FMEA (Failure mode and effects analysis)

Introduction

FMEA (failure mode and effects analysis) is a tool for identifying potential problems and their impact. FMEA is a tool to determine how equipment can potentially fail and what the consequences of those failures are in terms of various levels of effects.FMEA can be used as a “stand-alone” analysis technique but is also integral in other AIM (Asset Integrity Management) methodologies such as RAM (Reliability, Availability and Maintainability) and RCM (Reliability Centred Maintenance).FMEA can be applied to a single equipment item or component but is also applicable across complete assets (collections of equipment items working together to perform a specific set of functions).

FMEA includes review of the following:

• Steps in the process
• Failure modes (What could go wrong?)
• Failure causes (Why would the failure happen?)
• Failure effects (What would be the consequences of each failure?)

Purpose

FMEA is an analysis technique, which looks at how low-level failures of equipment items will affect the operation of the equipment, system and asset. It is a bottom-up approach to failure analysis. Recommended actions can then be generated to reduce the likelihood of failures and mitigate the risks if failure does occur.

Timing

FMEA can be conducted at any point in the project life cycle, however, the earlier the better.

Concept FMEA: analyse concepts before hardware is defined, failures of functions analysed and includes interactions between sub-systems.

Design FMEA: analyses products before production, examines failure modes related to design and operation, looks at three levels: component item, system and asset.

Process FMEA: analyses manufacturing or assembly processes, failures in the manufacturing or assembly are identified at three levels: component item, system and asset.

Ground Rules

The Ground Rules for each FMEA study must be established by study team at outset:

• Project Specific Procedures.
• Assumptions to be used.
• Hardware boundaries and exclusions justified.
• Level of indenture to be applied.
• Level of detail for failure modes determined.
• Mission phases / operating modes to be included.
• Performance data and functional limits are defined.

Ground rules established before start of study but may be modified as detailed analysis takes place.

Equipment Boundaries

Equipment boundaries required to be established, will vary with different Clients, Industries, Purposes of FMEA etc. – use “sound engineering judgement” and common sense.

Reasons for Failure

Some of the primary reasons for equipment items failing are:

• DESIGN of the equipment item, how complex, how robust, number of moving parts etc. all contribute towards failures.
• OPERATING LOAD of the equipment in service; are we asking too much of it or is it having an easy time?
• DUTY CYCLE of the equipment item; constantly running, switching on and off, sitting unused, etc.
• ENVIRONMENT that the equipment item is working in; dusty, humid, marine, hot, cold etc. all affect the way degradation mechanisms progress.

Sources of Failure Modes

Failure modes may be obtained from:

• Design Engineers.
• Operators / Craftsmen.
• Technical History Records.
• Data published in Maintenance and Reliability literature.
• Historical FMEA Studies for similar equipment.

Reference should be made to ISO 14224 – Petroleum and Natural Gas Industries – Collection and Exchange of Reliability and Maintenance Data for Equipment.

Failure Data Sources

Typical sources of failure data (failure mode and frequencies) include:

• OREDA Databases (various years).
• CCPS Process Equipment Reliability Data Book.
• J. Smith Reliability, Maintainability and Risk Book (FARADIP3 Database).
• Green & Bourne (Currently out of print).
• P. Lees Loss Prevention in the Process Industries.
• ISO14224 (Failure modes Only).
• Client provided information.

Failure Consequences

When a failure mode occurs on an equipment item the failure consequences need to be considered at several different levels:

• LOCAL – the direct effects at the equipment item when it fails.
• SYSTEM – the effects the failure mode exerts on the system in which the equipment item operates, and
• ASSET – the ultimate effects on the overall asset when the system and local failures have been considered.

FMEA Inputs

The basic inputs required for an FMEA Study are:

• Client’s requirements.
• Technical Documentation such as PFD’s, P&ID’s, Equipment Lists, Operating Description, Performance Standards etc.
• Method for FMEA recording (Excel, proprietary software, etc.).
• List of assumptions / Ground Rules.
• Defined equipment item boundaries and level of indenture.
• Failure mode and failure frequency data.
• Engineering experience and judgement of the contributing team members.

FMEA Outputs

The FMEA Study will generate the following key outputs:

• FMEA Study Report detailing the methodology applied, the Team composition and the key findings / recommended actions.
• FMEA Worksheets documenting the analysis sessions, failure modes considered / rejected (with justification), failure frequency and classification, effects at local, system and asset level and recommended actions (if any).
• Summary list of all recommended actions with Action and completion date assigned to avoid the consequences of failure to meet the Clients requirements.

Benefits of FMEA

There are specific benefits for each FMEA study carried out, these will be based upon the Clients requirements for conducting the study, however some general benefits will include:

• Identification of engineering changes required to prevent or mitigate failures and their consequences.
• Potential cost reductions by identifying early changes.
• Potential increase in throughput by elimination of potential failures.
• Potential decreased waste / rework due to plant upsets following failures that were avoided.
• Decreased warranty costs.
• Reduction of non-value adding operations.

Drawbacks of FMEA

There are several drawbacks associated with FMEA:

• It can be time consuming and labour intensive for large assets or complex equipment items.
• The level of detail can become overwhelming for in-depth studies (analysis paralysis).
• You may never consider some obscure failure mode, so failures may still occur.

FMECA

FMECA includes a “Criticality” ranking for each failure mode based on the consequences of failure. This can be done in two ways:

• A “Subjective Judgement” which qualitatively ranks the failure modes and consequences based upon FMECA Team judgement.
• Use of a “Risk Ranking” Matrix considering both the frequency of failure and an estimate of the consequences of failure which provides a more consistent, semi-quantitative selection.