Received 8 June 2014; revised 8 July 2014; accepted 8 August 2014

ABSTRACT

Background: Failure mode and effect analysis (FMEA) is a widely used quality improvement and risk assessment tool in manufacturing. The aim of this study is to assess potential hazards by failure modes and effect analysis (FMEA) method in Yazd Steel Complex. Methods: In this descriptive study, we evaluated the risks in different parts of the complex by using FMEA method and by using FMEA Worksheets (PFMEA) derived from the standard (MIL_STD-882). Failure modes and the various components and effects as using quantitative score to the risk priority (RPN) were obtained. PFMEA worksheets were completed and, we reevaluated the weaknesses part of the system. Activities related to each from the different parts of Yazd Steel Complex by using the scores risk priority (RPN) were evaluated. Then the results obtained by using SPSS software were performed by evaluation and analysis. Results: The findings showed that the steel maker lime unite and steel making ingot casting achieved the highest of RPN before and after corrective actions measures (490, 168) and environmental health unite and roll styles unite achieved the lowest of RPN before and after corrective actions measures (28, 20). Conclusions: The results show that the FMEA technique can identify a higher number of hazards than any other technique. The important point is that selection of an appropriate technique plays an important role in identifying a higher number of hazards.

Keywords:

Failure Modes and Effects Analysis (FMEA), Risk Management, Steel, Risk

1. Introduction

In the past few decades, many actions and research works have been undertaken to prevent potential accidents and to promote safety in the chemical processes; the output of these measures is the systematic management of safety in these processes. One of the key elements of safety management systems is to identify hazards, to assess risks and their control, which helps security professionals to investigate the ability of rational decision to reduce the risk and severity of accidents and their consequences [1] .

Failure mode and effects analysis (FMEA) is commonly defined as “a systematic process for identifying potential design and process failures before they occur, with the intent to eliminate them or minimize the risk associated with them”. The FMEA technique was first reported in the 1920s but its use has only been significantly documented since the early 1960s. It was developed in the USA in the 1960s by national aeronautics space agency (NASA) as a means of addressing a way to improve the reliability of military equipment [2] .

Despite the importance of risk assessment as a scientific basis for national and international activities, this category has different meanings among people and experts in various disciplines, and is often controversial and incorrect interpretations. Diversity and distribution of scientific topics, definition of risk assessment, the distinction between risk assessment and risk management, et al. are among the reasons that have offered different interpretations of the concept of risk assessment. Based on objectives, data, resources, and other factors for risk assessment, methods and definitions are introduced. Hazard identification and safety evaluation have several methods, including safety audits patrols and inspections of HAZOP, JSA, and FMEA. An OSHA guideline is one of the quality tools that every manager needs to be familiar with [3] .

Every day in the United States, a large number of workers are injured or killed at work. Considering work place conditions, providing proper work procedure, and training all workers are among suitable and useful strategies to prevent disease incidence, injury and trauma [4] . Risk management includes techniques to identify, assess and control risk, as other tools are multifarious. Generally it can be divided into two categories: qualitative and quantitative; qualitative methods are usually applied to small companies with a low number of activities, whereas quantitative methods are usually used for large organizations with high activity. One of the few ways to identify, assess and control risks is FMEA method [5] .

In 1950, FMEA method was established by engineers for reliability and safety assessment in military systems. It was quickly spread so that it was used to evaluate safety of Concorde and Airbus aircraft in America and France respectively. This method was also developed in nuclear safety after the Maryland disaster [6] . Failure mode and effects analysis (FMEA) is a comprehensive engineering technique that manufacturers are able to improve the quality, reliability, and safety of their products through applying this technique [7] . In particular, FMEA technique is used to identify, define, and eliminate known and potential failures, problems and errors in the products, programs, systems and services before they reach the customer.

FMEA is a systematic method, which is applied because of the following reasons:

1) To identify and prioritize potential failure modes in a system, product, process, or service;

2) To define and run measures in order to eliminate or reduce the incidence of potential failure modes;

3) To record analysis results in order to provide a comprehensive reference for solving future issues and problems [8] .

FMEA could be described as a structured method to find and identify failure modes in a system, object, or an activity and calculation of the failure effects on upper steps [9] [10] .

According to the 2011 disaster, which killed 14 and injured 5 people and the importance of steel industry as well as the preservation of labor force, we conducted a comprehensive and targeted study.

