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Average rating: 0 out of 5 stars, based on 0 reviews Write a review. Brian D DiGrado. Tell us if something is incorrect. Add to Cart. Free delivery. Arrives by Friday, Oct 4. On the other hand, many local jurisdictions did not allow aboveground fueling systems. They followed various national fire codes that carried either severe restrictions upon ASTs, or simply did not allow the aboveground storage of fuel. The typical owner of a public-accessible retail service station continued to prefer underground storage tanks as did most fire inspectors over potentially unsightly and potentially unsafe aboveground tanks.
As the compliance difficulties of UST owners became evident, some states began to express sympathy through legislation to ease restrictions upon the use of aboveground tanks. Thus, lawmakers in several states completely bypassed the fire prevention safeguards built into local and national fire codes.
Others, such as NFPA, did provide some exceptions for tanks with capacity smaller than gal and often used in rural applications at commercial, industrial, and governmental facilities also known as private fueling systems. With the suddenly strong demand for aboveground tanks, the codes needed to find a way to allow the safe siting of aboveground fueling facilities at service stations. Major additions were added to codes in the early s. NFPA saw the need as so urgent that a Tentative Interim Amendment, or TIA, was issued in to allow an aboveground tank to be installed inside a concrete room, whether that room was located above or below grade.
By , NFPA had added code language to allow other tanks to be installed aboveground, including traditional UL tanks, and another new technology, fire-resistant tanks. At the same time, the Uniform Fire Code was also modifying provisions that would lead to increased usage of aboveground tank storage. A special enclosure was defined as a 6-in. The goal was to emulate the fire safety obtained from an underground storage tank, which was completely backfilled and free of risks from vehicles, vandals, and fires. An associated fire test procedure was developed to fulfill the safety needs.
Tanks had to employ secondary containment and insulation . The appendix item gave local jurisdictions the option to adopt or disregard the new code language for aboveground fueling tanks . According to the Act, all aboveground storage tanks that contained fuels and chemicals had to provide diking as a means of containment in case of a release, and to prevent the flow of hazardous liquids into navigable waterways. In , EPA issued an interpretation that allowed secondary containment double-wall tanks to be installed without diking under certain conditions, which included a tank capacity below 12, gal and the use of overfill prevention equipment .
In , the NFPA 30 code issued a similar change. The fire codes required diking or remote impounding to assure a release would not fuel a fire at another location. The revision allowed secondary containment tanks as an exception to the spill control requirements. Again, a number of requirements to satisfy this exception were established, such as a maximum 12,gal capacity, openings at the top of the tank, emergency venting of the interstice, overfill shutoff devices, overfill prevention alarms, and gages for transport driver use.
The main goal was to prevent common causes of AST system releases. For service station tanks, NFPA 30A Automotive and Marine Service Station Code took this further by mandating security in the form of fencing and gates to prevent vandalism of the tank. Also required were antisiphon devices .
All of these changes paved the way for more secondary containment tanks. By , STI members were building more aboveground tanks than underground tanks, which reflected a dramatic change in the market. A survey of tank owners published by STI in verified this trend. The survey results indicated that most tank owners were concerned with overfills and vandalism as the two greatest threats for AST releases, and that fire codes had the most authority over such tanks .
Addressing the most significant risk of your storage tank
The EPA was also active during this time span on aboveground tanks. A major spill in Pittsburgh from the failure of a large field-erected tank, which caused pollution of the Ohio River for hundreds of miles, brought national attention to ASTs in Further, a slow but constant release in Fairfax, VA, caused flammable fumes to migrate into an affluent neighborhood and grab the attention of the Congress.
As a result, several U. However, none of the law-making initiatives garnered much popular support. It also proposed that ASTs employ diking that would be impermeable for 72 hours. As of this publication, several other revisions and additions had been proposed to the SPCC regulations, but the final rules had not been released. The shop-fabricated AST market saw a major change in customer demand. Specifiers were asking for steel dikes or tubs within which a tank would be installed.
Steel, an impermeable material, certainly met the requirements of the EPA proposal. But demand for integral double-wall ASTs also was growing. So between the fire codes and the environmental regulation proposals, the demand for secondary containment tanks increased exponentially. Prior to , a shop-built secondary containment AST was rare. National standard development work paralleled these significant changes.
Underwriters Laboratories in nearly tripled the size of its UL tank standard document by adding provisions for steel dikes, double wall tanks, and rectangular tanks. Rectangular tanks became very popular for ASTs smaller than 1, gal. Because of their flat-top design, the rectangular models made it easy to access the top of small tanks where fittings and fueling equipment could be located. STI also developed several standards that addressed changes in marketplace demand. Both construction standards met UL requirements.
But that was not the end of new standard development work. The UL standard was published in December It provided two listings, a fire-resistant tank and a protected tank. Code development work continued to accelerate at rapid pace. By , STI had developed a statistically valid database of insulated protected tanks and double wall F tanks. The insulated tank was called Fireguard—the specification for which was published in Private fleet facilities were the primary and dominant users of aboveground tanks for fueling vehicles.
