Damage Control: Sulfidation and High-Temperature H2/H2S Corrosion Assessment

Editor’s Note: This regular column offers practical insights into various damage mechanisms affecting equipment in the O&G, petrochemical, chemical, power generation, and related industries. Readers are encouraged to send us suggestions for future topics, comments on the current article, and raise issues of concern. All submissions will be reviewed and used to pick topics and guide the direction of this column. We will treat all submissions as strictly confidential. Only Inspectioneering and the author will know the names and identities of those who submit. Please send your inputs to the author at damagecontrol@inspectioneering.com.

Introduction

The last installment of Damage Control discussed how sulfidation (sulfidic corrosion) can adversely influence the useful life of pressure components operating in sulfur-containing process environments at elevated temperatures. Sulfidation can ultimately lead to catastrophic failures, if not properly identified and remediated. Commentary in Part 1 of this Damage Control series included the delineation of hydrogen (H₂)-free and H₂-containing service conditions, which represent the process environments necessary to initiation sulfidation and high-temperature H₂/H₂S corrosion, respectively [1-3]. Furthermore, the typical damage morphology of these damage mechanisms was presented, as well as common failure locations, critical variables influencing damage susceptibility, and refining units prone to sulfidation damage.

Part 2 of this series will offer an overview of fitness-for-service (FFS) methodologies for evaluating wall loss in pressure components subject to sulfidation, although many of the FFS techniques summarized herein are applicable to any form of internal or external corrosion. Specifically, the procedures in API 579-1/ASME FFS-1, Fitness-For-Service (API 579) will be outlined as the technical basis for practical engineering evaluation methods [4]. As highlighted herein, in addition to identifying all relevant damage mechanisms, accurate inspection and proper characterization of damage is a critical step in any FFS assessment, and as such, commentary on non-destructive examination (NDE) practices, including careful documentation of inspection findings, will be provided. Establishing reasonable inspection intervals is also a critical aspect of any FFS assessment as a means of monitoring future damage progression and managing risk going forward. While sulfidation corrosion continues to be a notable industry damage mechanism, once damage is recognized, leveraging FFS methods (again, that appropriately consider future corrosion rates), coupled with a suitable inspection/monitoring strategy offers owner-users a reasonable tactic to manage the risk associated with loss of containment/failure, at least in the short-term.

Overview of FFS Methods for Wall Loss

API 579 is delineated into different parts intended to provide procedures for evaluating distinct forms of damage mechanisms [4]. In general, when evaluating any type of damage in accordance with API 579, the following 8-step procedure is invoked:

• Step 1 ‒ Flaw and Damage Mechanism Identification
• Step 2 ‒ Applicability & Limitations of FFS Procedures
• Step 3 ‒ Data Requirements
• Step 4 ‒ Assessment Techniques and Acceptance Criteria
• Step 5 ‒ Remaining Life Evaluation
• Step 6 ‒ Remediation
• Step 7 ‒ In-service Monitoring
• Step 8 ‒ Documentation