Major improvements in status of the art of electron beam (EB) welding on large thickness chromium molybdenum steels have been achieved.
Beam measurements experiments were performed with a computer controlled electron beam diagnosis system, eliminating the need for complex and cost intensive welding tests to determine the optimal focus adjustments at different machines. The improved analyser is now suitable for use under industrial conditions.
Using the diagnosis system, progress has been made on the equipments investigated in the project. It was shown that, particularly in case of welding heavy thickness components, focus position, aperture, diameter and the distribution of the power density of the beam strongly influence the quality of welds.
Demonstration of defect free welds both on 100 mm and 200 mm thick chromium molybdenum material was made. Evaluation proved sufficient values for the mechanical values after post weld heat treatment. EB welding of linear or cylindrical components up to 100 mm is considered practical, without strong risks concerning the mechanical and geometrical quality of the weld. EB welding of higher thickness is still considered to be a risky undertaking, because of low reproducibility of quality. Demonstration of feasibility of good fade outs has only been partially done. Parameters and welding conditions influencing the quality of fade outs have been determined.
By nondestructive examinations (NDE), most of the typical defects occurring with electron beam welding have been detected. The only defects still needing development of adapted NDE methods are cold shuts occurring at the bottom of partial penetration welds. Use of radiographs associated with ultrasonics is strongly recommended.
High homogeneity of mechanical characteristics was reached on 2.25 chromium molybdenum steel after quality treatment. EBW welding was able to meet the most severe specifications. As this ability was directly linked to the purity of base metal, it is particularly important to specify a very high level of cleanliness of base metal.
A personal computer (PC) board control system was developed, which allows adjustment of focus current in dependence of the power and the focus position. The main innovative aspects of this system is the ability to adjust online and continuously the focus current to the respective beam power during the slope.
THE OBJECTIVES OF THIS WORK ARE AS FOLLOWS:
- DETERMINATION AND OPTIMIZATION OF THE EB WELDING PARAMETERS ON VERY THICK CR-O STEELS WHICH ARE USED IN MANY INDUSTRIAL COMPONENTS, I.E.: PRESSURE VESSELS, HEAT EXCHANGERS, GAS AND STEAM TURBINES, ETC.
THREE EB EQUIPMENTS ARE INVOLVED IN THIS PROJECT, TO COMPARE ELECTRON BEAM CHARACTERISTICS AND WELD QUALITIES ON FOUR KINDS OF CR-MO STEELS: 2 1/4 CRMO (PLATES AND CAST), 9 % CRMO, 12 % CRMO.
THE NECESSARY STEPS TO ACHIEVE THESE GOALS ARE:
- THE RELATIONSHIP BETWEEN BEAM CHARACTERISTICS, WELD QUALITY AND OCCURENCES OF DEFECTS;
- THE OPTIMIZATION OF WELDING CONDITIONS IN PARTIAL AND FULL PENETRATIONS (75 TO 200 MM);
- THE OPTIMIZATION OF THE WELDING PROCEDURE FOR A GIRTH WELD;- NON DESTRUCTIVE AND DESTRUCTIVE TESTS OF THE WELDS.
THE ACHIEVEMENTS OF THESE TESTS ARE TO ALLOW THE PERFORMANCE OF FULL SCALE MOCK-UPS AS A DEMONSTRATION OF THE RESULT VALIDITY.
Funding SchemeCSC - Cost-sharing contracts
92086 Paris La Défense
CV21 2NH Rugby
CB1 6AL Cambridge