Induction Heating

Introduction

The process of induction heating works on the principle of heating a magnetic material through I2R loss by setting up eddy current through the material. Although simple in concept, the technology of application is complex and required years of hard work to master it.

Since the creation of eddy current field is instantaneous and uniform, the heating of the material is also fast and uniform. This advantage of fast and uniform heating has been successfully applied for quick heating and easy loosening of turbine bolts, generator retaining rings, slip rings, turbine discs etc.

Heating of turbine bolts by resistance heating (resistance heating rods inserted in the bolt holes) and by gas heating not only takes time, but also creates high possibility of distortion and damage. It is unsafe and adds to the cost of operation due to longer opening time and also due to cutting of ceased and distorted bolts. Slow heating by resistance technique often heats both materials at a joint.

This not only prolongs the time to achieve sufficient differential expansion between the materials, but also creates distortion at the turbine horizontal joint and subsequently creates steam leak. One of the unique features of our bolt heating system is we only heat the unthreaded part of the bolt and this further minimize the chance of binding.

While gas or resistance heating requires between 35 to 50 minutes to open a single bolt, the SMIHPL's induction heating opens each turbine nut in about 5 minutes. For Retaining Ring opening operations a standard retaining ring of 1.3m diameter can be opened in less than one hour time without any problem. Within 45 to 55 minutes the temperature of the ring can be raised to 300°C. As the rate of heating is very fast heat transfer to the rotor body is minimum and hence rings get removed from the rotor body at ease. For smaller retaining rings (rings below 1m diameter) we normally use one equipment and for bigger rings (rings above 1m diameter) two equipments are used simultaneously.