ServicePRO - A combination of Preventive Maintenance and Reliability Centered Maintenance Part 1

Introduction

This document provides a method and gives two example of how cross direction (CD) control actuator systems best practice preventive maintenance (PM) tasks and their content can be determined for use in ABB’s new ServicePRO tool. The method may be applied to other equipment.

Following a brief Background description there are three main sections. The first summarizes preventive maintenance theory in general including approaches for determining PM tasks and content.

The second focuses on CD actuator systems and the aspects they all have in common. It uses those aspects and PM theory to develop a method for determining best practice PM. It identifies required content information for all the tasks, regardless of actuator type or where its information resides.

In the Part 2 of the Series , the third section develops task lists for Smart Weight Profiler (SWP) and Slice xP (SxP) actuators. These two cases are interesting as useful information exists for both but it differs in nature. SWP is more developed for PM practices due to the product’s age and extent of proliferation. SxP is relatively new on the market and well documented from a product perspective but not yet refined over time by any extensive PM practices in the field.

Background

ABB ServicePRO tool owners requested a review of tasks listed in the tool for PM of paper machine cross direction (CD) actuator system to ensure best practice. First steps in making the tool most effective are:

1. Determining best practice ServicePRO PM tasks for two initial actuator systems, SWP and SxP
2. Recommending task content requirements for CD actuators in general

Task lists and content requirements can be developed based on inputs from product data, experienced engineers, service advisors, web search materials, engineering handbooks and text books. There is considerable expertise and body of knowledge on this subject both from a generalized aspect and specific to each CD actuator system available.

In reviewing available material and interviewing service experts it became apparent that a generalized procedure for developing best practice preventive maintenance for paper machine actuator systems could be applied not only to all CD actuators but many complex automation and power systems by following proven practices available in literature and basing them on the information and expertise available for a specific machine. As such the only difference between cell phone PM and space shuttle PM is level of detail.

Level of detail is extremely important in that either too little or too much can result in the failure of any structured preventive maintenance program. Fortunately for CD actuator systems there are several good models and considerable experience that can be used to arrive at a level of detail suitable for these type systems.

Reliability - General method and content for PM
Types of maintenance
ServicePRO preventive maintenance is care and servicing for the purpose of maintaining equipment in satisfactory operating condition by systematic inspection, detection, and correction of incipient failures either before they occur or before they develop into major defects. Preventive Maintenance is conducted to keep equipment working and/or extend the life of the equipment. This includes tests, measurements, adjustments, and parts replacement, performed specifically to prevent faults from occurring.

Corrective maintenance (CM), sometimes called "repair", is conducted to get equipment working again after faults have occurred. The ideal preventive maintenance program would prevent all equipment failure before it occurs. There are external non-system sources that can cause failure of a specific system being maintained. An example would be an historical case where contamination in compressed air supplied to a pneumatic actuator system caused multiple failures. It is important to distinguish non-system Corrective Maintenance that may be required for specific equipment being maintained from Corrective Maintenance required on the equipment or system itself. System incidences vs. non-system incidences data is collected in the ServicePRO tool.

Common methods of determining what Preventive Maintenance procedures should be applied are; original designer’s recommendations, requirements of codes and legislation within a jurisdiction, subject matter expert recommendations, or the maintenance that's already done to similar equipment. In military, aerospace and some industry reliability-centered maintenance provides the most rigorous method to determine applicable and effective failure management policies for a system or machine.

Reliability-centered maintenance
RCM is focused on identifying and establishing operational, maintenance, and capital improvement policies that will manage the risks of equipment failure most effectively. It’s defined by technical standard SAE JA1011, Evaluation Criteria for RCM Processes, which specifies that RCM address seven questions:

1. What is the machine supposed to do?
2. In what ways can it fail to provide the required functions?
3. What are the events that cause each failure?
4. What happens?
5. Why does it matter?
6. What systematic task can be performed proactively to prevent, or diminish to a satisfactory degree, the consequences of the failure?
7. What must be done if a suitable preventive task cannot be found?

In the case of CD actuators much of these seven questions are answered by experience or existing data. For the purposes of ServicePRO the key question is number 6: What systematic task can be performed proactively to prevent, or to diminish to a satisfactory degree, the consequences of failure?

In Reliability-Centered Maintenance important functions to preserve with routine maintenance are identified, their dominant failure modes and causes determined and the consequences of failure ascertained. Levels of criticality are assigned to the consequences of failure. Some functions are not critical and are left to "run to failure" while other functions must be preserved at all cost. Maintenance tasks are selected that address the dominant failure causes.
This process directly addresses maintenance preventable failures. Failures caused by unlikely events, non-predictable acts of nature, etc. will usually receive no action provided their risk (combination of severity and frequency) is trivial (or at least tolerable). When the risk of such failures is very high, RCM encourages the user to consider changing something which will reduce the risk to a tolerable level.

ServicePRO is kept live for change improvement throughout the life of machinery, where the effectiveness of maintenance is under constant review and adjusted in light of experience gained. For example monthly reviews of Preventive Maintenance, Corrective Maintenance, non-system and system incidences in the case of CD actuators has resulted in changes to utilities sourced by the system such as air, water and power

RCM offers specific criteria for a system that presents a specific risk when it fails. Some are technical in nature (can the proposed task detect the condition it needs to detect? does the equipment actually wear out, with use?). Others are goal-oriented (is it reasonably likely that the proposed task and frequency will reduce the risk to a tolerable level?).

The result is a maintenance program that focuses scarce economic resources on those items that would cause the most disruption if they were to fail. RCM emphasizes the use of predictive maintenance techniques in addition to traditional preventive measures.

Application of maintenance theory to CD actuators
For the purposes of determining best practice Preventive Maintenance for CD actuators the tenets of Preventive Maintenance and RCM may be applied. Experience, existing data and practicality strongly suggest each ServicePRO task be reduced to the lowest common denominator activity level possible such as go-no go, measurement within limits or lubrication or replacement of specific parts.

ABB service of quality control systems (QCS) on paper making machines including CD actuators has shown implementing a structured PM program based on the best judgment of product designers and field engineers dropped Corrective Maintenance incidences or mean time between failures (MTBF) and mean time to repair (MTTR) dramatically. At one site quarterly averages of call ins per week went from five to seven to less than two including some weeks with no call ins. Not only does this make the field engineer more effective but expensive production downtime is reduced.

The RCM practice of keeping the effectiveness of maintenance under constant review and making adjustments based on experience lends itself to capability of the ServicePRO tool for data gathering and analysis. Keeping PM procedures live for the purposes of continual improvement over time was in practice long before RCM was originally introduced for the purpose of increasing airworthiness of jetliners.

Metrics
With regard to uptime or overall equipment effectiveness (OEE) it is well known a good maintenance program should reduce the number and intensity of breakdowns to the point where 5 to 15% of system maintenance effort is devoted to breakdowns requiring Corrective Maintenance. World class programs in some cases achieve CM less than 5% of system maintenance. Without a good Preventive Maintenance program breakdowns requiring Corrective Maintenance frequently account for 75% or more of total maintenance effort. Metrics required for evaluating the effectiveness of service programs exists in ServicePRO.

Next - Best Practice ServicePRO tasks for CD Actuator Systems