FIREPROOFING FOR PETROCHEMICAL FACILITIES

Mark S. SchillingCorrosion Probe, Inc.

INTRODUCTION

Fireproofing is employed in refineries and petrochemical plants to minimize the escalation of a fire thatwould occur with the failure of structural supports and the overheating of pressure vessels. The damage that firecould potentially do very early on, could add significant fuel to the fire. The purpose of fireproofing therefore, is tobuy time. The traditional method of fireproofing has been poured-in-place concrete or gunite. Other fireproofingmaterials, such as lightweight cements, prefabricated cementitious board, and intumescent coatings are used to alesser extent, primarily in areas deemed less critical and where weight reduction is a significant benefit.

Typically, fireproofing is designed to protect the structural steel which supports high risk or valuableequipment. The failure point is generally considered to be 1000°F, as this is the point where steel has lostapproximately 50% of its structural strength. The aim then, is to prevent structural steel from reaching 1000°F forsome period of time. Tanks, pressure vessels, and heat exchangers may experience a significant cooling effect fromliquid contents and so, less fireproofing protection is generally required. Some thermal insulation systems mayserve a dual role as fireproofing and this is common with some pressure vessels. Piping may be insulated but it isnot generally considered to be fireproofed.

Fireproofing needs to be durable to survive the rigors of every day life in the plant so that if and when a firedoes occur, the fire endurance properties have been maintained and the fireproofing can be depended on to functionsatisfactorily. Everyday exposure may involve mechanical abuse, exposure to oil, solvents, and chemicals, andoutdoor weathering for prolonged periods of twenty, thirty, forty years or more. As a coating for steel, fireproofingmay provide a good measure of corrosion protection. When applied directly to steel, concrete may passivate thesteel surface by providing an elevated pH. Experience has shown, however, that passivation is less than certain,especially in coastal marine environments. Corrosion under concrete fireproofing can be significant. Intumescentcoatings promise better corrosion protection than concrete by virtue of their low permeability but cases of severecorrosion under fireproofing (CUF) have been reported with these materials.

Intumescent epoxies are complex proprietary materials. Concrete and some of the other materials that are used forfire protection are more familiar. The materials themselves may seem simple, but the important details of systemdesign are often overlooked.

DISCUSSION

Fireproofing is a misnomer because no material is completely fireproof. All construction materials aresubject to fire damage. What we really mean is fire resistant - we seek to resist potential fire situations for a givenperiod of time. Fireproofing is passive, built-in protection that buys time to fight the fire, shut off the fire’s fuelsupply and shut down the process. The aim is to minimize the overall damage incurred.

The decision to fireproof is driven by risk-based analysis. One needs to first consider the nature of the firethreat and then make an assessment of the required period of fire endurance for a wide variety of equipmentincluding structural steel, pressure vessels, heat exchangers, pipe supports, LPG spheres and bullets, valves, andcable trays. The location of specific equipment within a process unit is important, as is a unit’s location with regardto neighboring facilities.

TEST METHODS AND REQUIRED TIME RATING

No fire test method is going to be typical of a real fire situation and so, there is no single correct or "best"fire test method. Standardized testing simply provides a frame of reference for relative comparisons of fireproofingmaterials and designs. In the 70s, ASTM E119 "Fire Test of Building Construction Materials" was the onlyinternationally accepted standard for investigating the performance of fireproofing materials. This test method,however, was designed to measure the fire performance of walls, columns, floors, and other building members insolid fuel fire exposures. It does not simulate the high intensity of liquid hydrocarbon-fueled fires. The slope of thetime/temperature heating curve for the typical solid fuel fire is significantly different than that of the moreinstantaneous and intense liquid hydrocarbon fire. Wood, for example, burns fairly slowly. Volatilization of thefuel from the surface is slow and wood can form a char which provides some protection. Liquid hydrocarbonsvolatilize quickly to feed a fire, and there is no protective char formation. In recognition of this, several of the majoroil companies developed their own outdoor hydrocarbon pool fire tests. These tests were more representative of thethreat posed to refineries and petrochemical plants but reproducibility was not very good. A better test was desired.

