Barrier Types and Definition

Degradation Management is about verifying Barriers in order to manage the risk of threats. 

Definition

The threats are, of course, caused by the Degradation Mechanisms and Barriers are risk controls or recovery measures. Barriers provide the means of preventing an event or incident, or of mitigating the consequences. A Barrier can be an item of Equipment or a human intervention and can also be a control on an escalation factor.

Barriers and their verification should manage the risk of all threats to as low as reasonably practicable (ALARP). Each threat should have at least one effective primary Barrier and a way to control the Barrier (assess its health, operational or maintenance intervention). Additionally, there may be one or more secondary Barriers.

Primary Barriers are those that are fully effective against a threat, provided they are properly maintained. Secondary Barriers provide “mitigation” (e.g., control the degradation rate to an acceptable level) and are normally selected for specific DMs.

Barrier Types

The possible Barriers are given in the next table.

The Barrier Types in IMS:

Mechanical Design and Cathodic Protection Barriers

The status of mechanical design Barriers (M and D) can only be determined through field inspections and should be managed through maintenance. Barriers of the mechanical design type should be risk assessed at the Equipment or Component level to determine their inspection frequency and tasks. This is where S-RBI comes in. All mechanical design Barriers should have acceptance limits for inspection. Similarly, Cathodic Protection Barriers (D) should be managed through monitoring and condition-based maintenance.

Applicable Barriers are:

• Resistant material (material selection)
• Design corrosion allowance (material selection)
• Internal cladding (material selection)
• Internal lining (coating)
• External coating (coating)
• Sacrificial anodes (cathodic protection)
• Impressed current (cathodic protection)

Operational Control Barriers

Barriers of the process control type (P) and chemical treatment (C) should be managed by operational controls and the process variables should be monitored for Barrier verification. The initial value for these variable limits should be selected such that the initial Susceptibility to Failure is “low” or “negligible”. These variables should be captured in a proactive monitoring plan for the asset, to ensure that they are monitored by Operations.

In IMS these variables must be captured in the Integrity Operating Window (IOW).

Other Barriers

Other Barriers (D) should be closely defined: what constitutes the Barrier (which Equipment does it protect); how should the Barrier be verified (inspection, measurement, replacement); and what should be the monitoring frequency.

Defining Barriers in IMS

Barriers are defined in the CL. See Defining Barriers (and linking to IOWs).