Chapter 4 Periodic Inspection

Section 1 General Provision

Article 158. General provisions

1.It must be confirmed that status of damage and operation etc. thermalof power facilities meets with the technical regulation taking account of this Guideline.

2.Power plants may refer to international standards (voluntary standards) regarding the pressure

vessels, lifting, fire fighting and other devices in addition to Vietnamese mandatory gulationsre and voluntary standards.

Article 159. Frequency of periodic inspections

1.The status of power plant varies depending on the type of system, type of fuel, whether new or old, whether design is good or bad, whether production is good or badThe. frequency of periodic

years; on the other handit of boiler at B power plant can be regulated 3 years becauseofit boiler is regulated within six (6) years in the technical regulation.

2.However, if power purchase agreement is concluded and time of periodic inspection is regulated in it, it must be regulated frequency of periodic inspection in line with it.

3.“Risk based maintenance”: When applying the new maintenance technology and conventional one to existing machines, it is necessary to formulate a maintenance planso as to be compatible, such as maintenance cost andthe rate of utilization. It can be mentioned the approach based on RBM (Risk Based Maintenance) as a method to establish the maintenance plan. The concept is shown in Figure 159-1. Maintenance costs will increase depending on the number of menu to

perform maintenance; on the other hand, the probability that equipment will be broken will decrease. Accordingly, the amount of damage tha is caused by broken equipment, therisk of accidents, will be reduced. Here, the necessary cost during operation of the unit, cost of economic risks is deemed as the sum of maintenance costs and accident risk, which type of bathtub curveas shown in Figure 159-1. It is deemed that the maintenance plan at the minimized point of economic

risk curve is the best anpl in this technique. System which supports the optimization of the maintenance plan based on this concept has been developed.

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Figure 159-1 Concept of optimizing for maintenance planning based on RBM

4. “Periodic inspection of boiler”: It takes 50 ~ 200days to perform periodic inspectionthat is required the replacement of boiler pressure part , though it is depending on the output of unit and replacement range. For example, replacement of reheaterand hot super-heater is performed in many units which have passed 100,000hours total operation time.The replacement of cold superheater, economizer, water wall tubeand the like is also expected in thecase more than 200,000 hours operation time is extended further as shown in Figure 159-2. It will be the important issue to shortening the construction period in case if it is required long periods of time.

Replacementofofwaterwall, coldsuperer--heater,economizer,hederheaderandandmajormajorauxaux. equipment. equipment

Figure 159-2 Location and timing of replacement of pressure part of boiler

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5.“Management of gas turbine hot part”:

(1)Type of inspection

Two kinds of inspection,“Full scale inspection” and “combustor inspection” are set as the inspection of gas turbine equipments and are performed. “Full scale inspection” is the inspection to decompose and open-up entire facility of gas turbine (GT, compressor, combustor), to inspect,

repair, assemble and perform function testing and the like.“Combustor inspection” is the partial inspection to perform the inspectionfor combustor, repair,assemble and perform function testing and the like

(2)Interval of inspection

The inspection interval of GT hot parts is determinedand the inspection is performed in the number of years considering the demand of power. In case of GT ofGE, full scale inspection is carried out once in 3 years and combustor inspection is carried out once a year as shown in Figure 159-3-(b).

which is recommended by GE, thoughfull scale inspection has been carried out once in 2 years at the beginning of operation.

For the purpose of further reduction of inspection costs, full scale inspection once in 3 years and combustor inspection once in 1.5 years have also started operation as shown in Figure 159-3-(c).

In case of GT of MHI, full scale inspection is carried out once in 2 years and combustor inspection is carried out once a year as shown in Figure 159-4. The full scale inspection for the second year is considered whether an extension is possible as well as GT of GE.

The reduction of the number and time of shut-down and high occupancy contribute significantly to reduce fuel costs and CO2 emissions, since combined cycle has a high thermal efficiency.

The continuous and furtherconsideration of full scale inspection and combustor inspectionis required.

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Combustor inspection Combustor inspection Combustor inspection

(a) Inspection interval at initial operation

(b) Inspection interval after the review

(c)(b)Inspectioncti nintervt all afterthe further review

Figure 159-3 Inspection interval of GE type gas turbine

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Figure 159-4 Inspection interval of MHI type gas turbine

6.“Periodic inspection of safety valve”:

(1)Japanese regulation and standard

Table 159-1 Japanese regulation of interval for safety valve inspection

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(2) International standard

Table 159-2 International standard of interval for safety valve inspection

Reference: P-2 of “Maintenance of safety valve”No.54 of Technical report of Fukui seisakusho

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