Fatigue failure of thermowells in feed gas supply downstream pipeline at a natural gas production plant

摘要

A natural gas production field has been set into operation about six years ago. Natural gas produced from the well is processed through different stages before being supplied through pipelines for local market. Temperatures of the gas during its different processing and supplying stages are being monitored using thermowells made of type 316L austenitic stainless steel. In this concern, flanged, straight type thermowells were used for the feed gas supply downstream pipeline (30 in. diameter). This thermowell type consists of a straight tube and a flange. The tube outer diameter, thickness and length are 19 mm (0.75 in.), 6.5 mm (0.256 in.), 260 mm (10.24 in.) while the flange diameter and thickness are 155 mm (6.1 in.) and 23 mm (0.91 in.) respectively. The thermowells are fixed in a vertical position where its flanges are 200 mm above the top of the pipeline. Actual operating conditions are given below. After only one year of operation, several thermowells have experienced failure.