What is maintainability?
Maintainability is one of the key concepts for equipment manufacturers, operators, and asset managers. In its simplest form, maintainability means “ease of doing maintenance”.
An easy way to define maintainability is through an event of a flat automobile tire. It is no coincidence that spare tires can be fitted at all tire locations and that automobile manufacturers provide bolts on each tire that can be tightened and loosened with the same wrench size.
Asset management professionals, responsible for the smooth operation of complicated and critical machinery in all sorts of industries and service sectors, are faced with a similar situation whenever an asset is down for unplanned or scheduled maintenance.
The focus is to get the equipment up and running as quickly as possible, with the lowest possible cost incurred on maintenance. The easier it is to perform repairs and maintenance on an asset, the higher its maintainability.
The concepts of reliability, availability, and maintainability are closely related, and together they equip asset managers with the tools to evaluate the performance of any asset management program.
The concept of RAM: Reliability, Availability, and Maintainability
The acronym RAM combines the three technical terms to signify a framework in which the assets are designed and operated using best practices to minimize downtime and life cycle costs.
That aforementioned framework is used to conduct RAM analysis where:
- Reliability is the probability of an asset to perform its desired function under predetermined conditions for a set amount of time. Reliability defines the failure frequency and determines the uptime patterns. It is often measured through the mean time between failures (MTBF).
- Maintainability describes how soon the unit/system can be repaired, which determines the downtime patterns. It can be quantified using the mean time to repair (MTTR). The lower the MTTR, the higher will be the maintainability of the asset.
- Availability represents the percentage of uptime over a specific time period. It is determined by reliability and maintainability. Since it considers system running time and downtime, both MTBF and MTTR are a part of its calculation.
In general, RAM studies are used as a tool for assessing a production system’s capabilities. Hence, any facility that relies on physical assets can use it to optimize operational performance.
Can we track and measure maintainability?
An important metric to gauge maintainability is the cost spent on maintaining an asset. Maintenance cost as a percentage of replacement asset value (RAV) is usually monitored to ensure that the costs are within the ranges obtained from the industry benchmark. Lower maintenance cost spent on an asset implies higher maintainability.
From the above discussions, it is evident that high maintainability is signified by low MTTR and low maintenance costs.
To ensure that an asset has the desired levels of maintainability, a thorough maintainability analysis is necessary for the design phase of the equipment. It involves considerations such as:
- Using readily available materials and components
- Utilizing standard fitting and bolting connections
- Enabling fault identification
- Ensuring the ease of assembly and disassembly
These considerations are discussed in detail in the next section.
Design for maintainability
There are several standards, best practices, and maintainability requirements that can be followed to ensure an asset is highly maintainable. Most of these guidelines can be broadly grouped under the following six categories.
Instead of using multiple different types of parts and components, it is recommended to minimize variety among parts in order to minimize inventory, tooling, and training requirements.
A common implementation of this rule is the use of standard USB connections in electronic devices. One USB port can be used to connect (or charge) a variety of different computer accessories with absolutely no compromises in functionality.
The practice of standardization is commonly employed in the industrial space to minimize the types and sizes of bolts and fasteners within any asset assembly. This has obvious benefits as discussed earlier in the article.
In practice, designers can achieve this objective by increasing the number of bolts and screws, wherever possible, for additional strength – instead of increasing the diameter and size of the fastener.
Modularization refers to designing complicated machines from smaller building blocks (modules or sub-assemblies) so that each block can be maintained independently of each other. This improves maintainability in the following ways:
- By facilitating easy disassembly and reassembly of the machines, thus improving the accessibility to the part requiring maintenance or replacement.
- It is often more cost-effective to replace the sub-assembly rather than repair the damaged part. The damaged assembly can later be repaired and used as a spare. These practices significantly decrease MTTR for any asset.
- System-level upgrades are usually possible by upgrading one or more sub-assemblies rather than changing the entire equipment.
A simple blender machine is a good example of modularity. The base which houses the driving motor is designed to separate from the jars which are easily removable and replaceable if blades get damaged (or you are more interested in grinding spices rather than blending smoothies).
All electronics around us – from laptops to smartphones – employ modularization principles allowing quick maintenance by replacing broken screens, burnt-out hard drives, etc.
In power industries, turbine rotors are designed such that turbine blades get assembled over turbine wheels, which in turn are fitted onto the rotor shaft. This allows easy replacement of damaged blades and, at times, upgrading of turbine rotor by installing more efficient blade designs.
Using commonly available generic components rather than custom-fit parts enables the end-user to use alternate spares from the market if original spares are not available or have longer lead times. In essence, it is an easily achievable optimization of maintenance activities.
A common example is the use of standard bearing sizes in pumps and other machinery. Bearings are manufactured to standard sizes by most of the popular bearing manufacturers. If an SKF bearing is damaged and a replacement is not available locally, it is usually possible to look for a similar bearing from FAG catalogue and use that one instead.
