Corrosive liquids are defined as liquids that cause visible destruction or irreversible alterations in human skin tissue (outer skin, eyes, lungs, etc.) At the site of contact or in the case of leakage from the system. They also have a severe corrosion rate on steel (in excess of 0.250 inches) per year at a test temperature of 130^of. Examples are inorganic acids (e.g., sulfuric, hydrochloric, nitric, phosphoric, hydrofluoric, hydrobromic, etc.), And alkalis (e.g., caustic soda, caustic potash, etc.).

These are classified according to NFPA 30 based on their flash point, boiling point, and vapor pressure. Flammable liquids are called class I liquids, while combustible liquids are called class II and class III liquids. They have further subdivisions as shown on table 1.

A toxic liquid is one that, through its chemical properties, is poisonous and/or may chemically produce an injurious or deadly effect on contact with body cells. Toxic effects may occur by ingesting a toxic liquid or inhaling a toxic vapor emitted from a toxic liquid. Table 2 shows the relative toxicity of liquids based on the probable oral lethal dose.

Table 3 shows a number of toxic exposure limits (by inhalation) which are used in industry. A key problem of using these limits in the course of emergency planning is that they are primarily intended for use in the occupational environment where presumably healthy workers are exposed to concentrations near these limits day after day throughout their working careers. This consideration and the desire to prevent health effects associated with chronic exposures mean that these values are often (but not always) much lower than what they have to be to protect the public from exposures associated with rare or infrequent spills of hazardous materials. Consequently, use of a TLV, PEL, etc. Value, although decidedly safe in the vast majority of cases, could conceivably result in a major over prediction of downwind hazard zones in many cases.

NIOSH’s IDLH limits are considerably higher, are defined for an exposure duration that is closer to what would be expected in an actual short-term spill emergency, and are closer to the borderline between levels that are barely tolerable and those that may cause significant injury. The IDLH is the maximum vapor concentration, in parts per million (ppm) from which, in the event of a respirator failure, one could escape within 30 minutes without a respirator and without experiencing any escape-impairing or irreversible health effects. Because of some of the problems with the IDLH, the EPA uses a toxicity rating scale based on a level of concern (LOC) equal to one-tenth of the IDLH exposure concentrations (see table 4).

Some flammable/combustible and toxic liquids may also be reactive (unstable) liquids, i.e., they will in the pure state or as commercially produced or transported will vigorously polymerize, decompose, condense (under- go condensation reaction), or will become self-reactive under conditions of shock, pressure, or temperature.

Several US regulations, codes, and industry standards are relevant to the storage and handling of hazardous liquids. Some of these are as follows:

• 29 CFR 1910.106–flammable and combustible liquids
• 29 CFR 1919.110–storage and handling of liquefied petroleum gases
• 29 CFR 1910.119–process safety management (OSHA)- see table 5
• 33 CFR 154, subpart e–vapor control systems (USCG)
• 40 CFR 68–risk management program (EPA)-see table 5
• NFPA 30–flammable and combustible liquids code
• NFPA 58–lp-gas code
• NFPA 70–national electrical code
• NFPA 77–static electricity
• API std. 2000-venting atmospheric and low-pressure storage tanks (non-refrigerated and refrigerated)

Additional relevant regulations, codes, and standards are given in the bibliography

Various types of tanks are available for aboveground and underground storage of hazardous liquids at both atmospheric or near atmospheric pressure (inerted tanks) and at higher pressure (e.g., for butadiene).

The selection of the proper materials of construction is critical to the prevention of premature failure of Storage tanks and ancillary equipment and subsequent loss of containment, which could result in fires, explosions, and serious health effects to plant personnel and people outside of the plant fence line. Failure may occur due to a number of causes, such as:

• Various forms of corrosion (see table 6)
• Brittle fracture
• Mechanical fatigue
• Thermal fatigue
• Creep
• Stress rupture
• Catastrophic oxidation
• Carburization

Trace components in a fluid stream may cause undesired results even though they are in small concentrations (e.g., traces of hydrochloric acid in organic streams can cause severe corrosion of metals, even stress corrosion cracking of austenitic stainless steels). Also, Minor constituents in metals may also cause undesirable fires and explosions when used with certain chemicals

(e.g., monomethyl hydrazine will cause fires when in contact with type 316 SS, but with type 304 SS). A complete chemical analysis and knowledge of these hazards are required in order to avoid these "booby traps". A qualified corrosion engineer should be consulted to ensure the selection of the proper materials of construction.

