Orbital Welding is a computer controlled GTAW process for welding tubing and pipe. Modern orbital welding machines are capable of printing out a detailed report of every weld performed and controlling the entire process. The actual process consists of placing a welding head over the welding joint. The powered head rotates a tungsten around the weld joint. Internal and head gas purges are programmed into the power source computer and a welding program is selected from the stored program list or a new one is created before welding proceeds.
It is now possible to orbital weld material diameters as small as 1/8 inch all the way up to 15 inch pipe with wire feed heads.
Orbital welding was developed in the 1950's by North American Aviation as a more cost effective and higher quality method to weld hydraulic lines on the X-15 rocket vehicle when leaks developed. In the 1980's portable orbital machines were developed that made field welding practical. Portable combination power supply/control units now weigh in at around 70-90 pounds and can run on multiple current supplies starting as low as 110 ac. Orbital welding is a versatile process allowing the welding of different materials such as aluminum, carbon steel, stainless and duplex steels, and titanium.
Specialized welding heads have been developed that allow orbital welding of difficult to weld joint configurations such as heat exchangers and super heater tubes in power plants. Orbital welding has become the standardized welding process in several industries such as food, dairy, breweries, and beverages, pharmaceautical, micro-chip, and many aerospace applications. Other industies are beginning to see the benefits of orbital welding such as utilities both fossil and nuclear, shipbuilding, refineries, chemical, offshore, and pulp and paper. Orbital welding produces a cleaner, more uniform, and higher quality weld in less time than hand welding. Operator training can be accomplished in as little as two days.
Fit-up
Fit-ups on tube are square butt machined with burrs removed on both the I.D. and O.D. Alignment is usually performed by using clamps on the O.D. The I.D. of the tube is purged with an inert gas (usually 100% argon) and minimal tacks are applied before placing the welding head onto the joint. In both the pharmaceautical and micro-chip industries a welder will usually have to produce a test coupon and have it inspected by a qualified inspector before beginning welding. Heavier wall thicknesses orbital welded with a wire feed head will still require a beveled joint for complete penetration.
Welding Setup
Calibration of of welding head needs to be performed before welding begins. This can be accomplished either manually or automatically. Improper head calibration can cause a condition known as "stub-out". A "stub-out" occurs when the tungsten strikes the work piece and arcs out thereby interrupting the welding arc. This portion of the weld will have incomplete penetration.
The next step after successful head calibration would be to select a stored welding schedule compatable with tube size and wall thickness. A new welding schedule can also be added into the database if necessary. A typical weld schedule separates the weld joint into four quadrants. These quadrants are timed to decrease the amperage from level one to level four to keep the weld uniform.
Although orbital welding equipment requires a substantial initial investment, the long term production savings can be even more substantial. Average time for welding joint completion is only about an hour. Any welding shop that does a large amount of piping work would benefit from switching over to orbital welding. More information on orbital welding equipment can be found at: Arc Machines Inc.