The growing demand for higher permissible stress levels at high temperatures in hypercritical power generation plants (620 °C and above) has required INT’s technical staff to make a considerable effort to comply with European design standards by introducing ASTM A335 Grade 92 steel into their processes.
The material’s specific chemical composition and microstructure require particular attention during the welding process (and heat treatment).
As no significant data on in-service performance is yet available, INT recommends carrying out NDE tests after 40,000/50,000 hours of operation in order to better assess its characteristics.
This new type of steel has been developed by adding the element W and reducing the base MO content of P91, which has been used in all plants until today.
However, the new material presents significant challenges during welding; accurate preheating stages and very careful post-welding treatment are required.
INT welding engineers team has made it possible thanks to the experience achieved over the last 50 years.
Proper initial engineering has enabled INT to reduce the thicknesses and weights of condensate POT, manifolds and steam line pipework.
