Handbook of Reliability, Availability, Maintainability and Safety in Engineering Design - Part 28 pps

The document is structured into three sectors, namely: • technical data obtained from the technical data worksheet, relevant to the equip-ment’s physical and rating data, as well as per

3.4 Application Modelling of Reliability and Performance in Engineering Design 253

Fig 3.57 Development list options for selected PFD system

• equipment physical data such as type, make, size, mass, volume, number of parts;

• equipment rating data such as performance, capacity, power (rating and factor),

efficiency and output;

• equipment measure data such as rotation, speed, acceleration, governing,

fre-quency and flow in volume and/or rate;

• equipment operating data such as pressures, temperatures, current (electrical),

potential (voltage) and torque (starting and operational);

• equipment property data such as the type of enclosure, insulation, cooling,

lubri-cation, and physical protection

The technical specification document illustrated in Fig 3.60 automatically formats

the technical attributes relevant to each type of equipment that is selected in the design process The document is structured into three sectors, namely:

• technical data obtained from the technical data worksheet, relevant to the

equip-ment’s physical and rating data, as well as performance measures and perfor-mance operating, and property attributes that are considered during the design process,

• technical specifications obtained from an assessment and evaluation of the

re-quired process and/or system design specifications,

254 3 Reliability and Performance in Engineering Design

Fig 3.58 Overview of selected equipment specifications

• acquisition data obtained from manufacturer/vendor data sheets, once the

appro-priate equipment technical specifications have been finalised during the detail design phase of the engineering design process

The second category in the RAMS analysis list is the analysis option that enables

selected users to access the major development tasks relative to the selected system

of the section’s PFD

The options listed in the selection box in Fig 3.61 appear after clicking on a se-lected system (in this case, the reverse jet scrubber), and include an analysis based

on the following major development tasks:

Equipment (technical data sheets) Tasks (maintenance/operational)

Systems (systems structures) Procedures (reliability and safety) Process (process characteristics) Costs (parametric cost estimate risk) Functions (physical/operational) Strategy (operating/maintenance) Conditions (physical/operational) Logistics (critical/contract spares) Criticality (consequence severity) Instructions (safe work practices) The major development tasks can be detailed into activities that constitute the over-all RAMS analysis deliverables, not only to determine the integrity of engineering

3.4 Application Modelling of Reliability and Performance in Engineering Design 255

Fig 3.59 Overview of the selected equipment technical data worksheet

design but also to verify and evaluate the commissioning of the plant These tasks can also be applied sequentially in a RAMS analysis of process plant and general engineered installations that have been in operation for several years

Some of these activities include the following:

• systems breakdown structure development,

• establishing equipment technical specifications,

• establishing process functional specifications,

• developing operating specifications,

• defining equipment function specifications,

• identifying failure characteristics and failure conditions,

• developing equipment fault diagnostics,

• developing equipment criticality,

• establishing equipment performance measures,

• identifying operating and maintenance tasks,

• developing operating procedures,

• developing maintenance procedures,

• establishing process cost models,

• developing operating and maintenance strategies,

• developing safe work practices,

256 3 Reliability and Performance in Engineering Design

Fig 3.60 Overview of the selected equipment technical specification document

• establishing standard work instructions,

• identifying critical spares,

• establishing spares requirements,

• providing for design modifications,

• simulating critical systems and processes.

The results of some of the more important activities will be considered in detail later, especially with respect to their correlation with the RAMS theory, and failure data that were obtained from the plant’s distributed control system (DCS) operation and trip logs, 18 months after the plant was commissioned and placed into operation The objective of the comparative analysis is to match the RAMS theory, specifically

of systems and equipment criticality and reliability, with real-time operational data after plant start-up

Analysis of selected functions of systems/assemblies/components is mainly a cat-egorisation of functions into operational functions that are related to the item’s working performance, and into physical functions that are related to the item’s mate-rial design The definition of function is given as “the work that an item is designed

to perform” The primary purpose of functions analysis is to be able to define the

failure of an item’s function within specified limits of performance This failure of

an item’s function is a failure of the work that the item is designed to perform, and

3.4 Application Modelling of Reliability and Performance in Engineering Design 257

Fig 3.61 Analysis of development tasks for the selected system

is termed a functional failure Functional failure can thus be defined as “the inability

of an item to carry out the work that it is designed to perform within specified limits

of performance”.

