Hang in There Al IFR
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HAZARDOUS CARGO BULLETIN May 2006 storage 2 Safety is the first and highest priority to Allentech and to all the petrochemical companies we work for and are associated with. Although we have been performing this work for many years, entering a tank while in service to change leg settings is a risky procedure. And because it takes three well trained workers, equipped properly, it is a time-consuming and an expensive job. In order to enter a tank in service the internal floating roof (IFR), whether steel or aluminium, must be floating within fifteen feet of the top of the fixed roof and be dormant for at least two hours with all tank vents open to exhaust the con- tained vapours. The lower explosive limit (LEL) inside the tank within the space between the float- ing roof and the fixed roof must not be greater than 10 per cent, measured comprehensively. The worker entering the tank must wear a fall and res- cue device (full body harness) connected via cable to a tripod with a rescue winch and fall protection device mounted over the manway on the fixed roof. He must be wearing a full face mask and Scott Air Pack or be connected to forced fresh air. The second worker, a dedicated standby, must be equipped with all of the same safety gear and fresh air equipment. The third worker, a second dedi- cated standby, must maintain contact with the worker in the tank and with the terminal via radio. The worker changing the leg settings enters the tank and walks all around the roof while it is float- ing on gasoline, ethanol or a similar product and removes or installs a bolt and nut, depending on the support leg design, changing the setting on all support legs. If a leg is inadvertently missed, the roof could be damaged when landed. Many petro- chemical companies today simply will not allow in- service entries and all of them certainly want to avoid it because of the risk. Since most aluminium IFRs weigh less than two pounds per square foot, new tanks can be designed, and most existing tanks can be retrofitted to suspend the AIFR from the fixed roof. Suspending an AIFR by cable eliminates the need for conventional two position legs and produces multiple demonstrative benefits. From a safety point of view it allows the IFR position to be changed from the top of the fixed roof, eradicating the requirement to enter the tank while in service. It becomes a one-man, much lower risk job that can be accomplished in approximately four hours by a terminal operator rather than two days by a three-man crew of specially trained and fully equipped workers. Eliminating in-service entries to make leg changes is an enormous safety improvement. Another safety factor becomes apparent when per- sonnel are in a tank, under a floating roof for clean- ing, inspections and repairs. While in the process of writing this article, a fatal accident occurred in a Southern California refinery involving personnel working under a steel floating roof. The initial report stated that the workers were jacking the sup- port legs in order to replace tank floor plate. One worker died and four were injured when the 120- foot diameter steel IFR collapsed. This is not the first time an accident of this nature has occurred. Safety advantages Conventional legs are either fixed or two-position types. Fixed legs are generally set at about 4 feet above the tank bottom. Two-position legs usually have a low setting at the lowest level above the highest obstruction at the bottom of the tank, usu- ally the shell manway, and a high setting at the maintenance level. With a manway plug the low setting will be about 3 feet (1 m). The high or maintenance position is usually about 6.5 feet (2 m) to give head clearance and provide a reasonable assembly height in the case of an AIFR. A cable suspension system allows multiple height settings not possible on a steel IFR. Therefore, in addition to the low and high posi- tion, our customers often specify a third position. We call the third position a high/high position, and it is usually set at around 15 feet (4.5 m). This third position provides clearance for future maintenance to the bottom of the tank such as bottom repair or replacement. The 15-foot position allows the con- tractor to bring a bobcat and other equipment into the tank to replace floor plate. Working on a tank floor without having to deal with support legs greatly improves safety and effi- ciency and significantly reduces the repair time and costs. In any case, the absence of legs is indeed an additional benefit when tank cleaning occurs. It is much easier and safer to clean a tank without hav- ing to negotiate around legs that can be moved and or damaged in the process. While on the subject of leg damage, conven- tional legs are frequently subject to corrosion dam- age, especially in crude oil service. In tanks with steel IFRs, it is not uncommon to find tank floor damage caused by heavy steel roof landings. Additionally, the absence of legs greatly improves the ease and speed of personnel evacuation should it become necessary. Emissions reduction potential For the purposes of the rest of this article all refer- ences and calculations will be made on a tank that is 120 ft (36.6 m) in diameter, 48 ft (14.6 m) high, with a fixed roof with eight roof support columns. Hang in there FLOATING ROOFS The introduction of cable suspension systems has taken aluminium internal floating roofs to a new level of safety. New technology and subsequent independent testing of bolted seams for certain full contact honeycomb roofs have also indicated significant reductions in emissions, as Allentech’s Bill Grimes* explains Allentech’s honeycomb seal is at the heart of the system This is a reprint from the May 2006 issue of Hazardous Cargo Bulletin, presented with the compliments of Allentech Allentech reprint.qxd 9/21/06 12:35 PM Page 2
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IFR
Transcript of Hang in There Al IFR
HAZARDOUS CARGO BULLETIN May 2006
storage
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Safety is the first and highest priority to Allentechand to all the petrochemical companies we workfor and are associated with. Although we have beenperforming this work for many years, entering atank while in service to change leg settings is a riskyprocedure. And because it takes three well trainedworkers, equipped properly, it is a time-consumingand an expensive job.
