Quantifying the Impact of Refrigerated Unit Failures

 

 

 

FINAL REPORT

 

for

 

 

Mack-Blackwell Transportation Center

(MBTC)

 

 

 

 

Project #2005

 

 

 

 

 

 

 

Wednesday, March 14, 2001

 

 

Darin Nutter, Ph.D., P.E.1

Richard Cassady, Ph.D.2

John English, Ph.D., P.E 2.

Don Taylor, Ph.D., P.E.3

Chet Tuck Wong2

 

 

 

1 – Department of Industrial Engineering, University of Arkansas

2 – Department of Mechanical Engineering, University of Arkansas

3 – Department of Industrial Engineering, University of Louisville

ABSTRACT

            The shipment of processed meats, like poultry, dictates the necessity of using refrigerated trailer units (commonly call reefers).  Reefer failures occur and have serious and costly effects on the performance of rural and urban transportation systems typical of the poultry industry.  This project explored the measurable impact of reefer failures through identifying potential reefer failure modes (using FMEA, FTA, and Pareto analysis) and the development of a simulation model based on common poultry industry trucking practices.  Reported performance measures include the number of reefer failures and 7-year costs due to both delays in delivery and refrigeration system repairs.

 

INTRODUCTION

The transportation system of the poultry processing industry embeds multi-layered pick-up and delivery points (like hubs): kill facilities, production facilities and distribution facilities.  Live birds are collected from the rural domain of the farmer and delivered to the kill facility.  From the kill facility, cleaned birds are transported to the processing facilities, and once the birds are processed, complex shipping rules are implemented to insure that appropriate inventory levels of various product types are maintained at the national distribution centers.  The hierarchical design is typical of many transportation systems, but the perishable aspect of the shipped material presents unique challenges. 

            The shipment of processed meats, like chicken, dictates the necessity of using refrigerated trailer units (commonly call reefers).  As the case with any mechanical device, reefer failures (of various modes) are observed and have serious and costly impacts on the operation.  At the kill facility, limited warehouse space is available, and the reefer units are used for storage following the killing process and prior to shipment.  The time the product is held in the reefer unit is limited, and the trailer time is spent in the facility grounds where local maintenance is available, yet any reefer failure still costs time and money.  As the product progresses through the operation, reliable reefer performance becomes even more critical.  Important issues include the dispatching rules, fleet size, season of the year, availability of third party reefer repair, time of day, freight/product mixture and geography. 

 

RESEARCH OBJECTIVE AND TASKS

            This project explored the measurable impact of reefer failures on the economical and logistical performance of the rural and urban transportation systems typical of the poultry industry. The work presented in this project was appropriate to any organization having refrigerated transportation systems.  In this project, we explored and documented the impact of refrigerated unit failures on the logistical infrastructure within the poultry processing industry, namely Tyson Foods, Inc.  As a result of these activities, industries having multi-layered pick-up and delivery points will be able to identify opportunities for improved performance and to determine how factors influence total cost.

This project evolved through four successive phases.  In phase one, reefer failure types and associated failure distributions were identified by reviewing the pertinent literature and discussion/validation with Tyson’s personnel.  The second phase of the project incorporated the failure distributions with the known logistical system at Tyson Foods, Inc. to construct a generalized simulation model to measure the potential impact of reefer failures.  The third phase of the project utilized the simulation model to construct a useful set of experimental scenarios and to identify how factors influence total cost.  The fourth phase of the project consists of documenting and distributing the findings of the research.

 

Phase I:  Reefer Failure Description

            Efforts during this phase included many discussions with Tyson Foods personnel (management and maintenance), the inspection of some reefer units under repair, and a thorough review of pertinent Thermo King operation and maintenance literature.  This first step identified the potential failure modes associated with the trailer’s refrigeration system.  There were two methods used to identify or analyze potential system failure modes and their effects on the local and system trucking operations.  One method used was Failure Mode and Effects Analysis (FMEA), and the second was Fault Tree Analysis (FTA).  Results from both are described below.

 

Failures Mode and Effects Analysis (FMEA)   

            Failure Mode and Effect Analysis  (FMEA) is a structured, qualitative analysis of a system, subsystem, or function to identify potential system failure modes, their causes, and the effects on operation associated with each failure mode occurrence (Bowles and Bonnell, 1998).  The FMEA can be extended to include an assessment of the severity of the failure effect and its probability of occurrence, i.e. a Failure Mode, Effects, and Criticality Analysis (FMECA).  A FMEA/FMECA provides a basis for recognizing component failure modes identified in components and system prototype tests and failure modes developed from historical “lessons learned” in design requirements.  It aids in identifying unacceptable failure effects that prevent achieving design requirements.  It is also used to assess the safety of system components and to identify design modifications and corrective action needed to mitigate the effects of a failure on the system.  It is used in planning system maintenance activities, subsystem design, and as a framework for system failure detection and isolation (Bowles and Bonnell, 1998). 

            In this project, the main purpose of using FMEA was to identify potential system failure modes and their effects on the local and system operations.  Before analyzing the system failure modes and their effects, the first step was to learn the system.  Currently, Tyson Foods is using the Thermo King refrigerated unit (reefer), and FMEA is based on Thermo King’s system.  The functional relationships between the different system components were most easily shown as a functional block diagram, such as in Figure 1 (refrigeration cycle) and Figure 2 (defrost/heating cycle).   Those functional block diagrams help analysts to understand the relationships between the system components.

            The next step of the FMEA was to determine all the ways in which each component can fail and the effect that each failure mode will have on the refrigeration system.  Effects were determined at each level of the system hierarchy – the effect on the module containing the failed component (local), the effect on every subsystem of which the component was a part, and the effect on the total system.  Results from the FMEA can be seen in Table 1. For example, a broken compressor crankshaft causes the compressor to fail at the local level, and subsequently causes the refrigeration system to fail at the system level.  The result of a total system failure can be product delivery delays, product damage, and incurred costs.  The process of identifying possible failure modes and determining their effects on the system operation helped develop a better understanding of the relationships between the different system components.

 

Figure 1.  Functional Block Diagram – Refrigeration Cycle (Thermo King).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 2.  Functional Block Diagram – Defrost and Heating (Thermo King).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Table 1.  FMEA of the trailer refrigeration system.

 

 

Component

Function

Failure Mode

                          Failure Effects

 

 

 

 

Local

System

 

Compressor

Moves refrigerant and increases

1) Bearing loose

Noisy compressor

Reliability of the system

 

 

refrigerant gas temperature

    or burned out

 

decreases

 

 

and pressure

2) Broken valve

Low head pressure

Unable to pump down system

 

 

 

    plate

Noisy compressor

Unable to pull/hold vacuum on

 

 

 

 

 

 low side

 

 

 

3) Too much oil

 

Unit not refrigerating

 

 

 

4) Broken crank     shaft and seals leak

Compressor not functioning

System failure

 

 

 

 

 

 

 

Discharge

Used for isolating and servicing

1) Leaking

Low head pressure

System will not function

 

service

the discharge side of the

 

Unable to pull vacuum

properly

 

valve

compressor

 

on low side

 

 

 

 

 

 

 

 

Discharge

Reduces vibration transfer

1) Leaking/wear

Flexibility decrease

Vibration will increase and

 

vibrasorber

allows for a flexible discharge

    out

 

damage the nearest