In order to reduce the number of welds (in service inspection costs), to improve the thermal ageing resistance and the internal soundness of components, Electricité de France decided to develop a solution for forged austenitic stainless steel in place of castings to manufacture the straight parts and the elbows of the primary piping of PWR power plants. The paper presents the interest of such solution and the manufacture conditions of such for-gings applied, first, to a cold leg for the Civaux 1 unit and, second, to a complete loop for the Civaux 2 unit.

To improve the in-service behaviour of Cr Mo (V) steel grades used for the pressure vessels operating in hydrogen environment at high temperature for the oil industry, the manufacture of heavy forgings needs a high quality. Improvement of the standard and enhanced strength (ASME Case 1960) 2 l/4 Cr 1 Mo steel grades may be achieved by reducing drastically the impurities (S, P, X, etc...) to extra low level and avoiding segregates at the inner surface of the shells. For high temperature operation, new V modified steel grades are proposed (ASME case 1961, Code Case 1973 and Code Case 2098). Their conventional mechanical properties are similar to those of enhanced strength 2 1/4 Cr 1 Mo but they offer higher creep properties and improved resistance to hydrogen damage.

The construction of large petrochemical reactors working at elevated temperature in a hydrogen environment necessitates the use of 21⁄4Cr-1Mo (ASTM A 387, Grade 22, Class 2) steel with increasingly thicker plates. With this in mind, the aim of this paper is to present information on plates from 150 to 500 mm (6 to 20 in.) thick. After describing the production process, the following points are discussed: (1) reproducibility of analysis on different heats, (2) homogeneity of the composition and material properties in a heavy plate, (3) analysis of the development of the metallurgical properties in relation to the thickness and heat treatment, (4) examples of industrial production plates up to 500 mm (20 in.) thick, and (5) influence of low residual element contents with regard to resistance to temper embrittlement associated with long-duration service at elevated temperature.