TPT January 2016

Technology News

Improved precision in pipe and pipe end heating

By Dr-Ing Peter Turewicz, Dipl-Ing Joachim Brettel and Dr Jürgen Kern

to approx. 610°C for a period of 1h for each 25mm of thickness (minimum of 1h for any thickness). At the same time, neighbouring regions should remain cold. In this manner, selective heat treatment is fundamental to achieve the demanded mechanical properties of the final product. Conceptually, this approach demands: precise heat source distribution with highest power at the surface (to compensate the heat loss to the environment) but also heat generation inside the volume to guarantee a uniform temperature distribution in radial direction; high power density for fast heating to avoid an undesirable spread of temperature in axial direction; and an intelligent regulation which controls rapidly all process parameters, with regard to the desired temperature distribution. Especially for pipe end heating, induction technology offers a reliable solution. However, the difficulty is to hold the desired temperature profile for a period of time retaining the required accuracy. In this regard EMA Indutec developed a technology for highest precision, which has already been proven in a large number of different applications. EMA Indutec pursues continuous improvements by finding innovative solutions for processes and products. In this respect, multi physical numerical simulations are used to analyse different technical concepts including all relevant process parameters in a virtual model. In order to achieve optimum levels of precision and accuracy the most suitable solution will then be chosen from a large number of possible variations. In this way numerous induction heating systems have been implemented successfully. An example of a heating plant for pipe ends is shown above right. The main issue was to increase or decrease the diameter and achieve a specific wall thickness. Providing defined thermal conditions by the induction heater, the material flow can be selectively controlled during the forming

THE heat treatment of pipes and pipe ends is an important process step, which occurs in the manufacture of a variety of different high quality products. There is a distinction to be made between preheating beforemechanical processing like drilling, sealing, threading or forming to increase/decrease the diameter and heat treatment to harden the metal, eliminate residual stresses or achieve a structural transformation. Induction heating offers many advantages in comparison with conventional heating systems. The main benefits are process reliability, high throughput and, in particular, the possibility to generate a precise temperature profile. The particular challenge is to provide a homogeneous predefined temperature distribution for different diameters, wall thicknesses or irregular geometries in one installation. Only by an interaction between experience, know-how and high-grade components is it possible to meet the high requirements regarding precision and quality. EMA Indutec, as a manufacturer of modern induction heating systems, is specialised in the area of pipe and pipe end heating, offering technical solutions with improved precision and efficiency. One of the most important factors to ensure a high product quality is the precision of the temperature distribution at the heat treatment. Particularly in the case of pipe and pipe end heating, it is important to generate a defined temperature for a certain period and only in a specific region. For example in the case of local thermal stress relief, a simple rule of thumb gives an exposure

Induction plant for pipe end heating

process. A variation of this installation type was designed for stress relief heat treatment. The plant’s flexibility allows both preheating for forming and for thread cutting. As a result two individual heating systems can be replaced saving space and costs. Pipe bending is also a widespread application for the induction technology. In order to prevent cracks, deformations or other damages during the bending process the pipe is preheated sequentially to approximately 1,000°C. The usual procedure consists of an integrated induction heater, which is shown for large diameters (see below left). The pipe is transported continuously through the coil, which is heated with high precision only in a defined narrow area. The process for manufacturing high quality pipes and tubes had to fulfil very demanding requirements in terms of precision during the heat treatment. The induction technology offers many advantages in comparison to conventional heating systems. However, only an accurate technical design guarantees high standards of the final product. Based on decades of experience combined with modern computer-aided calculation and simulation methods EMA Indutec sets new standards of accuracy. This new generation of induction heating system has proven successful in manufacturing tubes and pipes but can be also transferred to other industrial applications.

Bending machine for pipes with integrated induction heating system

EMA Indutec GmbH – Germany Website: www.ema-indutec.de

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J anuary 2016