Seco single-pass pull threading reduces oil pipe coupling cycle times

Oil-drilling companies rely on long stretches of steel piping, known as 'strings', to reach down deep into oil wells. To extend their reach they are joined together by heavy duty couplings which feature high precision, performance-critical internal thread forms. Coupling threading has traditionally involved multiple-pass push-threading with right-hand tooling systems. Generating internal threads in this way, however, results in long cycle times largely due to inefficient handling of chips. The Seco-developed process applies a left-hand tooling system using multi-tooth, chaser-style threading inserts that are pulled through to direct the cutting forces into the beds of the turning centres used to machine the couplings. These inserts are extremely reliable and wear resistant enabling higher cutting speeds to be employed. Robust couplings, made from Group 4 and P10 steel and higher cobalt compositions, are becoming more commonplace as oil-drilling companies go deeper into the earth and hit acid beds that quickly break down standard steel. Seco has designed its single-pass system specifically for these tougher materials and other corrosion-resistant grades and types of steel. A custom-built, heavy duty toolholder bar, which can range from 6 to 9 inches in diameter depending on the size of the coupling, keeps the single-pass cutting insert securely in place during the threading process. The mechanical chip-breaker's through-the-holder high pressure coolant also assists with chip control and promotes long tool life when producing coupling sizes ranging from 2.875 to 14 inches in diameter. Using the traditional push method, an operator cutting a thread with three to five passes has to stop the cycle, stick a hook down into the part, pull out the chips and then restart the cycle. Furthermore, without high pressure coolant running through the chip-breaker, operators continually have to interrupt the process to remove large, stringy chips to prevent them being re-machined. Seco's pull technique, on the other hand, efficiently removes the chips and drops them into machine tool chip beds, eliminating the problem of chips getting back into the coupling. The high pressure coolant also breaks the chips down, making them more compact and less likely to create safety and disposal problems. In fact, Seco's system can break 12 inch-plus long stringy chips down to tiny half-inch segments. The oil field industry typically uses two thread form types: the 8 API/RD and buttress. The former, often used for shallower wells, will require only a single pass of the Seco process, whereas the latter will require two passes to create a tight hydraulic seal, instead of the three or four required to create a buttress thread using the traditional method. Seco's method can also accommodate licensed thread forms, which are better suited to handle the powerful forces encountered with deeper drilling. Seco warns that to take best advantage of Seco's single-pass threading process, coupling manufacturers must have the right machine tool available. It recommends the use of newer, rigid machines equipped with powerful (22 kW/38 kW) spindle motors and well-made, strong jaws in the chuck capable of handling the forces generated when performing just one threading pass. Poor performing or even retrofitted outdated machines are unlikely to deliver a reliable or repeatable process. Seco also recommends that machines have at least 70 bar high pressure coolant capability to break down large, stringy chips effectively.