Analysis Of Life Extension Of Purification Unit In A Sulfur Gas Field

Underground natural gas is a kind of multi-component gas mixture.Gas purification after gas recovery is a key process to ensure the gas temperament of gas field transport.Since the reform and opening up,a large number of purification devices have played an important role in ensuring the supply of natural gas,promoting the development of economy and people’s livelihood.For decades,the related devices of many gas production plants have reached the design life can still be normal service,such as a simple approach to scrap equipment update,would waste resources,which is not in line with the cost reduction and efficiency of energy enterprises in our country.Therefore,the life extension analysis of the extended service purification device is of great significance to the safe operation of the device.At present,the life extension analysis technology for natural gas purification units at home and abroad is not mature,but the overall idea is generally based on the failure mode analysis of the purification unit,focusing on the analysis of time-related failure possibility and remaining life prediction.Therefore,this paper focuses on two typical failure modes,corrosion thinning and stress corrosion cracking,as well as taking into account creep and fatigue,which may cause material deterioration of the equipment,to carry out tests and calculation analysis,so as to initially find out the evaluation method of the purification device beyond the service period.The main work and conclusions are as follows:Through the statistics of equipment replacement records and maintenance results of the sulfur gas field purification device over the years,it is found that the main failure mode is the internal corrosion caused by corrosive components H₂S and CO₂ in natural gas.The analysis of corrosion degree shows that the wall thickness thinning caused by uniform corrosion is the main factor affecting the life of the purification device.At the same time,it was found that the acid gas aftercooler was the most serious device for corrosion and stress corrosion cracking,and a wide range of cracking and bulge were found at the head.The analysis suggested that the main reason for cracking was the wet H₂S working environment of the device and the hydrogen cracking caused by the material microstructure defects.No fatigue cracking was found in the relevant parts of the purification device that may have fatigue cracks,such as the regeneration tower,through field inspection.Through the analysis of the structure and performance of the materials of the purification device,it was concluded that the service temperature of the purification device did not cause significant creep and fatigue damage to the materials,and the materials did not deteriorate,which met the requirements of life extension.By simulating the corrosion law of 20R,20g and Q245R materials caused by the content of H₂S and CO₂ in different environments,it is found that there is no obvious difference in the corrosion rate of three materials in the same environment,but there is a significant difference in the corrosion rate of materials in different environments.In the simulated acid gas environment,the corrosion rate reaches the maximum at 90℃,which is 0.43 mm/a.The corrosion rate is 0.15mm/a in the simulated raw gas environment and 0.07 mm/a in the simulated wet purification gas environment.According to the wall thickness test data of each purification device and the actual material performance analysis data,the corrosion failure mode was investigated,and the strength check and residual life prediction of the purification device were carried out.Most of the purification devices were in good condition and the residual life was more than 30 years.But considering the subsequent temperament conditions and service environment may fluctuate and acid gas aftercooler and other key positions may exist hydrogen-induced cracking and other problems,so in the subsequent use process,on the basis of the existing regular inspection,should continue to synchronize the residual strength check,real-time calculation of residual life,to master the safety state of equipment;At the same time,it is important to increase the inspection proportion of acid gas aftercooler and shorten the inspection period to prevent the equipment failure caused by the rapid development of hydrogen cracking.Moreover,corrosion monitoring and protection of purification devices with high working temperature in acid gas environment should also be increased,such as regeneration tower.The paper has 58 pictures,25 tables,and 80 references.