UL 1709 "Rapid Rise Fire Tests of Protection Materials for Structural Steel" and ASTM E1529 StandardTest Methods for Determining Effects of Large Hydrocarbon Pool Fires on Structural Members and Assemblies,were first issued in the early 90s. Both tests involve a test furnace which develops an average temperature of2000°F (1093°C) within the first 5 minutes of the test. The principal difference is that UL 1709 involves a total heatflux of 65,000 BTU/ft2-hr (205 kW/m2), whereas the ASTM E1529 heat flux is only 50,000 BTU/ft2-hr (158kW/m2). Temperature is an important parameter but heat flux is a better measure of the amount of heat stress beingplaced on a material (how fast heat works on a material). Although the temperature is the same, the higher heat fluxof UL 1709 makes it a more severe test.

Where fireproofing is required, the level of fireproofing varies with the application in the plant. Typicalprotection requirements for a refinery or petrochemical plant might be as follows:

• For structural steel, a facility may require a fire test rating of two or three hours. Poured-in-place concrete orgunite is most common with a specified minimum thickness of 2.0 to 3.0 inches (50-75 mm). Lightweightcementitious products may also be used.

• For steel vessels, a facility may require a fire test rating of one to two hours. Gunite applied at 1.5 to 2.0 inches(40-50 mm) may be required. Alternative fireproofing materials that provide a comparable fire resistance ratingmay be used, including systems that function as both thermal insulation and fireproofing.

• Plate and frame exchangers are a special concern because of the rubber gasketing material between plates.These exchangers are provided with a protective enclosure designed to prevent the exchanger from exceedingits maximum operating temperature for an hour or so. The maximum operating temperature is vendor specifiedand typically less than 300oF (150oC).

• Electrical and pneumatic components (including manual initiators, valve actuators, aboveground wiring, cable,and conduit) essential to emergency isolation, depressurization, and process shutdown are generally fireproofedto achieve a rating of at least 15-20 minutes. This equipment needs to function properly in the first few minutesof a fire.

FIREPROOFING MATERIALS

Concrete

The excellent fire protection afforded by concrete has been demonstrated time and time again over 90 yearsof experience in the petrochemical industry. The high mass and low thermal conductivity of concrete make it veryeffective at reducing heat input to the underlying structure. Poured-in-place concrete, using forms, is common forcolumns and beams. Gunite is pneumatically applied to spheres and other structures where the use of forms forpoured-in-place concrete is impractical. The principal drawback with gunite application is that it can be very messy.

Post-fire inspections have shown that concrete spalls to various degrees but the general conclusion is thatconcrete/gunite performs satisfactorily with the steel structures well protected. Wire reinforcement is commonlyused. Reinforcement does not prevent cracking and spalling of the concrete but it does minimize the loss offractured material during a fire exposure.

Excellent Fire Endurance of 30 Year Old Concrete

A refinery fire initiated at a gas oil line from a crude distillation unit and burned for about 12 hours. Themain pipe rack near the crude tower at the center of the fire was damaged beyond repair. The support structure forthe crude tower overhead equipment was severely damaged. The aluminum jacketed thermal insulation on vesselsand exchangers was destroyed (aluminum melts at about 660°C or 1220°F) but most pressure vessels and heatexchangers, showed no visible signs of permanent damage, primarily due to the cooling effect of liquid contents.Gaskets that had been damaged and high strength bolts that had been tempered by the fire exposure, had to bereplaced.

