Tim Zaal

Emeritus Professor of

Integrated Maintenance and

Asset Management

HU University of Applied

Sciences – The Netherlands
tim.zaal@hu.nl

Dirk Kuijt

Senior consultant

Rijksrederij Rijkswaterstaat

dirk.kuijt@rws.nl

The Netherlands

The study revealed that by introducing critical analysis of the functions involved, the RCM approach can cut about 80 % of the original time, and considerable savings in time and effort can be achieved by assessing only the functional critical failure modes. A propulsion gearbox has been used as a test case to demonstrate this functional critical RCM approach (fc- RCM). There is a positive attitude amongst both classification societies and equipment suppliers of the principles of RCM in the maritime world and in fact it is the first step in achieving World Class Maintenance for fleet owners.

Introduction

Maintenance costs form a significant part of total overall operating costs in ship operations. Maintenance on ships is still seen as a cost item instead of the way to ensure safety, environment protection and efficient operation. Until today the Rijksrederij has performed maintenance in the traditional way according to the original equipment manufacturer directions. However, as they want to be more efficient, they are seeking for opportunities to reduce maintenance costs.

There is a need for a strategy that secures a good balance between performance, costs and risks. A risk-based maintenance strategy based on RCM (A.M.Smith, G.R.Hinchcliffe [2]) could be the solution, but is not yet applied by international shipping companies. As mentioned in the study published by Mokashi, Wang en Vermar [3], most of the attempts to implement RCM on ships have been done by shore-based consultants or academics and resulted in a lot of paperwork and have not yet been applied.

In the article published by Irakles Lazakis, Osman Turan and Seref Aksu [4], research has shown that reliability data is not available and quantification can only be done by expert judgement process. This indicates that in order to introduce the traditional RCM and to be able to do reliability calculations, there is still a long way to go and it is not yet applicable today. This article will present a methodology based on RCM, which promises a very efficient maintenance strategy for ship owners. 

Figure 1. Rijksrederij’s 245 Gross Tonnage Patrol Vessel Zeearend built in 2002.

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Figure 2. Functional decomposition of the system with the hamburger model.

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Figure 3. The criticality matrix.

Methodology

The RCM methodology is based on failure mode and effect analysis of the items involved and is focused on preserving system functions instead of preserving the asset itself. RCM is a qualitative approach in order to design an efficient maintenance plan.

Traditional RCM has two main problems for easy implementation of the methodology on the workfloor: first a lot of administration work and secondly lack of reliable failure data. In Utrecht Tim Zaal has developed an RCM approach based on the functional criticality of functions. This methodology reduces the amount of paperwork by 80 %, gives a good overview of all critical parts of the system and can work by applying a criticality matrix.

Due to the fact that failure data is not available in the maritime world, a quantitative risk assessment is often not possible. Introducing the fc-RCM (T. Zaal [5]) will result in applying the functional critical Failure Mode and Effect Analysis (fc-FMEA) in combination with the criticality matrix. The focus is to prevent system failure and to concentrate on those failure modes that result in critical functional failures.

Functional Decomposition

The methodology of fc-RCM starts with a functional decomposition of the system by applying the so-called Hamburger model (figure 2).

In this model the functions, functional specifications, and function solutions are visualized and by categorizing the criticality (very critical, critical, less critical, not critical) and the importance of each function in the system can be weighted. Only very critical and critical functions are subject for further investigation. The categories less critical and not critical are subject for task selection or even run to failure (Failure Based Maintenance). All the Hamburgers in the model can be given a special colour. So it is visual which hamburgers (functions) are critical and which are not critical.

Criticality Matrix

The criticality of each function in relation to the total system function should be analyzed. The criticality assessment is executed by applying the criticality matrix (figure 3), which is in fact a risk assessment of the functional failures.

The criticality matrix can be used for estimating the risk of a functional failure, by implementing the knowledge of experts. The criticality matrix is derived from the company main goals: to be an efficient ship owner with a highly available, safe and sustainable fleet. In this way the most critical failure modes are identified for further assessment in the function criticality analyses

fc-FMEA

Applying the fc-FMEA each function is weighed on its criticality using the criticality matrix (figure 3). For each system a functional decomposition is made including the function, functional specifications and the function solution (equipment). On each decomposition level is indicated how important the (sub) function is in relation to the main function. In case the sub function fails and as a result also the main function fails, the sub function is critical and indicated red in the decomposition.

The criticality matrix indicates which task selection procedure should be followed and must be executed with experts using their judgment. According to the Pareto rule the result of applying the fc-FMEA is that 20 % of all failure modes are more or less critical (orange or red) and need full attention in order to establish the most suitable maintenance activity. The remaining 80 % of the failure modes need only a simple maintenance task selection procedure resulting in time-based maintenance, condition-based maintenance or failure-based maintenance.

Example of a fc-FMEA Scheme for a Centrifugal Pump

In this fc-FMEA the following elements are presented: function, function solution, functional specifications, functional failures, criticality functional failure, selection criticality, failure mode and failure effect (Table 1). FS2.3 gives Quick Way (QW) and direct to Task Selection (TS). Another choice is the so called Comprehensive way with further function consequences analyses as result.

Although the International Safety Management code (ISM code 6) is not applicable to government vessels (7), Rijksrederij management has adopted the ISM code as a required safety system. The ISM code requires a safety assessment for all the equipment on board the vessels and a maintenance plan to secure the reliability. And this is what fc RCM delivers: maintenance focused on system reliability.

