IIW White Paper

easily weldable, the life expectancy in theory could be infinite through periodic weld repairs in critical areas. One less scrapped casting effectively can in effect reduce several tons less of harmful gases emitted into the atmosphere by an inefficient foundry. A major challenge for the refurbishment of aged plant is that welding specifications are firmly biased towards the requirements for building of new plant. Significant engineering intervention is often required to support weld repair procedures that sometimes appear to be outside or in conflict with established welding specifications. Of particular significance are: The non-availability of original construction material-advances in CrMoV type creep resistant alloys implies that aged material needs to be joined to a new generation alloy. The long term operating performance of new to old material joints is often based on extrapolation of limited laboratory test data. Welding personnel are not always familiar with the weldability of the latest alloys. Inspection techniques accurate and sensitive enough to isolate exhausted components from relatively undamaged components still good enough for extended operating life. The refinement and modernisation of traditional welding processes and techniques has contributed to significant improvements in efficiency of the welding activities. The introduction of more energy efficient inverter power sources has the potential to contribute towards reduced production costs, while the improved controls of the latest equipment proves to be more forgiving to inexperienced coded welders and in effect lightens the burden on the fast shrinking pool of highly skilled artisan welders. In a way, this might be in contradiction to the drive for skills development but in reality should rather be seen a saving grace situation while the welding industry struggles to reduce the acute shortage of skilled welders by luring young people towards the industry through rationalisation of training curriculum and efforts to introduce a universal qualification system acknowledged on a world-wide basis. The underground Coal Gasification (UCG) process is considered as one of the new emerging energy sources, which converts unworked coal into a combustible product gas. The gas is suitable for industrial heating, power generation or hydrogen and natural gas production while CO 2 can be readily removed from the product stream thus producing a source of clean energy with minimal greenhouse gas emissions. Future design, fabrication and safe operation of highly steerable and controllable down hole assembly for drilling in coal up to 450 m depth, will certainly require high performance structural steels and weld joints. This will be one of the highly complex technological challenges of the future applications of the welded structures. Figure 9.6 shows material grades which are currently used for high temperature components in fossil power plants. For all components exposed to high temperatures during service, the 100,000 hour creep rupture strength of base material (BM), weld metal (WM) and cross-welds is the major design criteria.

200

9-12% Cr-steels

12 CrMoV

Ni-/Co-base

Superalioys

Figure 9.6 Materials used for high temperature applications in thermal power generation (Reproduced courtesy P. Mayr, based on data from T.U. Kern, Siemens, Germany)

Austenitic steels

1 CrMoV

100

100,000 hours

Aim of COST536: Expansion of the application range of 9-12%Cr steels to higher temperatures

500 0

Creep Rupture Strength (MPa)

550

600

650

700

Temperature (°C)

88

Through Optimum Use and Innovation of Welding and Joining Technologies

Improving Global Quality of Life