Nearly two-thirds of stored-product applications were for less flammable Class II or III liquids, such as diesel, kerosene, or lube oils. Because of the ongoing code changes, Underwriters Laboratories made further modifications to its UL standard. Appropriate titles to reflect the type of tank were assigned to each standard .
UL also issued a standard for tanks installed in vaults. The UL standard covers below grade vault construction, design, and testing. Finally, authorities having jurisdiction continued to have concerns about important pipe fittings that were missing from ASTs upon installation, such as emergency vents. In this case, all important fittings and pipe attachments would be either shipped on or with the aboveground tank.
The number of retail service stations also dropped dramatically from over , in to less than , in . Consolidation among oil companies was continuing. Tanks were getting larger as the throughput of fuel at each service station increased. More compartment tanks were being installed.
The market had changed so dramatically during the decade that even prefabricated tank system designs tanks prefabricated with piping had begun to appear in the underground tank market. Petroleum and chemical storage was far advanced from the tubs, wash basins, and whiskey barrels rushed into use in Titusville when the first drill found rock oil .
Because of public safety and environmental concerns, the storage of flammable and combustible liquids is handled today with unprecedented attention to ensuring that product remains in reliable containment. D Yergin. The Prize. National Board of Fire Underwriters. NBFU standard, National Fire Protection Association. Steel Tank Institute. National Association of Corrosion Engineers. Versar, Inc. Washington, DC, Report to U. Environmental Protection Agency, Final Report: Tank Corrosion Study. Suffolk County, NY. Department of Health Services.
Farmingville, NY, Report to U. F Mosely. Ohio Environmental Council. Columbus, OH, Federal Register. International Fire Code Institute. Whittier, CA, DR Clay. Washington, DC: U. Environmental Protection Agency memorandum, Automotive and Marine Service Station Code. Product Evaluation, Inc. Underwriters Laboratories. Country Club Hills, IL, Standard Fire Prevention Code, Northbrook, IL, Subject Standard, Washington, DC, Besides adhering to environmental regulations, underground and aboveground tank systems must be sited and operated in accordance with local building and fire codes.
Local codes, mostly, reflect the work done by national or regional code-making bodies. A city council or county board may adopt for their jurisdiction a nationally developed code—and add some local distinctions as well. This chapter will provide some historical background on the regulatory function of codes and standards, and cite some of the codes that most affect storage tank systems. A standard is a series of requirements that tell you how to do something.
A standard tends not to have any enforcement requirements. A standard becomes an enforceable document when it is adopted by reference in a code . A code is a set of regulations that tells you when to do something. A code will have requirements specifying the administration and enforcement of the document. What is a Building Code? A building code is a set of regulations legally adopted by a community to ensure public safety, health and welfare insofar as they are affected by building construction.
What is a Fire Code? A fire code is a set of regulations legally adopted by a community that define minimum requirements and controls to safeguard life, property, or public welfare from the hazards of fire and explosion. A fire code can address a wide range of issues related to the storage, handling or use of substances, materials or devices. It also can regulate conditions hazardous to life, property, or public welfare in the occupancy of structures or premises . For at least years, man has exercised some limited controls over the construction and utilization of buildings and structures throughout the civilized world.
Historical Perspective of Codes 1. Portions of the Hammurabi Code of Law dealt with building construction. Many of these buildings collapsed even before they were completed, killing and maiming many of the workmen. The rebuilding of Rome was accomplished in accordance with sound principles of construction, sanitation, and utility.
Until the downfall of the Roman Empire, construction, public and private, was closely monitored and controlled. London was destroyed in the great fire of Destruction may have been more of a blessing than a calamity because London was a crowded, filthy city of low, timber-framed warehouses, churches, and houses. Most of its thoroughfares had open drains that carried raw sewage. Housewives threw garbage into narrow cobblestone streets. London had been ravaged by the plague for nearly a year prior to the fire.
Its people were dying at the rate of per week. The fire started in a rundown neighborhood near the Tower of London. The fire raged for five days and nights. Its toll was 15, buildings, including 84 churches. Miraculously, only six lives were lost in accidents directly attributable to the fire. In its attempt to prevent another devastating fire, Parliament decided to write requirements to control building construction. However, it took Parliament two years to enact such controls for buildings. Unfortunately, during those two years, London was reconstructed almost in the same style that existed prior to the fire.
The Chicago fire in was devastating, and the second most costly blaze in American history. Chicago at the time consisted of about 60, buildings, more than half of which were of wooden construction. The initial fire, which by legend was blamed on Mrs. Local officials thought after a few hours that the fire posed no more danger. However, on the night of October 8, a new fire broke out and, fanned by winds whipping off Lake Michigan, was soon raging out of control. The fire grew to such large proportions that drastic measures were employed by the army, including the use of explosives to create firebreaks.
Before the fire was extinguished two days later, 17, buildings had been destroyed and lives had been lost. Almost , persons were homeless. Sixty insurance companies went into bankruptcy because of fire-related claims. The insurers that survived the financial disaster threatened to leave the city unless adequate laws regulating buildings were enacted. In , a building code and a fire prevention ordinance became effective in Chicago. The San Francisco fire that started on April 18, , was the largest loss fire in U.