Thermal expansion and contraction on structural support columns near ground zero caused a good deal ofcracking and delamination of the concrete fireproofing; however, no evidence of deep damage to the concrete wasfound. The main concern was for the support structure of the crude distillation tower as the refinery is located in aseismic zone. The radiant heat and direct fire exposure caused spalling of the 30 year old concrete cover on theexterior of the vessel skirt. Firewater cooling added to the spalling problem. Some rebar was exposed at the crudetower foundation, most notably on the side of the tower that faced the fire. Concrete was removed for inspection ofthe crude tower skirt and anchor bolts. No heat buckling of the skirt or distortion of the bolt seatings was observed.Bolts were checked for cracks and hardness measurements were made to confirm strength. The concretefireproofing had prevented any permanent damage to the vessel skirt and anchor bolts. The 30 year old concretewas now a mess but it had served its function. Companies require that their fireproofing systems pass standardizedtests, such as UL 1709 or ASTM E1529. The test requirement is only a few hours, at most. Real world experiencewith concrete fireproofing confirms time and time again (unfortunately), that concrete can provide the neededprotection in real fire scenarios, for many hours.

Problems with Concrete

Concrete is a comparatively simple, well understood commodity item that is readily available around theworld. The fact that satisfactory properties can be achieved without specialized skill is a benefit. Still, there is apotential for misuse and misapplication of concrete. All concrete is not created equal. Poor quality water, sand,and/or aggregate have resulted in some notable and much publicized problems.

Concrete fireproofing was applied to structural supports at a U.S. Gulf Coast facility. The specificationcalled for 3000 psi (20.9 MPa) compressive strength concrete reinforced with 14 gage galvanized hex-mesh wire onuncoated structural steel. Concrete was applied in a boxed or blocked design to fill the web of the flange onstructural beams and columns and to a minimum cover of 2 inches (50 mm). After 20 years, concrete was spallingfrom the faces of many beams and columns. It was estimated that almost four miles of concrete on structural steelneeded repair due to corrosion damage of the underlying steel. An investigation was undertaken to determine thecause and to find a suitable repair.

Core samples of the concrete were taken for laboratory chemical analysis and testing which includedcarbonation, chloride content, permeability, and determination of compressive strength. Some carbonation was

found to a depth of about one inch (25 mm) but it did not correlate well with the overall problem. Chloride contentranged from 0.004 to 0.073 weight percent, a little higher than 0.001 to 0.043 weight percent for concretefireproofing in other process units. The permeability was in the range of 10-6 cm/sec compared to a normalpermeability of 10-10 cm/sec (adapted ASTM D5084). Capillary tests were consistent with the permeabilitymeasurements with a 20 mm column of water being drawn into the concrete in less than thirty hours. Eightcompression tests gave an average compressive strength of only 2305 psi (16.1 MPa). Five of the eight compressiontests gave less than the specified value of 3000 psi. The low value was only 785 psi (5.5 MPa).

It was concluded that the concrete was originally placed with inadequate attention to quality. Concrete is acommodity item but it’s still an engineered material. The high permeability of the concrete and the large surfacearea of uncoated steel on the structural members prompted rapid consumption of the zinc on the reinforcing wire.With the zinc lost, the thin wire had little remaining life. CUF can be more severe than the corrosion of nearby baresteel because a corrosive electrolyte may be trapped and held in constant contact with the steel. With typicalatmospheric corrosion, there is usually some opportunity to dry-out, but with CUF the corrosion process maycontinue uninterrupted. The build-up of voluminous corrosion products between the steel and the concrete create astress that may cause cracking and spalling of the concrete, further accelerating corrosion by providing more sitesfor water entry.

Corrosion protection and fire resistance are interrelated. Corrosion of the steel substrate weakens theadhesion of the concrete and renders the concrete fireproofing more susceptible to explosive spalling during a fireexposure. Corrosion of the steel substrate can be insidious and by the time it manifests itself as rust bleed-thru andspalling of the concrete, the fire resistive properties have already been significantly impacted.

