Availability Vs Reliability
Availability and Reliability are the two important metrics in the world of Maintenance and Asset management which are often used interchangeably. There is always confusion between these two terms among young engineers and maintenance personnel. Understanding the difference between these two metrics can help in identifying which metric is critical to their business objectives, and tailor the maintenance strategy as per the organization’s needs.
Let’s take a deep dive into these two metrics
Availability is the duration of time that an equipment can perform its intended functions under normal operating conditions. Availability is an operations parameter.
Reliability is the probability that an equipment will perform its intended functions without any failure.
A piece of equipment that is 100% reliable can be 100% available but it cannot be the other way round.
Below are some formulas to measure Availability and reliability,
Availability = (Uptime) / (Uptime + Downtime)
Reliability can be measured using MTBF(Mean time between failure)
MTBF = (Operating time) / (No. of failures)
Let’s understand the difference between Availability & Reliability from an industrial example,
A piece of equipment is designed to operate 20 hours a day without any failure. The operation requirement in the manufacturing unit for the equipment is to run 16 hours a day.
Let’s analyse the difference in three case scenarios,
- If the Equipment runs 20 hours in a day without any failure then we can say the equipment has 100% reliability and 100% availability.
- If the Equipment runs 16 hours in a day failing two times after 8 hours of running then we can say the equipment has 80% reliability and 100% availability as it is still fulfilling the operational requirement of running 16 hours in a day.
- If the Equipment runs 12 hours a day then we can say the equipment has only 75% availability.
Hope the above example clarifies the actual difference between Availability & Reliability.
Availability and Reliability Goal setting
Many Reliability and Maintenance Managers are always in a dilemma while setting availability and reliability targets in their manufacturing units for a fiscal year. Below are some of the factors to consider while setting the targets for these two metrics,
- Customer Expectations: Customer requirement is an important factor to consider while setting the availability target. In this case, the Operations team is the customer for the Maintenance team. Hence Availability of equipment is an Operations parameter.
- SBU Objectives: The objectives of a particular Strategic business unit influence the reliability of equipment in terms of cost, quality, and failure rate.
- Equipment Criticality: The assessment of equipment reliability depends on how it affects the operations, safety, health, and the environment of a system. Hence the equipment criticality on these parameters is to be assessed before setting the reliability target.
Conclusion
Availability and Reliability will always be the key performance indicators that evaluate the success of an asset-intensive organization. Understanding the difference between these two metrics helps the maintenance personnel in identifying which metric is critical to their production unit and business objectives.
You might settle with equipment giving 75% reliability and 100% availability in a manufacturing plant where the availability and production requirement is critical and safety is not. But you cannot compromise even a 1% decline in reliability for an airplane running on a single-engine where the safety of passengers is paramount. So the next time when you make a safe journey, thank the engineers who strive to make the airplane 100% reliable.
