FMECA allows to update the plant Risk Register by assessing the items with the greatest criticality. This enables to develop efficient and effective maintenance plans.

The first stage is the collection of documents for the following analysis. Source documents are:

• P&ID, electrical single-line diagrams, layout plans and PFD updated in the light of the latest revision of plants in manufacturing sites;
• Extraction of the installed items’ register from SAP PM (Maintenance Management System);
  operations manuals;
• Cause and effect matrices.

The process was divided into two phases:
Phase n°1 – Asset Register;
Phase n°2 – Failure Mode, Effects & Criticality Analysis (FMECA).

PHASE N°1– ASSET REGISTER

The extraction from SAP PM provides a register with a great number of installed items. Firstly, the number of the items has to be reduced in order to identify the items to be analyzed, i.e., only electro-instrumental items that send or receive a signal from the field (electrical, pneumatic, hydraulic).

PHASE N°2 – FAILURE MODE, EFFECTS & CRITICALITY ANALYSIS (FMECA).

The criticality analysis and determination of the risk level were carried out using the FMECA. For study execution and boundary condition, the procedures and the approach used are those of the company.


Starting from the Asset Register file, the outcome of phase n°1, the objects to be analyzed have been isolated, thus resulting in the source table for the FMECA. The following steps have then been followed:

TAXONOMY

For each item of the resulting FMECA table, a taxonomy has been developed based on the object type. The taxonomy is based on the different reliability databases found in literature.

FAILURE MODE – FREQUENCY

After having developed the taxonomy, the item failure modes – which characterize the reference taxonomy – have been identified. According to the company standard, for each failure mode has been associated the “Mean Time To Failure” with the related “Failure Rate” and the “Increasing Annual Frequency”. These parameters suggest the frequency, and therefore the probability, of a particular failure mode.

For the association item-failure mode the following criteria have been adopted:

• For each item, the first 3 critical failure modes with 80% of failure occurrence have been considered (the other critical failure modes, that have not been set out individually, were classified in the reference failure mode “OTHER”)
• The failure mode “ALL” represents the different item failure modes. Its failure rate is a sum of the failure rates of the item failure modes.

FAILURE EFFECTS – GRAVITY

Once the FMECA database has been developed, the next step is analyzing the documents (P&ID, electrical single-line diagrams, layout plans, cause and effect diagrams, operations manuals) and describing, for each failure mode of the items to be analyzed, the consequences of such events under normal conditions of plant functioning, considering the impact on the production. Consequences have been defined on three levels of details:

Effects on Equipment: failure mode effect on the item itself;
Effects on FFU/Plant: failure mode effect on the functional unit or plant of the item;
Impact on Production: failure mode consequences on production (e.g., halted production).

Each consequence has been associated with the corresponding Severity Asset (gravity of the failure mode consequences for impact on production), based on the table to be found in the company standard. The aforementioned table has been adapted to the case study, based on the following general criteria:

Table 1: Severity Asset adaptation to the case study

CRITICALITY

At the end of the analysis, for each failure mode was assigned a criticality level (1, 2, 3 – where 1 stands for the maximal and 3 for the minimum criticality) according to the risk matrix to be found in the company standard.

Criticality level is determined by the risk matrix, combining Severity and Increasing Annual Frequency data. At last, each item is associated with the maximal criticality level among its failure modes. The items in the red zone (criticality level 1, high risk) and in the orange zone (criticality level 2, moderately high risk) of the matrix have been identified as critical.

Figure 1: illustrative risk matrix for the adopted approach

Conclusions

The FMECA study represented the chance to carry out an important and relevant data and information systematization in the engineering field of plants maintenance. Starting with P&ID and the maintenance database on SAP PM, the Asset Register of the different plants has been defined, including the items of the study. Thanks to the FMECA study, the criticality analysis has then been carried out.

This study ensured the determination of the particularly critical items in production, through risk matrix Asset, and the assessment of the correspondence between items of the P&ID and the field items.

The result allows to channel maintenance resources on items of which failure has more consequences on production. In this way the implementation of a higher efficiency and effectiveness process is guaranteed.