• Cerjak, Horst-Hannes
• Mayrhuber, Josef
• Kirilowitsch, Ch.
• Enzinger, Norbert

Abstract

For the pumped storage power plant Reißeck II a steel lining for the pressure shaft is required.<br/>For the design phase all steel grades, which were successfully applied in recent projects were<br/>considered: e.g. quenched and tempered fine grained steels up to yield strength of 690 MPa.<br/>At the start of detail design of the project a thermomechanical (TM) rolled fine grain steel up<br/>to yield strength 690 MPa was available, which could offer several advantages, was<br/>considered for application.<br/>As no standards exist up to now and no detailed experience was available for the practical<br/>aspects of fabrication, welding and installation procedure for steel lining for grade 700 MPa<br/>TM type, a program was carried out, to investigate the material under conditions similar to<br/>practical fabrication, installation and service conditions. The program aimed for relevant<br/>mechanical properties for different plates and welded joints. Two plates were manufactured<br/>and welded by GTAW-HW (=”Gas tungsten arc welding-hot wire”), simulating the<br/>circumferential weld during installation. GTAW-HW as welding process with high heat input<br/>was considered representative for all applied welding processes (e.g. SAW, SMAW). Topics<br/>of interest were the material properties of the plates and of the weldment and the heat affected<br/>zone (HAZ). For this purpose two types of plates were welded with V – type edge preparation<br/>with backing strip. The investigation was carried out on different specimen size and types<br/>fabricated from the welded plates:<br/> tensile tests for base material, weld metal and integral specimen (welding seam<br/>included);<br/> impact testing for various directions and positions including welding and heat affected<br/>zone;<br/> fracture mechanics by CT-test for base metal and weld;<br/> wide plate tensile test of welded plate;<br/> further investigation of microstructure, hardness analyses and fracture surface<br/>The results: The candidate material thermomechanical (TM) rolled fine grain steel of yield<br/>strength 700 MPa represents a material of high ductility, good welding properties with low<br/>tendency of hardening of the heat affected zone. For the plates the “as rolled” conditions<br/>offers best mechanical properties. For welded specimen: All small scale specimens showed<br/>high strength and ductility (&gt; 700 MPa; &gt; 12%) and low transition temperatures. The integral<br/>wide plate tests of welded plates showed sufficient strength and strain when tested up to<br/>fracture. The TM steel proved to be qualified for use in the project, provided that the same<br/>quality assurance processes are applied for fabrication and welding as for QT-steels and is<br/>used for the lining of the pressure shaft in the high pressure zones with wall thickness of up to 33 mm. The results of the fabrication procedure so far confirmed the expected good welding<br/>properties

Topics

• impedance spectroscopy
• surface
• grain
• phase
• strength
• steel
• hardness
• yield strength
• tungsten
• ductility
• wire