A case study in environmentally responsive development
FyreWrap is used extensively in the marine and offshore fire protection environment
Unifrax has been manufacturing energy-saving high temperature fibrous insulation since the invention of the revolutionary Fiberfrax® alumina-silicate fibre in the 1940’s. Initially used as lightweight and highly efficient furnace linings, this type of technology was transferred to the marine and offshore passive fire protection market in the 1970’s.
In recent years the IMO has been actively involved with reducing greenhouse gas (GHG) emissions from commercial shipping and from 2013 new regulations come into force. In addition to the GHG issue, since 2009 the cost of bunker fuel has risen by around 56%. These two issues taken together make weight savings for marine operators of increasing interest. In light of these regulatory developments Unifrax undertook a development programme to reduce the weight of the FyreWrap marine and offshore fire protection systems with the goal being a typical weight reduction of approximately 25% versus the conventional systems.
FyreWrap Blankets are part of a group of materials known as Low Bio-Persistence Wools (LBPW) and are of a chemistry family known as alkali earth silicates (AES). The FyreWrap composition is SiO2 (61- 67%), CaO (27- 33%) and MgO (2.5 – 6.5%). Figure 1 shows the composition rage of AES fibre compared with typical mineral and glass wools. The fibres are needled to give strength and structure to the blanket and no binder is used. AES fibres shave the benefit that they do not melt until around 1330°C.
AES Wool Composition
High purity oxides are melted in an electric arc furnace at a temperature close to 2000°C and then fiberised by means a series of spinning wheels. Fiberisation is never 100% efficient and there is always a portion of material which is unfiberised and this is known as shot.
Standard AES Wool
The insulation performance of fibre products is influenced by a number of factors including shot content, fibre diameter, bulk density and product thickness. As the aim of the development was to reduce the system weight increases in density were discounted and the development efforts were focused on engineering the fibre diameter and shot content to give the required performance improvement. It was also believed to be important that system thickness should be maintained as close as possible to the traditional systems and the handling strength optimised. Following an exhaustive engineering and development exercise which looked at different designs of spinning wheels, number of spinning wheels, wheel sizes and speed of rotation, a new spinning system emerged and FyreWrap LT Blanket was the result.
Low Thermal Conductivity
The new LT grade blanket can typically contain around 30% more fibre than a conventional AES blanket product and 15% less large shot. This gives an improvement in thermal conductivity of at least 20%. Thermal conductivity is the measure of the ability to transfer heat so the 20% improvement in FyreWrap LT Blanket thermal conductivity means a significant improvement in insulating performance. Figure 4 shows the thermal conductivity curves for 128kg/m³ FyreWrap LT and conventional AES blanket.
Thermal Conductivity
What does this mean in the real world? If we take a standard restricted use H 120 steel bulkhead as an example the FyreWrap LT Blanket as shown in Figure 5 gives a weight saving of 27% vs. the conventional AES wool system and an impressive 33% versus a mineral wool mat system. In fact the saving is even more as the outer layer of the mineral wool system is a wired product and the weight of the chicken mesh also needs to be taken into account.
H120 Weight Saving
The weight saving per square metre versus the mineral wool is at least 3.5kg/m² so for each 1000m² of this system installed the saving is 3.5 tonnes.
Improved Installation
The new LT manufacturing technology also imparts benefits in the handling and installation characteristics. The higher fibre content gives the LT Blanket improved tensile strength as seen in Figure 6. Stronger blankets are more difficult to pull apart and are better able to withstand the rigours of installation such as bending around corners and stiffeners.
Tensile Strength Improvement
The nature of the fibre and the low shot content give FyreWrap LT Blanket a high level of resilience making it very forgiving to install and resist over compression.
Less large shot and 30% more fibre per unit mass allows the remaining smaller shot to be ‘locked away’ from the surface resulting in minimal free particles within the fibre matrix. This, along with the increased tensile strength results in higher vibration resistance.
The new LT version is softer and smoother to handle and during installation releases significantly less dust.
Applications
Unifrax now has over 20 tested systems for marine and offshore structural bulkhead & decks. Approved systems are available for steel structures with ratings from A30 to H120 and for aluminium structures with ratings of A30, A60 and both 30 minute and 60 minutes to the HSC code.
FyreWrap LT Blanket is now being used in new designs of jet fire pipe insulation where an air gap is utilised between the insulation and the pipe. The increased insulation performance of the blanket allows the overall diameter of the system to be kept low even with the presence of the air gap.
FyreWrap LT Blanket can be used to replace standard AES blanket in insulation on hot process pipework. As an example, on a pipe of 250mm operating at 400°C the replacement of 100mm of 128kg/m³ ‘old’ FyreWrap Blanket by 75mm of 128kg/m³ of FyreWrap LT Blanket gives essentially the same level of heat loss and cold face temperature. However the overall diameter and circumference of the system is lower, the circumference is reduced from 1413mm to 1256mm, 157mm. This becomes significant when stainless steel cladding is used. For every liner meter of pipe run this reduced insulation thickness gives a saving of 0.157m² of cladding or 157m² per 1000 linear metres of pipe run. On a large project the savings derived can be huge.
Other applications for FyreWrap LT Blanket include fire door infill and insulation in jet fire rated enclosures where weight and/or space saving have been important requirements.
Summary
The new FyreWrap LT Blanket from Unifrax is an important new development which offers designers in the marine and offshore passive fire protection markets the option to save significantly on weight of the systems installed. This gives significant potential for knock on cost savings through reduced fuel consumption, increased pay-loads and reduced material, use.
FyreWrap LT Blanket has:
Higher fibre – lower shot content
Much improved insulation performance
No binder to degrade or burn out
Improved handling characteristics
FyreWrap LT Blanket does:
Save Weight
Save Materials
Save Fuel
Save Lives
Save the Environment
