Reliability, Availability and Maintainability (RAM)
Objective of RAM study
The objective of the RAM study is to assess the reliability, availability and maintainability of the new equipment installed within the existing facilities. In cases where reliability, availability and maintainability do not meet required levels, this study will recommend measures to improve performance to meet project reliability, availability and maintainability targets levels.
Why is RAM study Important?
RAM study is a structured and quantitative approach to analyze the availability of an asset for its purpose. RAM modeling and simulation are usually performed in FEED stage to highlight the production losses caused by downtime due to equipment failures. With the complete analysis of the asset performance, system configurations, maintenance strategies and operational initiatives can be varied to determine the optimum approach to meet the required availability.
The selection of reliability data for the study is based on the type and failure mode of the equipment. The important parameters that contribute to the availability of the equipment for operations are Mean Time to Failure (MTTF) and Mean Time to Repair (MTTR).
The other input data for the study such as design life, production capacity, etc. will be collected from the below listed project documents.
- Design basis memorandum
- Process description
- Operation & control philosophy
- Cause & effect diagram
- P&IDs & PFDs
Assumptions will be made for the missing input data based on the good industrial practices and will be agreed upon with the Client prior to starting the study.
The system, which upon failure could result in downtime of the facility i.e. resulting in loss of production, are considered to be essential. The essential systems identified would contribute towards the overall availability. Failure of essential equipment could affect the availability of the overall system, depending on the equipment configuration and redundancies present.
The Reliability Block Diagrams (RBDs) define the interaction between the equipment, instrumentation and systems. It shows the effect of an equipment / system failure on the entire system. Each block in the RBD represents an equipment / system.
The RBDs illustrate the redundancies in the key equipment / systems and thus the single point failures on the facility. Failure of an equipment in series will result in the failure of the entire system. Components in parallel blocks represent the redundancy of the components in the system and failure of one of the parallel components would not cause a complete system failure.
The RBDs will serve as input into the development of the RAM model. Therefore, for an accurate assessment of the availability of the facility, it is imperative that accurate RBDs that represent the equipment redundancy are built.
The main process and utility systems of the facility will be reviewed and the RBDs are constructed for each system, based on the PFDs, P&IDs and BFDs.
The RAM model will be developed using a software. The following data are be used as inputs to develop the RAM model:
- Design life
- Production capacity
- Failure modes
- Failure rate or MTTF
RAM Study Report
Based on the output of the RAM model, the equipment / system in the facility will be ranked based on its criticality i.e. The criticality of equipment is inversely proportional to its availability, whereby the equipment with the highest unavailability is deemed to be the most critical, and vice versa. The criticality ranking of equipment can then be used as input in the development of the maintenance plan for the facility. The report shall represent a summary of the RAM study base case along with the results, analysis, conclusion and recommendations.
RAM study Assumptions
General assumptions for the RAM study, specific assumptions to the project and assumptions for the non-available data are made based on the expertise judgment / good industrial practices and agreed upon with the Client prior to starting the study.
- RAM model shall include all process systems that have a potential to impact production output.
- Only Production critical equipment will be analyzed in RAM Study.
- Availability of the equipment is calculated based on their redundancy and hence human or operator error would not be considered. Off – spec events will not be included in the model as failure of an off – spec event will only occur as a result of human error.
- The facility is assumed to be running at steady state.
- Production is assumed to be always at 100%.
- Piping are assumed to have an availability of 100%.
- Utility systems are assumed to have an availability of 100%.
- RAM model will not track every single flow, instead will establish dependencies between the equipment (system level) that are relevant from RAM perspective. Some flows will be combined with other flows to simulate the appropriate dependency between equipment using RBD.
- Severity Class type – Critical Failure will be considered for the study.
- Failure modes for natural disasters, terrorist actions or external caused damage (car or airplane crash, etc.) will not be considered in the study.
- Control systems, DCS and PLCs are assumed to be furnished with sufficiently redundant systems.