2. Materials and Methods

This is a descriptive study conducted in Yazd Steel Complex. In this study, we evaluated the risks in different parts of the complex using FMEA method. Using FMEA Worksheets derived from the standard (MIL_STD- 882), we obtained failure modes along with its different components and failure effects in quantity using risk priority number (RPN) equation and PFMEA worksheets were completed. Finally, we reevaluated the weaknesses of the system. Activities related to each of the different parts of Yazd Steel Complex were studied using RPN equation. The result of the evaluation and analysis was performed using SPSS software.

-System description

After visiting and studying different parts of Yazd Steel Complex, risks involved in the steel complex were examined in detail and likelihood, severity, and frequency of exposure were quantitatively studied. Moreover, the risk of each activity was obtained and in another part, the control measures were expressed. Later, we again stated the likelihood, severity, and frequency of exposure and risk reduced. At the end of this study, we would present tables of the risk probability, risk severity, frequency of exposure, and risk number obtained before control measures and after control measures separately. Figure 1 shows the FMEA process.

-RPN methodology

Decision making using RPN scoring and crisis level.

The RPN is a mathematical product of the severity, the occurrence and the detection. The number is used to identify the most critical failure mode, leading to corrective action [12] .

RPN scoring is based on the fact that numbers with higher risk priority have priority for analyzing and resource allocation aimed at improvement, and the team should work on failure modes having a higher RPN. RPN is obtained by multiplying three factors of intensity, possibility of occurrence, and detection possibility [13] . It is calculated using Equation (1).

(1)

RPN to evaluate the risk level of a component or process.

The RPN is obtained by finding the multiplication of three factors, which are the severity of the failure (S), the probability of occurrence (O) and the probability of detection (D). In this project, we used risk criterion number to determine the level of acceptable and unacceptable risk in RPN. Risk criterion is an index for separating acceptable and unacceptable risks in the system studied. A failure that its RPN number is greater than the risk criterion is considered as unacceptable risk and a failure that its RPN is lower than the risk criterion is called acceptable risk. This index is varied based on the laws and regulations of each organization and its ability to pay for needed projects costs.

-Determination of the severity rate

Severity is a rating corresponding to the seriousness of an effect of a potential failure mode. Severity or seriousness of the risk is considered just in case of “the effect”; reducing the risk severity is possible only through changing the process and the manner of performing activities.

-Determination of the occurrence rate

Occurrence is ranked according to the failure probability, which represents the relative number of failures anticipated during the design life of the item. The effects of a failure mode are normally described by the effects on the user of the product or as they would be seen by the user.

-Risk detection probability rate

Detection possibility is an assessment of the ability existing to identify a cause/mechanism of a risk occurrence. In other words, detection possibility is a rating corresponding to the likelihood that the detection methods or current controls will detect the potential failure mode before the product is released for production for design, or for process before it leaves the production facility. Assessing control process of standards, requirements and laws of labor and how to apply them to achieve this number are very useful.

In the RPN methodology the parameters used to determine the “criticality” of an item failure mode are, the severity of its failure effects, its frequency of occurrence, and the likelihood that subsequent testing of the design will detect that the potential failure mode actually occurs. Tables 1-3 show the qualitative scales commonly used for the severity, the occurrence and the detect ability indexes [14] .

In this research work, we considered both risks with high RPN and low RPN having one or two abovementioned factors, i.e. while determining risk criterion and decision making for considering a failure within the acceptable or unacceptable risk domain, the team attention was not only towards RPN values but also each of the tree failure factors were assessed. For this purpose, a criterion was defined as the level of crisis. The crisis is a criterion that expresses the importance of a potential/actual risk in the system studied. In addition, it is used to measure the level of crisis in the system. Crisis grade is composed of normal, semi-critical, and critical levels which are explained in detail below:

Level 1: Normal level in which all of the three factors of RPN (especially the severity and probability of occurrence) have values less than 5. Or RPN number is very low and does not require corrective and preventive actions (however, according to the concerned engineer, the corrective/preventive action could be presented (usually RPN < 70)).

Level 2: Semi-critical level in which at least a factor of three factors of RPN (especially the severity and probability of occurrence) has a value greater than 5 but RPN is relatively low. In this case, corrective/preven- tive action is essential (typically 70 < RPN < 140).