Lightweight Fireproofing

Concrete is heavy. A two inch thickness of concrete weighs approximately 25-30 lb/ft2 (125-150 kg/m2).The added weight may necessitate increased expense to beef-up new structures to be fireproofed. Existingequipment may have limitations on load bearing capacity that precludes the use of concrete. Lightweightcementitious fireproofing materials weigh significantly less, typically 5-10 lb/ft2 (25-50 kg/m2). Intumescentcoatings may contribute only 1-5 lb/ft2 (5-25 kg/m2). As the name implies, lightweight fireproofing materials have adistinct weight advantage. The increasing popularity of modular construction has widened the use lightweightfireproofing.

Lightweight Cementitious Products

Lightweight cementitious fireproofing products employ lightweight aggregates such as vermiculite, perlite,and diatomite in place of the usual sand and stone. The fire resistance is good and there is generally less spallingthan with dense concrete. The more porous structure of lightweight cementitious fireproofing materials betterenables water to escape. On the other hand, lightweight cementitious fireproofing materials are less durable thanconcrete, with lower resistance to physical abuse and a greater tendency for water absorption. It was once commonto apply these materials directly to steel. Today, most manufacturers no longer rely on the natural alkalinity of thePortland cement to passivate and protect the steel substrate. A primer coating is required for corrosion protection ofthe steel substrate. Lightweight cementitious fireproofing is often given a sealer coat to improve durability andresistance to moisture intrusion.

The main concern is in choosing a product that will have sufficient durability for the everyday non-fireenvironment. There s a wide range of products to choose from. The materials range in density from about 20 lbs/ft3

to about 55 lbs/ft3. Often, these products are divided into two groups - low strength (20-40 lb density) andintermediate strength (40-55 lb density). This promotes the perception that products in a group are equivalent, whenin fact that may not be the case. Lightweight cementitious materials can be designed to pass the standard fire testsbut in general, the lower density products are less durable during everyday exposure in the plant. Project engineersare always tempted — if two products are equivalent then it s strictly a matter of price. A rule of thumb is thatlower density means lower price. Be advised that some lightweights are truly lightweight, and may not meet one sexpectations for everyday durability. A bargain isn t a bargain unless the thing does what you need it to do. Oneneeds everyday durability if one is to have fireproofing capability some years down the road.

Intumescent Coatings

Intumescent coatings were first patented in 1948 and have been a commercial reality since about 1960.When exposed to sufficient heat, intumescent coatings expand to form a thick, insulating carbonaceous char. Theprocess is similar to that observed with the small black "magic snakes" Fourth of July novelty firework. Anyonewho has sat around a campfire knows that poking the fire around every now and then helps keep the fire going,because it disrupts the char.

Intumescence is a complex process involving thermal conduction through the coating with the heating ratedependent on the specific conductivity and thickness. The coating and steel substrate heat up until the reactiontemperature is reached. The chemical reaction then proceeds from the outer surface down into the thickness of thecoating. The thermal conductivity of the coating changes dramatically during this process and ultimately, reliance ison the thermal insulating capability of the char, and the ability of the char to remain adherent and physically intact.

Severe corrosion of the steel substrate has been reported beneath seemingly intact coating. In some casesthe problem has been tied to hot weather coating applications where chlorinated solvents were used to thin thecoating material. It s been reasoned that some of the chlorinated solvent remains trapped in the thick coating andthe chlorinated solvent may later degrade to give hydrochloric acid. However, it is possible that other things couldgo wrong with an intumescent coating.

Intumescent coatings are exceedingly complex coating materials. They need to perform all of the functionsthat other exterior weathering coatings do (adhesion, hardness, toughness, corrosion resistance, etc.) and then, whenexposed to sufficient heat, they need to transform and expand to form a thick, insulating, carbonaceous char. Theprocess is acid-driven with derivatives of phosphoric, boric, and sulfuric acid being most common. At elevatedtemperature, the acid is made available to trigger a chemical reaction with a carbonific component (e.g., starch orother carbohydrate, phenolic or urea resins, penterythritol, etc.) which results in its subsequent charring. A spumificcomponent (e.g., chloroparaffins, melamine) reacts to give the nonflammable gas, typically HCl, NH3, and/or carbondioxide, that is responsible for expanding the char into a voluminous, cellular mass. The escaping gases also act tocool the matrix and deprive the flame of oxygen at the surface of the char. All of these aspects - acid release, charformation, and gas generation, need to occur in a well coordinated fashion.

