PAT System Reliability

Site-Wide Analyzer System Reliability Requirements

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By Gary D. Nichols, PE

In the previous article in this series, (Process Analyzer Reliability, Maintenance & Service), we devoted most of the time to preparing to incorporate a new analyzer system into an existing site and into an existing computerized maintenance database (CMMS) correctly (see Patton below); we discussed little about the site or its reliability/maintenance organization.

For this discussion, we shall assume that the manufacturing site includes several operating/production units and a mixture of chromatographic, photometric, environmental and special process analyzer systems housed in an assortment of analyzer shelters and three-sided enclosures, and field-mounted. We shall further assume that an analyzer system maintenance and reliability organization exists, comprised of a supervisor, several analyzer system technicians and perhaps a maintenance planner.  Finally we shall assume that spare analyzer parts are ordered automatically, as they are used by the analyzer technician in the field and attributed as a cost against the respective analyzer.

As early as 1971 (See Upfold below), and reprinted in 1994 (See Dailey below), Table I shows what was believed to be typical analyzer technician service time requirements for various types of process analyzer systems. The reader may divide the annual time requirement in Table I by 52 to obtain the approximate weekly time requirement per analyzer type. Table I is reproduced here for convenience, but the reader is advised to generate his own maintenance data from actual maintenance and service times when embarking upon an effort to assign analyzer technician responsibilities to individual analyzer systems and analyzer system groups.

TABLE I: Man-Hours per Year for Analyzer System Types in 1971, Republished in 1994

Analyzer System Type 

Mean (MH/year)

Range (MH/year) 

Standard Deviation (MH/year)

Boiling Point 

80

74-85

4.82

Gas Chromatograph 

145

130-170

2.5

Combustibles

50

44-61

3.74

Infrared 

76

62-94

5.69

Oxygen 

38

35-42

2.3

pH 

29

20-40

6.21

Refractive Index 

40

33-49

6.31

Ultraviolet

59

42-78

6.00

 

If data such as that in Table I is customized for the site, we can obtain an approximate picture of how many analyzer system technicians are required to service and maintain all of the analyzer systems on site reliably.

We say “approximate” because some analyzer systems of the types noted in Table I may require more or less attention than others due to the sample in which they are placed, e.g., clean gas, clean liquid, two-phase, tarry liquid, liquid or gas with suspended solids, etc.

Analyzer system service time is not only affected by the complexity of the analyzer system and the difficulty of the sample, but also by the levels of training, experience, breadth of responsibilities, management support, union rules, system for obtaining spare parts and prevailing conditions of the analyzer systems. Training, experience and breadth of responsibilities apply to supervision as well as to analyzer technicians.

Analyzer technicians are typically assigned geographically, that is, an analyzer technician is assigned to maintain all the analyzer systems within the battery limits of one or more operating units, based on the number of analyzer systems and complexity within the unit(s).  Analyzer technician assignment by geography has the distinct advantages of permitting camaraderie and cooperation between the analyzer technician and operating personnel, greater analyzer technician familiarity with unit MoCs, task-specific safety procedures, unit safety procedures, control system and associated alarms, emergency procedures, unit operating chemistry and unit personnel hazards.

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