Oilfield components fabricator finds success in sawing heavy-wall tube

Conventional tube sawing may conjure images of relatively short, round pieces in which the wall thicknesses are about 5 to 10 percent of the tube’s OD. But what if the tubes are up to 26 feet long and the wall thicknesses equal the tube’s ID? Tri-Alta Oilfield Industries Ltd., Edmonton, Alberta, knows the answers. Tri-Alta manufactures submersible rod pumps, sucker rod, rod couplings, and accessories for oilfield applications. It processes thousands of feet of tube annually in its 24,000-sq.-ft. plant.

Tackling Tube Tasks

Tri-Alta’s world revolves around rigid API standards, which start with the material itself. For tubes, it’s a single material: ASTM A519-5, a mechanical grade of tube made from hot-finished bar having a minimum yield strength of 55,000 PSI and high tensile strength. With material this specific comes the challenge of supply. It is not uncommon for various combinations of lengths and thicknesses to be out of stock in oil country. This leads to alternative processing methods.

“If we can’t order tubing, we rely on plan B, literally making tube by drilling out shorter sections of solid bars under 12 in.,” said Chris Winter, Tri-Alta’s operations manager. Despite the premium cost of the purchased tube, plan B is still more expensive due to the extra time needed to process the bar and wear and tear on the machine.

After clearing the material sourcing and processing hurdles, the company faces cutoff challenges. Tri-Alta saws tubes that it manufactures as crossover collars, connectors, and other accessories for pumps and oil wells. Cuts need to be square and precise, often within ±0.032 in.

An interrupted cut can be difficult, but it’s all the more so when the wall thickness is up to 2.25 in. (see Figure 1). Thick walls generate excessive heat and stress. Considerable attention also needs to be given to speeds and feeds.

The result of these cutting difficulties is that the company routinely experienced tube sawing problems. Troubleshooting and remedying issues such as blade failure, inaccurate cuts, and part misalignment took up an increasing amount of time. Often members of the production team wasted three hours a day correcting sawing problems.

“We dealt with repeated blade failure, operator error, material loss, and especially time loss,” said Winter.

Stable Sawing and Strict Tolerances

After struggling with its old and ailing manual saw, the staff realized that it needed to increase the throughput and accuracy of the sawing operation.

Chad Tomlinson, Tri-Alta branch manager, attended a tradeshow where he saw a horizontal saw, one with an integrated material handling system, and was convinced it would solve their sawing problems. Six months later Tri-Alta purchased the system, a Behringer HBP 263A horizontal band saw equipped with an automatic chip conveyor, hydraulic bundle clamping system, and an inclined loading magazine.

The saw’s design is the key element. A large, dual-column design and a solid cast iron bow frame all but eliminate vibration, which is enemy No. 1 in any sawing operation. The band wheels also are cast, further enhancing the system’s rigidity. The dual-column design enables improved accuracy, smoother cut finishes, faster sawing, and longer blade life in that it applies uniform downfeed pressure across the blade and constant chip removal. The machine also has fully automatic hydraulic blade tensioning and carbide blade guides.

Figure 1
Hollow materials always present sawing challenges, mainly because every cut is really two cuts (known as an interrupted cut) as the blade cuts through both walls. Heavy-wall tube exaggerates the stress on the blade. By the time the blade breaks through to the wall, tooth strippage can occur at the material edge, resulting in blade failure.

Downfeed power and saw blade pressure are monitored by an automatic pressure-sensing system. This is especially helpful in interrupted sawing and situations in which the material thickness varies, both of which are common elements in cutting tube. Cutting pressure data is analyzed and the system automatically makes blade pressure adjustments as needed to ensure an optimal balance between feed rate and blade pressure. Operators can maximize material feed rates without concern of overloading the blade. Another contributing factor to the saw’s accuracy is the electronically controlled feed gripper, which positions the tube for cutting rapidly, before the gripper drifts away from the part, eliminating any drag against the tubes which could alter the measurement of the cut.

Reducing Sawing Time, Eliminating Headaches

Since the saw was installed, Tri-Alta has experienced a 50 percent reduction in man-hours, and operator error has been reduced by 80 percent. The company attributes these improvements to the saw’s precise cutting capability and the automated system features, both of which eliminate inaccurate cuts and misaligned parts. The company also has benefited from a greatly reduced scrap rate and an increased output of processed tube, owing to faster loading and faster sawing. Another bonus the manufacturer has realized is increased blade life, which in itself has translated into significant savings.

“Our new sawing operation cannot even compare to our old method,” said Tomlinson. “It’s like night and day. I only wish we had made the change sooner—it would have prevented a lot of headaches.”