In the early days, some intumescent coatings were recommended for application direct to steel. Othersrequired a primer. Some products required reinforcement; others did not. The weathering and chemical resistancewas purported to be excellent. Some products claimed to activate right at 300°F (149°C); others started to showsome activity at temperatures closer to 150°F (65.6°C). Generically similar but proprietary products can be verydifferent.

Intumescent coatings have natural limits on applied thickness and they need reinforcement in someapplications so that expanded char remains intact and doesn t fall off under its own weight. The shape of thestructure to be coated is an important factor. For example, intumescents consistently have a lower fire endurancerating on pipe than on I-beams because on pipe, the coatings do not intumesce in the tangential direction andlongitudinal fissures develop. On the outside diameter of a tubular, intumescence increases the circumference,creating tensile stresses that are not accommodated by the material. The tensile stress causes cracks. In the case ofI-beams, fissures may develop at flange edges but in other areas the developing char is placed in compression.

Experience with intumescent epoxies over many years has been mixed. The first consideration is that theseare complex proprietary products and there have been a number of formulation changes over the years. The enduser is confronted with new and improved products on a periodic basis. The problem for the facility owner is justthat — it s a new product. It s different, unknown, untested. Newness can be a major hurdle when the bottom line isrisk assessment and risk mitigation. The second consideration is that intumescent coatings, like other organic paintsand coatings, degrade with prolonged outdoor weathering and exposure to slightly elevated temperatures.

The intumescent capability may be degraded by prolonged outdoor weathering or exposure to elevatedtemperatures. An intumescent coating exposed for ten years on vessels in the U.S. Gulf Coast environment showeddelamination, softening, blistering and other signs of deterioration. Samples of the coating were collected for lab

testing. The aged coating was heated in a furnace. It showed no intumescent reaction. It simply burned anddisintegrated.

A 15 year old intumescent coating on a propane drum at a western U.S. refinery was seen to be chalked andfaded but it looked to be otherwise intact. A sample chunk of coating was removed for testing. When heated slowlyin a furnace, the intumescent reaction kicked in at about 315°C (600°F), a little late perhaps, but with good charformation, a volume increase of approximately 50%. An actual fire exposure would be one-sided, with the coatingbonded to steel and the steel substrate cooled by the contents of the drum. However, this simple test showed that the15 year old intumescent coating could still provide reasonably good fire protection.

The general industry opinion has been that surface weathering (chalking) is of little consequence forintumescence. If the aged coating is otherwise intact and looks to be in reasonably good condition, it is expected toperform properly in the event of a fire exposure. That may not always be the case. Furnace testing is simple, quick,and inexpensive. If there s any doubt, a quick test is a prudent choice.

Thermal Insulation as Fireproofing

Fireproofing protects by insulating the substrate from the heat of a fire and so, thermal insulation systemscan provide a dual role. Insulation materials for low temperature service typically do not have good fire resistance.Most plastic foams are quickly destroyed by the heat of a fire. To improve fire resistance, polyurethane foaminsulation is commonly formulated with flame retardant additives. These are generally organo-phosphorouscompounds and/or halogenated organic compounds (chlorinated or brominated). Phosphorous compounds are usedto help provide a more stable surface char. Halogenated compounds interrupt flame chemistry. The two approachesare different and synergistic. Fire retardants do slow flame spread but the toxic fumes may contribute to problems.Corrosive residues may remain for months after a fire. In addition, some of the halogenated fire retardant additivesmay be leached from aging foam insulation over time. Many cases of severe CUI have been reported on tanks,primarily cold tanks (e.g., LPG), beneath polyurethane foam insulation. In such cases, the polyurethane foam is wetor damp, it tests high for chlorides, and may show a surprisingly low pH. Polyurethane foam is an excellent thermalinsulation material when dry. It is widely used for cryogenic applications and up to about 500°F (482°C). Theproblem is that the formulation routes to improving fire resistance (in terms of smoke and flame spread ratings)bring potentially deleterious side-effects.