Fabrication and installation of storage tanks and ancillary equipment are also important as many corrosion problems are related to the welding and fabrication processes. The welding procedures should be well defined and included in material specifications.

Corrosion monitoring and control techniques are also of great benefit in avoiding corrosion problems that may result in catastrophic events occurring. Corrosion control techniques include:

• Addition of inhibitors
• Barrier coatings (cladding, paint or plastic films, electroplating, etc.)
• Cathodic and anodic galvanic protection

Chapter 5 in the CCPS guidelines for engineering design For process safety is a good overview of this subject and contains many useful references to materials of construction selection and corrosion occurrence and protection.

Adequate spacing is necessary to reduce the possibility of the spread of fire from the tank initially involved to adjacent tanks or exposed structures. Fire may spread by radiant heat or by the flow of burning liquids. Other factors which should be considered are:

Above ground tanks should be located on ground sloping away from main plant buildings and plant utility installations. On hilly terrain, drainage or dikes should be provided to bypass buildings or installations at lower levels.

NFPA 30 presents tables giving location distances of aboveground storage tanks with respect to property lines, public ways, and important buildings on the same property for class I, class II, and class iii liquids. It also gives minimum tank spacing (shell-to-shell) distances between any two adjacent aboveground tanks for all three classes of flammable and combustible liquids.

NFPA 30 stipulates that "facilities shall be provided so that any accidental discharge of any class I, II, or IIIa liquids shall be prevented from endangering important facilities, and adjoining property, or reaching waterways". Containment may consist of curbing with drainage to a containment sump or tank, diking for full containment of the largest tank, or a combination of the two. Section 2-3.4.3 of NFPA 30 discusses various aspects of diking requirements and design. When the drainage system is normally valved closed, the holdup capacity or the curbed or diked area shall be large enough to contain the contents of the largest tank plus any additional holdup required by the applicable regulations for rainwater, fire water, and freeboard.

Tanks containing unstable (reactive) liquids shall be located in separate curbed or diked areas or in separately subdivided areas within the main curbed or diked area. The intent is to minimize fire exposure to the unstable liquid tanks. The subdividing dike or curb should be a minimum of six inches in height.

Tanks containing incompatible liquids shall be separately curbed or diked from each other. When spills of the incompatible liquids could cause violent reactions, spontaneous ignition, toxic gases, or rapid corrosion of equipment or piping, provision shall be made for full containment (either dike for full containment or provide partial containment and open drainage).

Preferably, dike walls should be constructed of earth. Where land values are high, space is limited, or it is necessary to locate tanks on a steep slope, steel or reinforced concrete may be used instead of earth dikes. Dikes should be constructed to withstand the maximum

Hydrostatic pressure that would be developed by release of the largest tank contents. Where practical, limit the height of dikes, regardless of construction, to 6 feet to minimize the chances of pocketing flammable vapors and to facilitate fire fighting.

Drainage within diked areas should be provided at a minimum slope of 1 percent away from the tanks toward a sump, a drain box, or other means of disposal located at a safe distance from the tank. Drains should be designed o prevent flammable liquids from entering natural water courses, public sewers, or public drains. Drain lines should be trapped, and valves should be provided on the lines outside the dike so that they are accessible under fire conditions. Traps should be protected from freezing.

Inerting (also called blanketing) is often used for the prevention of explosive mixtures in fixed roof storage tanks because such mixtures can be ignited by unforseen and often unknown sources. Inerting of storage tanks is usually accomplished by maintaining a closed system under vent gas pressure (usually 3 to 6 inches water column) by means of pressure reducing regulators and back pressure valves.

Inerting gases are those which, when mixed with flam- mable process gases containing air, reduce the oxygen concentration in the storage tank below the limiting oxygen concentration (LOC), or which prevent entrance of air into the tank by maintaining a positive pressure (blanketing). The most commonly used inerting gas is nitrogen, but other gases such as flue gas, steam, carbon dioxide, argon, and helium have been used.