The Aboveground Steel Storage Tank Handbook
As can be seen, building regulations, as we know them today, are the result of an evolutionary process that has its roots deeply embedded in disaster and tragedy. The absence of controls, and the absence of enforcement, must share the responsibility for the needless loss of lives and property. It would be proper and safe to say that in the past years, millions of lives have been sacrificed for lack of such laws . These committees are composed of a balanced membership of technically competent individuals from industry, government and independent experts.
One-third of these codes and standards are revised every year. All NFPA Codes and Standards are usually on a three-year revision cycle unless the committee for a code or standard requests an extension of a year or two. The BOCA code change cycle covers three years. The year the full edition of the Code is published serves as a moratorium period for any code changes.
Only code-official members can vote on changes to the BOCA national codes. SBCCI issues code supplements for the first two years. Only code-official members can vote on changes to the standard codes. The last edition of the Uniform Building Code was published in The IFCI will continue to publish and maintain the Uniform Fire Code with supplements in and , and a completely revised edition in Formation of the ICC. Its mission is to promulgate a single model code system to meet global economic trends. The law must adopt a specific edition year of publication of a code or standard, and may include amendments to specific portions of the code or standard being adopted.
RL Sanderson. Chicago: Building Officials Conference of America, One of the most prominent codes in modern use is the Uniform Fire Code, which regulates underground storage tanks, aboveground storage tanks, and a vast array of products and services that could affect public safety. The Uniform Fire Code, which is cited within the ordinances of communities in 38 states, is like many other codes. The current version is the result of an evolutionary process. That organization developed and first published in the early s a model code called the National Fire Code.
In the early s only a few large cities had comprehensive codes. Many of those codes were based upon the model National Fire Code. A few cities actually took it upon themselves to develop and adopt a code unique to their communities.
There was a wide variance as to what each state adopted for a code. Many adopted, or simply used, some or all of the National Fire Protection Association NFPA pamphlets, which covered a broad spectrum of fire safety subjects. Public safety officials became concerned with how to manage population growth, urban density, new materials and processes of a hazardous nature, and transportation issues.
The postwar era led to a realization by officials in smaller cities of the value and necessity for adopting and enforcing a fire code. That necessity was emphasized to local decision-makers by the activities of the Insurance Rating Bureau, another organization whose function was primarily to look out for the interests of insurance companies.
Communities were encouraged to adopt the National Fire Code. As more communities adopted codes, enforcement personnel became more experienced, organized, and sophisticated. Recognition was growing that the National Fire Code was focused primarily on property protection. It was generally lacking in regulations aimed at the protection of life.
Further, there was a generalist approach to the document. Communities that were home to industries with special hazards were forced to be creative in amending the code to provide for their unique needs. NFPA offered a solution for some of those needs. They continued to expand the selection of fire safety pamphlets and standards, giving communities choices that were not earlier available.
It was focused on assuring that people were protected, not just property. The thrust was to assure that buildings were designed safely enough that occupants could exit in the event of a fire. Meanwhile, building codes were evolving and becoming more widely adopted. Nevertheless, it is interesting to note that as recently as the s a large number of cities and counties had no comprehensive building codes. Building code adoption at the state level was not common until even later. Even today, there are areas of the country that do not adopt or enforce building codes, which typically are written and dominated by code enforcement officials with input and support from architects and representatives of the building materials industry.
Those conflicts created problems of enforcement between building and fire code personnel. Architects, builders, building owners and operators, and many other stakeholders were constantly caught in the middle of turf battles. A case in point, in the extreme! A large apartment building was constructed—allegedly in compliance with the building code—and given a certificate of occupancy by the building official. Once it was opened, the local fire official inspected it for compliance with a conflicting fire code, found it in noncompliance, and ordered the building demolished. When the case went to court, a judge upheld the fire official and a brand-new building was knocked down.
While that was an unusual case, the problems of conflict persisted to an intolerable degree. Out of that came the recognition that a solution should be more broadly based than the concerns raised in just one state. Both of those organizations were based in the western states. Party to those conversations were CFCA representatives, who had already developed an expanded fire code based upon the National Fire Code. Out of those conversations came agreement to develop—jointly and contractually—a new Uniform Fire Code based upon the California Fire Chiefs code.
Their charge was to create a draft fire code, carefully reviewed and amended to eliminate, as nearly as possible, conflicts between the Uniform Building Code and the proposed fire code. Staffing for the effort was through the International Conference of Building Officials. The future development of the code would be by the WFCA. The document staffing and publication responsibilities would remain with the ICBO. The development of the first Uniform Fire Code draft consumed the better part of the year.
The WFCA at their annual meeting considered and voted to approve the document. The work committee was dissolved. The code was published. A new WFCA code development committee was appointed to assume the task of conducting code change hearings on an annual basis. The next code was published in Since then a new edition has been published every three years with supplements printed in the off-publication years.
For example, the consensus was that training and inspector certification programs would be beneficial. There was also an increased desire to broaden the use and influence of the Uniform Fire Code from its original western states base to a national constituency. Its board was made up of persons from both organizations, as well as individuals from other code groups throughout the United States. Its purpose was to assume all of the responsibilities for administration, code development, training services, and other related activities previously carried out jointly by WFCA and ICBO.
