Condition based maintenance – a need to know basis?

What is CBM?

CBM is not a new concept, it is used in many other industries such as aeronautics and petrochemicals. Using CBM for drilling rigs is a relatively new concept and a number of drilling rig owners have implemented condition monitoring (CM) and CBM strategies to reduce costs by maintaining equipment based on measured physical condition, rather than fixed calendar-based maintenance schedules where appropriate.

Planned maintenance activities are typically assigned on a time frequency basis; however, they do not take equipment usage into consideration, and this can cause maintenance scheduling problems on rigs which have been non-operational for significant periods of time.

One of the reasons rig owners have implemented CBM is because maintenance tasks are based on measurement data, rather than fixed time schedules. CBM maximises the interval between scheduled maintenance according to the equipment’s condition and can provide an early warning of deterioration before failure, therefore avoiding unplanned downtime.

What is condition monitoring?

Condition monitoring is a maintenance activity which is used to detect potential equipment failure so that corrective action can be taken to prevent this occurring. Condition monitoring is generally used in situations where there is a reasonable probability of detecting a defect before failure of equipment occurs. Monitoring techniques typically include:

1. Equipment diagnostics
2. Vibration analysis
3. Oil analysis
4. Corrosion monitoring
5. Non-destructive testing
6. Electrical testing
7. Infrared thermography
8. Ultrasonic leak detection
9. Remote monitoring

Who supports CBM?

Condition monitoring and condition-based maintenance are recognised by ABS and DNV-GL and supported by major equipment manufacturers including National Oilwell Varco (NOV) and HMH.

NOV provides customers with its Rigsentry condition monitoring service which can be deployed on drilling and well control equipment, while HMH offers its DrillCon service to allow clients to develop a continuous class strategy. Service providers including RigQuip, IKM, and AMPS also provide a range of CBM services.

Can CBM be applied to all equipment?

It is not practical for CM/CBM to be used in all instances; therefore, the maintenance system should be designed to identify and monitor the most critical equipment with the highest frequency or probability of failure.

As a result, some rig owners have implemented maintenance strategies which are a combination of planned maintenance activities and condition-based maintenance activities. Condition monitoring is increasing being adopted on drilling and pipe handling equipment to prevent failure of safety and operationally critical equipment which has no redundancy.

Case Study 1: Fast line Sheave Bearing

During a rig reactivation project, ModuSpec identified a maintenance deficiency on a jack-up rig which had implemented CBM strategy for the drilling hoisting equipment. The identified issue could have led to significant downtime had it not been properly addressed prior to the rig commencing operations for the operator.
The crown was installed in 2016 and a category IV (5-yearly) inspection was due in 2021; however, the rig owner had recently implemented CBM on the drilling hoisting equipment. The Original Equipment Manufacturer (OEM) was subsequently instructed to conduct a condition assessment in 2020. Based on the results, the rig owner had determined that the crown was fit for continued service and rotated the assembly by 180 degrees in 2021 to minimise uneven sheave wear. In addition to rotating the crown cluster, the position of the dual deadline and fast line sheaves was also swapped.

This strategy meant that the deadline sheaves were now going to be used as the fast line sheave, and the deadline sheave bearings which had been in a static position for the previous five years were going to be subjected to high-speed rotational loads.

Vibration analysis had been carried out by the OEM on some of the sheave bearings; however, ModuSpec identified that an early-stage fault had been discovered on several of the bearings. The OEM recommended repeating the vibration measurements monthly to verify the original results, but this had not been carried out by the rig owner.
ModuSpec also identified that vibration analysis had not been carried out on deadline sheave bearings (after they had been placed in the fast line sheave position), and the OEM had not obtained any sheave wear measurements as part of the condition assessment.

Several further sets of measurements were obtained during the survey, unfortunately, these confirmed that the fast line sheave bearings were defective and needed to be replaced. This resulted in the fast line sheave being replaced only a few days before the rig was due to depart the shipyard.

On this occasion, the CBM strategy had not fulfilled its objective.

Case study 2: Misalignment between the MMS and CBM strategy

During another rig intake project, the operator wanted ModuSpec to assess how well the rig owner was managing its CBM strategy. During this assessment, ModuSpec identified several weaknesses which needed to be addressed:

1. The MMS was not aligned with the CBM strategy which meant that some equipment such as the travelling block was not being monitored.
2. Some of the CM data was unreliable due to a variety of issues including sensor faults which were not being addressed.
3. When the CM data indicated that further actions needed to be taken, there was a delay in the rig owner performing the necessary work.
4. Several of the annual NDT work orders had been closed; however not all the inspection activities had been carried out.

So, what do you need to know?
When we talk with our clients from the operator community, we tend to see that CBM is not a subject that they know much about. Which is no surprise really as CBM is still a relatively new concept and we don’t expect our clients with a drilling engineering background to know in detail what CBM is.

Here are a few pointers if you are currently operating or in the future are to likely operate with a rig utilising CBM:

1. Establish what equipment is being monitored – generally safety and operational critical equipment – it’s good to know as it will differ per rig.
2. Find out if any if any downtime is related to equipment under CBM – this could be a sign that the CM is not effective.
   
3. Ask the rig owner to provide you with information on what maintenance may be required on equipment under CBM when the rig is under contract to you, and how they plan to manage continuity of operations.
   
4. Ask the rig owner to confirm its strategy for inspecting the drilling load path equipment. Some rig owners have moved away from routinely conducting NDT techniques such as Magnetic Particle Inspection (MPI), because they have opted to conduct annual visual inspection and only carry out MPI on occasions where surface cracks are identified.
   
5. Find out which processes are in place for the analysis of measurement data and where the data is being stored on the maintenance management system.
   
6. Establish if the rig owner has sufficient levels of spare parts on the rig or onshore to support any failure of equipment under CBM.
   
   

Conclusion
The purpose of this article is to explain at a high level what CBM is and what to consider if your rig is using CBM.

It’s clear that CM and CBM has been developed to ensure that maintenance activities and repairs are planned and executed before they turn into major failures. This is dependent on all necessary measurement data being obtained by the rig maintenance crew and analysed, and that all analysis recommendations are logged in the maintenance system and addressed.

With the upturn of the industry in 2021 and positive market outlook, we see that many more rigs currently using CBM will be operating for longer periods – rig owners may look to implementing CBM as a way of improving maintenance efficiency and the bottom line.

The case study examples provided highlight the importance of asking the right questions during a rig intake.

The ModuSpec team is well versed in CBM and has, on many occasions, advised clients during a rig intake project on the effectiveness of CBM and its risks.

It’s our role to provide assurance that the equipment has been properly maintained and is in serviceable condition – in most cases this means a review of the rig owner’s maintenance strategy to verify that maintenance activities have been executed correctly.

We often find that while the CBM is effective, we identify and highlight gaps and risks where additional corrective maintenance activities may need to be completed before the rig commences operations.

So, ask the question ‘is it a need-to-know basis?’