Maintenance and inspection

The previous chapter discussed some of the normal operating issues to do with process facilities. This chapter describes the related topic of maintenance, where the term maintenance refers to repairing equipment that has failed or taking corrective action before the item actually does fail. Larger changes to the system are handled through the Management of Change (MOC) program-discussed in detail in Process Risk and Reliability Management. Even larger changes constitute stand-alone projects in their own right.

Keywords

Maintenance; Reliability-centered maintenance; Condition-based maintenance; Scheduled maintenance; Job Hazards Analysis; JHA; Pressure test; MAWP; Maximum allowable working pressure; Tightness test; Strength test; Cleaning; Repair; Inspection; Risk-based inspection

Chapter Outline

Introduction 25

Types of Maintenance 25

Repair Maintenance 25

Condition-Based Maintenance 25

Scheduled Maintenance 26

Reliability-Centered Maintenance 26

Maintenance Task Organization 27

Step 1-Plan the Work 27

Step 2-Conduct a JHA 29

Step 3-Issue a Work Permit 29

Step 4-Shutdown and Isolate Equipment 30

Step 5-First Break 31

Step 6-Perform the Work 31

Step 7-Close Out the Work/Permit 31

Step 8-Handover to Operations 32

Readiness review 32

Mechanical completion 32

Pressure Tests 33

Maximum Allowable Working Pressure 33

Test Medium 34

Tightness Tests 35

Strength Tests 35

Testing Procedures 36

Hydrostatic (liquid) 36

Pneumatic (gas) 36

Installing blinds 37

Pressure Test Manual 38

Online Cleaning and Repair 38

Inspection 42

Regulations and Standards 42

Inspection Frequency 43

Inspection Records 44

Risk-Based Inspection 44

Analyze risk 44

Spare Parts 45

Determine costs 45

Allocate resources 45

Introduction

The previous chapter discussed some of the operating issues to do with process facilities. This chapter describes the related topic of maintenance, where the term maintenance refers to repairing equipment that has failed or taking corrective action before the item actually does fail. Larger changes to the system are handled through the Management of Change (MOC) program-discussed in detail in Process Risk and Reliability Management. Even larger changes constitute stand-alone projects in their own right.

Also discussed in this chapter are inspection and the terms "Mechanical Completion" and "pressure test."

Types of maintenance

Maintenance work falls into one of the following four categories:

1. Repair

2. Condition-based maintenance

3. Scheduled maintenance

4. Reliability-centered maintenance (RCM)

All but the first of these can be placed in the overall category of preventive or preventative (either spelling is acceptable) maintenance.

Repair Maintenance

The most common type of maintenance is the repair of an item which has failed or which is showing imminent signs of failure. This type of maintenance tends also to be the most hazardous because there may not be much time to plan the job, and the repair work may be going on while the rest of the facility is in operation. In addition, the maintenance workers may be under pressure to get the work done quickly in order to avoid a larger system shutdown. Such pressure may lead to shortcuts being taken.

Condition-Based Maintenance

Condition-based maintenance is carried out when an equipment item starts to show early signs of failure or when its performance becomes degraded. For example, if the discharge pressure of a pump starts to fall the pump may be taken out of service and repaired before it actually fails.

Condition-based maintenance tends to be less hazardous than repair maintenance because it can be properly planned, and it can be carried out without the workers feeling that they are in a rush. Ideally, condition-based maintenance will be carried out while the unit is shut down, thus making conditions even safer for the maintenance workers.

Examples of monitoring activities that could lead to the need for condition-based maintenance include the following:

 Process performance

 Vibration analysis

 Oil analysis

 Thermography.

Scheduled Maintenance

Some equipment and instrument items are serviced on a scheduled basis, regardless of the actual performance or condition of those items. A common example of this type of maintenance is the routine replacement of lubricating and seal oils.

Table 2.1 provides an example of the maintenance schedule of an instrumentation system.

Table 2.1

Example of an Instrument Loop Maintenance Schedule

Reliability-Centered Maintenance

Reliability-centered maintenance (RCM) uses a risk-based approach to organizing maintenance activities. As such, it is analogous to risk-based inspection (RBI), a topic that is discussed later in this chapter. This approach is based on the elements of risk as shown in Equation (1.1). Those items that contribute the most to overall risk receive a higher maintenance priority than those that are considered to be less critical. (In practice, the RCM program may focus more on the consequence term than on overall risk.)

An RCM analysis is typically built around the following steps:

1. A component list is developed for the section of the facility that is being analyzed.

2. A failure analysis, possibly using the Failure Modes & Effects Analysis (FMEA) method, is carried out for each component.

3. A criticality is assigned to each failure mode.

4. A scheduled maintenance program that focuses on the high criticality items is set up. This program can be condition-based.

The RCM program should include a process for analyzing equipment failures and applying the lessons learned from those analyses such that overall risk can be reduced. The analysis can also help determine the required inventory for spare parts.

Maintenance task organization

The organization of a maintenance task can be divided into the following eight steps:

1. Plan the work

2. Conduct a risk assessment or job hazards analysis (JHA)

3. Issue a work permit and prepare tools and personnel

4. Shutdown and isolate the affected equipment

5. Make the first break

6. Perform the work

7. Close out the work and the permit

8. Handover to operations

Figure 2.1 shows an overview of the above steps.

Step 1-Plan the Work

The first step is to determine what the task is and how it is to be done. This step also means identifying and listing the affected pieces of equipment and determining what impact the maintenance work is likely to have on the overall operation. For a large, continuously operating unit, an important part of the plan is to determine what other parts of the facility will have to be shut down and to determine how those items that are to be left running are to operate during this particular maintenance task. Therefore, an isolation plan is required.

It is very important at this stage to determine if the work is truly routine maintenance, or if it falls under the scope of the MOC program.

Before maintenance work starts it is important to check that the following activities have been carried out:

 All equipment is either on site or scheduled for delivery (components should be assembled in an area adjacent to where the work is taking place).

 Piping is fabricated in advance.

 Everything is field verified and...