Duplex stainless steel (DSS) is selected for wet gas pipeline to minimize OPEX and eliminate maintenance activities for internal corrosion control. DSS, however, requires a combination of coating and cathodic protection (CP) for external corrosion mitigation due to harsh external conditions (e.g., high operating temperature and high chloride level in the soil) in the Middle East. CP design and operation for DSS pipeline faces a major challenge as there is no applicable published industry standard or technical research for protection criteria for DSS.
Laboratory testing was performed with soil samples removed from the field to determine whether an applicable CP potential range exists that can provide the required protection and avoid hydrogen embrittlement at the same time. Overall findings of the lab tests in 2 representative soil samples indicated that a CP potential range exists. This range, which is between -600 to -800 mV vs copper-copper/sulphate electrode (CSE), is consistent with predicted values from the thermodynamic stability of water. Simultaneously there was no reported hydrogen generation in that range
Field data confirmed DSS pipelines are operating within the protection range and mitigating hydrogen embrittlement (HE) risk accordingly.
A life cycle cost assessment led to the selection of DSS for field gas gathering network composing of more than 200 miles of pipelines. Buried portions are provided with external coating. Furthermore, due to high chloride content in the soils, the external corrosion threat was mitigated through the use of an external coating supplemented with CP.
As there was no industrial reference covering onshore DSS pipeline CP criteria, lab testing was conducted to establish the criteria and confirm if the risk of hydrogen embrittlement is managed appropriately. This is further evaluated with field data to confirm pipelines integrity.
Laboratory testing was performed to determine if CP is feasible to mitigate the corrosion threat for DSS pipelines. The primary objective was to determine if a CP potential range exists that can provide protection and avoid hydrogen embrittlement of DSS in field soils.