In the chemical process industries (cpi), it is common practice to provide inerting gas for all atmospheric storage tanks containing flammable liquids (class i), combustible liquids (class ii and iii) heated above or within 20^of of their flash point, or liquids with dissolved flammable gases.

Care must be taken to ensure that the inerting system is sized to deliver the maximum flow of gas needed during liquid pump-out to prevent under-pressurizing the tank and causing vacuum collapse (imploding). It is also necessary to decide on what should be done in the case of the plant nitrogen system (or other supply of inerting gas) failing in the off position. A vacuum safety valve can be installed so that air is used as the backup for the inerting system to prevent tank failure so long as no additional hazards are introduced. Some companies install a backup nitrogen system using banks of nitrogen cylinders, but some companies, however, prefer to let the tank collapse rather than introduce air into a tank containing flammable materials.

The inerting gas system should be designed to provide a reliable and continuous supply of gas. It is good engineering practice to install a low flow or low pressure switch and alarm in the gas supply line to alert the operators of a possible problem. A pressure safety valve should also be provided after the pressure regulator to vent the gas to the atmosphere should the regulator fail in the open position, and thus prevent the tank from being subjected to full inerting gas line pressure, which could rupture the tank. Inerting gas supply piping should be designed so that there are no Low-point pockets in the line downstream of the pressure regulator. NFPA 69 also discusses other inerting gas piping system design criteria and practices.

Electrostatic discharges can ignite flammable vapors in the vapor space of storage tanks. Therefore, flammable and combustible liquids should be introduced into storage tanks by means of fill pipes (also called dip pipes) which terminate within 6 inches of the bottom of the tank (per NFPA 30),i.e., no splash filling above the liquid level. Splash filling is hazardous for two reasons: (1) it introduces a liquid which may have a considerable charge (e.g., toluene) into a flammable gaseous atmosphere, and (2) splash filling creates mists, which are much easier to ignite because mists of combustible liquids can be ignited at initial temperatures well below the flash point of the liquid. Ordinarily, special tank electrical grounding connect- ions will not be needed if the tank is in contact with the earth or if its connecting piping is grounded. However, grounding connections should be provided on tanks that are not in contact with the earth (e.g., on concrete foundations) if the piping is ungrounded or non- Conductive. For tanks containing class i liquids care should be taken that tank plates, internal structural members, and tank fittings are electrically bonded to reduce the danger of internal sparks from lightning.

Grounding and bonding connections can be made with pressure-type ground clamps; brazing, welding, battery-type clamps; or magnetic or other special clamps that provide good metal-to-metal contact. Surfaces to which grounding clamps are attached must be clean and free of paint, oil, grease, or other materials which would impede good contact.

All storage tanks for flammable and combustible liquids must be provided with adequate vents to permit the intake and discharge of air during emptying and filling operations and to permit the expansion and contraction of vapor due to temperature changes. This is called normal venting requirements. In addition, emergency venting is required to prevent over pressurizing the tank from external fire exposure. Atmospheric and low-pressure tanks may also require emergency vacuum vents to provide protection against tank collapse should the normal "breather" vent be plugged and the tank is being pumped out.

Venting capacity depends on a number of factors such as filling and emptying pumping rates, volatility (vapor pressure) of the liquid, strength of the tank, rate of heat transfer to the vapor and liquid in the tank, and size of the tank. When a mixture of several liquids is stored in the same tank, the most volatile should be used as the design basis. Normal venting capacity is calculated based on the pump-in or pump-out rate plus a thermal venting (breathing) rate. NFPA 30 states that normal vents shall be sized in accordance with either:

NFPA 30 states the following with respect to normal vents:

Aboveground storage tanks should be provided with a method of relieving excessive internal pressure that develops from external fire exposure. Emergency relief vents have weighted pallets which stay closed except when opened by increased pressure (see figure 6). Emergency vents should be provided on all aboveground storage tanks except for floating-roof tanks and tanks with weak roof-to-shell seams (used in the petroleum industry but not in the chemical industry).

