Case Study on Frequent Failure of Dry Gas Seals

Abstract

Case study on frequent failure of dry gas seal in centrifugal compressor The process gas high pressure compressors used in oil & gas industries requires highly safe and reliable operating requirement. This case study represents the frequent failure of dry gas seal (DGS) in Re-injection Gas Compressor within 20 Days of previous dry gas seal replacement. DGS systems are specially designed to seal the process gas in centrifugal compressor. The seal gas is extracted from the discharge of same compressor and supplied to DGS after filtration with necessary control (Pressure or flow) based on the requirement in the seal cavity. Ingression of foreign material into the running gap of the seals leads to degrade sealing performance and eventual failure of the seal. After sealing the process gas, a very small amount of the sealing gas passes through the primary seal faces which are connected to the flare. In this case study we found sudden increase in primary vent leakage was observed during operation and after investigation it is decided to perform the internal inspection of DGS. Black/brown contaminates were found in seal cavity and DGS cartridge. After cleaning seal cavity the spare DGS was replaced. After restart, the unit tripped again due to high primary vent pressure within 20days in normal operation. It was decided to disassemble the DGS cartridge again. The same contaminants were found in next inspection. Additionally inspection on DGS panel and piping were checked. ➢Seal gas supply line which was taken from compressor discharge was confirmed as heat traced.➢External gas supply into the dry gas seal during startup and shutdown ensured.➢Found C6+ component percentage higher in the seal gas than the previous gas composition which was analyzed before 5 years.➢The condensation occurs in the seal gas injection line due to JT effect and condensates/liquid drops affects the seal faces of DGS which leads to high leakage in the primary vent.✓Performed DEW Point analysis for the current gas composition and identified the required seal gas temperature.✓The heat tracing was found insufficient to meet the changed gas composition.✓Installed heater (15 KW) in the seal gas injection line after the gas filter to maintain the gas temperature.✓Increased the heat traces capacity from 5 KW to 10 KW in the seal gas injection line. The gas compositions changes over period of time from the offshore well which requires period analysis (Every 6 months) and monitor the heat tracing system. This case study is providing the trouble shooting experience and useful information for all the re-injection gas compressors incorporated with dry gas system in oil & gas industry to have more reliability.