Cellular glass has many unique properties. In particular, it is lightweight, dimensionally stable, essentiallyimpermeable to moisture, and it is noncombustible (ASTM E136) with a flame spread rating of 5 (ASTM E84) andno smoke. Each cell is an insulating air space containing primarily carbon dioxide and a trace of hydrogen sulfide.Extractable halogens are nil. The tiny amount of hydrogen sulfide has not been shown to be a corrosion concern. Insum, cellular glass is an ideal insulation material for cold service and properly designed, it can provide the dual roleof fireproofing.

Some folks argue that cellular glass cannot possibly pass the UL1709 or ASTM E1529 fire test protocolsfor any appreciable period of time. It s simple. Both of these tests provide an exposure temperature of 2000°F(1093°C) within the first 5 minutes and glass begins to melt near 1700°F (927°C).

A key aspect of fireproofing that is often misunderstood or overlooked is that the performance of thematerials is intimately tied to the design of the system. For example, cellular glass may be used with or without anadhesive and it may be used with different types of exterior jacketing. Cellular glass is not resistant to direct flameimpingement, and so metal jacketing is required to obtain fire resistance. Aluminum jacketing is common for coldthermal insulation systems but it cannot be used for fireproofing since aluminum melts at about 660°C (1220°F).Stainless steel jacketing is generally employed to obtain fire resistance. But there are additional details if one wantsto achieve fire resistance with cellular glass:

• A minimum of two layers of cellular glass, each two inches (50 mm) thick for a total minimum thickness offour inches (100 mm).

• The individual layers are staggered so there are no through-thickness seams.

• Each layer needs to be mechanically fastened and supported with stainless steel bands or clips.

• A polymeric adhesive needs to be used to glue the blocks of glass together and to provide a final surfacecoating.

It seems counterintuitive that adding a flammable material such as a polymeric adhesive to anoncombustible material such as cellular glass, would improve performance in fire testing but it clearly does (Figure#1). The reason is that the adhesive burns early and forms an insulating char that extends the time it takes to get tothe failure point, where the cellular glass begins to slump.

UL 1709 fire testing of cellular glass

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Figure #1 This plot compares the increase in average steel substrate temperature over time for 4 inches of cellularglass used with and without an asphaltic adhesive. The temperature early in the test was a little higher when theadhesive was used, but the slope then levels out for the duration of the test. The early temperature is lower when theadhesive is not used, but the slope is then steep to the failure point of 1000F. The use of the adhesive effectivelydoubled the time to failure in this comparative test.

Spheres

Fireproofing is not always the preferred approach to providing fire protection. Water will not extinguish ahydrocarbon fire but water is a very effective cooling agent due to the combination of high specific heat and largelatent heat of evaporation. If enough water is sprayed onto and well distributed over the surface of a vessel, thecontents of the vessel stay below 100°C (212°F), the boiling point of water. (The same is true for a pan of boilingwater on the kitchen stove; the pan cannot much overheat until the water is lost to evaporation and the pan goes dry.)The difficulty is being able to apply the water when and where it is needed. For spheres, fire protection is oftenprovided by a water deluge system sized to deliver 0.15 gpm/ft2 or more, to the top of the sphere. This system takesadvantage of sphere geometry to distribute the water uniformly.