The result of functional failure can be assessed as either a complete loss of the item’s function or a partial loss of the item’s function From these definitions it can

be seen that a number of interrelated concepts have to be considered when defining

functions in complex systems, and determining the functional relationships of the

various items of a system (cf Fig 3.62)

The functions of a system and its related equipment (i.e assemblies and compo-nents) can be grouped into two types, specifically primary functions and secondary functions The primary function of a system considers the operational criteria of

movement and work; thus, the primary function of the system is an operational function The primary function of a system is therefore a concise description of the reason for existence of the system, based on the work it is required to perform Primary functions for the sub-systems or assemblies that relate to the system’s pri-mary function must also be defined It is at this level in the SBS where secondary functions are defined Once the primary functions have been identified at the sub-system and assembly levels, the secondary functions are then defined, usually at component level (Fig 3.63) Secondary functions can be both operational and phys-ical, and relate back to the primary function of the sub-system or assembly The

258 3 Reliability and Performance in Engineering Design

Fig 3.62 Analysis of selected systems functions

secondary functions are related to the basic criteria of movement and work, or shape and consistency, depending on whether they are defined as operational or physical functions respectively

The third category in the RAMS analysis list is the specifications option, which is

similar to the overview option but with more drill-down access to the other activities

in the program, and includes specifications as illustrated in Fig 3.64 of selected major development tasks such as:

• Equipment specifications

• Systems specification

• Process specifications

• Function specifications

• Detailed tasks

• Detailed procedures

• Spares requirements

• Standard work instructions.

An engineering specification is an explicit set of design requirements to be satisfied

by a material, product or service

3.4 Application Modelling of Reliability and Performance in Engineering Design 259

Fig 3.63 Functions analysis worksheet of selected component

Typical engineering specifications might include the following:

• Descriptive title and scope of the specification.

• Date of last effective revision and revision designation.

• Person or designation responsible for questions on the specification updates, and

deviations as well as enforcement of the specification

• Significance or importance of the specification and its intended use.

• Terminology and definitions to clarify the specification content.

• Test methods for measuring all specified design characteristics.

• Material requirements: physical, mechanical, electrical, chemical, etc targets and

tolerances

• Performance requirements, targets and tolerances.

• Certifications required for reliability and maintenance.

• Safety considerations and requirements.

• Environmental considerations and requirements.

• Quality requirements, inspections, and acceptance criteria.

• Completion and delivery.

• Provisions for rejection, re-inspection, corrective measures, etc.

260 3 Reliability and Performance in Engineering Design

Fig 3.64 Specifications of selected major development tasks

The specifications worksheet of selected equipment for consideration during the de-tail design phase of the engineering design process automatically integrates matched

information pertaining to the equipment type, with respect to the following;

• equipment technical data and specifications, obtained from the technical data

worksheet and technical specifications document,

• systems performance specifications relating to the specific process specifications,

• process performance specifications relating to the required design specifications,

• equipment functions specification relating to the basic functions from FMEA,

• typical required maintenance tasks and procedures specification from FMECA,

• the essential safety work instructions obtained from safety factor and risk

analy-sis,

• installation logistical specifications with regard to the required contract warranty

spares

The specifications worksheet is a systems hierarchical layout of selected equipment,

based on the outcome of the overall analysis of specifications of selected equip-ment for consideration during the detail design phase of the engineering design process The worksheet (Fig 3.65) is automatically generated, and serves as

a systems-oriented pro-forma for electronically automated design reviews Com-prehensive design reviews are included at different phases of the engineering design

3.4 Application Modelling of Reliability and Performance in Engineering Design 261

Fig 3.65 Specifications worksheet of selected equipment

process, such as conceptual design, preliminary or schematic design, and final de-tail design The concept of automated continual design reviews throughout the engi-neering design process is to a certain extent considered here, whereby the system al-lows for input of design data and schematics by remotely located multi-disciplinary groups of design engineers However, it does not incorporate design implementation through knowledge-based expert systems, whereby each designed system or related equipment is automatically evaluated for integrity by the design group’s expert

sys-tem in an integrated collaborative engineering design environment.

The fourth category in the RAMS analysis list is the diagnostics option that

en-ables the user to conduct a diagnostic review of selected major development tasks such as illustrated in Fig 3.66:

• Systems and equipment condition

• Equipment hazards criticality

• Failure repair/replace costing

• Safety inspection strategies

• Critical spares requirement.

Typically, systems and equipment condition and hazards criticality analysis includes activities such as function specifications, failure characteristics and failure condi-tions, fault diagnostics, equipment criticality, and performance measures

262 3 Reliability and Performance in Engineering Design

Fig 3.66 Diagnostics of selected major development tasks

The following RAM analysis application model screens give detailed illustrations

of a diagnostic analysis of selected major development tasks.

Condition diagnostics in engineering design relates to hazards criticality in the development of failure modes and effects analysis (FMEA), and considers criteria

such as system functions, component functional relationships, failure modes, failure causes, failure effects, failure consequences, and failure detection methods These criteria are normally determined at the component level but the required operational specifications are usually identified at the sub-system or assembly level (Fig 3.67) Condition diagnostics, and related FMEA, should therefore theoretically be de-veloped at the higher sub-system or assembly level in order to identify compliance with the operational specifications, and then to proceed with the development of FMEA at the component level, to determine potential failure criteria In conducting the FMEA at the higher sub-system or assembly levels only, the possibility exists that some functional failures will not be considered, and the failure criteria will not

be directed at some components that might be most applicable for design review

It is necessary to conduct a condition diagnostics, and related FMEA, at the

com-ponent level of the equipment SBS, since the failure criteria can be effectively iden-tified only at this level, whereas for compliance to the required operational spec-ifications, the results of the FMEA can be grouped to the sub-system or assembly levels In practice, however, this can be substantially time consuming because a large