Level 3: Critical level in which at least two factors of the three-factor of RPN have high values or RPN number is too high. Since this level has been considered for high RPN, it is obvious and clear that it has a corrective/preventative action (usually RPN > 140) [15] .

3. Results

Table 4 and Table 5 summarize the results of implementing FMEA in Yazd Steel Complex. These tables tabu-

Tables 4. The sample FMEA work sheet in the steel making (unit of lime).

Tables 5. The sample FMEA work sheet in the steel making (IC unit-ingot casting).

late the risks and their causes, severity and occurrence possibility of risks in two parts of steel making (unit of lime) and ingot casting in order to show the way of filling risk assessment sheets.

Graph 1 and Graph 2 show the risks involved in the systems before and after corrective actions in different units of Yazd Steel Complex.

4. Discussion

After determining the level of risk associated with different parts of the steel industry, the following results related to the MAX and MIN, mean and SD, RPN before and after corrective actions was defined with regard to the job in the process function (Table 6).

Although initially it seemed that there is no big and much risks in these sections and the subset employees persist this problem, our results indicated that there are many unknown hazards with a higher risk.

A part of the forms of hazard identification, harmful factors, and risk assessment at steel industry (lime unit).

Equipment failures analysis using FMEA provides the possibility to identify various factors having the potential to create conditions for the possibility of an accident or stop operating phases [16] . Because no preventive and control measures are conducted on them and finally one day they could cause an accident.

It is noteworthy that most of the known risks threaten the system while they could be eliminated or controlled easily and by spending the minimum cost. However, the accidents resulted from them could impose huge losses on the system [17] . FMEA is applied in the industry at all stages of an industrial project from the manufacturing stage to the production stage to improve product quality and productivity [18] . Given that the traditional approach to the design industry without considering the risk of accidents has caused many deficiency and failures in past, nowadays, in implementing industrial plans, especially in the early stages of design, FMEA technique has limited and minimized failures through identifying and assessing risks involved [19] .

OSHA believes that the process of risk analysis should be at best as a team work with expertise in engineering and process operations. Moreover, it should involve at least one person from the workers, who has expertise and knowledge in the field of the method used to identify risks [20] .

In a study, Rezvani showed that among the possible existing risks in milk company, noise from the production line equipment including tetra packing equipment and basket washing machine had the highest relative frequency (64%) followed by hazards such as inhaling NaOH and acid fumes (32%), and burns from acid and NaOH (32%). In this study, the number of employees studied was 28 and the number of hazards identified was 280 risks [21] .

In another study in oil refining company, Asadi reported that the risk of falling from a height with a relative frequency of 12% and the risk of slipping with a relative frequency of 10% led to accidents. The total number of identified risks was 4250 cases [22] . Benjamin showed that accidents and disasters could be significantly prevented if during the production process of the system, FMEA could be launched and carefully managed at the beginning of the process [23] .

In another study conducted by Ebrahimzadeh et al. at Shiraz Refinery, Iran, it was found that activities with low RPN have more priority than the activities with higher RPN in terms of severity. In addition, scoring high RPN in some activities such as handling and transportation of objects and milling, one can apply appropriate control measures to the level of acceptable risk indicating usefulness and effectiveness of FMEA method [24] .

Naturally, not only organization culture but also community culture must booster safety. Economic condition of the organization is also an influencing factor on the risk assessment. Organizations in which productivity is low and revenue is not satisfactory, is not able to pay for safety. This, in turn, reduces the level of safety in the organization and would result in more accidents or disasters. These disaster themselves will bring about direct losses and reducing product quality and quantity. This means lower productivity and profits, and thus reducing the organization funding on safety. Organizational factors have also remarkable influences on the development or progression or system safety development [25] .

5. Conclusion

In order to prevent potential accidents and improve safety in industrial processes, systematic management of safety is essential in these processes. It seems that the implementation of a documentation system for recording equipment deficiencies and events can be basic information needed to assess the subsequent safety ideally. In addition, performing preventive maintenance can reduce the possibility of the equipment defects and their consequences. Our results showed that compared with other methods of risk assessment, FMEA can identify more risks and an important point is that choosing an appropriate method plays a crucial role in identifying more risks.

References

NOTES

^*Corresponding author.