One common factor in CUI/CUF is wet insulation or fireproofing. Water frequently gets behindfireproofing on spheres at the top of the sphere where there are a number of penetrations for piping and for structuralsteel platform supports. These obstructions make it difficult to install fireproofing. Any gaps need to be wellcaulked. Although the risk of CUI/CUF is true for any equipment that operates below about 149°C (300oF), thereare particular risks that should be considered when deciding whether spheres should be covered with passivefireproofing. LPG spheres tend to operate at ambient temperature or below and there is a cooling effect (auto-refrigeration) with product draw down that likely drops the surface temperature to below the dew point.

And if that wasn’t enough of a threat, spheres are regularly soaked when the water deluge systems aretested. There have been many instances over the years where severe CUI/CUF has resulted as a direct result of localjurisdictions requiring periodic testing of fire water systems. Clean, potable water is often in limited supply.Coastal plants may use seawater for firewater. It may not suffice to prove that a deluge system works or forexample, that a water cannon can hit a target, but deliberately miss. No, some facilities have been forced to soak thevessel, just to prove that they can.

Fireproofing of spheres is not generally considered mandatory or even necessary. There are a number ofreasons; water deluge systems are generally regarded as adequate, the proper application of fireproofing is difficult,fireproofing may promote CUF, and fireproofing hinders external inspection of the steel shell of the vessel.Fireproofing may be deemed necessary for spheres when congestion is a concern. For example, in older plants, thespheres may be too closely spaced according to modern standards. It may also be that a neighboring community hasencroached on an older plant. In such cases, fireproofing may be added to further reduce the risk of a BLEVE(boiling liquid expanding vapor explosion).

Fireproofing is not just a simple materials issue. Fireproofing is an important part, but it s just one part of alarger effort in risk assessment and risk mitigation.

A Novel Lightweight Design

A refining company required concrete for structural steel, and a minimum two hour fire test rating. Acontoured design, in which the minimum concrete thickness of two inches followed the shape of beams was allowedin some cases, but their standard practice was a boxed design, in which the web of the flange is filled with concrete.The boxed or blocked design required a minimum concrete thickness of two inches over the outside of the beam butthe concrete thickness over the web of the flange was of course, much greater than 2 inches.

Savings on weight, constructability and cost, are important project concerns. On a construction project forthis refinery, an engineering firm provided a novel design. The fireproofing system for smaller columns and beamswas to be the solid boxed concrete design but for larger columns and beams there would be two inches of concretecover over Styrofoam block filling the web of the flange (Figure #2):

Concrete 2" ThicknessMinimum Cover

Steel WireReinforcement

Steel I-Beam

StyrofoamFiller

The Styrofoam blocks were approximately four feet long and individual blocks of Styrofoam wereseparated with a four inch wide band of concrete (Figure #3):

4’ 0" typ

4" Concrete typical

Styrofoam Fireproofing

Side View W21 or Greater Fireproofed Beams

Steel Beam

This novel fireproofing design had somehow slipped under the radar during the planning stage of theproject. It wasn t discovered until a refinery engineer walked through the lay-down area and saw the Styrofoamblocks and how they were being used. Knowing that that just couldn t be right, the engineer brought the noveldesign to the attention of the project engineers. The work ground to a halt. This needed to be sorted out.

The engineering firm argued that this novel design met the refinery s requirements because (1) it wasessentially a boxed or "blocked" design and, (2) the cover material was concrete at the required minimumthickness of two inches. The refinery s materials engineers quickly countered that the refinery s requirements werefor concrete, period — not concrete and whatever else someone might want to use. The refinery could not beexpected to keep a long list of all the things one could not use. Certainly, Styrofoam can t be used for fireproofing!

The engineering firm then argued that they had installed this novel design at other refineries. One of theirfireproofing specialists proceeded to explain that the fire resistance of concrete was dependent on the water content.Concrete was said to function by maintaining a temperature at about 100°C (212°F) until all of the water had beenboiled away. Two inches of concrete was known to be sufficient for the required two hours, so this novel designwill work. This seemed like a convincing argument but it was very wrong and it was no surprise that the requiredfire test data was not forthcoming.