In order to enter a tank in service the internalfloating roof (IFR), whether steel or aluminium,must be floating within fifteen feet of the top ofthe fixed roof and be dormant for at least twohours with all tank vents open to exhaust the con-tained vapours. The lower explosive limit (LEL)inside the tank within the space between the float-ing roof and the fixed roof must not be greaterthan 10 per cent, measured comprehensively. Theworker entering the tank must wear a fall and res-cue device (full body harness) connected via cableto a tripod with a rescue winch and fall protectiondevice mounted over the manway on the fixedroof. He must be wearing a full face mask andScott Air Pack or be connected to forced fresh air.The second worker, a dedicated standby, must beequipped with all of the same safety gear and freshair equipment. The third worker, a second dedi-cated standby, must maintain contact with theworker in the tank and with the terminal via radio.
The worker changing the leg settings enters thetank and walks all around the roof while it is float-ing on gasoline, ethanol or a similar product andremoves or installs a bolt and nut, depending onthe support leg design, changing the setting on allsupport legs. If a leg is inadvertently missed, theroof could be damaged when landed. Many petro-chemical companies today simply will not allow in-service entries and all of them certainly want toavoid it because of the risk.
Since most aluminium IFRs weigh less than twopounds per square foot, new tanks can be designed,and most existing tanks can be retrofitted to suspendthe AIFR from the fixed roof. Suspending an AIFRby cable eliminates the need for conventional twoposition legs and produces multiple demonstrativebenefits. From a safety point of view it allows theIFR position to be changed from the top of the fixedroof, eradicating the requirement to enter the tankwhile in service. It becomes a one-man, much lowerrisk job that can be accomplished in approximatelyfour hours by a terminal operator rather than twodays by a three-man crew of specially trained and
fully equipped workers.Eliminating in-service entries to make leg
changes is an enormous safety improvement.Another safety factor becomes apparent when per-sonnel are in a tank, under a floating roof for clean-ing, inspections and repairs. While in the process ofwriting this article, a fatal accident occurred in aSouthern California refinery involving personnelworking under a steel floating roof. The initialreport stated that the workers were jacking the sup-port legs in order to replace tank floor plate. Oneworker died and four were injured when the 120-foot diameter steel IFR collapsed. This is not thefirst time an accident of this nature has occurred.
Safety advantagesConventional legs are either fixed or two-positiontypes. Fixed legs are generally set at about 4 feetabove the tank bottom. Two-position legs usuallyhave a low setting at the lowest level above thehighest obstruction at the bottom of the tank, usu-ally the shell manway, and a high setting at themaintenance level. With a manway plug the lowsetting will be about 3 feet (1 m). The high ormaintenance position is usually about 6.5 feet (2m) to give head clearance and provide a reasonableassembly height in the case of an AIFR.
A cable suspension system allows multipleheight settings not possible on a steel IFR.Therefore, in addition to the low and high posi-
tion, our customers often specify a third position.We call the third position a high/high position, andit is usually set at around 15 feet (4.5 m). This thirdposition provides clearance for future maintenanceto the bottom of the tank such as bottom repair orreplacement. The 15-foot position allows the con-tractor to bring a bobcat and other equipment intothe tank to replace floor plate.
Working on a tank floor without having to dealwith support legs greatly improves safety and effi-ciency and significantly reduces the repair time andcosts. In any case, the absence of legs is indeed anadditional benefit when tank cleaning occurs. It ismuch easier and safer to clean a tank without hav-ing to negotiate around legs that can be moved andor damaged in the process.
While on the subject of leg damage, conven-tional legs are frequently subject to corrosion dam-age, especially in crude oil service. In tanks withsteel IFRs, it is not uncommon to find tank floordamage caused by heavy steel roof landings.Additionally, the absence of legs greatly improvesthe ease and speed of personnel evacuation shouldit become necessary.
