Methodology Step 2

Step 2 Identify Threats and Barriers (Define the CL): 

Below the Step 2 Methodology is described. See also Software Step 2.

Define the Corrosion Loop Boundaries

For more information on where to place the Boundaries see Corrosion Loops (CLs) - Theory.

Define the Corrosion Loop Process and Potential DMs

DMs should be identified based on the prevailing process conditions and selected material. This step should thus include:

• A review of the asset in general: Typical operation, exceptional operating conditions, potential DMs; and
• A review per DM: The susceptible areas, parameters that affect the degradation, expected/observed damage rates, and the process variables that should be controlled.

The following should be assessed (and described in the CL):

• Premises to corrosion control, risk-based assessment, and inspection/monitoring plans.
• Materials selection per (group of) Equipment and piping, including relevant properties such as:
  • Coatings
  • Cladding
  • Corrosion allowance
  • Post-weld heat treatment (PWHT)
  • Type of heat tracing
  • Type of insulation
• Degradation under normal operating conditions:
  • Name of degradation mechanism (from globally managed list)
  • Expected degradation rate based on degradation models
  • Historical damage rate
  • Parameters that affect the degradation mechanism
  • Variables that should be controlled with their limits
• Degradation under other operating modes:
  • Start up and shut down of the asset
  • Likely excursions and when they occur (e.g., water carry over)
  • Special modes (e.g., decoking, regeneration, hot standby)
• Special Emphasis Components (e.g., Deadlegs, Injection Points). 

Identify Degradation Mechanisms

Based on the information gathered to Define the Corrosion Loop Process and Potential DMs, the DMs can now be identified and defined in the CL. See Degradation Mechanisms - Classification and Definition

Identify Barriers

For each of the identified DMs, one or more Barrier should be in place that allow management of the risk of the threat to ALARP. See Barrier Types and Definition. These Barriers must be identified and defined in the CL. Ideally, to be able to verify the Barriers, all Barriers should also be associated either with an IOW (P- and C-type Barriers - Operational Control Barriers) or a Component (M- and D-type Barriers - Mechanical Design and Cathodic Protection Barriers).

As part of the Barrier defining process, for P- and C-type Barriers, variables should be selected to be monitored (via the IOW), while for M- and D-type Barriers, Components should be identified for inspection (and risk assessed). The IOWs can directly be linked, when defining the Barriers. However, the Components are identified later, when the DMs are assigned to them during the start of the Risk assessment process (Step 3).

At this time, an initial Barrier Assessment should be performed to ensure that everything, with regards to the Barriers, is in place to enable Barrier verification.

A Barrier Assessment should verify:

• Actual process conditions against the recommended limits for the DMs.
• DM theoretical damage rates at the actual process conditions.
• DM theoretical damage rates against the actual damage rates (inspection history).
• The operational control Barriers against the asset’s operational variable table (panel and LIMS limits) and update the variable table if needed (use MOC).
• Historical time in exceedance for operational control Barriers and the resulting damage rate.
• That operational control Barriers are in place:
  • The initial value for limits should be selected such that the initial Susceptibility to Failure is “low” or “negligible”. Response time should according to ESP standards.
  • Where field instrumentation or samples are missing to form a necessary Barrier, the Barrier should be defined, but with status “absent/missing”, and must be managed.
  • Where field instrumentation is missing to monitor the Barrier control, the Barrier should be defined, but with status “compromised”, and must be addressed.
• That Cathodic Protection systems have periodic inspection and potential measurements to indicate the system health.
• That all mechanical design Barriers are within their performance standard (definition of performance standard if unavailable).
• That all mechanical design Barriers have acceptance limits for inspection (e.g., internal lining, cladding, refractory, external coating, sufficient wall thickness and absence of cracks and mechanical damage). Inspection records should be available that cover all identified DMs and assess the technical status of the Barrier. If no effective inspections have been performed in the past, the Barrier status should be “compromised” or “absent/missing”.

Define the Operation Control Barriers (Integrity Operating Windows)

The process variable, especially those related to the Operational Control Barriers, should be captured in the Integrity Operating Windows (IOWs). These variables should be measurable and controllable. The IOWs can then be used as a bases to monitor these variables for Barrier verification (Step 13). The variables to be monitored should also be captured in a proactive monitoring plan. Note: Sustained operation outside the IOW increases the Susceptibility to Failure in S-RBI.

For more information on IOW Limit Classification and Measurement Frequency see Corrosion Loops (CLs) - Theory.

IOWs and Operational Control Barriers: An operational control Barrier should be defined as a Barrier in the Degradation Management section of the CL and as controlled variable(s) in the IOW. The Barrier is the controlled value with its limits for operation. The IOW itself can be more than the controlled process value. The IOW should contain all variables that should be monitored to ensure the Barrier is effective. For Example: The Barrier against the threat, erosion, is flow control. The flow control should have an (ESP) integrity low and high limit. The IOW also includes measurements for water and sand, which determine permissible limits for the flow rate.

Threat and Barrier Overview / Degradation Management Board / CMF Records

By identifying the Threats and Barriers, an overview table (see Corrosion Loops - Theory) is created in the CL Degradation Management section. Additional information (Indicators, Actions Planned, and Barrier status) will automatically be added to the table as they become available. This overview can be used for Barrier verification, which is necessary to ensure that the Barriers (and their verification) are doing their job (i.e., managing the risk of the threat to ALARP).

Barrier Verification is an ongoing process, which should be performed regularly, and specifically when inspection results are documented (Step 13) since this updates the Barrier status Indicators. One will thus often need to return to this overview, as additional information becomes available during the Degradation Management Workflow cycles, to re-assess the Barriers.

Assign Components to the CL

The CL describes a group of Components. Thus, to completely define the CL, the related (S-RBI) Components must be assigned to the CL. Thereafter it is possible to assign the relevant DMs to the individual Components and start the risk assessment on the Component level (per DM) (Step 3).

Specific Guidance Summary

For additional information with regards to defining the CL and specific IOW parameters for Special Emphasis Components and specific DMs, refer to Guidance per Special Emphasis and Guidance per DM (see the table below).

Specific guidance summary - Defining the Corrosion Loop (including the IOWs):