USING DIAGNOSIS AND LIFE CYCLE COST TO IMPROVE RELIABILITY OF AN EXCAVATOR

Diagnosing of equipment before actual failure and reduced total ownership cost of excavator (TOC) is a significant issue for the mining and civil construction industries to unavoidably consider. Consequences of prolonged project execution time and extra cost due to sudden breakdowns are better minimized by studying the reliability of the equipment and having knowledge of life cycle cost model which was used in this research to ascertain the economic replacement time and cost of an excavator. Results from life cycle cost analysis carried out on an excavator show that the replacement time and total ownership cost of excavator 320C from 2010 to 2017 is 8 years and N10, 214 respectively.


I. INTRODUCTION
For every mining and construction company that owns or hires equipment for business purposes, it is very crucial to regularly monitor and analyze the reliability of their equipment to enable them increase productivity, favorably feature in the ever increasing competition and improve on their profit margins biannually or annually.
An important equipment commonly used for various projects in the mining and construction industries is the excavator.The excavator is an important heavy duty equipment in the mining and civil construction industry, which is primarily used for digging, loading and dumping Xiangyu et al. [1].It moves on wheel or track and consists of boom, stick and bucket that are driven by their corresponding hydraulic actuators.Necessary steps which includes good operating practice and proper preventive maintenance (PM) actions for impending failure, proper corrective maintenance (CM) actions for failed excavator must be taken in other for it to be profitable Sharma, [2].According to Qing and Hongqin [3], maintenance is primarily provided for the purpose of reducing failure by replacement, repair or servicing in order to achieve the economic utilization of the construction equipment during its work life.Reliability analysis is important in order to identify the equipment weakness and quantify the impact of component failure Qing & Hongqin, [3].Therefore, reliability study of equipment and early prediction of failure (unreliability) with a reasonable degree of accuracy will mitigate losses associated with time and cost Qing & Hongqin, [3].
An important aspect of reliability study which considers saving cost as well as answers the question of the most economic decision to replace an old equipment with a new one, is Life cycle cost analysis, Hamodi, [4].According to Douglas et al. [5], for proper replacement analysis of construction equipment the data from its history card is collected, bearing in mind that the older an equipment gets the higher the repair and maintenance cost which constitutes the largest amount of the operating cost.
It is basically estimating the procurement and ownership costs of an acquired equipment, which may include acquisition cost, operation cost, maintenance cost, installation cost, transportation cost, taxes, scrap value and equipment useful life.Life cycle cost analysis comprises of life cycle costs, equipment decision procedures, and replacement analysis models, Gransberg and Edward [6].They further stated that life cycle costs for equipment has two component which are ownership and operating cost that determines the decision to repair, overhaul or replace equipment.According to Okoye [7], equipment replacement decision is hinged on the knowledge or outcome of a comparative cost analysis of how much cost is saved when old equipment is replaced with a new one as well as the consequences of nonreplacement.It is worthy to know that equipment is not only replaced for the reason of its deterioration, but also for a reason of its failure to meet the advanced developmental standard, irrespective that it is in a good working condition, Mahajan, [8].However this research work emphasizes on the need to replace and old equipment with a new one on the basis of its deterioration, after carrying out a life cycle cost on excavator 320C through a period of 10 years, using the excavator's history details which includes procurement cost, operating and maintenance cost and yearly interest rate.
As an effective approach to improving the reliability of equipment (excavator), studies show that early diagnosis of equipment fault is of great benefit as it brings about increase in plant and personnel safety, decrease in maintenance cost, reduction in spare parts provision, lowered insurance rates, minimized downtime and increased availability, Rosaler et al. [9].Fredriksson & Larsson [10] in their research, guaranteed that failure will recur if the root cause of failure is not identified, as such the problem is not solved and losses as per cost of maintenance and delay will be incurred.They further stated that documenting this root causes in the work order history will prevent futuristic recurrence of failure.Tung and Yang [11] explained fault detecting as the task of indicating whether something is going wrong with equipment; fault isolating as locating the faulty component while fault identification as determining the nature of the fault when it is detected.Literatures review of Xu et al. [12], Tung &Yang [11] show that there is basically the data-driven and model-based methods of diagnosing equipment faults.Xiangyu et al. [1] proposed the principal component analysis (PCA) as fault diagnosis method.
This research considers the PCA and adopts the use of expert system which is a type of the data driven method to diagnose faults in excavator due to its convenience.

