March 7, 2006
As pipe fabricators continue to employ more modern welding processes, they also should consider the role that end preparation plays in productivity. Cutting and clamping methods are two areas to study when it comes to pipe fabrication efficiency.
The pipe fabrication industry continues to evolve because of changes in the work force, materials, welding specifications, and fabrication methods. These changes have caused companies to look for more efficient and modern ways to complete projects in less time with improved profits, while meeting new welding standards.
Fabricators sometimes analyze only one step of the fabrication process when appraising labor costs, product quality, and delivery time. They also should consider the total cutting and clamping alignment process, including shop layout, material handling, cutting, grinding, and alignment before welding to maximize cost savings. Poor shop layout, for example, can decrease output per hour considerably, as excessive material handling can increase operational costs.
Process efficiency, material handling, and safety are major factors that affect output per hour. Fabricators should ask themselves the following questions when laying out a pipe fabrication shop and investigating the cutting and clamping alignment process:
Pipe cutting machines are broken down into two categories: flame and cold cutting. Some machines are stationary, while others are more lightweight and portable, designed for field or shop use. Flame-type machines listed below are used with oxyfuel or plasma torches.
Computerized Cutting Machines. These flame-type machines cut pipes to length, cut holes in the side of a pipe, or contour the end of the pipe by changing the computer program. While these machines can be versatile, they require a large amount of material handling time, because the pipe must be positioned on the machine either manually or by crane.
Saddle Machines. Many fabricators find these flame-type cutting and beveling machines offer cutting accuracy, as well as simple and fast setup and use. These machines can accommodate four pipe sizes each and can be fitted with double-torch, out-of-round, or contour cutting accessories.
Magnetic Machines. Magnetic cutting and beveling machines require little or no setup time because they don't require spacers or boomers to hold them to the pipe during the cutting process. These flame-type machines also can be used for straight-line gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) applications to help alleviate welder fatigue.
Chain Machines. Chain machines can be an economical way to cut a variety of pipe sizes. The cutting capacity of these flame-type machines can be increased or decreased by adding or shortening chain. Accessories available include out-of-round devices and a second sliding torchholder to cut and bevel both sides of the joint simultaneously.
Band Machines. Light-gauge stainless steel bands with a band crawler cut small and large horizontal or vertical pipes with small radial clearances. Each band is designed for only one diameter of pipe, while a crawler can fit all band sizes.
Cold-cutting Machines. While cold-cutting machines are slower than flame-cutting machines, they produce a smooth, machined finish without spark. Rotating blades or cutting tools can produce a beveled or curved surface, such as compound and J bevels.
Pipe alignment has become more critical as fabricators need to find more efficient pipe welding processes. If pipes are stored or stacked on top of each other, the pipe can be flattened or misshaped and will require various clamps to pull the pipe into round. Otherwise, mismatched pipe ends can cause resistance to flow of liquids and gases in the piping systems. Clamping systems help minimize failure found in nondestructive testing.
Chain Clamps. Chain-type aligning and re-forming clamps are available for pipe diameters from 1 inch to 20 feet. Chain clamps allow the pipe or fittings to be held safely and securely in an accurate alignment during the welding process.
Full-Circle Clamps. Full-circle clamps are available for 4- to 72-in.-dia. pipe with up to Schedule 80 wall thickness. Multiple jackscrews apply pressure at high points on the pipe to bring it into precise alignment with the mating pipe or fitting to help reduce weld time.
Frame-type Clamps. These clamps make three-point contact with the pipe or fitting. The jackscrews of the clamp allow the inside or outside diameter of the pipe or fitting to be aligned when pipe re-forming is not required.
Cage Clamps. A cage clamp is a full circle clamp designed to align the ODs of two pipes. It comes in tack and no-tack, ratchet, and hydraulic models. This type of clamp should not be used to perform the actual re-forming of one pipe to another.
Internal Alignment Clamps. These clamps are available in manual, pneumatic, and hydraulic models. They press against the pipe's inner wall, bringing the pipe ends into alignment.
Fabricators who operate and maintain cutting and aligning equipment should be involved in process improvement decisions. The following questions should be asked when selecting a system for a particular cutting, aligning, and welding process:Is the equipment for shop or field use?
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