In this competitive era of industry, many companies try to increase their productivity by conducting several methods such as reducing equipment downtime. To be able to compete, spare parts availability is one of the critical aspects in a company. The equipment downtime can be reduced when the spares needed for repairing are available. On the other hand, if the spares are not available, the company has to wait for a certain length of time which results in production losses. According to Information Science Consultants, approximately half of the inventory value may consists of spare parts which are used at the rate of one per year, and parts which have inventory value of 10%-30% can sit on store’s shelves for 25 year plant lifetime. By looking at this in the financial perspective, the company should have never purchased these parts.
To overcome this problem, Reliability Centered Spares (RCS) is used to find the optimum level of spare parts in the inventory based on the equipment requirement and maintenance operation. To examine the RCS, Reliability Centered Maintenance (RCM) process is conducted by understanding the potential failure mode and the effects of failure as well as the effects of part unavailability, and then developing the predictive and preventive maintenance strategy. After obtaining the information, the company can decide which spare parts are needed in inventory and which can be ordered as needed. The information flow of this process can be seen in the figure below :
To implement RCS, there are five questions that must be answered sequentially, which are:
The first question is answered through RCM analysis. The team who performs RCM contains of people that have a good knowledge of the equipment and the consequences of the downtime, thus this team able to provide good data about downtime costs of the equipment, failure rates and redundancy structure of the equipment.
In the second question, RCS bases the decision of stockholding on the effect if no spare is available. This step makes it easier to decide whether the consequence of stock out matters. Basically there are five categories of consequences, which are:
- Hidden (Increased Risk): failure or stock out has no direct impact but we may expose to an increased risk from another failure.
- Safety: failure or stock out has direct impact which could result in injury or death.
- Environmental: failure or stock out has direct impact that could lead to the breach of an environmental standard or regulation.
- Operational: failure or stock out results in the loss of production
- Non-operational: failure or stock out leads to the expense of repair or purchasing parts.
The third question considers whether we can anticipate the need of spare part and plan the requirement. In reality, some parts can fail randomly without any signs that a breakdown is about to occur. However, the requirements can be anticipated for parts replaced during overhaul or replacement routine and parts which are subject to condition monitoring.
Fourth question covers the condition where it is not possible to anticipate spares requirement. When this condition occurs, RCS analyze the performance standard which depends on the impact of stock out to determine number of spares needed. Here is the table which consists of performance standard from each category :
In most of the cases, stock out has the consequences on operations even if the stock out has safety or environmental consequence thus RCS uses through-life costing method to determine number of spares needed. Finally, the last question asks about how the company would respond if the forecasted number are wrong and the company has unexpected stock out of critical spares.
RCS might sounds very simple and beneficial, but it also has some problems. Even the company with high standard of maintenance sometimes finds that the maintenance plans are not well documented or not well developed. Often, the company holds spares but they don’t know in which equipment and where to use the spares. Sometimes, the bill of materials are not well documented or well developed. Moreover, RCS not yet consider the supply constraint in its process. Therefore, to implement RCS the company should have more preparation and combine it with a more complete framework.
- An Introduction to Reliability-Centered Spares. (2009). [PDF] Lechlade: Information Science Consultants, pp.2-8. Available at: http://www.relogica.com/main/readpapers/7 [Accessed 23 Nov. 2016].
- Jaarsveld, W. and Dekker, R. (2010). Integrating Reliability Centered Maintenance and Spare Parts Stock Control. [PDF] Rotterdam: Econometric institute, Erasmus University Rotterdam, p.4. Available at: http://repub.eur.nl/pub/18590/EI2010-16.pdf [Accessed 22 Nov. 2016].
- Slater, P. (2016). The What, Why and How of the Reliability Centered Spares (RCS) Process. [PDF] pp.1–8. Available at: http://textlab.io/doc/9088170/the-what–why-and-how-of-the-reliability-centered-spares-… [Accessed 22 Nov. 2016].