Emergency venting requirements are derived from a consideration of the probable maximum rate of heat transfer to the tank contents; the tank area likely to be exposed; the time required to heat the tank contents to the boiling point; the time required to heat unwetted portions of the tank shall or roof to a temperature Where the metal will lose strength; and the effect of drainage, insulation, and the application of water streams in reducing fire exposure and heat transfer.

Methods and formulas for calculating the heat absorption from a fire and venting rates required are presented in NFPA 30 and API std. 2000. Heat absorption from an external fire can be calculated from formulas or obtained form a chart. The amount of heat absorbed can be decreased by applying certain environmental factors for insulation, water spray, drainage, and a combination of insulation, drainage, and water spray. API Std. 2000 is somewhat more conservative than NFPA 30 in that it does not take credit for water spray.

Vent pipes should be provided on open vents or emergency vent devices where necessary to conduct vapors discharged to a safe location. Some recommendations for vent piping design include:

Where flame arresters are installed on vent nozzles they are usually deflagration type arresters. If they are located right on the vent nozzle, without any discharge piping, they are called "end-of-line" arresters. If they have discharge piping attached to direct the vapors away from the tank, they are called "in-line" arresters, and the vendor should be questioned as to how long the discharge pipe may be. If the discharge pipe is too long, flame acceleration may occur and a

Transition from deflagration to detonation may occur. Only flame arresters that have been certified in accordance with accepted test protocols (us coast guard, factory mutual, etc.) For the particular service should be used. Untested flame arresters may not perform as desired, i.e., a flame will not be quenched. Condensation should be prevented in flame arresters on vent lines from tanks containing liquids which solidify during cold weather by providing a heating arrangement such as a jacketed flame arrester or steam tracing on the arrester. Where polymerization of a material may occur at the arrester, dual arresters equipped with a three-way valve should be provided so that one arrester

Is always in service.

A tank rupture is the sudden loss of tank integrity over a relatively large area of the tank structure, causing a large loss of contents. It can be caused by any of several conditions: overfilling, overpressure due to an internal chemical reaction or material boiling due to a constant exposure to reaction heat, continuous impingement of flame over an area of the tank causing it to lose strength, loss of wall integrity due to corrosion, or loss of wall weld integrity. The chances of tank rupture can be reduced by attention to several design features, such as:

• The proper use and sizing of overflow piping The proper use and sizing of pressure relief devices (safety valves, rupture disks, etc.)
• The installation of the appropriate high level alarms and flow shutoffs to prevent overfilling
• The installation of water sprays to protect exposed tanks walls during a fire
• The diked area should be sloped to a sump within the diked area
• The proper specification of tanks materials and thickness, including corrosion allowances
• The inspection of tank welding during and after construction and the pressure testing of the tank prior to use

A frothover occurs when a tank storing an organic liquid also contains some quantity of water and the tank temperature increases to the point where the water in the tank starts to boil, forming a froth of organics and steam. If froth formation is violent, it may result in frothover of ignitable organics or other fluids, causing a major fire. Frothovers may be caused by:

• Mistakenly routing water into a storage tank containing hot oil, creating a steam explosion
• An equipment failure upstream causing water to leak into products being routed to storage
• Routing cold light hydrocarbons to hot tanks or hot heavy hydrocarbons to cold tanks
• Water in the bottom of mixed or crude oil storage tanks vaporizing during a fire

Storage temperatures should be at least 12^of below the boiling point of water to avoid water boilover.

The severity of flammable liquid storage tank fires requires that fire protection facilities be provided, applicable to the type of tank to be protected. This can include fire loops with hydrants and monitors in the storage area, foam systems for the individual tanks, and deluge spray systems to keep the exposed surfaces of tanks cool in case of fire in an adjacent tank.

Normally, only hydrant protection is required. Fixed or portable foam-making equipment or water spray systems may be required to control fires when the quantities of liquids stored or tank sizes are unusually large. For all flammable liquid storage tanks, sufficient hydrants should be provided within 350 feet of the tanks so that they can be reached by hose streams or monitor nozzles from outside the diked area or other safe locations. Each hydrant should have a minimum of two outlets controlled by individual valves. Approved combination straight stream/water spray nozzles at each hose. A straight stream discharge will effectively cool exposed Tanks or facilities, while a high velocity spray discharge can control or extinguish fires in class III liquids. Foam systems usually consist of a foam storage tank, an incoming firewater line, a mixing device, Foam/water piping up the side of the tank, and foam/ water applicator nozzles. The systems for fixed roof tanks are design to create a foam layer over the flammable liquid in the tank. The systems for floating roof tanks are designed to cover the space immediately over the seal area, but if an internal floating roof is constructed of lightweight materials, the foam system should be designed as if the tank were a cone roof tank.

