Improving Global Quality of Life
Improving Global Quality of Life
Improving Global Quality of Life
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
9 Needs and challenges <strong>of</strong> major industry sectors for future applications<br />
Welding Challenges<br />
CA-6NM/GX4CrNi13-4 castings are commonly used for turbine runners and wicket gates. It is a 13Cr-4Ni<br />
martensitic stainless steel developed in the early 1960s. An improved version “Super Martensitic S.S” is very<br />
popular these days in the <strong>of</strong>f-shore oil & gas industry due to vastly improved resistance to Stress Corrosion<br />
Cracking (SCC). CA6-NM is a material <strong>of</strong> relatively high strength, and has a good cavitation resistance. Due to<br />
the relatively low chromium and nickel content, this material is subject to pitting in salt water or a similarly<br />
corrosive environment.<br />
While welding CA-6NM, relatively higher preheat and post weld heat treatment (stress relief) is required to<br />
prevent cracking when welded with matching martensitic welding consumables. Field repairs with austenitic<br />
weld materials are feasible with minimal preheat and no post weld heat treatment. The deposited weld<br />
material does not have the same strength as the CA-6NM base metal, however.<br />
Tragic failures in different engineering disciplines in history were one <strong>of</strong> the main driving forces for<br />
accurate investigations <strong>of</strong> failure mechanisms and the development <strong>of</strong> improved techniques. In the field<br />
<strong>of</strong> hydropower plants the recent case, Cleuson-Dixence, was a significant failure, which clearly showed the<br />
necessity <strong>of</strong> understanding the mechanisms and the consequences <strong>of</strong> not doing things correctly. To avoid<br />
such accidents in future, new materials and their processing have to be understood in advance. Therefore<br />
accurate scientific investigations have to be performed with respect to the basic understanding <strong>of</strong> the<br />
weldability <strong>of</strong> the materials selected and their service behaviour such as:<br />
Fracture mechanics and fatigue properties.<br />
Quantitative description <strong>of</strong> the relation between materials properties, namely strength, fracture<br />
toughness and fatigue and NDT procedures and the evaluation <strong>of</strong> its results.<br />
Influence <strong>of</strong> modern welding processes (including filler material) and parameters on the<br />
microstructure and their properties. Definition <strong>of</strong> significant parameters for the characterisation <strong>of</strong><br />
welding processes and their influence on possible failure mechanisms.<br />
Corrosion in weld metal and heat affected zone under service conditions.<br />
Reliable QA measures in production and during service.<br />
All these efforts should result in modern standards and recommendations for the selected materials and<br />
welding processes which enable welding engineers to contribute to effective renewable energy production<br />
for a better future <strong>of</strong> the world.<br />
Future Developments<br />
Materials selection, welding and fabrication technology are very mature for hydroelectric turbines. As<br />
the demand increases for hydroelectric plants, turbines with higher capacity may be required in future.<br />
Development <strong>of</strong> steels with high strength and extremely good resistance to cavitations are <strong>of</strong> paramount<br />
importance, accordingly the welding challenges required to be dealt with. With the present day available<br />
resources such challenges are very <strong>of</strong>ten met by the Original Equipment Manufacturer (OEM) and the end<br />
users/utilities.<br />
9.1.7 Hot topics<br />
Research and development <strong>of</strong> light weight high strength water resistant materials for turbine<br />
runners and associated welding processes and procedures.<br />
Through Optimum Use and Innovation <strong>of</strong> Welding and Joining Technologies<br />
<strong>Improving</strong> <strong>Global</strong> <strong>Quality</strong> <strong>of</strong> <strong>Life</strong><br />
95