Leveraging RBI and Corrosion Management Programs

Introduction

The story of the old operator and the hammer rings true today. As the story goes, a retired operator is called back to the plant because a machine he spent years working on wouldn’t start. He walks up to the machine, looks around, listens closely, and promptly smacks the machine with a hammer. Amazingly, it starts right up. The next day he sends a bill to the plant manager for $5,000. The plant manager is furious and refuses to pay without an itemized bill. The old operator sent the following:

• Hammer: $5
• Knowing where to hit the machine with the hammer: $4,995

The same can be said today for establishing and executing effective equipment strategies and repairs in processing facilities. Knowing what to look for and where to look for it is more important now than ever. Often, the “what,” “where,” and “when” for inspection of fixed equipment are dictated by a solid understanding of damage mechanisms. This article will review the link between damage mechanism assignments and risk-based inspection (RBI). The focus will be the advantages of combining efforts for revalidations of both programs.

Damage Mechanism Identification

Proper identification of damage mechanisms is the first and most critical step for any proactive fixed equipment inspection program. Identifying “credible” damage mechanisms provides the guidance necessary to select appropriate monitoring locations and nondestructive examination techniques for equipment and piping. The fourth edition of API RP 580 defines credible damage mechanisms as “determined to have a reasonable likelihood of occurrence, by a Corrosion / Materials Engineer or Specialist, considering the equipment design, process conditions, environment, history and operation.” Understanding the potential and severity of these damage mechanisms also validates existing inspection data and future inspection intervals.

Although both API 510 and API 570 include requirements to identify damage mechanisms for targeted inspection plans, more guidance was needed on how to accomplish this. In 2018, API published the first edition of Recommended Practice 970, “Corrosion Control Documents.” This RP provides definitive guidance on assessing credible damage mechanisms and consensus approaches to documenting these mechanisms. It should be noted that corrosion control documents (CCDs) are not a new concept in the process industry. Some owner-users have had damage mechanism identification programs in place for decades. Since publication, the concepts of API RP 970 have seen widespread acceptance as a best practice for the identification and documentation of damage mechanisms. The second edition of API RP 970 is currently under development.

There is no universally agreed-upon standard format for CCDs. Different operating sites and companies have developed templates that suit their requirements. However, I believe there is a consensus that the essential items of a CCD should include:

• Process description with important factors and precursors for damage (basis)
• Mechanical/materials information on the equipment and piping
• Process information such as temperature and pressure
• Summary of key inspection history
• Anticipated damage mechanisms
• Level of likelihood and/or thinning rate for each mechanism
• Nuances of the damage mechanisms on a corrosion system level
• Identification of applicable integrity operating windows (IOWs)