Much useful information on fire protection for storage tanks and other chemical plant equipment is found in NFPA 13, 15, and 16, and chapter 16 of the CCPS guidelines for engineering design for process safety.

Recent EPA regulations have required that emissions of volatile organic compounds (VOCs) be controlled and minimized. This has resulted in vents from atmospheric storage tanks containing flammable and combustible liquids being manifolded and the vapors conducted to control equipment such as flares, thermal oxidizers, and scrubbers. Although this has reduced the environmental problem, it has created safety problems. Among the most severe hazards are

If manifolding of vents is to be done, the following recommendations should be followed:

Where detonation flame arresters are used, they should be installed at the following locations:

Figure 7 is a schematic of a manifolded vent collection system.

It should be noted that detonation flame arresters may not be appropriate in systems where particulate matter may be in the vent vapors as the flame arrester could become plugged and fail to handle normal in- and out-breathing, leading to a tank failure.

There are no federal regulations for chemical plant manifolded vent (vapor collection) systems, but the USCG regulations (33 CFR 154, subpart e), which apply only to ship and barge loading and unloading vapor control systems, are followed by many CPI companies.

Hazardous liquids are transferred in the cpi by a number of different types of pumps. These include:

• Centrifugal
• Rotary (gear, vane, lobe, screw, etc.)
• Diaphragm and plunger positive displacement

Centrifugal and rotary pumps are available with mechanical seal systems or as seal-less pumps (canned motor and magnetic drive). Diaphragm pumps do not have mechanical seals and are also inherently safer.

The sections below discuss safety considerations for pumps with mechanical seals, canned-motor and magnetic drive pumps, and diaphragm pumps.

The following safety features are recommended:

• Centrifugal and rotary pumps for hazardous liquids should be provided with double mechanical or tandem seals with a barrier fluid between the seals. If a seal fluid reservoir is used, it should have a low level switch and alarm, and it may be desirable to interlock the switch with the pump motor to shut off the pump. See figure 8 for mechanical seal system installation features. Api std. 682 is a good reference source for shaft sealing systems for centrifugal and rotary pumps.
• Assure compatibility between any buffer or seal fluid and the process fluid including potential variations in the process fluid during startup, shutdown, cleaning, and upset conditions.
• Provide piping arrangements and supports that assure that pump flange loadings are the minimum practicable and do not exceed loadings specified by the pump manufacturer. Excessive flange loads can have a deleterious effect on mechanical seal life.
• Assure that the mechanical seal is properly installed as this also could affect seal life.

Canned-motor and magnetic drive pumps can reduce leakage concerns, but have special requirements of their own. Seal-less pumps circulate a portion of the process fluid internally to lubricate the internal rotor bearings and remove eddy current heat. For this reason, they must be applied more carefully with regard to vapor pressure, specific heat, viscosity, and chance of boiling internally than a sealed pump. The process fluid should have a viscosity greater than 0.5 cp for proper lubrication, and specific heat greater than 0.5 for cooling.

Canned-motor pumps offer freedom from the worries of shaft seals, ball bearings, base stiffness, flexible couplings, and shaft alignment since the pump and motor are mounted on the same shaft and sealed inside two layers of containment (the so-called "can"). It is the only design that can provide near-zero emissions during normal operation and during failure. Very reliable bearing wear sensors are available. See figure 9 for a schematic drawing of a canned-motor pump.

Although magnetic drive pumps do not have a shaft seal, many of the problems common in shaft sealed pumps remain. Ball bearing are still used on the input shaft, and a flexible coupling to the motor is still needed. Since the pump is driven by a separate motor, a stiff base and precision alignment are still required. Most magnetic drive pumps can be fitted with a thermocouple, and some designs have optional bearing wear sensors. The main advantage of a magnetic drive pump has over a canned-motor pump design is lower heat input to the pumped liquid. However, except for a few known double can designs, magnetic drive pumps do not offer true secondary containment (i.e., no leakage even when the primary barrier is breached). See figure 10 for a schematic of a magnetic drive pump.

