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A view through a different lens

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Oilfield Technology,

In an exclusive article for the March/April issue of Oilfield Technology, Austin J. Wells, Arnco Technology, USA, explains how changing the way problems are considered is often how solutions are developed.

As the onshore drilling industry continues to advance, downhole equipment is constantly pushed to its limits. In particular, operators strive to use their drill pipe and workstring tubing for as long as they possibly can, leading to irreparable damage that is often due to wear. The abrasive formations can easily grind away upset connections and/or tube bodies, meaning they are often rejected during inspection.

This can cause entire strings of drill pipe or workstring tubing to be scrapped, even if there is little or no other damage. Such consequences are expensive and frustrating for the operator, who ultimately pays the price for the scrapped material.

Few solutions exist for this pervasive problem of wear. Tool joints and upset connections can be protected with hardbanding, which involves a sacrificial hard metal alloy being applied to the connections through welding. However, tube bodies have historically been too thin to be welded on. When the formation wears the tube bodies of drill pipe or workstring tubing below the accepted values of wall thickness for premium class pipe, entire joints must be discarded.

Yet where there are challenging problems, there are ample opportunities for innovative solutions. The industry has for years struggled with the ability to modify pipe bodies. How do you get a sacrificial metal or composite material to adhere to the tube if it cannot be welded on? How can this need be balanced with the equally important need to offer something cost-effective and simple?

Some attempts at a solution have been made, whereby thermal sprays are used to apply composite material to a tube body. However, the process is cumbersome as it involves very particular preparation of the surface to be sprayed. Furthermore, the spraying can only be performed in a clean shop environment; there is no way to do this in the field.

With all these considerations, it has become necessary to look at this problem with a different lens. The easiest way to get hard metal to adhere to a metal tube is by fusing the metal together, by welding it. It was previously accepted that this cannot be achieved as welding on tube bodies would damage them, weaken them or embrittle them. However, by no longer accepting this as an immutable truth, a new solution could be formed.

What if the problem was to be solved not by developing a new way to adhere the hard metal to the tube but rather by improving the welding process so that it could be done on tube bodies? This paradigm shift allowed Arnco to discover an established welding process that could help solve this age-old question.

The answer lay in the heat input during the welding process. To weld on thin components, the heat had to be minimal. Typical hardbanding procedures involved preheating the component, so as to avoid severe temperature differentials that could lead to embrittlement or softening. By definition preheating inputs significant heat, so the first step was to prevent preheat.

Without having to preheat, a thin tubular was already exposed to less heat. The second step was to minimise the voltage and current used during the process, as these are directly proportional to the heat input. This was achieved by changing the welding process entirely to a low heat input process using special equipment that works with low volts and amperes, which resulted in the heatless welding solutions (HWS).

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