Safety Evaluation Investigation Of Welding Repairing Oil-stolen Orifice Of In-service Oil Pipeline

The welding of pipeline in service is the key operation to repairing technology of pipeline in service. It refers to welding in the pipeline with the purpose of repairing and reforming the pipeline under the condition of the oil in the pipeline keeping transportation or invariable in flow rate, pressure, etc. Drilling the pipeline to steal oil seriously affected the normal transport. At present, workers usually use the method of welding repair in service to make urgent repair on the stolen oil holes of pipeline at site. The method of covering cap welding repair is used most widely with the operation of directly welding a bar iron cap with one end sealed in stolen oil valve. The welding repair technology of oil-stolen orifice of pipeline in service not only shorten the repairing cycle but also can ensure the normal running of the oil transport, so the welding repair technology in service has fairly huge economic benefit, and the research on its safety evaluation is extremely important. This paper analyzes and investigates the main way of drilling and stealing oil, the existing dangerous, harmful factors and some important existing problems through investigating the pipeline stolen oil drilling at site and analyzing the way and process of repairing of oil-stolen orifice. Besides, the paper also lists and analyzes some repairing methods of different ways of stolen oil emphasizing on analysis of the danger of the approach of welding mask on the cap restoration. From the investigation, we conclude that it mainly exist electric shock accidents, burning hot accident, explosion accidents, leakage accidents, etc in the process of welding repair mask cap. This study finds some main problems of the pipeline welding repair in service: burning through and hydrogen-induced cracking and analyzes the risks of these problems; proposes some factors to avoid such accidents. The main factors influencing burning through are thick wall, fusion seam being deep, additional stress and the condition of flow media; the main factors affecting hydrogen-induced cracking are hydrogen, welding consumables organization, additional stress in the welding lines. In the light of these factors, some requirements of safety welding repair are proposed. This article divides the process of welding repair of oil-stolen orifice roughly into four procedures of excavation repair homework pit, dismantling stolen oil device, welding and sealing stolen oil pipe anticorrosion holes, restore the original; elaborates each procedure in detail; provides sufficient preparation and materials for making systematic safety assessment to the welding repair process. Through the analysis of the characteristics of safety assessment methods, and advantages and disadvantages, this research determines the common security evaluation methods in the process of welding repair of the pipeline in service: analogy standard evaluation method, logic analytical method, fuzzy comprehensive evaluation method and the computer simulation method. Through the analysis, the paper utilizes safety checklist assessment method to make safety evaluation of electric welder in the process of repairing; electric accident tree evaluation method to make evaluation and analysis to common accidents of system. Finally, according to the evaluation results and the risk analysis of system, the paper puts forward some accident prevention measures and emergency measures in the welding repairing process of oil-stolen orifice in oil pipeline in service.