What is a scheduled discard task?
A scheduled discard task involves replacing a specific part or component of a piece of equipment at regular time intervals, regardless of its performance quality.
Most of us perform scheduled discard tasks in our personal lives such as changing the oil in our cars every 3,000 miles or replacing our furnace filter twice a year. Certain components or parts of machines or mechanical systems must be replaced regularly to optimize the performance of the equipment and extend the overall life of the machine.
This is also true for a wide variety of machines and equipment in facilities and businesses. Scheduled discard tasks are a regular part of a good preventive maintenance plan which ensures that equipment performs optimally at all times.
Manufacturing companies or other businesses that run production lines will scheduled discard tasks on key pieces of equipment and machines. Construction, logistics, or transportation firms perform scheduled discard tasks on their vehicles, machines, and equipment. Municipalities require these tasks to keep their building systems and street cleaning or snow removal equipment in good working order.
Example of a scheduled discard task
Industrial gearboxes are commonly used in a wide variety of facilities. This enclosed system transmits mechanical energy and can change its torque or speed to convert that raw energy into usable energy.
When evaluating a piece of equipment such as an industrial gearbox, maintenance managers must consider safety, operational, and economic consequences of malfunctions. In this case, bearings, gears, washers, and shafts can wear down and cause overheating or seal failure.
One scheduled discard task, as part of an overall preventive maintenance program, would be changing the oil. To make the frequency decision, a maintenance manager needs to consider the economic ramifications for the change and weigh them against the potential malfunction for not performing the discard task.
Small gearboxes that use half a liter of oil may benefit from a scheduled discard of oil where a large gearbox, which could hold up to 400 liters of oil, may warrant oil testing before a discard task is scheduled.
How discard tasks are scheduled
Before scheduling discard tasks in a CMMS, a maintenance manager must systematically consider a particular asset’s functions, areas for potential failures, and the likely reasons for those potential failures. Scheduled discard tasks are often called life-limit tasks because some component of the system has reached the end of its dependable life.
Safety considerations and risks, as well as economic considerations, must be taken into account to determine when to schedule a discard task. For example, if a scheduled discard activity can significantly reduce the chance of a workplace accident or injury, and if the discard activity is inexpensive and easy to implement, it should be clear to proceed. However, if a scheduled discard task does not impact employee safety and is costly to implement, the cost of production downtime resulting from a malfunction should be analyzed.
When the decision is made based on safety, this is often called a safe-life limit and usually involves a single part being discarded before its maximum age. A part manufacturer establishes this safe-life limit based on developmental testing and research conducted during the manufacturing process. If a part has a critical impact on safety, it is first manufactured to last a long time and then tested in real-life conditions. Some fraction of the actual life span of the part is then selected as the safe-limit life.
When a decision is made based on economic considerations, the item to be replaced must not have safety consequences for failure. Maintenance managers must determine the point when the chance of equipment failure increases rapidly and select a period before then when the majority of equipment is still operational.
Once that evaluation has been completed, discard tasks, as well as other preventive maintenance activities, must be identified and scheduled to maximize asset management activities and prioritize technician workload and resources.