TPT July 2015

Article

SMS Elotherm GmbH

Typical homogeneous temperature between head and tail of long products moving through an Elotherm TemperLine™

Easy change-over of the induction coils to a different diameter

It is for these reasons that, for example, the safety-critical fastener elements in offshore platforms for the production of oil and gas are heat-treated with the described induction technology. Heat treatment without surface decarburisation Due to the long residence time of the heated material at high temperatures, especially in the austenitic area, an undesired surface decarburisation of the heated material normally takes place in conventional combustion furnaces. This negative effect weakens the workpiece in the area close to the surface and leads to an inhomogeneous hardness over the whole cross section of the material. No such decarburisation takes place in induction quench and temper, as the material is kept at a high temperature for a very short period of time only. The microstructure produced by the induction heat treatment does not contribute to a further decarburisation of the surface, but, on the contrary, even reduces the ferrite pockets. The extremely short preheating and residence time at

austenitisation temperature also minimises the formation of scale during heating. In this way, not only the material yield is all in all higher, but especially the service life of the roller tables is significantly extended. In conventional heat treatment lines, these conveyor units are heavily stressed by the strongly abrasive effect of the brittle- hard scale and they wear rapidly, with the rollers having to be re-machined or replaced frequently.

Innovative solutions for new products

The exploration of some oil or gas fields requires casing tubes for lining the actual drill hole that must withstand extreme loads. For example, in many particularly deep drill holes, low ambient temperatures or salt water require the use of casing tubes that must satisfy very stringent requirements in terms of strength or leak proofness. These casing tubes typically have an outside diameter from 5 to 10¾" with upset-end diameters of up to 16". The special challenge in the induction process lies in the substantial difference in weight between the straight tube body and the upset ends, which according to the relevant specification API 5CT may amount to 65 per cent. To be able to still have a uniform austenitisation temperature and homogeneous hardness and microstructural conditions after tempering, additional heating of the upset ends is needed. For this, induction preheating coils are arranged upstream of the actual austenitisation system.

The result of the induction Q & T process of tubes: convincing straightness

SMS Elotherm GmbH – Germany Website: www.sms-elotherm.com

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J uly 2015