the perils of overdesign tamilnadu engineers forum perils in design... · tamilnadu engineers forum...
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Tamilnadu Engineers Forum5th International Conference – November 2014
The Perils of Overdesign
Background
Over design is not apparent
Under design has an implied failure
Design Targets are set Internally by business Externally by authorities
These are minimums engineers must achieve
Targets can be any range of variables Safety Environmental Health Production rates Quality of product Cost & Schedule
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Failure to meet a target
Visible to many – e.g BP Deep Water Horizon – Poor design and inadequate installation management – did not meet requirement
Can have serious impacts – short and long term – workers on platform, fisheries, tourism, local businesses – life, cost, business reputation, business failure
CEO - “I want my life back”
Impact on UK Pension values
Still in legal dispute
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Overdesign
Myths about over design
Nobody notices or visible to few
Its always safer
It does not matter to anyone
We meet our target so no one will care
It will be noticed and there will be a price – in terms of resources including materials manpower and money.
Sustainability is about protecting all resources and using them to our best adavntage
In the long run it does matter
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Oversizing
Causes of oversizing can be many
We don’t know the feed stock when before we build – wells to be drilled in upstream, oil to be purchased for downstream refinery– so we estimate and add margins to cover uncertainty
We don’t know how much we need to produce – what is the market going to be in 1 year, 5 years, 10 years and beyond – so we estimate and add margins to cover uncertainty
We set environmental limits – maximum and minimum temperatures for instance
We then add a “design” margin – typically 10% without actually defining its purpose
Supply chain adds its margins based on the terms and conditions
Impact will be seen when we put the facility to use
Commissioning takes longer as plant is not running at the optimum point
Plant running unstable or inefficiently
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Typical Issues – Centrifugal compressor
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Limited turndown Head is impacted by fluid composition Power requirements impacted by fluid
composition The oversizing results in Loss of efficiency Running closer to unsafe surge
conditions Larger ancillary equipment Increase wear and maintenance on
recycle controls used to control machine
Greater Capex and Opex
Similar applies to Pumps
Typical Issues – Tanks
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Improved Performance! Larger tanks – diameter
increases as height is limited Takes more land More materials in construction
(pipe and cable) due to greater distance
More cost for utilities due to greater demand
Greater risk in the event of fire Increased capex – tank cost is
proportional to volume
Typical Issues
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Pipeline Larger diameter and wall thickness More construction costs – welding,
PWHT, logistics due to weight Deeper trenches – cost and safety
issue In operation stratification / separation
of process fluids Increased settlement of solids Increased corrosion – including
failure
More frequent cleaning / inspection requirements
Greater Capex and Opex
Utility Larger facilities usually require more
utilities Power – transfer of materials, lighting Air Water Control systems Buildings Land
All result in greater Capex and Opex
Typical Issues – Processes
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Distillation Liquid channelling / loss of seal Insufficient vapour Loss of separation efficieny Products don’t meet specification
Cyclonic Separation cyclones / hydrocyclones Insufficient velocity to effect separation Carryover of products into the wrong streams Failure of downstream processes
Getting it right
Requires Planning and Control
Gate systems are used to plan and control Appraise – Concept – inputs / output targets including tolerance must be defined Define Execute Operate
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We must have the right targets and basis before moving to next stage
Conflict of Requirements
Projects have HSE, Quality, Cost and Schedule goals
We cannot always balance all requirements perfectly
Safety standards are fixed
Cost / Schedule changes limited
Quality takes the strain
Oversizing protects quality
Oversizing increases cost
Oversizing can increase time
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Quality
CostSchedule
HSSE
Risk
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The threat associated with uncertainty is often managed by over-sizing to remove the uncertainty.
Risk is defined as being:‘An uncertain event, feature, activity, or situation that can have a positive or a negative effect on your objectives’Risk are opportunities (positive effect) or threats (negative effect)
Risk is the product of the uncertainty of an event occurrence combined with the impact if it happens.
The threat of under-design results in over-design creates an opportunity that we overlook.
Acceptable Risk
Statutory authorities impose their own minimums with legal backup –often driven by society’s opinion
Business has its own targets – determined by stakeholders Standards of risk change over time – e.g. safety There are rarely the same for each project Example - Flood defences
New Orleans – 1 in 100 years failure Netherlands – 1 in 10,000 years
So designing for 1 in 1000 years would be seen as under design in Netherlands but over design in New Orleans.
Same applies to weather conditions – how often are we prepared to accept disruption due to snow, rain or wind
Perception and willingness to bare cost is critical and is this society, business or consumers.
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Risk Management
Typical Mitigation Approaches
Avoid – eliminate completely
Limit – accept not always
Insure – pay to cover loss
Provision for
Cost for
Time for
Manage
PROBABILITY
IMPACTLow High
High DETRIMENT
Avoid orlimit
Treat as cost and thereafter opportunity
Insure, provisionand limit
Provisionandmanage
Using appropriate Risk Management techniques is a tool to measure the effectiveness of design management
Over design generally “Avoids” – other approaches may be more appropriate based on actual risk.
Summary
We do not need to avoid all risks - some may be tolerable to the stakeholders
Tolerable risks should be acknowledged and managed
Every society and business has its own acceptance criteria –learn these before starting work
Challenge waste – think sustainably
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THANK YOU