The Uniform Fire Code copyright remained with the originating organizations. Staffing remained with the ICBO. The IFCI continues to operate today. The most recent Uniform Fire Code edition is with supplements issued after the annual meeting in the summer of But for 98 percent of USTs and ASTs manufactured, when you strip away the latest product features, you still are working with a steel cylinder equipped with a few fittings that will be used for the storage and handling of petroleum or chemical products. In the remaining cases, you are likely to be working with a flat-top rectangular tank—most often storing less than gal.
From a quality control perspective, tank buyers should be aware of essential fabrication requirements to ensure receipt of a quality tank that will provide many years of trouble-free service. These essentials would include quality control QC , design, materials, tank suppliers, fabrication and welding, surface preparation, coatings, and inspection.
Equally important are shipping, handling, and installation. Each of these areas should be considered prior to ordering a tank. Does the supplier have a QC program with qualified inspectors and well-documented procedures? Even in the best QC programs mistakes will happen; however, a good manufacturer will identify the problem, make the necessary correction and try to prevent the situation from reoccurring on the next tank.
Most tanks are made from commercial-quality hot-rolled steel. More important to the steel, whether it be certified ASTM, or commercial quality, is the carbon or carbon equivalency content. The carbon content of the steel should not exceed 0. In addition, the carbon equivalency should not exceed 0. To calculate the carbon equivalency CE of steel, use the following formula: Increased amounts of carbon reduce the weldability of the steel and increase the hardness and tensile strength, which can make the steel difficult to work with.
Other materials that are very important and will be discussed in greater depth are the welding electrode or filler material and the corrosion protection coatings. The steel is usually purchased in coil form before it is flattened and cut to length. Many fabricators will purchase their steel from a supply house that will flatten and cut the steel to length prior to shipment. In many instances only the inside surface is welded prior to further assembly.
Many fabricators will use what is called an offset or joggle joint to connect the cylinders or cans together. The joggle joint has a couple of advantages. Because there is an offset, the assembly and fit-up of one can—or course of steel—to another is relatively easy. Also, the resultant weld joint is relatively consistent, making it desirable for automatic welding processes. Most fabricators will use a flat, flanged head on their tanks. Flanged heads are often purchased from outside suppliers, although just about every fabricator has a flanger on site for making heads.
All flanged heads should have an inside knuckle radius of two times the thickness of the head. Most fabricators will use a single piece of steel for making a head, whenever possible. However, because of the diameter required on larger tanks 12, gal capacity or greater , stock materials matching the diameter are often unavailable. When this happens, a fabricator will have to piece together two or sometimes three sheets of steel to meet the required dimensions. The fabricator will then weld the sheets together and cut them to match the radius required for the tank.
Prior to flanging the head, the fabricator will grind the weld flush with the base metal in the areas that will come in contact with the flanger die. The stress created at the weld during the flanging operation can feasibly produce cracks. Typically, most tank interior welding is completed prior to fitting the last head on the tank. Then the openings are cut for placement of the fittings, or other attachments. Once the tank is complete, welds will be cleaned and prepared for leak testing. Of course, not all facilities will follow this procedure. As a matter of fact, it is very rare to find any two fabricators building tanks in an identical manner because every production shop has found special success formulas that make them unique.
How Tanks Are Welded Four basic welding processes are used in fabricating steel tanks and pressure vessels. Each of the four processes whether manual or automated will repeatedly produce quality weldments. But they each have strengths and weaknesses. Prospective tank buyers should be aware of the different processes.
In general, the best fabricators focus intensely on assuring outstanding fit-up. Equipment and materials are inexpensive, portable, and relatively simple to operate, even outdoors. However, the SMAW process is slow. Because it is a manual process, the operator must stop and replace the consumed electrode approximately every 18 in. In addition, the operator must remove slag from the weld surface.
The type of electrode used in the SMAW process has a significant impact on the mechanical strength created by the weld. For example, a jet rod known for its speed will not penetrate as easily into the base material; thus, the strength of the joint is not as great as other types of electrodes, such as pipe rod. The wire is fed usually automatically or semiautomatically through a welding gun from a spool or reel. A shielding gas protects the weld from environmental contamination principally oxygen.
The GMAW process has a high deposition rate i. However, because the process uses shielding gas, it is very susceptible to drafts or wind that might blow the shielding gas away from the arc. Thus, it is not well suited for welding outside. Many fabricators will limit its use to thinner gauge steel. Undesirable weld spatter metal particles expelled during welding that do not form a part of the weld is generally greater with this process, but can be significantly reduced with the proper mixture of gas and the use of anti-spatter material on the tank surface.
Also, instead of a bare wire, a tubular wire containing granular flux is used. When a self-shielding flux is used, no shielding gas is required. The FCAW process is very popular because of the deep-penetrating arc that reduces fusion type discontinuities, and because it has a quick deposition rate. The self-shielding electrode is popular in field applications as well. Like the SMAW process, solidified slag must be removed from the surface of the weld. The FCAW process is known for generating smoke, which often hangs in the air of a manufacturing plant.
