Achieving 96.7% mechanical reliability for a chemical plant.

Our client, a global manufacturer and marketer of differentiated chemicals, wanted a dynamic way to determine when and where to expect in-service deterioration. The solution also needed to effectively predict corrosion under insulation (CUI) damage, chloride stress corrosion cracking and other damage mechanisms. Other objectives were also key.

The solution had to support our client’s fitness for service evaluations and provide a maintenance strategy that would ensure safety, equipment reliability and uptime were delivered, while reducing cost.

We implemented our fully integrated risk-based inspection (RBI) software package, Reliability Based Mechanical Integrity (RBMI), into our client’s operations to meet the project’s objectives. This involved over 11,000 plant equipment items, from fixed vessels and relief devices through to piping circuits across multiple process units. The project ran over 32 months, including urgent non-destructive examination (NDE) inspections following inspection planning review. These were required before a pending turnaround.

• The project involved data collection, reviewing inspection histories, corrosion studies, criticality analyses and prioritised NDE inspections.

• The corrosion study provided key inputs for the RBMI programme, including potential damage mechanisms, corrosion types, corrosion rates and predictable or potential locations, as well as flow considerations to allow inspectable risk to be calculated.

• We used a cumulative risk curve to illustrate a process unit’s overall risk by assets or risks by different damage mechanisms.

• Corrosion under insulation (CUI) prediction found pitting, nozzle thinning and chloride stress corrosion cracking (CSSC). 

• We identified that the contribution to cumulative risk for the example exchanger alone was almost half the risk of the all the assets associated with this process unit.

• The majority of risk was due to NO inspections previously conducted for CSSC as a damage mechanism for this asset. 

• A number of exchangers showed high risk for CSSC.

The potential for CSSC was determined from the corrosion study and made urgent by the criticality models for likelihood and consequence in the RBMI software.

Insight

Risk-based inspection is a systematic process for factoring risk into decisions concerning how, where and when to inspect a process plant. RBI focuses inspection resources on the highest priority equipment to determine asset integrity.

An RBI programme’s greatest contribution is to effectively managing plant risk and improving reliability. A properly designed and implemented programme will refocus an inspection plan to manage the risk contribution from all of the damage mechanisms by making sure the proper inspection tasks are performed on each piece of equipment. It will also eliminate inspection activities that do not make a contribution to a risk reduction.

• RBI cost effectively helps make process plants safer and more reliable. 

• Compared with a typical inspection programme, RBI programmes can reduce both the risk in an operating unit, as well as inspection costs.

• RBI programmes can reduce the overall costs of the inspection programme, affecting both turnaround and on-stream inspection activities.

We helped our client improve its ability to identify damage mechanisms, resulting in prioritised inspection strategies. The work eliminated inspection activities that did not make a contribution to a risk reduction.

• Prioritised inspections revealed no damage in the asset, meaning a reduction in risk of over 70%.

• Focusing inspections on the higher criticality items led to a cumulative risk reduction of 80%.

• Our client achieved 96.7% asset mechanical reliability, a significant improvement.

Repairing and replacing the damaged exchangers further reduced the risk dramatically to the facility. In addition, the significant findings in CUI and CSCC as a result of the RBMI study delivered significant value in avoiding lost production.

Business benefits

• Systematic application of risk-based inspection to all equipment types.

• Carefully defined steps to improve plant performance.

• Optimised inspection, test and maintenance work.

• Eliminated unplanned equipment downtime.

• Continuously improving equipment reliability. 

• Improved performance metrics.

• Reduced costs.

• Enhanced community safety, personnel safety and environmental protection, while simultaneously improving equipment integrity and reliability.