Dipak Mistry of International Paint explains the key criteria for the correct specification of passive fire protection used on offshore oil and gas platforms in some of the world’s harshest environments.
Dipak Mistry has 24 years’ experience in the protective coatings market, 16 of those in passive fire protection. He is protective coatings technical director for International Paint, part of AkzoNobel, the world’s largest coatings and paint supplier.
What is passive fire protection (PFP)?
Dipak Mistry: PFP protects steel from the effects of fire. Historically, cement-based ‘fire protection’ was used to protect steel structures in the offshore oil and gas industry. However, the use of cementitious products was found to lack the required durability in harsh offshore environments.
Born in the 1970s from NASA’s Apollo space programme, Chartek was the world’s first epoxy intumescent PFP material. Chartek swells or intumesces when engulfed by fire. The intumescence provides an insulating and durable char layer that slows the temperature rise of the steel substrate, which means that steel maintains its integrity for longer and so gives people more time to escape a burning platform before structural collapse. Chartek can be seen as a material that helps protect people’s lives.
Why is it important that PFP is used on offshore oil and gas platforms?
Fire protection is a moral and legal requirement to ensure the safety of people at work and therefore a great deal of thought should go into the specification of such systems.
Unprotected steel will reach 400°C (752°F), in less than five minutes in a fire on an oil and gas installation. This typical critical core temperature is when steel starts to lose its load-bearing capacity. Chartek materials will significantly prolong the time for the steel to reach the critical core temperature and allow safe evacuation of personnel from the structure.
What should an owner or engineer take into account when specifying PFP?
Given that for most of its life epoxy PFP acts as an anti-corrosive system, it is important that it has excellent durability and corrosion-protection properties in exposed, harsh, offshore environments.
Critically, it is also important that epoxy PFP systems maintain their fire performance after prolonged exposure. The industry accepts that if after ‘weathering’ the time to reach the design critical core temperature (typically 400ºC) is within 10% of the non-weathered sample when exposed to a hydrocarbon fire then an acceptable insulation is maintained for structural stability.
What performance test standard should be used to assess the effects of weathering?
The most accepted accelerated corrosion test standard in the oil and gas industry is ‘ISO20340 – Performance requirements for protective paint systems for offshore and related structures’. It most closely reflects the cyclic wet/dry weather environments faced by coatings in the oil and gas offshore market.
The ISO20340 standard is used by NORSOK M501 Edition 6 System 5A to pre-qualify epoxy passive fire protection systems. The standard assesses epoxy PFP systems after exposure to 25 weeks of QUV/ condensation, continuous salt spray and -20°C freeze cycles.
The System 5A pre-qualification requirements recognise that in the real world top coats may not always be present on epoxy PFP and so cannot be relied on to ensure that the epoxy PFP coating system remains mechanically robust and able to provide both optimum corrosion protection and fire performance. For this reason the standard expects the epoxy PFP coating system to pass System 5A without a topcoat.
This means that the epoxy PFP coating system must demonstrate mechanical integrity by having a pull-off value greater than 3MPa, which is greater than 50% of the initial un-weathered pull-off value, and a corrosion creep value less than 3mm when using a zinc primer. Epoxy PFP materials with a high retained pull-off value tend to correlate well with products having low water absorption and high hardness retention, whereas the reverse is the case if water absorption is high.
Norsok M501 Edition 6 System 5A also critically requires that the epoxy PFP systems maintain their fire performance after weathering. The standard requires that the weathered sample must have a time to reach the design critical core temperature, typically 400°C, within 10% of the non-weathered sample when exposed to a hydrocarbon fire.
What about jet fires? What is the key test standard we should use?
A jet fire is created when hydrocarbon pressurised gases are released through an orifice and then ignited; peak temperatures can exceed 1,200 °C.
Until recently, epoxy PFP jet fire assessment was inconsistent, done on an ad-hoc basis using various technical reports and test setups. With the introduction of the only internationally recognised jet fire standard – ISO22899-1 and the accompanying ISO TR22899-2 – the oil and gas industry now has a formal procedure to accurately assess and reliably rate epoxy PFP jet fire performance.
ISO22899 is also the only jet fire standard for which classification societies, currently giving type approvals for passive fire protection, will give type approval certificates (TACs). The ISOTR22899-2 standard gives guidance on how to assess epoxy PFP jet fire resistance at different temperatures
The TAC should state the critical core temperature for which it is valid so that it is clear under what conditions the jet fire thicknesses have been determined. This is the only way to ensure that specifications are correct for the required jet fire duration.
Any product used for offshore structures should ideally have a proven track record, be qualified to internationally recognised standards for fire and environmental performance and also be subject to a third-party follow-up service to ensure product quality. This is the only guarantee that the product is fit for purpose.