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A new twist on threading

Story added 27 January 2012.

MORE NEWS

Seco Tools’ new single-pass pull threading process significantly reduces cycle times on threading oil pipe couplings.

Seco Tools, the leading manufacturer and supplier of carbide cutting tools and tooling systems solutions, has developed a new process for the threading of oil pipe couplings.

Oil-drilling companies rely on long stretches of steel piping, which are known as ‘strings’, to reach down deep into oil wells. These individual strings are joined together (thereby extending their reach) by robust, 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. This process of generating internal threads is inefficient, in large part due to the process’s inefficient handling of chips, and resultant long cycle times.

The new process from Seco is called single-pass pull threading, and it can take as much as 40 seconds off the typical one-minute cycle time required to put the internal thread on a coupling.

(When one considers that some companies can produce hundreds of thousands of couplings each month – the cost saving potential is clearly dramatic).

Additionally, Seco’s method also improves chip control and increases productivity by 50 percent.

The 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 are now going deeper into the earth and hitting 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 tool holder bar, which can range in size from 6” to 9” 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 ensures long tool life when producing coupling sizes ranging from 2.875” to 14” in diameter.

With the traditional push method, an operator cutting a thread with three to five passes had 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 would be faced with having to continually intervene in the process to remove large, stringy chips and 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 I.D.

The system’s 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 long 12” plus stringy chips down to tiny half-inch segments.

When it comes to thread forms, the oil field industry typically uses two types: the 8 API/RD and buttress.

Often used for shallower wells, the 8 API/RD thread requires only one single pass of the Seco process, whereas the buttress thread involves two passes to create a tight hydraulic seal. (The traditional push threading method to create a buttress thread would take three or four passes).

Seco’s method can also accommodate licensed thread forms, which are better suited to handle the powerful forces encountered with deeper drilling.

To fully optimize Seco’s single-pass threading process, coupling manufacturers must have the right machine tool available. Older or poor-performing equipment is often not capable of handling the process, and even retrofitting outdated machines may not deliver the reliable or repeatable process required.

Instead manufacturers need to have newer, rigid machines equipped with powerful spindle motors (e.g. 22kW/38kW) and well-made, strong jaws in the chuck capable of handling the forces generated when performing just one threading pass.

Seco also recommends that machines have at least 70 bar high-pressure coolant capability to break down large, stringy chips effectively.

Over the last few years, performance breakthroughs in the manufacture of couplings for the oil-drilling industry have been few and far between. With the development of its single-pass threading process, Seco has changed the rules of the game…for good.

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