Principal Research Results

Rationalization of the Inspection for a Spillway Radial Gate based on
the Maintenance History Record
Background
Maintenance cost reduction of power facilities is widely needed due to the change in the business environment that surrounds the electric enterprise. Thus, maintenance rationalization to deal with progressive deterioration of old facilities is discussed especially in thermal power and nuclear power maintenance sections. On the other hand, since the deterioration speed for civil engineering facilities is slower than that for other facilities including electric equipment in general, it is difficult to collect damage history datathat can quantitatively analyze the deterioration frequency for them. Therefore, Attention is paid to a maintenance rationalization
methodology called Reliability Centered Maintenance (RCM) ＊ 1 whose theory focuses on qualitative analysis.

Objectives
The purpose of this research is to propose a maintenance rationalization support system based on RCM that mainly targets
civil engineering facilities and to demonstrate its applicability using an actual spillway radial gate.

Principal Results
1. Summary of the proposed system
The proposed system consists of two analytical stages; qualitative and quantitative (Figure 1). In qualitative analysis basedon RCM, the following three rationalization points of view are discussed and reasonable rationalization alternatives that can be applied
are selected: (1) Change in maintenance policy, (2) Rationalization of the inspection work, and (3) Change in repair, renewal andpainting criteria. On the other hand, the quantitative analysis using the maintenance history data is performed in order to evaluate thereliability and cost-effectiveness of the maintenance rationalization alternatives. As a result, the facility manager can reasonably selectan optimum alternative for the maintenance rationalization which fills a limited budget.
2. Discussion of the applicability of the proposed system (application to an actual spillway radial gate)
The proposed method was applied to an existing spillway radial gate (Figure-2). In the qualitative analysis, it was shownthat the postponement of the inspection interval is one of the reasonable rationalization alternatives for the target gate. Based on thequantitative analysis using maintenance history records of repair, renewal and repainting from 1957 to 1997 for the same type of targetgate, average availability ＊ 2 was estimated. As a result,we demonstrated that average availability (the decreasing rate is within 5%) isless affected by the change of the inspection interval from once/0.5 years to once /two years (Figure-3). It was also shown that when
the inspection interval was fixed to once/two years, annual expected total cost (=inspection cost + expected damage cost) becomesminimum (Figure-4).
On the basis of the above results, we suggested that the inspection interval for the all components of the target gate should
be changed from once /0.5 years to once/a year.

Future Developments
We will accumulate the maintenance history data while increasing the application examples of the proposed system.
Main Researcher: Yoshihatru Shumuta, Ph.D.,
Research Scientist, Earthquake Engineering Sector, Civil Engineering Research Laboratory
Reference
Yoshiharu Shumuta, Kosuke Yamamoto, Kiyoshi Saito (2004), Study on a maintenance management system based on Reliability
Centered Maintenance (RCM) - Application to a spillway gate-, CRIEPI report, U03032.

＊1：Reliability valuing maintenance (Reliability Centered Maintenance, RCM): Generic name of an analytical procedure to choose effective
maintenance alternatives systematically based on qualitative analysis. The proposed system enables us to deal with serious maintenance troubles for engineering facilities.
＊ 2：Availability: A probability (ratio) which maintains the healthy condition of structures during a target period.
This research is a part of the result for a cooperative study with Electric Power Development Co., Ltd.

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A. Cost reduction and ensuring reliability

Hoist

Hoist

Based on thequalitative
analysis, weunderstandthat it ispossible todiscuss thereasonable
inspection
interval as amaintenancealternative.

Alternatives of the maintenance method
are examined considering the economic
rationalization target

1.0
0.9
0.8

No0.7

Average Availability hardly changes(within the decreasing rate 5% comparedwith before it changes)

0.6
0.5
0.4
0.3

A deficiency which needs painting All surface of gate
A deficieny which needs repairing wire rope
A deficiency which needs replacing wire rope

0.2(3) Cost effectiveness analysis(economy evaluation of rationalization
scenario)
・Evaluation of expected total cost in eachunit time(4) Confirmation of restriction condition
Is the rationalization target filled ?
Is the selected alternative safe ?

Yes(5) Decision of the best maintenancerationalization alternative0.00234567891011Fig.3 Relationship between the simple inspection
interval and the average availabilities

The point: The availability is utilized as a scale ofthe maintenance reliability level.

Annual expected total cost
Anuual expeted inspection cost
Annual expected damage cost

1514131211109876543210

Annual expected total costmin (once / 1.9Year)

The inspection interval(once/1.9year)
minimizes the expected
total cost.

Annual expected total cost= inspection cost＋damage cost

0Fig.1 Flow diagram of maintenance rationalization
support system

1Simple inspection interval (Year)

Annual expected total cost (Unit/Year)The second analysis(quantitative analysis)

0.1(3) Availability analysis(Reliability assessment ofrationalization scenario)

The point: The proposed system consists of two
analytical approaches: the quantitative
based on RCM and the qualitative basedon maintenance historical data.

Gateguguide
GateideGateleaf leaf
Gate

Fig.2 Target spillway radial gate

(2) Selection of maintenance method
based on RCMi) Selection of damage modeii) Selection of influence factor for eachfailure modeiii) Selection of maintenancerationalization alternatives based on thefollowing points of view
・Change in maintenance policy
・Rationalization of the inspection work
・Change in repair, renewal and painting
criteria

Average Availability

The first analysis(qualitative analysis)(1) Setting of rationalization target(Example: 5% maintenance cost is reduced
more than the current state )Anchorage
Anchorage

12345678910Simple Inspection Interval (Year)

Fig.4 Relationship between the expected total Costand simple inspection interval
The point: The proposed system enables us to evaluate
the cost-effectiveness for maintenance alternatives.

The inspection interval is changed from once/0.5
years to once /a year.

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