Buy for Maintainability

It’s often stated in reliability and maintainability training that more than 95% of the life-cycle cost of machinery and equipment is established at the time it’s constructed (see graph below). What does that mean and what should you do about it?

While you won’t pay for that cost at the time of purchase, you’ve decided about how much it will cost over the lifetime of the equipment. Purchasing departments typically get rewarded for saving on initial costs. However, acquisition cost represents only 15% to 30% of the total life-cycle cost. So, doesn’t it make sense to consider the other 70% to 85%, when deciding on new assets? This is done by “designing-in” maintainability concepts.

Some examples of principles of maintainability design from NIOSH (National Insitute for Occupational Safety and Health, Washington, cdc.gov/niosh) are:

• Maintainability should be a designed-in capability.

• Great maintenance procedures cannot overcome poor design.

• A complex design solution is often easier than a simple solution until you have to maintain it.

• Every maintenance point should be directly visible and fully accessible to the maintainer.

• All parts or components are replaced eventually; design for these eventualities.

• Do not design for the “average” or 50th-percentile person. To do so could exclude as many as 60% of the users. Design for the user population, which includes the 10th- to 90th-percentile person.

• Design maintenance and troubleshooting procedures to put the odds in the maintainer’s favor.

• To help a maintenance person remember instructions, write them down and post on the machine where he/she will make the repair decision.

• Design every interface so you can install only the correct replacement part or component correctly.

• Since the unexpected can occur at any time, ensure that you sufficiently de-rate all mechanical, electrical, hydraulic, and pneumatic systems to withstand unexpected overloads without failures, degradation in performance, or safety consequences.

• Design line-of-sight visibility for all maintenance tasks that require visual inspection, servicing, adjustment, alignment, in-place repair, or removal and replacement of components.

• Design all systems and subsystems to fail to a safe mode or state so that a component or subsystem failure will not result in additional asset damage or employee injury.

• Because it is sometimes difficult to see what is right in front of you, design all systems so that failures are obvious.

• Special tools are rarely available when maintainers need them, so design all maintenance tasks to eliminate the need for special tools.

• Design and locate all components and interfaces so that they are directly and easily accessible for maintenance.

• Because operators sometimes cause equipment failure and damage, design machines with operator-controlled systems that include emergency relief valves, overload safety devices,  and other precautionary features.

Use maintainability concepts (specific to your operation) in equipment purchasing specifications and buy-off procedures to assure you realize the full benefits of life-cycle asset management. EP

Based in Knoxville, Klaus M. Blache is director of the Reliability & Maintainability Center at the Univ. of Tennessee, and a research professor in the College of Engineering. Contact him at kblache@utk.edu.