Hydrocarbon Fire Protection for Structural Steel
Fire is a terrible and ever present danger for hydrocarbon processing facilities, capable of inflicting huge social, political, financial, and ecological devastation. The 2012 fire and blast at Venezuela’s Amuay refinery killing 48 people and causing an estimated US$1.7billion of damage, is just one of dozens of reported fires that occur annually at refineries around the world.
Many blame these incidents on cost-cutting and lack of preventative maintenance of safety critical systems. All involved in protecting these facilities have a duty of care to help mitigate against such disasters by reducing the potential for fire to acceptable levels.
Hydrocarbon & Jet Fire
The two most common types of fire that are likely to occur at a hydrocarbon processing facility are hydrocarbon and jet fire. Hydrocarbon or ‘pool’ fires occur when a flammable liquid leaks from a vessel or pipeline to form a reservoir, which then ignites. A hydrocarbon fire will generate temperatures of up to 1100°C within ten minutes of ignition and create heat fluxes of around 150-200 kW/m2.
A jet fire usually involves a forceful flame, created by highly combustible fuel that is released in a particular direction as a result of a rupture to a pressurised vessel or gas line. This situation can create particularly intense levels of localised heat, plus exaggerated degrees of heat flux and turbulence, and it is far more capable of eroding fire protection measures, damaging structural steelwork and rupturing other vessels and pipework than a non-hydrocarbon blaze.
Structural Steel Protection
Petrochemical facilities often include major structural components made from steel including structural steel columns and beams, steel pipe-racks and steel supports for storage vessels containing flammable, combustible or toxic liquids.
Steel is a material often viewed as being less prone to the damaging effects of fire due to its rigidity and strength, with the ability to withstand whatever comes its way. Unfortunately this is not always the case. When exposed to temperature rises, steel can begin to lose its strength with alarming speed, particularly when under duress from hydrocarbon and jet fires. Passive fire protection measures slow the rate of heat transfer into the steel structure and significantly delay the time it takes to reach the point where structural failure occurs. This allows more precious time to evacuate personnel, activate emergency shut-down valves (ESDVs) and bring a fire under control, helping to limit the destructive effects of a major blaze.
Traditional methods for protection of structural steel elements include cementitious sprays and intumescent coatings that are applied to the surface of the steel element providing a permanent barrier. Increasingly those responsible for designing and maintaining petrochemical facilities are seeking more flexible solutions that allow ease of upgrade, maintenance, and periodic inspection for damage and degradation, including corrosion under insulation.
Corrosion under Insulation (CUI)
Corrosion under insulation (CUI) is a severe form of localised corrosion that occurs in carbon and low alloy steel equipment that has been insulated. CUI occurs when water is absorbed by the insulation and, over time, the equipment begins to corrode as it is exposed to water and oxygen. CUI is particularly common in refineries and process plants that operate equipment at high temperatures.
Research suggests that CUI is responsible for the highest incidence of leaks in refineries and chemical facilities and costs the industry tens of millions of dollars a year in repair and maintenance costs.
CUI is often difficult to detect on steel that has been fireproofed with cementitious spray or intumescent coatings because the insulation hides the corrosion problem until it is too late. Inspecting for corrosion under coated fireproof insulation usually requires cutting small sections in the coating surface and carrying out ultrasonic testing. If corrosion is ultimately discovered, the entire coating system must be removed and replaced. This whole process is expensive, time consuming and disruptive to ongoing operations. Subsequently, inspections for corrosion under insulation are not completed regularly enough often resulting in tragic consequences.
US Gulf Coast Refinery
More than 15 years ago, a large oil and gas refinery on the US Gulf Coast installed 3M E-mat to protect structural steel. The material was applied to protect the vessel skirts and two-story tall steel legs that support many large spherical tanks containing flammable petroleum distillates in the refinery.
Two layers of 3M E-mat were wrapped around the approximately 61-centimetre-wide legs and held in place with stainless steel banding. Although not required, a stainless steel jacket was then applied on top of the 3M E-mat to protect the material from rain, salt in the humid air, dust, and ultraviolet light in sunlight.
An engineer at the refinery recently contacted 3M and requested assistance in identifying the 3M material. At the time, the plant was conducting a periodic inspection of the structural steel in various areas of the refinery to determine if corrosion beneath the 3M E-mat was occurring. “It only took a moment to identify the 3M Interam Endothermic Mat. The 3M product was well protected by the stainless steel jacket and looked like it was new. There was no deterioration at all,” said Matthew Aguirre, Sales Representative, 3M Building & Commercial Services / Fire Protection Products. “The structural steel also looked great and showed no sign of rust or corrosion.”
The non-destructive inspection and testing for corrosion and compliance was performed quickly, and the 3M E-mat that had been removed without being damaged was simply reinstalled. A few damaged pieces that occurred during inspection needed to be replaced. “Refinery officials were very pleased with the inspection results and they were surprised by the longevity of 3M E-mat,” said Aguirre. “The material does not dry out so maintenance is effortless. It also allows easy inspection. Just cut a piece to inspect the structural steel, then foil tape it back into place and add the stainless steel band. It’s that easy.”
Flexible materials using endothermic technology release chemically bound water to slow heat transfer when exposed to high temperatures or flame and can protect structural steel components from hydrocarbon fire for up to four hours. Unlike fireproof coating systems, endothermic mats can be easily removed and re-applied for routine corrosion inspections, maintenance, or repairs.
This sheet material has a bonded aluminium foil outer layer and is both flexible and tough enough to be wrapped around a wide variety of potentially exposed vulnerable equipment. 3M Interam Endothermic Mat (or ‘3M E-mat’), for example, incorporates endothermic technology and has been proven to provide outstanding performance for a range of fire scenarios including large hydrocarbon pool fires in accordance with UL 1709 (ASTM E 1529).
3M E-mat wraps around structural steel elements and is held in place by stainless steel strapping, with aluminium foil tape and fireproofing sealant used to cover gaps, seams and termination points. In most circumstance, little or no preparation to the steel substrate is required. E-mat can also be applied directly over existing cement or block where upgrade in fire protection is required. 3M E-mat does not encourage corrosion and can be installed with or without a stainless steel jacket, which helps preserve the system in extremely harsh conditions. The material satisfies UL 1709 environmental test standards both with and without the stainless steel jacketing.
CUI is a common problem shared by hydrocarbon and gas processing facilities around the world. CUI is difficult to detect because it is often hidden by a fireproof coating that masks the corrosion problem until it is too late. Flexible and re-enterable endothermic wrap systems such as 3M E-mat offer many functional and economic benefits to asset owners.
3M E-Mat has been used extensively around the world for over 30 years and is ideal for effective fire safety solutions for both offshore and onshore energy environments.
For further information, go to www.3M.com/firestop