Method for determining and controlling the cooling rate for metal alloys in an electrical resistance welding process

A method for controlling the cooling rate of metal alloy pipe in an electrical resistance welding process in a homopolar welding system, comprising:

• positioning an end of a first said pipe and an end of a second said pipe to form a weld interface;
• mounting a first movable electrode on said first pipe and a movable second electrode on said second pipe, such that a distance between said first electrode and said second electrode defines an electrode gap;
• adjusting said electrode gap by moving said electrodes relative to one another to provide a selected cooling rate;
• resistively heating said weld interface by discharging energy from a homopolar generator through said electrodes and said electrode gap to weld said first and second pipes at said weld interface to form a welded pipe segment;
• and
• allowing said welded pipe segment to cool.

A method of welding two sections of pipe end-to-end which comprises:

• resistance welding a plurality of sets of two opposing ends of pipe sections at an elevated welding temperature;
• cooling the sets at different rates;
• and
• analyzing the resulting welds for one or more metallurgical properties to provide cooling parameters correlating cooling rate with each such property.

A system for homopolar pulse welding sections of a given pipe end-to-end, which comprises:

• (a) positioning the electrodes of a homopolar pulse generator on two sections of the given pipe proximate ends of the sections to be welded together, said electrodes defining an electrode gap spanning said ends;
• (b) homopolar pulsing the electrodes with sufficient energy to weld the ends of the sections;
• (c) measuring the rate of cooling of the resulting weld;
• (d) repeating steps (a)-(c) for different pairs of sections of said pipe and for different said electrode gaps;
• and
• (e) analyzing the resulting welds for one or more metallurgical properties to provide cooling parameters correlating said cooling rates with each said property.

An apparatus for welding two sections of pipe end-to-end comprising:

• hydraulically actuated mounting members to support the pipe sections end-to-end at a weld interface and actuable to press the ends together at different pressures;
• a first electrode attachable to a first said pipe section in axially adjustable relation with the first said pipe section;
• a second electrode attachable to a second said pipe section and in axially adjustable relation with the second said pipe section;
• and
• a homopolar pulse generator connected to said electrodes and operable to supply sufficient energy to the electrodes to weld the pipe sections at said interface to form a welded pipe segment.

A method of controlling a metallurgical parameter of a weld joining two pipe sections end-to-end by homopolar pulse welding in which energy is transmitted to the pipe sections through electrodes attached to the pipe sections, said method comprising:

• homopolar pulse welding a sufficient plurality of pairs of pipe sections of a given pipe at different welding energies, electrode gaps, and weld cooling rates;
• analyzing the resulting welds for the values of a given metallurgical parameter;
• correlating said values with said energies, electrode gaps and cooling rates;
• and
• controlling the value of said parameter for a said weld of a particular pair of said given pipes in accordance with such a correlation.