How to improve the pass rate of the pressure vessel weld repair (from China Welding Information Network)
Read the number：(2816) Time：2014/3/6 19:38:40
How to improve the pass rate of the pressure vessel weld repair (from China Welding Information Network)
[Abstract] This paper discusses the weld repair process measures the pressure vessel quality control, thus improving the passing rate of the weld repair, welding consumables savings, improve efficiency and ensure product quality.
Pass rate; [keyword] Rework
An Overview
Weld repair of pressure vessels in the product under rigid restraint larger circumstances. Increase the number of repair will not only bring a waste of time and materials, but the main cause is the decline in the quality of products, in principle, the provisions of generally not more than twice the number of repair. Therefore, in case of repair, you must have the appropriate measures to ensure that a qualified repair. I plant manufacturing pressure vessels, especially large container wall thickness generally take the following methods to ensure a competent and repair weld pass rate.
Two technical measures
(1) thick container (thickness greater than 20mm) stratified hierarchical testing of welding methods, especially in the smaller diameter of the container can not be double-sided welding, the weld at the back end of the weld radiographic examination ended about 5mm eliminate the root defect (because weld thinner, but also easy to repair if found defective). The following weld bead may stop certain thickness and then layered film. Exclude re-weld defects until full seam welding. Stratified stratified welding flaw detection method is also suitable for welding of thick-walled pipes, which greatly improved the pass rate of the weld.
(2) When the weld repair occurs after usually take anyone who welded back. However, we believe that this concept is not necessarily desirable, because unlike normal welding weld repair work, the situation is much more complex, relatively speaking. Rework welder must hold and possess repair projects, should have a wealth of experience repairing high pass rate, a strong sense of responsibility as a welder.
(3) before the repair, should determine the nature of the defect, analyze the causes, the preparation of the repair program, developed rework process. And in strict accordance with "the welding process card" specification parameters repair.
(4) before the start of the repair, the notice should be based on non-destructive testing and X-ray film inspection departments to determine the site of the weld repair. To reduce rework blindness, to be approved by the ultrasonic flaw detection repair parts, probing defect depth. Finally, determine clear from the planing surface defects (assuming the vessel wall thickness of 30mm, the defect depth 28mm, inside should rework appropriate. Defect depth of 12mm, the repair should be appropriate to the outside, so that ruled out the repair blindness, improve efficiency savings and ensures the quality of welding consumables).
(5) When using a carbon arc gouging to remove defects stratified gouging method. When it reaches the depth of the defect is located, should be carefully examined edge planing tight until all defects cleared. If you can not determine whether the defect has already cleared, it is best detected by radiographic inspection once to avoid the defect left in the welding seam on foolproof. Before testing the first planing to clean and polish with the angle grinder.
(6) for cracks, lack of penetration of the weld repair defects such as line, when going to dig to a depth where the defect should try to use angle grinder grinding, edge grinding edge coloring test stratified test. Also after exclusion of defects confirmed by qualified before welding, weld repair, and its length is not less than 100mm.
(7) defects clean, you must grinder for grinding of gouging with the angle, the plane iron tank, carburizing layer Clear All. And polished into the V-shaped groove plane (or U-shaped) angles on both sides of the inner surface of the weld repair 10-15mm range of rust, oil should be cleaned of all, in order to facilitate welding.
(8) the weld repair, the workpiece restraint stress is large, should adopt the preheat and post-weld treatment process measures, such as elimination of hydrogen, with a thermocouple. When preheating, the far-infrared panel heaters on the back side of the repair. When hydrogen elimination process will be placed in the far-infrared heater plate welds positive and negative sides, and affix asbestos cloth or glass wool. Heating temperature of 250-350 ℃, holding time less than one hour.
(9) After the repair, welding department should be consistent with the original polished into the weld reinforcement and width, and garden slide transition to the base material. Visual inspection qualified, as required by 24 hours after the requirements of NDT.
Three Conclusion
Weld repair work is a particularly important job. Work quality directly affects the life of the product should be special attention.