Table 7 is a comparison of canned-motor and magnetic drive pump characteristics. Table 8 lists causes of seal-less pump failures and their effects, while able 9 Lists types of failure detection monitors for seal-less pumps.

Diaphragm pumps are also seal-less pumps. They can be motor-driven or air-driven. However, single diaphragm pumps can leak if the diaphragm fails. Therefore, they should be specified with double diaphragms to ensure freedom from leaks. The space between the diaphragms can be fitted with any of several leak-detection sensors (using pH, liquid conductivity, or pressure instrumentation with alarms) which will detect a leak when the primary diaphragm develops a leak or fails. One advantage of a diaphragm pump is that a smaller temperature rise occurs in the process fluid when operating at low flows. Air-operated diaphragm pumps usually vibrate because of their mode of operation. Therefore, the suction and discharge piping should not be hard-piped, but should have flexible hose sections

Of sufficient length to dampen the vibrations.

For tank farms, many companies prefer to locate the transfer pumps outside of the dike with a separately curbed and drained area to prevent spread of seal leaks. One of the reasons for this is that in the event of a large spill, the pumps may become submerged because of the normally high dikes used in tanks farms. For some chemicals (depending on the properties of the chemical-flammability, corrosiveness, etc.) Fire or Electrical and/or equipment damage could occur when the pump is submerged. In special circumstances, such as when handling high flash point combustible liquids or viscous liquids that necessitate a short suction line, the pump may be located inside the dike wall. If the pump is located inside the dike wall, a local motor start/stop control station should be provided outside the diked area and properly identified. Also, consideration should be given to locating the pumps in a subdivided area for containment of seal or lube oil leakage.

The preferred location for pumps in unit process storage areas (not tank farms) is inside of the diked area. Pump locations should consider the effects of loss of containment on operator health and the environment.

In general, pumps handling hazardous liquids should be located in well ventilated, open areas to prevent accumulation of flammable or toxic vapors and to reduce

Fire exposures. Location of such pumps under pipe racks should be avoided.

Some companies mount the transfer pump (a self-priming centrifugal pump with a suction dip leg into the tank) directly on the tank so that there is no possibility of a leak occurring from a bottom nozzle on the tank.

Operating centrifugal pumps at severely reduced flows can cause excessive vibration and damage to drivers(motors, turbines, etc.), Piping, and adjacent equip- ment. Therefore, centrifugal pumps should be provided with a minimum flow bypass line returning back to the supply tank to avoid the instability conditions caused by low flow rates. It may be desirable to also install a cooler in the bypass line to remove excessive heat buildup in the process fluid.

Shutoff valves on the suction and discharge of the pump should be provided. When the supply tank is nearby, the pump suction line valve should be mounted on the tank nozzle, and the valve should be able to be operated from a remote, safe location, or be a fusible-link type of valve which will close when exposed to fire. This can prevent dumping the tank contents in the event of a fire near the suction line, assuming that the pump discharge line valve is closed. (lines in which there is no flow may fail quickly when exposed to a fire). Consideration should be given to providing shutoff valves at both the pump inlet and the supply tank if the pump has a long suction line.

A check valve should be installed in the discharge line of centrifugal pumps to inhibit backflow of the pumped fluid to the suction source when the pump stops and to limit reverse rotation of a non-running installed spare pump.

Provide overpressure relief for situations where:

• Centrifugal pump shut-off head exceeds the pressure rating of the system.
• Overpressure can result from thermal expansion from centrifugal pumps that can be valved-in when there is a remote start-up capability,or when the suction and discharge lines both have automatic closing valves.
• Overpressure of a positive displacement pump could be caused by operating the pump with a closed or restricted discharge line unless the design of the pump is inherently limited in pressure generation, such as air or steam driven pumps. Do not take credit for relief capability built into a positive displacement pump unless safe operation can be verified by manufacturer’s data or by capacity test, and the relief valve can be removed for periodic test and inspection.

