Failure Analysis of Gas Separator Cooler Tube Leak During Service After Passing Inspection Test During Turn-Around Inspection

Abstract

Failure analysis is performed by most companies in the oil and gas industries; to identify the cause of failure and to institute mitigation strategy to avoid any future occurrence. Localised corrosion is one of the difficult damage mechanisms to manage in the oil and gas sector, material selection is often used as mitigation against this threat. Generally most Nickel-based alloys have shown excellent pitting corrosion resistance and good mechanical properties for extended service; these are selected for services where localised corrosion such as pitting corrosion threat is predicted on case by case basis. There are variance of Nickel-based alloys with different critical pitting temperature (CPT) and despite its superior performance compared to many other corrosion-resistant alloys (CRA), some of these alloys are prone to localised corrosion such as pitting and crevice corrosion.

As expected during normal operation, the wet gas from a HP Separator goes into a Suction Scrubber via the cooler where the temperature is cooled after coming out from the outlet of the compressor. Following a shut down the cooler was inspected with Eddy current and no defect was noted, however after start of the platform a tubed side of the gas cooler leaked into the cooling medium.

This paper presents findings of the failure analysis report. Subsequent investigation revealed an erroneous selection of Incoloy 800 material for the gas separator tube instead of Inconel 625 and Incoloy 825 which have shown excellent pitting corrosion resistance, the mechanism of damage was investigated, and recommendation from the conclusion has been proffered.

INTRODUCTION

The gas processing platform comprises the separators, coolers, import and export lines, the main function of the processing platform is to remove impurities and other contaminants from the gas to meet sales requirements before export. During normal operation the wet gas is separated in the High Pressure Separator vessel (V-01) it is then cooled in cooler (E-02) and routed to a Suction Scrubber (V-02) where entrained liquids are removed. The gas is then routed into a gas compressor then further to a cooler (E-03) where the high temperature gas is cooled. The gas is then routed to a Suction Scrubber (V-03) and dehydrated at a contactor. The dry gas is subsequently compressed, cooled and sent for export via a riser.