Pipelines, such as oil, water or sewer distribution or collections systems, are constructed by welding together a plurality of pipes, often at the installation site of the pipeline.
Known in the art are automated orbital pipeline welding systems, such as disclosed in U.S. Pat. No. 4,373,125, issued Feb. 8, 1983 to Kazlauskas. These automated systems are capable of forming accurate and strong welds on large diameter pipes. Such systems are relatively large, typically weighing over 500 kilograms, and are installed at a stationary location, such as an oil rig. Accordingly, such systems are not suitable for mobile field use.
More mobile welding systems are known. Typically, such systems comprise a welding carriage, or "bug" as often termed in the art, which includes a welding torch. The torch may be suited for Gas Metal Arc Welding (GMAW), Shielded Metal Arc Welding (SMAW) or Gas Tungsten Arc Welding (GTAW). The carriage is typically the size of a hand-held power tool and is mounted, via constrained rollers, on an annular rail or guide disposed on the weldment. The carriage includes a driving pinion which meshes with a toothed rack of the annular guide, thereby providing a means for guiding the carriage and torch around the weldment. Typically, the carriage has at least one d.c. brush type motor mounted thereon for driving the carriage on the guide as well as a motor for oscillating the torch. Typically too, the electronic control system for controlling the motors is housed in a separate unit, remote of the carriage, and linked thereto through a plurality of control cables.
There are various types of control systems for these types of bugs. One type of control system, based on analog electronics, employs potentiometers which are adjustable by an operator during the welding process. These potentiometers control the speed of the carriage drive mechanism motor, the torch oscillating motor, and, if present, a consumable electrode wire feed motor. Operators using such a system almost always adjust the speeds of the various motors during the welding process, particularly in order to avoid the problem of having the deposited weld bead, which is liquid, drip due to the influence of gravity. The problem with using such systems, however, is that welders have complete control of the welding process and can adjust the speeds of the motors such that the resulting weld does not always fall within the requisite specifications for the weld. The problem is further compounded by the fact that often the potentiometers are not linear.
Other known bug control systems employ largely digital control systems wherein, in combination with suitable carriages, many of the weld parameters can pre-programmed. For example, one known type of mobile automated welding system allows the weld current, arc voltage, welding speed, oscillation speed, width and dwell time, torch height, tilt angle and annular position, to be digitally programmed. This system also provides a programmed means for controlling the carriage travel speed to deal with the deposited metal drip problems. Similar systems known in the art, such as disclosed in U.S. Pat. No. 5,534,676 issued Jul. 9, 1996 to Rinaldi et. al., have more sophisticated methods for accomplish this objective. However, one limitation common to these types of systems is a lack of flexibility in enabling the welder to vary the pre-programmed parameters during the welding process.
In any event, these mobile welding machines are often used in some of the harshest and most remote environments in the world. Thus, reliability of the machines is important. There are a number of limitations in the present design of mobile welding machines of the types described above that affect their reliability. Welding machines having the known fully automated digital control systems tend to have many sensors and other delicate mechanisms which are prone to breakage in use, particularly under heavy use in harsh construction environments. Welding machines having the analog control systems require frequent recalibration, particularly under operating conditions wherein the ambient temperature fluctuates widely. In addition, irrespective of the type of control system, brush-type motors mounted on the carriage have a tendency to bum out within a relatively short period of time. Moreover, the signals carried by such cables can be prone to electromagnetic interference caused by nearby operating machinery, particularly high frequency inverter type power sources which radiate relatively large amounts of electromagnetic energy.
In addition to having a reliable welding system, it is also important to ensure the quality of the resulting weld, particularly as the weld is being formed. Thus, it is desired to have a real time weld monitoring system. Some of the welding machines of the prior art having automated digital control systems provide a feedback to a remote computer indicating what the actual values of some of the carriage and welding parameters are. However, these systems do not inform the operator in real time whether the weld is being properly made. It would be helpful to have more comprehensive weld quality information readily available so that the operator could immediately adjust certain operating parameters to ensure the quality of the weld.
The present invention seeks to address many of the limitations of the prior art mobile pipeline welding systems described above.