Because the tubular wire has flux inside, there is greater opportunity for slag entrapment in the weld. Undercutting melting away of the base material along the edge of the weld forming a groove is very common with this process because the arc creates significant heat. The deposition rate of the SAW process is excellent, especially on thicker materials requiring multiple passes.
The SAW process produces a very smooth and uniform weld, but it can also pose problems. With the automatic process the tank must be rotated at a constant speed, and the weld joint fit must be uniform. With other processes manual and semiautomatic , the welder can make adjustments to conform to the joint geometry. With SAW, the welder cannot see the arc and is limited to only minor adjustments while the unit is in operation. Again, slag entrapment and fusion discontinuities are fairly common with this process. Also, because of the amount of heat at the arc, some caution is important—many SAW operators have burned right through the base metal.
Good tank suppliers will have welding procedure specifications WPS for each process. A fabricator will have visual, mechanical, and sometimes nondestructive tests performed on weld samples to qualify a WPS or a welding operator. Most cylindrical atmospheric tanks are tested at 5 psi. It is important to consider the volume of air applied to the tank when pressurizing.
While the test pressure is not that great, the volume of air is significant and, in the event of an accident, can cause severe injury to nearby personnel. Fabricators are required to have a safety relief device on the tank to prevent over- pressurization. Once the test pressure is achieved, a soap solution is applied over the welds to identify leaks.
Bubbles are created when air leaks through the weld and are readily identified by the tester. Testing of tanks should be performed in a well-lit area. All gages, relief valves, and testing equipment should be in good working condition. Soap testing solution should be protected from contaminants. The tank welds should be free of slag, spatter, or foreign materials that prohibit testing. Most double-wall tanks will, in addition to the bubble test, have a vacuum applied to the interstitial space. Comparing a vacuum to the bubble test is like comparing apples to oranges.
The vacuum is much more sensitive to leaks than the bubble test, and is most effective at proving simultaneously that both the primary and secondary tanks are tight. Some distinctions exist for testing on various UST and AST technologies: All single-wall and double-wall steel tanks should be tested with an air test that includes soaping of the weld seams to look for pinhole leaks—some fabricators recommend an additional vacuum test on Type I blanket wrap design double wall tanks. Jacketed tanks typically are shipped with vacuum, but if a leak develops in the jacket the external shell could be tested with an ultrasonic device or a helium leak detector.
Steel dikes on AST systems can be examined using a dye penetrant, or penetrating oil, on weld seams. Typically the resultant profile left on the steel is between 1. The blast medium used is often coal slag, silica sand, or recycled grit. The profile depth depends upon the size, type, and hardness of the blast media; particle velocity; angle of impact; surface hardness; and maintenance of the working mixture.
However, the sand tends to remove mill scale easier from the surface. Under most circumstances shot or wet blast should not be used for surface preparation on steel tanks. Prior to coating, the tank should be free of abrasives, oil, grease, or other contaminants. Most fabricators will apply the coating to the tank as soon as possible after blast. The longer a blasted, uncoated tank is exposed to the environment, the greater the chance that rust-back will occur, especially in locations subject to high relative humidity. Should rust-back occur, the entire tank should be reblasted.
Years ago, many tank suppliers used a coal-tar coating on their USTs. The coal tar was an excellent coating, and was relatively trouble free. The problem with the coal tar was that it took roughly 24 hours to cure before you could move the tank. Coating manufacturers eventually introduced a polyurethane product that provided the necessary corrosion protection and reduced the cure time significantly—enabling the fabricator to move the tank within minutes on a hot day, or just a few hours in cooler weather.
With the reduction in curing time most fabricators switched from the coal tar to the polyurethane coatings. While the polyurethane is a very good coating, it is much more susceptible to application errors or defects. Since the coating is a two-part system, the coating actually mixes at or near the spray nozzle. Many coating defects are directly attributed to the mixing ratio and may cause the urethane to blister if the ratio is off. Many jacketed and composite tanks use an isophthalic fiberglass-reinforced polyester FRP laminate to provide a corrosion barrier. The fiberglass laminate is an excellent coating for corrosion protection.
The application of the laminate requires a skilled operator and well-maintained equipment. The operator must ensure that the correct ratio of glass to resin is maintained at all times. A skilled operator will be able to work around attachments and manways and maintain a holiday-free coating. Most fiberglass-clad tanks require a holiday test—a high-voltage examination of the external tank surface that will discover any exposed metal. All fabricators will use some kind of inhibitor to protect the tank from ultraviolet light while the tank is in storage.
Prior to adding the gel coat color, fabricators can visually inspect the coating for flaws. Many jacketed tank technologies also use FRP as a corrosion barrier. Because the jacketed tank design calls for the FRP to serve as an outer tank, there is always some spacer material between the steel tank and the FRP shell. This eliminates most of the need to blast the tank. Blasting only occurs where the laminate directly makes contact with the steel. This is usually around the fittings and manway.
Construction of the jacket is critical since it is considered a double-wall tank. The tank surface must be relatively smooth and free of abrupt changes that would create stress on the jacket. Many fabricators reinforce the flanged head and weld seams to reduce, or prevent, such stress. Most jacketed tanks are suspended at the heads during application. The heads are the final area of laminate application, and must be thoroughly inspected during the vacuum integrity test for leakage.