Monitoring of pump bearing temperature with alarms and/or shutdown on high temperature should be considered, especially for highly hazardous liquids, due to the probability of sequential failures whereby bearing failures will cause seal failures.

Avoid using cast iron for pump casings and other pressure resisting components when pumping hazardous or highly hazardous liquids. Cast iron is brittle and can be cracked by mechanical or thermal shock, which could result in leaks and subsequent fires. It should be noted that ductile iron can revert to cast iron when exposed to temperatures produced by flammable liquid fires, and may therefore require replacement if directly exposed to a fire condition.

All piping systems should be designed in accordance with ANSI/ASME b31.3. This code covers metallic piping, nonmetallic piping, and piping (both metallic and nonmetallic) lined with nonmetals. B31.3 prohibits the use of thermoplastics in flammable fluid service aboveground.

The primary concern in designing and installing piping systems transporting hazardous liquids is to avoid leaks and emissions. This is accomplished in several ways, as follows:

• Minimize joints that can leak (e.g., flanged and screwed joints).
• Minimize piping sizes, run lengths, and complexity
• Specify the correct materials of construction.
• Design the piping to withstand temperature and/or pressure excursions.
• Design the piping to take care of cyclic operations if they are part of the process (e.g., batch processes.
• Design the piping to take care of thermal gradients or stresses.
• Size the piping to avoid erosion
• Design the piping to handle hydraulic transients (water and steam hammer).
• Design the piping to handle dynamic loading and vibration if they are part of the process (connected to reciprocating and/or rotating equipment).
• Adequately support and anchor the piping, as needed (especially important for plastic piping, which needs more support points than metallic piping).
• Use butt-weld joints as they do not produce a local stress riser as do some other types of welded joints, and they have good fatigue resistance. A butt-weld joint can also be readily examined by most conventional nondestructive techniques.
• Use spiral-wound gaskets preferably as they are less prone to leakage than nonmetallic type gaskets (e.g., plastics, graphite, etc.) Because they have inner and outer rings that retain the gasket in the flanged seal surface.
• The flange should have a minimum surface finish of 125-250 AARH to ensure a tight joint.
• Use valves that minimize fugitive emissions. Newer types of packing designs and bellows seals can accomplish this.
• If flanges are used, consider providing flange shields that protect operators by containing any leaks or emissions.
• Consider the use of fire-safe valves where a loss of valve integrity due to a fire would result in a large leak of flammable liquid.
• Minimize the use of expansion joints to provide piping flexibility. Use flexible hose or pipe loops to provide the required flexibility. If expansion joints must be used, a multiple ply (double-walled) construction joint should be specified. Where the expansion joints can be exposed to a fire, speccify a fire-resistant design.
• The piping for one or more tanks in a diked should not pass through the dike wall to an area containing other tanks. In a dike fire, flammable liquids could flow along the pipe and spread the fire to adjacent tanks.

Listed below are a number of references relevant to the storage and handling of hazardous liquids that are in addition to the ones mentioned in the presentation. The latest editions of API, ASME, NFPA, and other industry standards and codes should be used.

Api Rp 520. Sizing, Selection, And Installation Of Pressure-Relieving Devices In Refineries. Part I, Sizing And Selection; Part Ii, Installation. American Petroleum Institute, Washington, D.C.

Api Rp 521. Guide For Pressure-Relieving And Depressuring Systems. American Petroleum Institute, Washington,

D.C.

API Rp 2001. Fire Protection In Refineries. American Petroleum Institute, Washington, D.C.

API Rp 2003. Protection Against Ignitions Arising Out Of Static, Lightning, And Stray Currents. American Petroleum Institute, Washington, D.C.

API Rp 2350. Overfill Protection For Storage Tanks In Petroleum Facilities. American Petroleum Institute, Washington, D.C.

API Publ. 2030. Application Of Water Spray Systems For Fire Protection In The Petroleum Industry. American Petroleum Institute, Washington, D.C.

API Std. 620, Design And Construction Of Large, Welded, Low-Pressure Storage Tanks. American Petroleum Institute, Washington, D.C.

API Std. 650. Welded Steel Tanks For Oil Storage. American Petroleum Institute, Washington, D.C.

API Std. 682. Shaft Sealing Systems For Centrifugal And Rotary Pumps. American Petroleum Institute, Washington, D.C.

