Using Rolling Averages for IOW “Informational” Monitoring

Introduction

Integrity Operating Windows (IOWs) have a subset of operating variables that are important for degradation monitoring, but may not have direct operational controls. Per API RP 584 Integrity Operating Windows, these are known as IOW Informational Limits (IILs).

“An established limit or standard operating range for other integrity parameters that are used primarily by SME’s (e.g., process engineer, inspector, corrosion specialist, etc.) to predict and/or control the longer term integrity/reliability of the equipment. These “Informational” IOW’s are typically only tracked by the appropriate SME’s and may or may not have alarms or alerts associated with their exceedances. In some cases the Informational IOW’s are used for parameters that cannot be directly (or indirectly) controlled by operators, whose primary duty would be to make sure any exceedances are communicated to the designated SME for attention and corrective action, if any.”

These are often neglected or misunderstood by operations or technical personnel within a plant. They argue that they cannot control this variable, so should not bother monitoring or loading it into the IOW managing system. They see the variables as having limited value and which may restrict the operation or creates noisy limit flags. In this article, we will try and explain the value of the IIL, and a process by which to better analyze the parameters to capture changes to the degradation exposure and avoid noisy limit responses.

Management of Change

It has been the author’s experience in participating in many reliability incident investigations that drifting changes in operating conditions have often led to increased degradation that may be subtle (corrosion rate increases) or dramatic (wet chloride salt formation threshold). Feed changes, operational rate creep, stripping rate changes and process routing are just some examples that may have significant degradation impact. The fact that these changes have been made without a thorough Management of Change assessment is often due to a lack of understanding of the impact of the change, and a lack of an IIL that if in place would have identified the potential impact of the change. A thorough corrosion degradation review of an operating unit by a Subject Matter Expert (SME) should include identification of operating conditions that can impact and change the degradation exposures through the unit. The identification of the critical and standard IOW type limits are typically “low hanging fruit,” easy to identify, and easy to obtain operational support for.