Aboveground tanks require exterior paint for protection from climatic conditions in a variety of areas. If the AST will be located in areas near saltwater, deserts, urban pollution or high humidity, a specifier should check with tank manufacturers and coating suppliers about the recommended application of AST paints. Once coated, evaluation of the fabrication and welding is often difficult, if not impossible. By inspecting prior to coating, you have the opportunity to examine all weld profiles to ensure they meet specification. This also enables the removal of excess spatter.
Prior to applying the corrosion barrier, it is important to ensure that no sharp edges are present to inhibit the coating process. Once the coating has been applied, the inspector should determine if the urethane, FRP, or coal-tar epoxy has the minimum dry-film thickness required by the specification on the entire tank.
Inspectors can measure dry-film thickness in a number of tank shell locations with a gage. The coating should be free of sags, runs, blisters, or other surface defects. Composite tanks require a 10, to 35, V holiday test to ensure that the laminate completely protects the steel from corrosive elements. Check with local officials on requirements.
It is recommended that the ground wire lead from the holiday tester be connected directly to the tank for maximum detection of coating defects or flaws. Tank design and fabrication can be influenced by economic factors, regulatory requirements, the liquid to be stored, internal pressures, external environmental forces, corrosion protection, leak detection, and welding needs.
As its name implies, the single-wall tank is fabricated by welding together a shell and heads made of a single thickness of steel. The single-wall AST can be found most often on farms and in applications that run no risk of contaminating aquifers or waterways. Another, major use is for the storage of heating fuels.
Double Wall This is the tank-within-a-tank concept, which creates an interstitial space that can be monitored. Fabricating a built-in leak detection system requires the use of more material and more time by craftsmen at the fabricating plant, so the double-wall designs are naturally more expensive than single- wall tanks. The interstice the area between the inner and outer tanks, also known as the annulus enables leak detection without fear that a hazardous substance has been released to the environment.
The secondary tank, or outer shell, is designed to contain any liquid that may have leaked from the primary tank to contaminate soils or water wells. With the ever-increasing demand for USTs and ASTs to be environmentally friendly, double-wall tanks have gained in popularity. Areas considered ecologically sensitive by regulators are requiring tanks to have secondary containment.
Sensitive areas are in close proximity to water supplies—groundwater aquifers, public waterways, lakes, rivers, etc. Underground tanks storing chemicals or hazardous materials are required by regulation to be double-wall. Chemical storage via an AST can be accomplished with a double-wall tank or one of several secondary containment options. Many of the larger metropolitan areas are requiring secondary containment, which often means specifiers are asking for the double-wall design. A steel double-wall underground tank can be fabricated by one of four primary methods: A tight-wrap design in which a second layer of steel is in intimate contact with the primary tank, which creates a small, but viable, interstitial space A steel outer tank surrounding a steel inner tank with 2-in.
Compartment Tanks The use of compartmentalized tanks is increasing with every year. The ability to store multiple products and save on overall tank system costs has led to increased demand. This approach allows tanks to be divided into two or more compartments. These tanks are fabricated by adding as many bulkheads as needed to create distinct compartments. Single-wall or double-wall tanks can be fabricated into compartment tanks. A distinct economic advantage is obtained with the use of a secondary containment tank featuring multiple compartments—the end user gets the benefit of several storage containers, but only pays for one secondary containment tank, one interstitial monitoring port and one release detection device.
Whether the tank design is single-wall or double-wall, tank owners have reduced costs with compartmentalized tanks by 1 lowering the total number of tanks at one site, which decreases the resources allocated to leak detection, or 2 installing one tank rather than several, which lowers installation costs. In some states, a compartmentalized tank can save on underground storage tank insurance costs—again, because the owner is insuring one tank rather than several.
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However, other states treat a three-compartment tank as equivalent to three normal tanks for UST financial responsibility requirements. With the increasing demand for compartment tanks, the specifier should consider whether fabrication with a single- or double-bulkhead configuration is most appropriate. Bulkheads are basically made the same way as the tank heads. By minimizing the use of weld seams within the bulkhead construction, the risk of leakage from one compartment into another is reduced.
Some manufacturers routinely fabricate two- or three-piece bulkheads, which is permitted by Underwriters Laboratories UL standards for double-bulkhead designs. Several methods can assure proper bulkhead construction under the UL 58 Steel Underground Tanks for Flammable and Combustible Liquids standard, and model fire codes.
The most conservative approach requires two separate bulkheads in a secondary containment design. Under this design, if liquid escaped past one bulkhead, it would drain into an interstitial area. However, a failure at the weld seam between the tank shell and the bulkhead—in the single-bulkhead design—would lead to petroleum leaking directly into the soil from a single-wall tank Fig.
The complete separation of products is a critical factor for compartment tanks that store, for example, gasoline in one compartment and kerosene in another. Flange for testing may be located anywhere on tank circumference, between two bulkheads. A camper lighting a stove that accidentally is carrying a mixture of kerosene and gasoline would be subject to an extreme safety hazard.