4) Malfunction annunciation
Whenever an asset is not performing its desired function, this faulty condition of the asset should be obvious to the operator in real-time, so that the required maintenance task can be planned and undertaken before a catastrophic failure occurs.
For example, the temperature gauge in a car will inform the driver about early signs of engine overheating so that corrective action can be taken in time.
Complicated machinery in heavy industries (process chemical, power, manufacturing, etc.) has elaborate systems of monitoring installed on them. These systems include temperature sensors, pressure sensors, vibration monitoring devices, and other condition-monitoring equipment that is used as a part of CBM and/or predictive maintenance.
Any deviation from the set limits raises alarms to the operator who can then take necessary action and notify relevant personnel. They can use that info for the allocation of the required resources and for scheduling maintenance work, usually through a computerized maintenance management system (CMMS).
5) Fault isolation
Whenever an asset breaks down or malfunctions, the first step is to diagnose the root cause of the problem. If the root cause is not obvious, a lot of effort (and hence time and cost) goes into the inspection and diagnosis of the faulty component.
This wastage of time and resources can be easily avoided by incorporating design features that limit the influence of human factors, make the issue obvious, and consequently simplify the necessary corrective maintenance.
For example, most electronic home appliances (like washing machines and dishwashers) show an error code for commonly occurring issues and/or failure modes.
Error code E1 will tell you that the discharge pipe of the washing machine is blocked. You can resolve the issue by readjusting the pipe and removing the source of the blockage. What happens when an ‘unknown error’ code is displayed? A significant amount of time and money has to be spent on bringing in a technician who can troubleshoot and repair the issue.
It was mentioned in the previous section that monitoring systems are installed on machinery for fault detection. While a high vibration signal can tell the operator that something is wrong with the machine, a detailed analysis of the vibration signal can then allow a trained vibration diagnostic engineer to exactly identify the part or component which needs maintenance (or replacement).
In absence of such a monitoring system, a costly and time-consuming hit-and-trial strategy shall be adopted – decreasing the maintainability of the asset in the process.
6) Identification and tagging
Assets, equipment, assemblies, and sub-assemblies should be identifiable from each other to facilitate communication and record-keeping. Asset operators achieve this by assigning unique and meaningful tags to assets and components.
For instance, heat exchangers are assigned an alphanumeric tag starting with the letter ‘E’ and followed by dashes and numbers. Similarly, pumps can be assigned tags in the sequence of ‘P-XXX’ etc. Components within equipment are given specific part numbers by the manufacturer so that queries can be made regarding the specific parts without any confusion.
Asset management professionals utilize this elaborate system of identification to improve maintainability in a variety of different ways.
Assigning unique part numbers ensures that correct parts are arranged for a maintenance job avoiding unnecessary downtimes. Equipment-specific historical records and maintenance instructions can be made readily available (usually through a CMMS) using the equipment tagging system which helps maintenance personnel identify the right asset during on-field activities.
Other ways for improving maintainability
Purchasing assets that are easy to maintain is an important factor to consider during the procurement process. After all, you don’t have a say in how the equipment is designed.
But there are maintainability aspects you do have some control over. There are several small improvements you can make to simplify maintenance work on complex assets. You should:
- Provide quick access to preventive maintenance checklists, drawings, logs, and procedures. The easiest way to do that is to store them in a CMMS database. Technicians and mechanics can just open their mobile CMMS app and pull up the required resource.
- Upskill maintenance workers and operators. Even a simple task can be hard for untrained hands. The maintenance department should ensure adequate maintenance training, especially if new requirements are set in motion.
- Standardize equipment and MRO inventory. The organization should try to stick with the same types of equipment and tools (when possible and appropriate) to minimize the need for additional training and misuse.
- Standardize routine work. One way to reduce operating and maintenance costs is by increasing employee productivity and reducing the number of human errors. Alongside training programs, standardizing operating procedures is the way to do that.
- Focus on proactive maintenance. More proactive maintenance leads to fewer major breakdowns, which require significantly more resources and skill to address.
These small changes can make a big difference in the long run.
The primary focus of any maintenance professional is to ensure that the equipment performs the desired function with minimum interruption.
The key to achieving this objective is to follow best practices in regard to asset reliability and maintainability. Maintainability, or “ease of maintenance”, can be monitored through metrics such as mean time to repair (MTTR) and maintenance cost per replacement asset value.
Assets can be designed to achieve a higher level of maintainability by ensuring the use of standardized components and assemblies, employing block-wise or modular designs, enabling simple fault detection techniques, and utilizing identification and tagging systems.
To top it all off, maintenance and plant managers should consider implementing CMMS software to simplify the execution of maintenance work and indirectly improve the maintainability of their facility.