TPT July 2015

Technology News

Induction heating for oil country tubular goods

unwanted heat transfer to occur along the pipe. The benefits mentioned above are due in large part to induction heating producing heat in the wall of the pipe end itself. This fundamental fact not only contributes to the speed of induction heating, but also makes it a no-contact technology – a feature that helps minimise the risk of unwanted interference or contamination of the pipe end. Another crucial factor is customisation. As induction coils are available in a practically unlimited range of designs, the actual heating process can be optimised to the specific composition, dimensions and requirements of particular work pieces. Coils are only one element in an induction heating system. The other key component is the heat source (also referred to as generator or converter, as it converts the mains supply into the high frequency supplied to the coil). Today’s solid-state induction heating systems typically feature the actual generator – those used in EFD Induction systems feature Sinac units – as well as matching and cooling equipment. Power ratings and frequency ranges vary widely. For example, EFD Induction has to- date built systems for pipe ends with outer diameters as small as 60.33mm (2 3 / 8 ") with a wall thickness of 4.83mm (0.19"), up to an outer diameter of 558.8mm (22") with a wall thickness of 23.42mm (0.92"). The particular features of an induction

Concentrators are components that focus, or concentrate, the heat into particular areas of the work piece. Undoubtedly beneficial in other induction heating applications, their use in pipe end heat treatment is questionable. This is because concentrators are relatively short lived, and must be replaced at regular intervals – leading to production shutdowns and additional costs. Concentrators can, however, be dispensed with if good quality customised coils are used – preferably coils designed using advanced simulation software. The saving delivered by maximised uptime and output soon recovers any additional capital outlay caused by using such coils. A final argument in induction heating’s favour is its track record. A tried-and- tested method, induction heating for OCTG heat treatment is a technology currently in worldwide use. EFD Induction, for instance, has devised and built systems for some of the leading names in the tube and pipe industry. Induction heating, thanks to its high efficiency and absence of toxic by- products, helps manufacturers satisfy tough environmental and energy- consumption regulations – not a bad bonus when making products needed to meet the world’s growing energy demands.

Aurélien Lechoisne of EFD Induction outlines the benefits of using induction heating for pre-heating and stress relieving tubes and casing destined for the world’s toughest environments. OIL country tubular goods (OCTG) refers to tubing and casing meeting the specifications of API 5CT. Although the standard states that API 5CT pipe may be made by the seamless or electric resistance welding (ERW) process, the reality is that OCTG typically refers to seamless threaded pipe. OCTG also includes seamless and ERW transmission pipe that carries media such as oil, gas and water, conforming to API 5L standard. The diameter of a pipe’s end must be reduced or expanded prior to threading. This change in diameter is achieved by swaging, a process that introduces additional stresses into the pipe end. Left untreated, such stresses render pipe ends brittle, making them susceptible to deformation. Two heat-treatment methods are used to overcome this problem: the first involves avoiding the stresses altogether by pre-heating the pipe end prior to swaging; the second method involves removing the stresses by ‘stress relieving’ after swaging. Various heating technologies exist for bringing the pipe ends to the temperatures needed in both methods. Induction heating, however, has the ability to meet four criteria critical to OCTG manufacturers in today’s hyper- competitive market. Firstly, induction heating is extremely accurate. Target temperatures and heat penetration depths can be reached and maintained for very specific areas for exact time periods. Secondly, induction heating is highly productive. Because heating occurs only in narrowly defined zones, no time is wasted heating adjacent areas or the ambient air. Thirdly, induction heating is extremely controllable. This makes it suitable for maintaining temperatures within pre- determined narrow tolerances. Finally, induction heating – by virtue of its speed and accuracy – confines the heat to the pipe end. The induction heating process is simply too quick and controllable for

EFD Induction – Email: sales@efdgroup.net Website: www.efd-induction.com

heating solution will vary from supplier to supplier, but there are some points of differ- ence that merit careful consideration. One such factor is the use of ‘flux concentrators’ with the coil.

Induction heating for OCTG heat treatment is a technology currently in worldwide use

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J uly 2015