How to use RBI results to develop an effective OSI and T&I Program

What is OSI?

OSI (On-stream Inspection) is where a pressure boundary examination is done from the outside of pipe systems while they are in operation utilizing NDE techniques to determine the pressure boundary’s suitability for ongoing operation.

OSI Optimization Approach:

Originally, while establishing a new OSI operation, Corrosion Loops were designed to help in identifying possible damage causes and expected corrosion rates. API 571-compliant damage mechanisms are discovered and a risk assessment is conducted.

The assignment of CML number, location, and NDT type is based on the risk ranking, corrosion class and susceptible damage mechanism identified from the developed corrosion loops as per API 510 and API 570 for CML assignation.

The risk ranking result for each asset is the basis for selecting  the locations and numbers of CMLs to be assigned. Risk categories range from High, Medium-High, Medium and Low for each equipment and piping system and this ranking provides the decision tools about the appropriate number and location of CMLs. A change in risk ranking following greening necessitates a review and update of existing monitoring locations.

CMLs are used to show the pipe system on isometric drawings. All CMLs are properly placed in the efficient inspection. Integrity Operating Windows are defined for valuable assets based on possible damage mechanisms, and the number of CMLs is raised when process circumstances deviate from specified limits.

The Generic inspection drawings for each type of equipment and piping system are prepared to identify applicable NDT techniques along with percentage coverage by each technique. The inspection techniques, locations, and inspection intervals are chosen based on the service, MOC, and type of equipment. ,

The straight portion of the pipe is also chosen for the NDT application at several points to assess the condition of the pipe, which may be affected by GTP (General Thinning and Pitting) and other cracking damage mechanisms. The same method is used for other static equipment and different types of generic inspection sketches are prepared for equipment and piping systems.

The OSI program is not a conceptual model; It will evolve in response to changes in the corrosion profile of the equipment. These modifications will be reflected in the number, position, and NDT techniques of CMLs assigned to each component. The corrosion and Inspection unit must conduct a yearly thorough assessment of the OSI program to fine-tune the number and placement of CMLs based on the findings of the previous inspection.

Following figure-1 shows the OSI Optimization Work Proceedings flow chart:

What is T&I?

T&I is a thorough inspection and testing in which inspections are performed by plant inspectors to ensure the mechanical integrity, operation, and safety of the plant/structure.

T&I Approach:

After new or rebuilt equipment has been in service for a specified period of time, initial T&I is performed.

Also, T&I is performed to establish baseline data about the asset after inspecting it internally for expected or unexpected corrosion, fouling, possible construction debris, internal coating/lining deterioration, the effect of chemical injection, and mechanical damage. T&I intervals and next T & I dates are determined based on equipment service condition, operating experience, and risk ranking results from risk assessment.

Unexpected deterioration due to process upsets and wet lay-ups requires early inspections to be performed. After performing the OSI, corrosion rates are available along with condition monitoring information which can be used to check the remaining life of equipment, and T&I intervals are updated based on available data.

After the equipment has been inspected internally, the Inspection’s findings become the best basis for determining the new inspection frequency. Also, the operational and repair history of equipment under similar process conditions are reviewed as this data is an accurate indicator of the required T&I interval.

Risk assessment results are used to prepare a simplified guide that can be used to effectively manage the corrosion threats to assets and subsequent effective inspection techniques along with inspection intervals. This reduces the company’s corrosion costs by predicting and preventing failures and increasing plant availability.