Failure mode and effect analysis (FMEA) is one such reliability improvement tool. It was developed in 1950s and gradually fine-tuned with the advent of technology and software. Being a semi quantitative method, FMEA is widely used to predict failures of components and reduce the risk of these failures.

FMEA can be broadly classified into two categories: Design FMEA (DFMEA) and Process FMEA (PFMEA). Lubrication FMEA belongs to PFMEA and we like to confine our discussion to lubrication (or lube) FMEA. We will not go into the detailed description of FMEA. Plenty of literature is available [1-5]. Interested readers may go through these articles to have a deeper understanding on FMEA.

Concept defined & described
Rolling element bearing (or roller bearing), one of the most critical components in any machine (mining, construction, cement, large gearbox system, etc.), is taken as an example. Most common causes of roller bearing failure are well documented in literature [6], which is summarised in Table 1. We have considered the last four causes, which contribute to 80 per cent of failure.

Moreover, we have segregated ‘contamination’ in two parts: particle contamination and moisture/water contamination. Failures can be largely eliminated when these two contamination related issues are properly addressed. As our present focus is on lube FMEA, lubrication related failure modes are relevant which are discussed elsewhere [7, 8]. This is summarised in Table 2.

Next, we have conducted FMEA of roller bearing system. It is essentially a process to estimate the risk the machines are currently operating with. This is the base line ‘as is’ process and the results are appended in Table 3. Following assumptions have been made while conducting this assessment:

These assumptions are very sensible and the facilities following these practices exist in reality across the globe.

Explanation of FMEA results
While conducting FMEA in Table 3, we have assigned nine against severity. Severity will be always high because it’s not possible for any facility to afford unscheduled downtime, production loss and repair cost. Unlike severity, occurrence can vary depending on the type of failure mode. Detection would be on higher side (hard to detect), if there is no condition monitoring system in place. It is important to mention here that these numbers may vary but the team must be logically consistent to arrive at these numbers. Looking at the Table 3 more closely, we find that RPN values for the first three failure modes are not very different.

Excess lubrication (mostly in grease application) is a major problem in many facilities. Grease guns are not calibrated and maintenance team cannot tell the amount of grease delivered after a single use. Both over greasing (excess lubrication) and under greasing (insufficient lubrication) pose threats to the rotating component. That’s why its RPN value is higher than the other two failure modes. Contamination related failure modes, on the other hand, are extremely dangerous. Contaminants silently invade the system and damage the critical parts. So, RPN values for particle and fluid contamination are highest and these failure modes are extremely costly.

Our next step is to understand when the organisation takes a major decision to get rid of the current practices and implement global best practices in its facilities. Accordingly, investment in terms of money and manpower would be approved. Now, it is interesting to watch what pain and problem the particular facility in the organisation has to come across to become a world class facility. Three stages have been identified:

Respective FMEA for each stage is conducted to assess how the risk is mitigated with gradual implementation of best practices at site. These are described in Table 4-6. Again, the figures related to RPN, may be changed but in a logically consistent manner. Improvement pattern in various stages will remain same even if the numbers are changed. The results are compiled and summarised in Table 7 and the corresponding graphical presentation is shown in Figure 1. Timeline to achieve the goal (green curve in Figure 1) would be normally two to three years, but it would depend on the preparedness of the core maintenance team even if strong support and cooperation is ensured from the top level of the organisation.

Reality and remedy
Now, it’s time to leave the classroom and reach the ground reality. Let’s go to any customer’s site and assess the present conditions and work practices. In more than 95 per cent of the occasions we find the following practices:

This is the scenario in a typical site and that is hard reality. Site assessment, therefore, is necessary to understand the current conditions, to design and implement best practices which would help the maintenance team to mitigate the risk associated with the fluids as well as the machines. Continuous monitoring, periodic training and audit, continuous improvement and sustaining the new culture are also very challenging and crucial to keep pace with this new culture transformation.

Items, accessories, tools required for process modification can be classified into two types - consumable items with low investment and CAPEX items with moderate to high investment. A brief list is given below:

Summary
Although FMEA is a pseudo-quantitative technique, it works well when applied seriously. All the members of the team must arrive at the same figures during estimation of RPN. FMEA is a team activity and is consensus based. This classroom concept can be turned into knowledge judiciously when the team actually applies in the field. Process FMEA becomes necessary when existing process needs to be modified with better detection systems. Ultimate goal is to mitigate the risk the machines are operating with.

That’s why site assessment is of utmost importance. Risk of failures can be sufficiently reduced only when there is total control over the machines. The maintenance team, at any point of time, must be able to predict the condition of any machine with sufficient accuracy. Moreover, the team must attend any minor problem in the machine before it turns into major breakdown. This entire activity is essentially transformation of culture.

Achieving the goal is certainly difficult but sustaining it is even more challenging. It is a top-to-bottom approach. Strong and correct leadership from the senior management coupled with technically competent and dedicated maintenance team in the organisation can perform this seemingly impossible task.

References
1. FMEA Handbook - Ford Supplier Portalhttps://fsp.portal.covisint.com › documents › FMEA
2. https://www.moresteam.com/toolbox/fmea.cfm
3. (HTTPS://WWW.JURAN.COM/BLOG/THE-ULTIMATE-GUIDE-TO-CAUSE-AND-EFFECT-DIAGRAMS/) Guide to Failure Mode And Effect Analysis – FMEA
4. Failure Mode and Effects Analysis (FMEA)https://www.lehigh.edu – technically equivalent to SAE J – 1739
5. https://quality-one.com/pfmea/ - related to process FMEA
6. https://www.bearing-news.com/the-most-common-causes-of-bearing-failure-and-the-importance-of-bearing-lubrication
7. https://www.machinerylubrication.com/Read/17/fmea-process - FMEA process for lubrication failures
8. https://reliabilityweb.com/articles/entry/lubrication_fmea_the_big_picture/ - Lubrication FMEA – The big picture

ABOUT THE AUTHOR:
The article is authored by Dr Debasish Mukherjee, Sr Consultant, Gainwell Commosales.