June 27, 2002
This article describes different ways to contain tube and pipe welding fabrication costs, focusing on the option of using particular weld prep equipment. It outlines specific applications in thin-wall tube and pipe fabrication and installation and pipe with a heavier wall thickness.
Many efforts have been made in welding technology to help control the costs associated with tube and pipe fabrication. Faced with a shrinking work force of skilled craftspeople and increasingly demanding fabrication requirements, companies must have the ability to predict output and control cost more than ever before.
Welding technology for such processes as orbital gas tungsten arc welding (GTAW), orbital gas metal arc welding (GMAW), and robotics is only part of the answer. Advanced technology for these processes can alleviate some problems, but it's not the cure for all ills. With higher technology comes increased capital expenditures, and training a work force can be more difficult if the technology is new to both the company and the trainees. High-tech welding can be useful in controlling cost and increasing production, but it may not be the solution for every company or application.
Some weld preparation methods can cut production costs and increase quality and output. By looking at other areas of tube and pipe fabrication or installation, fabricators may be able to find cost savings in places other than welding automation. One of these places is cutting and weld preparation, an often untapped source of cost control.
Prepping thin-wall tube and pipe for welding or cutting is one way fabricators can lower production costs. Industries that use this type of tube and pipe include sanitary food and dairy, pharmaceutical, chemical processing, semiconductor, and brewing and beverage processing.
For instance, in sanitary applications, tube has to be cut to length and then prepared for welding. The conventional way to do this is to use a portaband (a hand-held, portable band saw) or tube cutter and then file the end to a burr-free square.
To cut a typical 2-inch-outer-diameter (OD), 0.065-in.-wall 304 stainless steel tube with a portaband can take an operator about one to two minutes, not including measuring and handling time. The cut might be anywhere from 0.0625 to 0.125 in. out-of-square (free-hand cut) and have a substantial burr that has to be removed. Squaring and deburring may take another five to 10 minutes (times are approximate; no time allocated for in-position or out-of-position work).
A square-cutting cold saw combined with a squaring and deburring tool can cut the same tube in approximately 10 to 20 seconds (again, not including time for measuring and handling), and facing and deburring with near-lathe-quality squareness and finish take 30 to 45 seconds. This translates into time savings of approximately five to 11 minutes per tube segment.
Saving even five minutes per cut on a job that requires hundreds or thousands of cuts can add up. Often the cost of consumables is reduced because the quality of blades and bits on these machines lengthen consumables life. This equipment also can be used to repair fittings that may have been damaged in the manufacturing process.
Other applications requiring weld preparation are heavy-wall process pipe and new pipes that tie into existing piping. Any welder will say that the root pass will go in smoother and weld time will be improved if fit-up is both consistent and of high quality.
The conventional way of cutting and prepping process pipe in a fabrication application (new pipe, out-of-position) is with acetylene or plasma. On smaller pipe, a portaband cuts the pipe and then the operator grinds it to remove slag and finish the end. This type of cutting equipment has advantages and disadvantages.
Portabands are fairly inexpensive, and their operator doesn't require a lot of training. However, a portaband is limited in the size range it can cut, and blade replacement can be costly. Flame cutting equipment also is relatively inexpensive but requires consumables such as gas and nozzles. Slag removal and lack of squareness can be problems with these kinds of equipment.
Heavier wall thicknesses (10-in. Schedule 160 or 16-in. Sch. 80, for example) sometimes are difficult or impossible to cut and bevel simultaneously because of the physical effects of burned-on preparation.
The flame used for beveling is directed at the workpiece at an angle. This works on thin material because the flame can be controlled and the heat can be directed at the desired angle. On heavier materials, however, the heat tends to dissipate linearly and is less controllable because the flame beveler has decreased travel speed. The cut sometimes is gouged out, leaving a rough and out-of-square edge that requires additional time to correct.
In both of these examples, a grinder is necessary to get the required final finish. Depending on size and material, the actual prep time can be anywhere from several minutes to several hours for heavy wall, large-OD applications.
As an alternative, a pipe severing and beveling machine can perform two operations at the same time. These tools can be used for in-position or out-of-position work and can work on almost all alloys. Some of these machines are called "clamshells" or "split frames" because they open up and allow the operator to clamp the tool on existing pipe and cut in position. Such machines require the operator to center and square the tool. No hot work is necessary because no flame or grinding is needed.
Other tools of this type are designed for cutting and beveling new pipe. Used in combination with split frames, they can perform either simple pipe severing or single, double, or compound beveling. The pipe is passed through the machine on a table similar to a flame-burning table. These machines also can help taper the pipe's inner diameter (ID) for transition welds.
Even when a flame cutter or portaband is used for cutting, an ID-mounted beveling tool can improve the consistency and squareness of the cut. Also, the material is placed under less stress because the severing and beveling machines use low heat, which also can improve aesthetic appearance.
Key considerations for buying a cutting, facing, ID-mounted beveling, or OD-mounted severing and beveling machine include the following:
Selecting the right cutting and weld prep tool is not the solution for all welding and production issues, but these processes can help overcome some of the hurdles confronting fabrication and installation companies in the piping industry. Pipe machining and welding equipment distributors can help fabricators analyze which tools will work best for a particular application.
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