Study On Quantitative Risk Assessment Method Of Acid Natural Gas Pipeline

Along with the national increasing demand for natural gas resources, the development of sour gas field has become an important energy strategy. Pipeline transport is the main form of natural gas transportation. Soul gas is the gas which contains substances such as H2S, CO2 and others.The strong corrosion environment makes the transpotion pipeline more prone to corrosion perforation and rupture which not only causing huge economic losses and environmental pollution, but also may endanger the personal safety of staff and affect the normal production of the gas field. Risk assessment technique is an effective way both to reduce risk and to identify risk and now is widely used in oil and gas pipeline system.The soul gas pipeline and purified natural gas pipeline are quite different. On one hand the soul gas pipeline has a higher probability of failure due to the harsh corrosive environment, on the other hand, the soul gas contains H2S which is toxic.So in addition to the thermal radiation and explosion overpressure, the consequences of failure of soul gas pipeline also need to consider the impact of poisoning. Based on the above analysis, this paper mainly studies on the following aspects:(1)Based on the analysis of failure datas of the domestic and foreign purified gas pipelines and sour gas pipelines, the cause of failure and failure of probability of the soul gas pipeline are analyzed. The general failure frequency representation method is used to calculate the failure of probability of soul gas pipelines in Sichuan province and compared it with foreign data.(2) Based on the diffusion influence factors the soul gas diffusion process is analyze. Compared the advantages and disadvantages of commonly used gas diffusion models and Gaussian diffusion model is selected. Analyze the the consequences of failure and determine the the failure hazards of soul gas pipeline are thermal radiation injury, explosion injury and poisoning injury.(3)Jet fire model and Gaussian diffusion model are applied to calculate the affected area at different thermal radiation threshold and H2S concentration threshold. Comparison to verify the reliability of the models is made with the API 581 recommended calculation method at the same thermal radiation threshold and H2S concentration threshold. The jet fire model made the assumption that the flame is vertical and the height of the jet fire is took into account. The Gaussian diffusion model considers the leak diffusion area as ellipse which is recommended in API 581 and ellipse area formula is adupted.(4)By analyzing the characteristics of soul gas, the soul gas pipeline quantitative risk assessment model is obtained. Take Longgang 001-6 to 001-7 pipeline for example, the improved quantitative risk assessment model is applied. The result is compared with purified natural gas pipeline in the same condition. Comparison found that the probability of failure, finance loss and risk of the soul gas pipeline are higher than the purified natural gas pipeline.(5)Risk is calculated by using the Gaussian diffusion model at the H2S concentration threshold of 15ppm and 100ppm. It was found that the consequence area and the finance loss changes with the safety threshold. The poisoning area is greater than the thermal affecting area at the H2S concentration threshold of 15ppm, which making the proportion of poisoning finance losses increase in the total losses of the consequences. For this reason, the pipeline risk increases with the increase of the content of H2S. However, when using the H2S concentration threshold of 100ppm, the thermal injury area is the main consequence area. So with the increase of the H2S or reduces of the hydrocarbon components, the thermal injury area and the pipeline risk reduces.(6)Pipeline risk assessment are implemented for Calss 1 region with a pupolation of 10 families, Calss 2 region with a pupolation of 20 families and Calss 2 region with a pupolation of 100 families and find that the the pipeline risk increases with increasing population density. The higher the H2S content, the greater the increased rate of the risk. In the content range of 5% to 20%, the increase of population density does not increase the risk level of the pipeline and all are in grade "low".