Britton, L. G. "Operating Atmospheric Vent Collection Headers Using Methane Gas Enrichment." Process Safety Progress, Vol. 15(4), Pp. 194-212 (Winter 1996).

Britton, L. G. Avoiding Static Ignition Hazards In Chemical Operations. American Institute Of Chemical Engineers, New York, NY (1999).

Ccps. Guidelines For Engineering Design For Process Safety. American Institute Of Chemical Engineers, New York, NY (1993).

Ccps. Guidelines For Pressure Relief And Effluent Handling Systems. American Institute Of Chemical Engineers (1998).

Ccps. Guidelines For Safe Storage And Handling Of High Toxic Hazard Materials. American Institute Of Chemical Engineers, New York, NY (1988).

Cheremisinoff, P. N. (Editor). Storage Tanks. Gulf Pub-Lishing Company, Houston, Tx (1996).

Digrado, B. D. And Thorp, G. A. The Aboveground Steel Storage Tank Handbook. Van Nostrand Reinhold, New York, NY (1995).

Dillon, C. P. Corrosion Control In The Chemical Process Industries. Mcgraw-Hill Book Company, New York, NY (1986).

Geyer, W. B. (Editor). Handbook Of Storage Tank Systems: Codes, Regulations, And Designs. Marcel Dekker, Inc., New York, NY (2000).

Grossel, S. S. "Highly Toxic Liquids: Part I. Moving Them Around The Plant." Chemical Engineering, Vol. 97, No 4, Pp. 110-115 (April 1990).

Grossel, S. S. "Safe, Efficient Handling Of Acids."

Chemical Engineering, Part I, Pp. 88-98 (July 1998) And Part Ii, Pp. 104-112 (December 1998).

Grossel, S. S. Deflagration And Detonation Flame Arresters. CCPS, American Institute Of Chemical Engineers, New York, NY (To Be Published In 2001).

Grossel, S. S. And Crowl, D. A. (Editors). Handbook Of Highly Toxic Materials Handling And Management. Marcek Dekker, Inc., New York, NY (1995).

Landrum, R. J. Fundamentals Of Designing For Corrosion Control-A Corrosion Aid For The Designer. National Association Of Corrosion Engineers, Houston, Tx (1989).

Myers, P. E. Aboveground Storage Tanks. Mcgraw-Hill, New York, NY (1997).

Nayyar, M. L. (Editor). Piping Handbook, 6^th Edition. Mcgraw-Hill, Inc. New York, NY (1992).

NFPA 11. Low Expansion Foam. National Fire Protection Association, Quincy, Ma.

NFPA 11a. Medium And High-Expansion Foam Systems. National Fire Protection Association, Quincy, Ma.

NFPA 13. Standard For The Installation Of Sprinkler Systems. National Fire Protection Association, Quincy, Ma.

NFPA 15. Water Spray Fixed Systems For Fire Protection. National Fire Protection Association, Quincy, Ma.

NFPA 16. Installation Of Foam-Water Sprinkler And Foam-Water Spray Systems. National Fire Protection Association, Quincy, Ma.

NFPA 69. Standard On Explosion Prevention. National Fire Protection Association, Quincy, Ma

NFPA 70. National Electrical Code. National Fire Protection Association, Quincy, Ma.

NFPA 77. Static Electricity. National Fire Protection Association, Quincy, Ma

Pasquariello, M. "Safe Handling Of Caustic." Chemical Engineering, Vol. 107 (10), Pp. 78-85 (September 2000).

Sixsmith, T. And Hanselka, R. (Editors). Handbook Of Thermoplastic Piping System Design. Marcel Dekker, Inc., New York, NY (1997).

Schweitzer, P. A. (Editor). Corrosion Engineering Handbook. Marcel Dekker, Inc., New York, NY (1996).

Skousen, P. L. Valve Handbook. Mcgraw-Hill, New York, NY (1998).

Zappe, R. W. Valve Selection Handbook, 4^th Edition. Gulf Publishing Company, Houston, Tx (1999).

Ziu, C. G. Handbook Of Double Containment Piping Systems. Mcgraw-Hill, Inc., New York, NY (1995).