The water content of concrete is important but it doesn’t take long in a fire exposure to loose the free water.Water of hydration is not the same as free water. It is lost more slowly and at more elevated temperatures.Consequently, concrete does not maintain a temperature near the boiling point of water for very long. Fire test datafor a concrete boxed beam shows a small plateau in the time-temperature curve near 100°C (212°F) at about the 20minute mark but thereafter the temperature rise is slow and uniform (Figure #4). It s primarily the high mass andlow thermal conductivity of concrete that make it effective at reducing the heat input to the steel.

UL 1709 fire testing of concrete box design on 10W49 beam

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Figure #4 This shows the increase in average steel substrate temperature over time for the concrete box or blockeddesign, with a minimum two inch cover over the outside. The web of the flange is filled with concrete so thethickness there is much more than the 2 inch minimum requirement. The initial temperature spikes and then levelsoff for several minutes near the boiling point of water. Then there is a smooth slope all the way out to the failurepoint of 1000F.

The data provided by Figure #4 is for a boxed design in which the web of the flange is filled with concrete,so the concrete thickness is much greater than two inches over the web. A two inch concrete cover of the web iscertainly less protective, whether it is two inches directly on the steel (contour design), two inches over Styrofoamblocks, or two inches over void space (air). Polystyrene melts at about 340°F. In a fire situation, one should expectthat with the novel design, the Styrofoam would soon melt and flow. And polystyrene burns, adding fuel to the fire,and it would do so from within this novel fireproofing system.

A clear-thinking engineer can immediately see that this novel fireproofing design has no chance in Hell ofsurviving a two hour UL 1709 test. But that didn t stop the engineering firm from selling it, and then defending itwhen confronted. The structure had been designed with significant weight savings. Steel had been delivered. Asolid concrete box design was no longer an option. The project continued with concrete applied in a contour design.Fortunately, the problem was identified early and corrected on this particular project. However, one should takenote of the fact that in defending this novel design, the engineering firm was quick to point out that they hadinstalled this novel design at other refineries. Somebody has a built-in problem.

CONCLUSION

Each type of fireproofing material offers a different combination of physical and chemical properties, andeach has its own application requirements. As with any protective coating, the quality of the applied fireproofing isa function of the surface preparation, the materials used, and the care with which it is applied. Poorly designed,installed, and/or maintained fireproofing will not likely provide the expected level of protection during a fire, andmay promote corrosion of the underlying steel substrate.

References

1. ACI 222R-89, Corrosion of Metals in Concrete, 1989

2. API Publication 2218, "Fireproofing Practices in Petroleum and Petrochemical Processing Plants"

3. ASTM E119, "Fire Tests of Building Construction and Materials

4. ASTM E1529, Standard Test Methods for Determining Effects of Large Hydrocarbon Pool Fires onStructural Members and Assemblies,

5. NACE RP0198 "The Control of Corrosion Under Thermal Insulation and Fireproofing Materials - ASystems Approach"

6. NACE Publication 6H189 A State-of-the Art Report of Protective Coatings for Carbon Steel andAustenitic Stainless Steel Surfaces Under Thermal Insulation and Cementitious Fireproofing

7. Underwriters Laboratories UL 1709, "Standard for Rapid Rise Fire Tests for Protection Materials forStructural Steel"

8. Walker, A.G., Flame-Retardant Paints, Progress in Organic Coatings, 7 (1979) pgs. 279-287

9. Blake, Melvyn, Fireproofing Structural Steel in the Hydrocarbon Processing Industry, Journal ofProtective Coatings & Linings, January 1986

10. Lazar III, Peter, "Conference on Corrosion and Infrastructure," November 28-30, 1995,Baltimore, MD

11. Papa, Anthony J., Reactive Flame Retardants for Polyurethane Foams, Ind. Eng. Chem. Prod. R es.Develop., Vol. 9, No. 4, 1970

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