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A life cycle cost based approach of O&M support for mechanical systems

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International Journal of System Assurance Engineering and Management Aims and scope Submit manuscript

Abstract

Performance of mechanical systems over their life cycle is the main concern of users. Original equipment manufacturers (OEMs) of such systems are made to deliver customized products with documented support to meet the objective. The product support is of various kinds, one of these is operation and maintenance (O&M) support. Cost incurred for each support action adds to the system life cycle cost (LCC) and therefore, a trade-off between O&M support, operational objectives and design characteristics is required to optimize the LCC. In this paper, important issues are identified for O&M support of mechanical systems and steps are proposed. Mathematical models are developed to assess the support objectives i.e. LCC and operational availability of the system. The LCC takes into accounts the acquisition cost and discounted sum of support activity cost, which consist of operating cost, inspection, corrective, preventive, overhaul and logistic cost. The proposed methodology has been implemented on a real life problem, in which the OEM provides O&M support to their compressors, installed at compressed natural gas workstation in national capital region, India. The results shows that a vital saving can be made in system’s LCC, when the support has been optimized in context to preventive maintenance, viz: age based at system level, while group maintenance based on optimum replacement interval and components’ scale parameter of their failure distribution. The sensitivity analysis validated the robustness of the solution methodology and the obtained results. This work will be helpful to OEMs, customers, academician, researchers, industrialists, and other concerned persons, in understanding the importance, severity and benefits obtained by the application and implementation of the O&M support.

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Abbreviations

a:

Restoration factor

A:

Operational availability

Caq :

Acquisition cost of a system

\( \,{\text{C}}_{{{\text{C}}_{\text{i}} }} \) :

Cost of ith subassembly within the system

Cfix :

Fixed cost to perform each corrective or preventive action, which includes the cost of material required like lubricating oil, etc.

CfixOH :

Fixed cost to perform the overhaul that includes the cost of material required like lubricating oil, etc.

CfixI :

Fixed cost associated with every inspection action

d:

Discount rate per annum

Di :

Demand of ith subassembly per annum

dij :

Distance from demand location i to a candidate site j

E[CCA]:

Expected cost of corrective action during any investigation period for a system

E[Ch]:

Expected cost of holding the spares during any investigation period for a system

E[CIA]:

Expected cost of inspection during any investigation period for a system

E[CL]:

Expected logistics cost during any investigation period for a system

\( {\text{E}}\left[ {{\text{C}}_{\text{OH}} } \right] \) :

Expected cost of overhauls during any investigation period for a system

\( {\text{E}}\left[ {{\text{C}}_{\text{op}} } \right] \) :

Expected operation cost during any investigation period for a system

E[CPA]:

Expected cost of preventive action during any investigation period for a system

E[CT]:

Expected cost of transportation of spares during any investigation period for a system

E[NCAi]:

Expected number of corrective action of ith subassembly in the system

E[NIi]:

Expected number of inspection of ith subassembly in the system

E[NOHi]:

Expected number of overhauls of ith subassembly in the system

E[NPAi]:

Expected number of preventive action of ith subassembly in the system

E[ST]:

Expected cost of O&M support during any investigation period for a system

E[TDT]:

Expected downtime for which the system is not available

L:

Operating life of the system, in years

Lc :

Labour cost per unit time

LPCA :

Lost of average sales of product per unit time, during the uneven breakdown or failures

LPPA :

Lost of average sales of product per unit time due to preventive actions

m:

Support activities during a planned operating period

MTTCAi :

Mean time to perform the corrective action on ith subassembly of the system

MTTIi :

Mean time to perform inspection on ith subassembly of the system

MTTOHi :

Mean time to perform overhauls on ith subassembly of the system

MTTPAi :

Mean time to perform the preventive action on ith subassembly of the system

N(t/V):

Conditional number of failure

O:

No. of operators required for operating the system

Oc :

Overhead cost per unit demand

P:

Profit generated per unit of product sold

Pt:

Preventive maintenance schedule

PVc:

Present value of LCC

RL :

Revenue lost due to maintenance actions

S:

Salary of one operator per day

Sc :

Storage cost per unit

SSC :

Supervisory staff cost per unit

T:

Total time

Topr :

Actual operating time

ti :

Inspection interval for ith subassembly of the system

tOHi :

Overhaul interval for ith subassembly of the system

tpmi :

Preventive maintenance interval for ith subassembly of the system

V n :

Virtual age of the unit at the time of the nth repair completion

V(n−1)i :

Virtual age of the component before carrying out a particular maintenance action

X n :

Preventive maintenance interval

Y:

Required level of availability

αi :

Cost per unit distance per unit demand

β:

Shape factor, defines the shape of distribution in Weibull

η:

Scale parameter, defines where the bulk of the distribution lies in Weibull

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Acknowledgments

We are thankful to the M/S Burckhardt Compression Limited, Pune, Maharashtra (India), for agreeing to jointly work with us in this research study. We express our heartfelt appreciation of Mr. Sanjay Pathak, Mr. Vinod Sharma and Mr. R. K. Sachdeva, of Burckhardt Compression Limited, for sharing their experience with us.

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Correspondence to Mohammad Asjad.

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Asjad, M., Kulkarni, M.S. & Gandhi, O.P. A life cycle cost based approach of O&M support for mechanical systems. Int J Syst Assur Eng Manag 4, 159–172 (2013). https://doi.org/10.1007/s13198-013-0156-7

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