Emissions reduction potentialFor the purposes of the rest of this article all refer-ences and calculations will be made on a tank thatis 120 ft (36.6 m) in diameter, 48 ft (14.6 m) high,with a fixed roof with eight roof support columns.
Hang in thereFLOATING ROOFS The introduction of cable suspension systems has taken aluminium internal floating roofs to anew level of safety.New technology and subsequent independent testing of bolted seams for certain full contacthoneycomb roofs have also indicated significant reductions in emissions, as Allentech’s Bill Grimes* explains
Allentech’s honeycomb seal is at the heart of the system
This is a reprint from the May 2006 issue of Hazardous Cargo Bulletin, presented with the compliments of Allentech
Allentech reprint.qxd 9/21/06 12:35 PM Page 2
May 2006 HAZARDOUS CARGO BULLETIN
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It is equipped with an aluminum IFR and is locat-ed in Houston, Texas, US. It is assumed the prod-uct service is motor gasoline with a Reid VaporPressure of 10 psi and the tank experiences 36turnovers per year. All calculations are based on theUS Environmental Protection Agency (EPA)Tanks 4 program, the standard method for calcu-lating emissions losses for permitting and enforce-ment purposes in the US. More information canbe found on the US EPA website athttp://www.epa.gov/ttn/chief/ap42/index.html.
In simple terms, using the Tanks 4 program cal-culations, eliminating conventional two-positionlegs and replacing them with a cable suspension sys-tem on a new AIFR or by retrofitting an existingAIFR with a cable system that seals off the legsleeves reduces vapour emissions by approximately30 per cent. The subject 120-foot tank with an alu-minium pontoon IFR with 75 legs and a primaryshoe seal emits 17,232 lbs (7.8 t) per year. Replacethe conventional legs with a cable system and itemits a total of 11,854 lbs (5.4 t) per year. Althoughit is not possible to remove the legs and cable sus-pend a steel IFR because of its weight, it is possibleto retrofit an existing AIFR with a cable suspensionsystem. Allentech’s retrofit design completely sealsoff all leg sleeves, eliminating all leg sleeve emissions.It is important to mention this because we have seen
cable systems in the field that do not.The latest technology in bolted seams for
AIFRs has the potential to further reduce emis-sions. The Tanks 4 program has a default factor tocalculate the emissions losses though the totalnumber of linear feet of bolted seams on an AIFR.This factor is 0.14 lbmol/(ft yr). Using this factorthe resultant loss is 5,488 lbs per year in our sub-ject tank. EPA allows for alternative control devicesif the emission factor is less than the standard butthis alternative factor must be the result of inde-pendent testing using strict EPA protocol and cri-teria. The bolted seam illustrated, manufactured inthe US by Allentech and used in its Full ContactHoneycomb AIFR has a factor of 0.0085 lbmol/(ftyr). Utilizing this factor in our subject tank resultsin an emissions loss of only 333 lbs per year.
Cost savings tooGenerally speaking, a new aluminium skin andpontoon type AIFR will cost one half or less thanthe price of a steel pontoon IFR. The more expen-sive aluminium honeycomb full contact type IFRwill be competitive with and probably in most casescost less than a steel pontoon IFR. With the addi-tion of a cable suspension system to either designoperational costs are also reduced due to the timesavings during maintenance discussed at the start of
this article. With mobilisation the leg change jobwill probably cost about $9,000. The approximatecost of the cable suspension system for our subjecttank is $15,000. This gives the purchaser a payoutfor the system after less than two leg changes.
In both cases the aluminium IFR can beinstalled in as existing tank without a costly doorsheet and subsequent hydro test. Additionally, theinstallation time for an AIFR is generally aboutone-third that of a steel IFR, saving money oninstallation and tank downtime.
When AIFRs were introduced about 40 yearsago they were a very low-cost alternative internalfloating roof with problems. Over the years consci-entious manufacturers have solved the problemsand in so doing produced a product that is morethan a low-cost alternative. High quality AIFRstoday have an operational life of 30 years or more.They are reliable but still economical. And, asdetailed in this article, quality cable-suspended alu-minium internal floating roofs greatly improvesafety and dramatically reduce emissions. *Bill Grimes is a sales engineer for Allentech(Bethlehem, PA), which designs, manufactures andinstalls aluminium internal floating roofs, perimeterseal systems, and related products for abovegroundpetrochemical storage tanks. telephone: (+1 520) 5751443; e-mail: [email protected].
storage
This is a reprint from the May 2006 issue of Hazardous Cargo Bulletin, presented with the compliments of Allentech
Allentech reprint.qxd 9/21/06 12:35 PM Page 3
