The Basics
Composite Material
- Reinforcements for strength - glass, carbon, synthetics, fibres, flakes
- Thermoset resin matrix protects reinforcement and transfers loads to reinforcement - isophthalic, vinyl ester, epoxy resins
- Manufacturing methods varied - contact moulding, filament winding, spray up, resin transfer moulding, prepregs, pultrusion
- All fibreglass pump station for residential wastewater
Features of Fibreglass
- High strength/weight ratio
- Ease of fabrication - eg complex shapes, coloured
- Fibres can be placed where the loads are
- Dimensional stability - shapes can be duplicated accurately
- Good weathering properties - eg can be placed outside
- Good chemical resistance - with correct resin choice
- Proven performance worldwide in industry for over 50 years
Stress & Strain
Ultimate Strength
- Yield and Ultimate Strength are same
- Ultimate Strength reduces with increasing temperature
- When failure does occur it can be sudden and dramatic
- Failure initiates at point of max stress
Good Design
- Use high safety factors, SF = 5 minimum for structural FRP
- Build to standards
- Analyse stresses fully with FEA (Finite Element Analysis)
- Ensure no over-stressing can occur
- Avoid stress concentration points
- Maintain regular inspections
- If cracks or “weeping” occur, initiate maintenance immediately
Creep
What Happens
- Ultimate Strength of FRP under load (pipes, tanks) reduces with time
- Can lead to failure some years after installation
- Reduction in Ultimate Strength depends on service temp and HDT (heat distortion temp) of resin
Good Design
- Use higher safety factors for FRP under constant load ... minimum 10, eg for tanks and pipes
- Use resin with HDT preferably 20ºC above max service temp
- Avoid stress concentration points
Chemical Resistance
Fibreglass has wide range of corrosion resistance depending on resin selection, and is ideal for industrial applications. See How do I choose the right resin for my fibreglass products for more information.
Standards & QA
Standards to specify include:
- AS 2634 - good all round standard used in NZ and Australia - still in use and in process of being superceded.
- BS 4994 - for tanks and pipes especially
- EN 13121-3-2004 - European standard
- ASTM RTP1 - USA standard includes pressure vessels
- AS/NZS 3751 - FRP pipe for public utilities
- AS/NZS 2566 - for buried flexible pipelines
- AS/NZS 1170 - for seismic and wind loads
Quality Assurance available
- ISO 9001 Accreditation
- Materials traceability
- Design Audits
- Standardised laminates tested (see table)
- QA checks during manufacture
- Post fabrication thickness checks
- Post cure Barcol hardness checks
- On site QA logs for coatings and linings
- Coatings and linings - sparktesting
- Coatings and linings - thickness check
Barrier Coatings
Key Success Criteria
- Withstand chemical attack - choose correct resin
- Resist permeation - less than 0.1 perms (ASTM E-96) or impedance greater than 1 x 10^8 ohm-sq.cm at 0.1Hz per EIS testing
- Withstand other service conditions - eg abraision, flexing, cleaning, temperature fluctuations, physical abuse
- Properly designed and prepared substrate - cleaned, steel blasted to minimum profile, concrete surface strength adequate
- Be installed correctly - using specifications and QA procedures
Lifecycle Cost (LCC) Analysis
LCC is better than Initial Cost in evaluation that relative cost of a coating. Costs above are current day costs. No allowance is made for downtime or lost manufacturing time when coatings replaced.