METALLURGY FOR HIGH PRESSURE & TEMPERATURE APPLICATIONS

Name: Asutosh Khandelwal 

L&T-MHI Power Boilers Pvt. Ltd

Head Quality 

Name: Satish Tilva 

L&T-MHI Power Boilers Pvt. Ltd. 

Head – QA/QC/NDT 

 

Name: Swarajya Kumar 

Organisation: L&T-MHI Power Boilers Pvt. Ltd. 

Manager QA/QC and Lab 

Introduction 

The current thrust is on thermal power development in the country on supercritical units so as to improve the conversion efficiency and reduce carbon footprint. 

L&T-MHI Power Boilers Private Limited is a joint venture company with a manufacturing facility for Super Critical boilers (Forced Flow Steam Generators) in collaboration with Mitsubishi Power System Limited, Japan. The joint venture is in the business of design, engineering, procurement, manufacturing, erection and commissioning of Super Critical Boilers and all incidental activities for this business. L&T-MHI Power Boilers is also having the manufacturing capacity of coal pulverisers and Heavy castings. 

Supercritical technology with a pressure of 225-300 kg/cm2 and main steam/ reheat steam temperatures of 600/6100°C is an established and proven technology with over 500 supercritical units operating worldwide and reliability & availability of supercritical units being at par with that of subcritical units. However, there are critical metallurgies where utmost care is required at the time of manufacturing for trouble-free operation. 

Abstract 

As the reduction of CO2 emissions becomes an important issue worldwide, in the boiler plant for power generation, improving high power generation efficiency- (steam condition) is used as a solution to limit the reduction of CO2. With the improvement of steam conditions, there is a substantial development in material grades with higher creep strength. Desired performance of these materials is due to the certain microstructure. Hence, retaining this microstructure is very much important during manufacturing. 

SA 213 UNS 30432 is widely used in most of the superheater and reheater coils. This material is stronger at high temperatures (superior creep strength) and more resistant to steam oxidation than ferritic heat-resistant steel, and for this reason, the former is used mainly for high-temperature parts of power generation boilers. 

There is a need to perform heat treatment after subsequent forming operations of this material for obtaining the required service life. Various trials have been conducted for establishing the desired heat-treatment parameters. This paper describes 

  • Stresses associated with cold working deformation of stainless steel 
  • Impact of deformation on the operational life of tubes 
  • Solution treatment methods and parameters 
  • Metallurgical acceptance criteria 

Further SA213 UNS30432 is used at various locations in the supercritical boiler. This material is welded to other ferritic steels (such joints being referred to as dissimilar welded joints, at the interface between the high and low-temperature sections of the boilers). There is an impact of welding parameters and post-weld heat treatment on the properties of weld metal and heat-affected zone. Various trials have been conducted for establishing the desired welding parameters for obtaining the desired properties of these dissimilar joints. This paper describes 

• Problems associated with dissimilar metal welds
• Method to overcome these problems including welding parameters and heat treatment parameters
• Testing and metallurgical acceptance

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