Techniques such as critical nature analysis or RCM that lead both to an almost immediate costs reduction, used to be the first selected when reliability strategies had to be implemented. Nevertheless, analysis of troubles and failures carried out in main-impact equipment, could point to more significant long-term savings effects. Such analyses are more applied when incidents involve safety problems. Unfortunately when failures hit equipment availability, analysis reaches lower standards: e.g. - no working team, no procedure and essentially based on technicians’ experience.

Javier SERRA PARAJES,
Improvement Coordinator on Technical Services,
ENAGAS

Therefore, establishing tools as root-cause effect analysis in the asset management operating strategy are critical aspects for getting an integral asset management model running to its right development.

Methodology of the root-cause effect analysis

Techniques applied to the root-cause effect analysis are tools that allow, by means of logic procedures and systematic causes, the identification of the background or the root of troubles and failures leading therefore to improve equipment reliability and productive procedures. The identified causes that are in the origin of failures or troubles are actually logical causes and are related to the failure effects. These sources of failure are obtained using a deductive procedure that identifies the specific relationship cause-effect that points the system, the equipment or the part that cause a particular failure.

There is a bibliography about different techniques dealing with such questions, making recommendations about the method to follow, step by step, and which points can be made in order to get effective solutions. A large scope of technical tools can be applied and their selection depends on the kind of trouble, data available and knowledge of technicians as: Root-cause effect analysis, fault-tree, gates and events analysis, causal factors analysis, etc.

Regarding RCEA (Root-Cause Effect Analysis), the identification of common causes can be gathered together into levels that are logical and intuitive when monitoring them, what simplifies their subsequent spreading.

Physical root cause:

Where all situations or signs of physical origin that could directly affect the equipment operative continuity are identified. i.e.: the failure mechanism of the element.

Human root cause:

Where the mistakes made due to “human factors” may affect directly or indirectly a failure to occur.

Latent root cause:

Where all kind of problems which, even having never happened before, have a possibility to occur are identified. Essentially they derive from troubles in the company organization that led to the appearance of human root causes, placed mainly in deficiencies: training, information, resources adaptation, etc.

Key aspects of practical applications

One of the main troubles in methodology applications in industrial environments is usually the trend of the technical staff to face the solution of the problems under an intuitive way, based on experience and technical knowledge. Nevertheless, applying methodology not only drives us to establish a defined process and therefore getting it known all over the company organization, but makes possible too documenting the problem so it can be traceable and the information comparable and useful to similar cases. This is the reason for emphasizing in methodologies application. If the amount of analyses mean an excessive workload, it will be better to decrease the quantity of analyses instead of keeping all of them but with a poor quality. The target should be to guarantee the sustainable improvement of a management model, instead of the urgent solving on a trouble.

The key aspects for a correct application are:

Definition of the problem

In the definition of the problem all information needed to begin the analysis has to be specified. In this kind of research however, it is common to interlace hypothesis with suppositions, going sometimes too far away from the original problem. Therefore in this definition very specific answers to three very specific questions are also needed: What? When? Where?

Working crew

All professional profiles that can aid the analysis have to be completed (including Maintenance & Operation), with a special leading role given to the methodology expert, who leads and documents the analysis work.

Studying system and process

In order to get a complete previous analysis basis, a good acknowledge and a detailed display of the system to be analyzed is required and its implication in the regular Plant process understood. To be as specific as possible and to obtain a definition that fulfils an understandable standard, apply process diagrams based in current standards. Standard ISO 14224 suggests determinate diagrams, as do OREDA, for instance, with diagrams of common application.

Fig. 1. Diagram E-P-S (according ISO 14224).

Drawing up the logical tree

A Logical tree has to be as complete and illustrative as possible. It has to show a visual summary of the analysis carried out, following the methodology:

- Definition and priority of the failure forms.

- Definition and validation of the hypothesis: particularly rejecting the weak ones.

- Definition and validation of root causes. Then establish the root causes of each one of the validated hypothesis.

The complexity lays not so far in the consideration of hypotheses, but in the different validation of them. Sometimes it could take weeks or even months, due the need for the study of operation parameters, equipment, laboratory tests …

Fig. 2. Cause Effect Logical Tree.

Corrective actions

One of the main weaknesses of this kind of methodology results when an expected answer is obtained and the remaining hypotheses are automatically refused. Any way it is important to keep going until closing all raised hypotheses to ensure the reliability of the results. On the other hand, the proposed corrective actions have to be periodically checked to get rid of the risk of repeating the analyzed trouble.

CONCLUSIONS:

The application of trouble analysis methodologies is a simple and very effective procedure, carried out in a rigorous and procedural way. The key aspects are:

- To limit and restrict such research to the events worthy of the needed investment in time and resources.

- To be strict in the fulfilment of the methodology, so bear in mind that the research itself and getting answers is just as important as obtaining the information and records that will treasure the technical know-how.

- To integrate all these procedures and methodologies into the Company processes in a logical and well-organized way, obtaining enough guarantees so these “working procedures” can be applied in other situations, filed and kept in the proper medium, and so avoiding that they are considered as a “fashion idea” or “pilot study” as happens sometimes to certain established technicians.

This article was published in the technical magazine MANTENIMIENTO, issued on January-February 2018, nº 311