If so, a double-wall steel or a jacketed tank may fit that underground storage application. With a double-wall steel tank, communication of a leak into the annular space is not much of an issue for detection. However, the specifier may consider requiring an additional fitting on the annular space—at the tank end opposite of the monitoring port—for removal of fluids in the event of a primary- tank leak.
The placement of the additional fitting is not a standard practice among tank manufacturers. This fitting allows easier venting of the interstice, which enables the tank to be reused or retired. On jacketed tanks, communication of leaks is not so cut and dry. This is not mandated for double-wall steel. It relates directly to properties of the outer-tank material.
For instance, it is impossible to pull two walls of steel together so tightly that an interstice will not exist. But with jacketed tanks, an interstitial vacuum or geotechnical forces from surrounding soil can compress the flexible jacket so tightly against the steel primary tank that interstitial communication could be partially eliminated. For instance, if the product must be maintained at a constant elevated temperature, some tanks and accessories such as nylon bushings, zinc anodes, and certain coatings may not be suitable for this application.
If the product stored is caustic, the fabricator may need to assemble a stainless steel storage tank. The internal pressures on USTs that hold flammable and combustible liquids are seldom a concern because tank burial virtually assures a lack of extreme fluctuations in product temperatures. Fabricators, however, face an entirely different situation with ASTs loaded with fuel and exposed to sunlight in hot weather, or potentially at risk to catch fire at the tank site.
Fire codes require the addition of a fitting for an emergency relief vent to prevent AST fueling tanks from building up explosive internal pressures. Internal pressures also affect the fabrication of vertical ASTs. Because liquids exert greater pressure at the bottom of a container, vertical aboveground tanks employ thicker-gage steel at the bottom of the cylinder than the top.
Vertical ASTs also are tested to hold 2. Earthquakes and highwater tables created by localized flooding are probably the most dramatic examples of natural events that can place undue pressure on tanks. But years of experience have shown fabricators that special burial conditions can also influence the selection of materials for tank construction. For example, if the tank is going to be buried deeper than 5 ft below grade, additional steel thickness may be required to assure structural integrity.
On rare occasions, deep tank burials take place in areas where high groundwater levels exist. There are documented instances when marginal steel thicknesses have been used in the production of the tank, which deformed the tank bottoms—in essence, crimping the shell upwards. When fabricators are apprised of unusual conditions at the tank site, a UST can be stiffened through thicker walls, or by incorporating steel structural elements.
For example, all nonmetallic USTs use reinforcing ribs to obtain the necessary integrity to prevent buckling. When coupled with proper backfill and placement, the FRP tank design will minimize the risk of cracking. On ASTs, fabricators routinely reinforce larger-diameter tank heads to assure minimal deflection caused by static forces inherent with stored liquids.
With underground tanks, the backfill provides resistance to such movement. On steel tanks, fabricators provide corrosion protection to the primary tank through dielectric coatings, cathodic protection, secondary containment or sometimes a combination of methods e. Fabricators provide protection against corrosion for ASTs by painting exterior steel surfaces that could be affected by rain, snow, or other climatic conditions.
Some ASTs require cathodic protection of the tank bottom when the bottom is in direct contact with corrosive soil, though this is primarily an issue for large-capacity, field-erected tanks. An internally mounted interstitial or secondary containment monitoring pipe makes coating application easier for the manufacturer, and is standard on many jacketed tank systems. For ASTs or USTs of small capacity gal or less , an externally mounted monitoring pipe can be effective when several fittings limit space on the top of the tank.
Some tank fabricators will recommend extending the secondary containment steel tank head to provide a monitoring well. Much of the tremendous growth in demand for small-capacity AST systems relates directly to the ease of monitoring aboveground leaks with a visual inspection. The remediation of an AST system leak also is considerably less expensive than a release from an underground tank. For instance, the AST cleanup requires no tank excavation costs. The engineer or specifier may want to inquire on the type of joints typically employed by the manufacturer, especially on tanks that will have a lining, such as a vessel used for jet fuel storage.
Some weld joints are better than others for internally lined tanks. Some fabricators of vertical ASTs employ the option of a weak roof-to-shell joint to meet venting requirements. If internal forces build to an unacceptably high level, the roof will rise in a hinged motion and release the excess pressure. It may be prescriptive or performance based. The tank specification may itself constitute the entire document or it can be but a small component of an extensive project design-and-build. The customer generally will dictate the scope—or how extensive a specification will be.
However, it is the specifying engineer who will likely determine whether a specification is prescriptive or performance-based. Done properly, either approach can lead to a good specification. The difference is that while prescriptive documents enumerate every component down to the specific manufacturer and part number, a performance-based specification incorporates validated third-party standards and recommended practices in establishing basic performance and safety levels. The principal argument for a prescriptive specification is that by tending to every detail, there can be little room for error.
However, performance-based advocates maintain that referencing third-party standards that have already been exhaustively researched provides a solid basis and avoids reinventing the wheel, and potentially erring along the way. Prescriptive Provide an integrated electronic tank gauging and monitoring system for release detection and inventory control meeting the following requirements: 1 The automatic product level monitor test must detect a 0.