The outcome of the fc-RCM study is the input for task selection and creation of the basic maintenance plan.

Result

The new maintenance model is based on fc- RCM and focuses on critical functions and the maintenance plan is established by applying the following steps:

1. System selection for collecting system information.
2. Determine the system boundaries, what is in the system and what is not.
3. Determine system functions descriptions, functional block diagram and decomposition.
4. Determine the functions, functional specifications, and functional failures
5. Determine the functional critical Failure Mode and Effect Analysis (fc- FMEA)
6. Perform the functional consequences analysis (FCA) and risk management matrix for critical and very critical components
7. Perform maintenance task selection
8. Determine the maintenance plan.

Table 1. fc-FMEA scheme for Centrifugal Pump.

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Example Rijksrederij

The new maintenance strategy fc-RCM has been applied to a vessel of the Rijksrederij. Applying the criticality matrix resulted in the propulsion gearbox being critical equipment in relation to the main function of the vessel. It appeared that in the past the gearbox broke down and resulted in total loss just before the OEM’s prescribed standard overhaul at 20,000 running hours. Applying the fc-RCM methodology resulted in a maintenance plan, consisting of mainly con- Table 1. fc-FMEA scheme for Centrifugal Pump. dition-based maintenance tasks. Vibration measurement of the bearings, oil analysis for wear particles and visual inspections of gearwheels and seals will deliver the necessary information in order to prevent functional failure or even worse, total breakdown. Comparison between the new and existing maintenance strategies resulted in a decreasing annual maintenance costs of 17,000 € (reduction 30 %), and increased vessel utility 3 % in the year that the gearbox broke down. This is exactly what fc-RCM is about: not only decreasing the necessary maintenance resources, but increasing the reliability and availability of the vessel.

The Rijksrederij wants to reduce the overall operating costs. Implementing a riskbased maintenance strategy based on RCM is a bridge too far for the Rijksrederij due to the fact that necessary information and failure data is missing. Creating a maintenance strategy using fc-RCM can be the solution for an efficient maintenance strategy, which contributes in achieving company goals. Due to the fact that applying the fc-FMEA focuses on preventing functional failures, it will also reduce the necessary resources in creating an efficient maintenance plan.

There is also a growing awareness among the regulatory bodies like Lloyds Register, that a new view is necessary concerning the maintenance strategies. Also the Original Equipment Manufacturers (OEM) are able to deliver measuring equipment necessary to perform Condition Based Maintenance. This application (which is a favourite strategy in RCM) is a possible solution for the ship-owner to increase reliability and availability and reduce the downtime costs due to class inspections. The Lloyds Register rules apply an inspection regime based on a five-year special survey cycle. When the shipowner is able to monitor and verify the degradation status of the components on board it is possible to extend the requested inspection interval resulting in reduction of downtime and inspection costs.

The Rijksrederij’s main goal is to become an efficient ship-owner by managing a safe, efficient and sustainable fleet. The ISM code is adopted by the Rijksrederij and requires a risk assessment of equipment on board and a maintenance strategy in order to secure the reliability and fc-RCM is able to fulfil this requirement. The main conclusion is that applying fc-RCM will not only contribute in achieving company goals, but is also a practical way to implement the RCM methodology in the maritime environment.

»»About the authors Tim Zaal Emeritus Professor of HU U niversity of Applied Sciences, U trecht , The Netherlands Consultant at TZConsultancy, Hoorn, The Netherlands (tim.zaal@hu.nl) Tim Zaal is author of two books: ‘Integrated Design and Engineering’ (April 2009, I SBN 978-90-79182-03-9) ‘Profit Driven Maintenance’ (May 2011, I SBN 978-90-79182-10-7).

Dirk Kuijt

Senior C onsultant and Advisor Maintenance Strategy at Rijksrederij Rijkswaterstaat. MoE in Maintenance and Asset Management HU University of Applied Sciences, The Netherlands

»»References ››(1) Bogaard J., Akkeren K ., (2011), Leidraad Risicogestuurd Beheer en O nderhoud, ››Steunpunt ProBo, Rijkswaterstaat Dienst Infrastruktuur, V enlo, versie 1.0 - 1e druk. ››(2) Smith A.M.; Hinchcliffe G .R.(2004), RCM gateway to World. C lass Maintenance, O xford, Elsevier (ISBN -13: 978-0-7506-7461-4) ››(3) Mokashi A.J, Wang J., V ermar A.K. (2002), Marine Policy V olume 26, A study of reliability-centered maintenance in maritime operations, Elsevier Science Ltd, Article nr PII : S0308-597 X (02) 00014-3 ››(4) Lazakis .I, Turan O , Aksu S., (2010), Increasing ship operational reliability through the implementation of a holistic maintenance management strategy, Taylor&Francis, Ships and O ffshore structures, V ol.5, No4, (2010) 337-357 ››(5) Zaal, T (2011) Profit Driven maintenance for physical assets. Maj Engineering Publishing (ISBN 978-90-79182-10-7) ››(6) http://www.imo.org/ourwork/humanelement/safetymanagement/pages/ismcode.aspx ››(7) Source international convention for the safety of life at sea 1974, C hapter IX reg 2.2