Study On Calculation Method Of Potential Radius Of Sulfur Natural Gas Pipeline

The potential impact radius is defined as the radius of an area where public security and property may be seriously affected after the pipelines failure. The calculation of the potential impact radius is the basis of pipeline’s high consequence areas identification, and Is the key to ensure the effective implementation of integrity management. In2005and2006, China promulgated the standards of integrity management of gas pipeline in accordance with the fundamental realities of our country. In the standard, the potential impact radius is calculated according to the recommended model in ASME standard B31.8S. This model is put forward based on the single point source model for the radiation calculation on jet fire, and ASME B31.8S pointed out clearly that it is not suitable for sour natural gas pipeline because of its ignoring to the poisoning consequences caused by the releasing gas. These years, research on the potential impact radius calculation model of hydrogen sulfide poisoning is relatively less, and the existing literature about the pipeline’s releasing and diffusion mostly did not fully consider its unique characteristics, this will cause the calculation result unreliable, hardly be used in practical engineering. Therefore, proposing the calculation model according to the characteristics of sour natural gas pipeline failure is an urgent problem need to be solved today. This paper carries out the following researches:(1) Through the study on the failure mechanism, the electrochemical corrosion, cracking mechanism of sulfur containing natural gas pipeline, we determine the main failure modes of sour natural gas pipeline to be the full diameter rupture caused by hydrogen induced cracking, hydrogen induced cracking and bubbling and the stress oriented hydrogen sulfide. Through the analysis of leakage event tree for sour natural gas pipeline failure, the occurrence probability of all kinds of failure consequence such as jet fire, fire, explosion, poisoning of hydrogen sulfide is discussed, and the typical sour gas pipeline failure consequence is identified as jet fire and hydrogen sulfide poisoning. Based on the above research, the basic methods and steps of calculating the potential impact radius for the sour natural gas pipeline is established based on literature;(2) According the identified failure modes, and the characteristics of release rate changing with time, based on the general calculation model of release rate for natural gas pipeline, the calculation model of the leakage rate of natural gas pipeline under the condition of full diameter fracture is established. The PHAST software is used to calculate the key parameters in the model, the release rate decay factor X, and the corresponding formula is obtained through the fitting of the curve;(3) Through the comparison of different injection heat radiation calculation models, the Chamberlain model of the solid flame model is determined as the basis model. based on the Chamberlain model, the fire potential impact radius for the sour natural gas pipeline is established. And the model parameters such as Flame area, visual factors, gas leakage rate, heat flux threshold is reasonably determined;(4) Through the analysis of sour natural gas pipeline’s release and dispersion, the characteristics is determined as:the main failure mode of full diameter rupture, the release rate is always changing with time, the dispersion process is composed of injection stage and passive diffusion stage. Based on the above analysis, the Gauss model is selected as the basic model from the existing gas diffusion model, and the multi-puff superposition calculation model for the potential poisoning radius is established. According to the related literature material, the calculation method of model parameters such as puff quality, dispersion parameters, release puff height, hydrogen sulfide poisoning threshold is be studied respectively. When Putting into the corresponding parameters, and simplifying the model, the final expression of the multi-puff superposition calculation model is obtained;(5) According to the problem of the relatively complex calculation progress in the model, the potential impact radius calculation software of the hydrogen sulfide poisoning, HSCC, is compiled with the VB language. We select7pipelines as example, the wind speed in the calculation is determined, and the established fire potential impact radius calculation model is used to calculate according to the selected pipelines. The HSCC is used to calculate the potential impact of hydrogen sulfide poisoning of selected pipelines, and the study of sour natural gas’s release and dispersion law is carried out with the calculation result. Though the contrast of fire potential impact radius and the hydrogen sulfide poisoning radius, we can draw a conclusion that the potential impact radius of sour natural gas pipeline should be determined based on the potential impact radius of hydrogen sulfide poisoning.