Tank monitoring system must incorporate magnetostrictive probes in each tank and a monitor with LCD display, printer, audible and visual alarms, and battery backup. System must be UL listed. An engineering firm or corporate engineering department should establish a master specification format that all specifiers will follow.
This assures not only uniformity and clarity but also that all critical elements of a design specification are addressed. There are tools available to guide the specifier in the creation of a comprehensive specification. CSI provides templates and software that can be used to create a general specification format. The Internet is another resource for specifiers with sites ranging from code and standards developers to manufacturers of tanks and components.
See Appendix for a partial list of websites with information related to tank codes and standards. Environmental Protection Agency. However, specifiers must also check for state or local regulations or fire codes relating to USTs or aboveground storage tanks ASTs. Fuel dispensing, in particular, is addressed by fire codes—as are AST installations—and engineers should not even begin to specify such projects before checking with the local fire marshal on what systems and components are allowed.
For example, even if a community generally follows a national model fire code such as NFPA 30 or 30A, which allows ASTs for fuel dispensing, the local fire marshal may prohibit such a use for aboveground storage systems. Several organizations publish standards and recommended installation practices that are routinely referenced in storage tank specifications. Many other countries also recognize UL standards.
Also important is compatibility of the product with the tank, piping, seals, and other components that come in contact with the product. This is particularly pertinent to chemical storage, where an internal tank liner and special pumps and valves may be necessary. For example, even if secondary containment is not mandated by federal or local regulations, the extra measure of protection it provides merits consideration. Can the customer use compartmented tanks to store multiple products with less tankage and subsequent lower installation and insurance costs? If an aboveground tank is being considered, is there enough real estate at the site to allow for required separation distances from buildings, public rights-of-way, dispensers, and other tanks?
Do the potential up-front cost savings for an AST installation outweigh long-term maintenance costs? For more AST vs. UST considerations, see Chapter 7. Compiled by the Steel Tank Institute, these are not intended to be all-inclusive or universally applicable. Nonetheless, they provide good examples of a fairly comprehensive specification.
These are written in CSI MasterFormat and are designed to allow the specifier latitude to write either a prescriptive or a performance-based specification. Note the bracketed [ ] text, which indicates sections requiring further action or decision on the part of the specifier. To allow relative comparison of an AST to a UST project specification, both are written for a vehicle fueling application. Scope of Section a. This section describes requirements for providing the equipment, labor, and materials necessary to furnish and install petroleum storage tank system s utilizing underground sti-P3 double-wall tank s.
Requirements include furnishing and installing all equipment and accessories necessary to make complete systems for the storage and dispensing of gasoline. The following components shall be provided by the owner and installed by the contractor. The following components shall be provided by the contractor, but not be installed as a part of this contract. Related Sections a. All material and installation sections relating to site preparation, painting, concrete, and other related work not specified herein are covered in the appropriate sections.
Definitions a. Agreement consists of the conditions of the contract between the owner and the contractor, including referenced specifications, drawings, and related documents. Construction documents consist of the general and supplemental conditions, specifications, drawings, and any addenda issued prior to bidding. Contractor is the person, firm, or corporation with whom owner has entered into the agreement. Furnish means the contractor shall supply the item specified, at the job site, unloaded, and secured against damage, vandalism, or theft.
FRP is an abbreviation for fiberglass-reinforced plastic. Install means the contractor shall perform all work required to place the equipment specified in operation, including installation, testing, calibration, and start-up.europeschool.com.ua/profiles/meqobena/agencias-para-conocer-chicas.php
Handbook of Storage Tank Systems: Codes: Regulations, and Designs
Interstitial refers to any space between primary and secondary containment of tanks as well as containment sumps and piping. EPA technical standards. Liquid tight means prevention of the infiltration of ground or surface water into a contained space, or the release of product from contained spaces into the surrounding soil. Owner is the person or entity identified as such in the agreement.
Product means the gasoline stored and dispensed from the tank. Provide means the contractor shall furnish and install the equipment specified, and perform all work necessary to provide a complete and functional system. Spoil means all material removed by demolition or excavating. Substantial completion is the stage in the progress of the work when the work or designated portion thereof is sufficiently completed in accordance with the contract documents so the owner can utilize the work for its intended use.
Work means all materials, equipment, construction and services required by the contract, whether completed or partially completed. General Requirements a. Unless otherwise specified, equipment furnished under this section shall be fabricated and installed in compliance with the instructions of the manufacturer. The contractor shall ensure that all equipment, accessories and installation materials comply with the specification and that adequate provision is made in the tank design and fabrication for mounting the specified system equipment and accessories.
The contractor is solely responsible for construction means, methods, techniques, sequences and procedures and for safety precautions and programs. The contractor shall provide all labor, equipment and material required to provide a complete and functional system. To avoid delays in construction, the contractor shall ensure that all components of the system are available at the time of installation. The contractor shall obtain necessary permits, arrange for inspections and obtain approval of the appropriate authority having jurisdiction over the work described.
Work shall be performed in accordance with applicable federal, state, and local fire protection, environmental and safety codes and regulations, and the latest version of the following industry standards: 1. Box , Tulsa, OK Box , Quincy, MA Department of Labor, Region V, S.
Box , Houston, TX