current having a waveform comprising a constant background current level and fixed frequency current pulses, wherein said waveform is configured to produce an arc voltage within a range of about 16 VDC to about 25 VDC, to produce a stable focused arc that penetrates a root pass area of the first and second facing edges.
19. The method of claim 18 wherein the root pass is welded using a GMAW-Pulse process in a generally horizontal position.
20. The method of claim 18 wherein the welding process is performed with moving the electrode at a travel speed in the general range of about 5 inches per minute to about 25 inches per minute.