Pressure Vessel Assessment Research On 1PE Devices Using Over 20 Years

This paper is based on an assessment on 1PE production devices which have served over 20 years. The work includes data collection and analysis, the field inspection and RBI assessment for the 1PE devices.Through analyzing the yearly inspection data, the corrosion situation in and outside the 89 pressure vessels in service over 20-30 years have been learned and the corrosion rate is calculated according to the inspection data. Some of the devices have been transformed in structure during service, such as jacket structure, sealing structure of heat exchanger and so on.Based on the comprehensive analysis of the material and corrosion data offered by the Plastic Division, API 581 and references about the same kind of failure cases from experts on materials and corrosion, it is concluded that the main damage mechanism of 1PE devices are internal corrosion thinning and external injury (atmospheric corrosion and corrosion under the insulation layer)Based on API 581 method, an risk assessment is carried out about 1PE production devices to tell the possible risk factors and potential consequences and determine the risk class of each device. This paper also puts forward inspection suggestions about the devices to the factory and carried out by them. In this study, it is required to check the thickness and strength of the 4 ultrahigh pressure vessels and 22 high pressure vessels and calculate minimum wall thickness in order to make sure that these high pressure vessels can serve safely during their extended service life.Due to the high purity of the medium, mainly polyethylene, in the 1PE devices, low corrosive impurity and proper material selection, the average corrosion rate is low, the medium corrosion basically does not to consider about. Since the presence of cooling water or high-temperature steam in heat exchangers, corrosion is prone to happen at these locations, so it is required to strengthen the monitoring or replace stainless steel. Because the devices have extended their service for many years and have a relative large range of risk distribution, the device failure probability level increases year by year, it is recommended to increase efforts to inspection.