Considerations in Developing an Inspection Plan for Equipment in Wet H2S and Carbonic Acid Service

The American Petroleum Institute

May 29, 2018

Wet H2S damage and carbon dioxide (CO2) corrosion are common damage mechanisms affecting offshore oil and gas processing equipment. Depending on the properties of the production stream, these damage mechanisms can be active separately, in tandem, and/or contribute to erosion-corrosion if the process stream contains sediments or other solid particles. The American Petroleum Institute (API) publication RP 571, Damage Mechanisms Affecting Fixed Equipment in the Refining Industry, describes four types of damage, including blistering and cracking, associated with wet H2S. H2S damage initiates from a sulfide corrosion process, wherein sulfur reacts with iron to form iron sulfides (FexSy) and hydrogen, which diffuses into the metal, causing blisters and/or cracking. API 571 describes carbon dioxide (CO2) corrosion as general corrosion and/or pitting due to the action of carbonic acid, which is created when CO2 dissolves in water. The carbonic acid (H2CO3) reacts with iron to form iron carbonate (FeCO3) and/or iron oxide (FeO4). API 571 describes Erosion/Corrosion as the combined effect of the removal of protective scales and subsequent corrosion of unprotected surfaces.

The production manifold feeding the production fluid to an oil platform includes a combination of well streams, with a wide range of chemical constituents and compositions. As part of the production process, the production fluid is separated into gas, hydrocarbon, and aqueous fractions. A typical production platform includes a high-pressure separator, a low-pressure separator, and the associated compressors, storage tanks, and process piping. Unwanted contaminants (e.g., H2S) are removed from the gas and hydrocarbon fractions are delivered to shore for further processing (e.g., refining) and/or sale, while the aqueous fraction is disposed of, or used as an injection fluid. The gas fraction may also be flared or burned for energy recovery. Over the lifetime of a production platform, the composition of the process fluid and products produced by a platform can change significantly. Therefore, the damage mechanisms affecting the vessels and piping of the platform can also change, and the operator should ensure that their asset integrity management plan can adapt to damage mechanisms becoming active and/or more severe.

This paper addresses the development of an integrity management (IM) plan for offshore production facilities susceptible to wet H2S damage and CO2 corrosion, as well as the challenges associated when both damage mechanisms are present, possibly in combination with Erosion/Corrosion damage. Three aspects of an effective and efficient IM plan are discussed in this article: i) understanding the nature of the threat, ii) developing an inspection plan for fixed equipment that addresses this threat, and finally, iii) challenges that might occur during implementation of the inspection plan.

Starting approximately 2010, petroleum refineries have been developing and revising IM plans with an increasing focus on damage mechanism reviews, integrity operating windows, and risk-based inspection strategies in response to their growing understanding of process threats, industrial incidents and evolving regulatory environments. As part of this exercise, inspection circuits are often grouped by common damage mechanisms to determine a common inspection strategy for all fixed equipment affected by a specific damage mechanism. The complexity of oil and gas production facilities, especially due to new construction and upgrades to handle sour resources, continues to increase. This exposes operators to additional and more complex asset integrity threats. In response, the oil and gas production industry may rely on the lessons learned from the petroleum refining industry and their practices in developing and refining their IM plans. In this paper, we incorporate certain practices in relation to wet H2S and CO2 corrosion and propose a simplified IM plan for an offshore oil and gas production facility.

Dr. Ott, Mr. Reza, and Dr. Veloo will be presenting their paper based on this abstract at the annual ISOPE 2018 Conference, in Sapporo, June 10-15, 2018.