A. Excavator Fault Diagnosis
For efficient diagnosis of equipment fault using expert system (shown in Figure 1), the equipment information data must be effectively communicated via a data link situated in the equipment as shown in Appendix A. The diagnostic expert system chosen for this research work is the Caterpillar Electronic Technician device (Cat ET).
The procedure for diagnosing excavator faults is outlined as follows:

B. Equipment Replacement Models
The decision to replace equipment is hinged on knowing the appropriate time to replace equipment as well as the most cost effective maintenance strategy to adopt.Therefore equipment replacement model for this research is discussed as follows:

III. RESULTS
The running cost history of excavator 320C for 9 years, according to the plant admin department of MCC is shown in Table : 3.1.Procurement cost show that the initial cost of excavator 320C is N 5,000,000 and the yearly interest rate of 10%.The result of life cycle cost (LCC) analysis performed is shown is Table I.

V. CONCLUSION
Judging from the increase in running cost of the equipment during life cycle cost analysis, from N538, 000 to N3, 786,000 between 2010 and 2017 respectively; which has consequently increased total ownership cost from N538, 000 to N21, 505,000 is attributed to the constantly increasing maintenance cost of the equipment hinged on frequent contracting of maintenance of equipment to third party, owing to their use of expert system for diagnosis and better procurement management.
Based on the prevailing issues of poor equipment fault diagnosis and inadequate knowledge of equipment replacement time for effective decision and maintenance policies, it is recommended that: • Expert diagnosing system be used as a preventive and corrective measure for diagnosis of equipment faults, in other to save time and cost.• Life cycle cost analysis be carried out to help the management of any organization plan, make replacement decision and set maintenance policies that will save cost and time.
Figure1: A pictorial view of an electronic technician expert system.

Figure 2 :
Figure 2: Block diagram of Excavator diagnosis 9) where n = Number of years P = Initial or purchase cost of equipment TOC n = Total ownership cost in n years   = Running cost at n years  = Depreciation value  = Annual interest rate RV = Resale or Scrap value RT = Replacement Time () = Weighted average of all cost

Figure 4 :
Figure 4: Economic replacement time for excavator 320C

Table I :
a life cycle analysis of Excavator 320C for 8 years TableII: running cost of excavator for 9years in MCC Enyindah Ndamzia Clement obtained a Bachelor of technology (B.Tech.) in Mechanical Engineering in 2013, and is currently pursuing a Master of Technology (M.Tech.) in Mechanical Engineering (Production Option) all in Rivers State University of Science and Technology.He has 5 years hands-on experience in maintenance in the construction industry.His research interests are in Manufacturing Technology, Safety and Reliability.He is a student member of both institute of mechanical engineering (UK) and Nigerian Society of Engineers.Amadi Rex Kemkom received a Bachelor of Technology (B.Tech.) in Mechanical Engineering from Rivers State University of Science and Technology in 2002, Master of Technology (M.Tech.) in Mechanical Engineering (Thermo-fluid Option) from River State University of Science and Technology in 2010, and currently have completed 95% requirement to obtain a Ph.D. in mechanical engineering (Thermo-Fluid Option) in April, 2019.He has research interest in Thermal and Solar Power Generation.He joined the Rivers State University in 2014 and currently is Lecturer in the Department of Mechanical Engineering.He has published many papers in scientific journals and conferences.He is professionally affiliated to Counsel of Registered Engineers in Nigeria (COREN) and Nigerian Institute of Mechanical Engineers (NIMECHE).