Feature Cover Story ReportAcids Handling Vapor pressure, bar General guidelines on materials, storage, pumping and other concerns for the proper and safe handling of acids Alberto Baumeister Sebastiano Giardinella Mayhell Coronado Ecotek norganic acids play a major role in the chemical process industries (CPI). They are used as raw materials, catalysts or finishing and pH control agents in the manufacture of a wide range of chemical products, from fertilizers to detergents, and even foods. Given their widespread use, a major issue in the CPI is the proper and safe handling of the acids, the adequate materials selection for the pieces of equipment, piping and fittings used in the process, and the correct storage and even disposal of these materials. These are important factors that need to be taken into account from the design phase throughout the operating life of a facility, in order to ensure there will not be integrity problems that may negatively impact project economical turnover, personnel safety or the environment. This article covers the most important inorganic acids: sulfuric acid (H2SO4), nitric acid (HNO3), phosphoric acid (H3PO4), hydrogen chloride (HCl) and hydrochloric acid, and hydrogen fluoride (HF) and hydrofluoric acid; providing general guidelines on their physical properties, safety data, appropriate materials, storage, pumping and other common issues encountered when handling such fluids in the CPI. 26 Acid vapor pressure versus temperature 100.00 10.00 1.00 0.10 I 0.01 -150 -50 50 150 Temperature, °C HNO3 (100 wt.%) HNO3 (90 wt.%) HNO3 (70 wt.%) H2SO4 (70 wt.%) H2SO4 (80 wt.%) 250 350 HCl (pure) HF (pure) HCl (34 wt.%) H2SO4 (100 wt.%) H2SO4 (98 wt.%) FIGURE 1. The vapor pressure as a function of temperature for the acids covered in this article Physical properties Some acids are naturally present as liquids (H2SO4), some are solids at ambient conditions (anhydrous H3PO4), and others are gases (HCl, HF). Acids are very soluble in water and thus also widely available as aqueous solutions at different concentrations. Some of these solutions are also enhanced by dissolving additional compounds (for example, fuming sulfuric acid is made by dissolving SO3 in sulfuric acid). Given that there are several available grades, the knowledge of physical properties for each one is important in order to avoid freezing, the formation of hazardous fumes, or other problems when storing and handling these materials. The physi- cal properties of the acids covered in this article are briefly presented here. These properties for common available grades are presented in Table 1. Figure 1 plots their vapor pressures at different temperatures. Sulfuric acid. Sulfuric acid is the single most important inorganic chemical in tonnage produced and in use. H2SO4, can be described as a colorless, oily, hygroscopic liquid with no odor; it is the largest inorganic chemical manufactured and one of the most widely used inorganic chemical in the manufacture of many other products. By the year 2004, North America and Asia were the biggest producers of sulfuric acid, recording almost 60% of world total production. Sulfuric acid CHEMICAL ENGINEERING WWW.CHE.COM OCTOBER 2012 the largest use for nitric acid is for the production of fertilizers. It is corrosive to metals. it is extensively used as a solvent for ores and as a catalyst in the petroleum industry. HCl forms an azeotropic constantboiling mixture that contains 20.CHE.579A 42.97 1.COM OCTOBER 2012 . such as turpentine.29 –36.8 3. Higher concentrations. used in the manufacture of chemicals.50 Acrid Odor 108 1.5 3.5 200 155. but also in the manufacturing of agricultural feeds.6105C 1. reducing agents and combustible fluids.6 –83 Disagreeable (can Pungent odor cause choking) 121 2. among other uses. and ore reduction among others. Hydrochloric acid is a solution of the gas hydrogen chloride.50 1.TABLE 1. H3PO4 or orthophosphoric acid is a white solid with a melting point of 42°C.% 98 Liquid Fertilizer Tower Pure WFNA Strong Common Gas (anhydrous) 100 Gas Aqueous Aqueous 78–80 Liquid 62–70 Liquid 35 H2SO4. combustible.2F 1.7 1. HF occurs naturally in volcanic gases and may result from industrial activities. As a strong electrolyte it is used in electroplating baths for pickling.16 1. HCl plays an important role in pickling of steel.5 6. Finally. It is commercially available at concentrations of 75. Hydrogen fluoride and hydrofluric acid.4 1.2 2 340 3.079 Fuming.56 1. detergents.3 Pungent odor 100 0. 65% oleum H3PO4 766438-7 97. HNO3 is a solution of nitrogen dioxide (NO2) in water. Phosphoric acid.% (polyphosphoric) are also available.202 –40 1. However. acid treatment of oil wells. H3PO4 has two main methods of production: the wet process and electric furnace. according to purity. stainless steel. chemical cleaning and processing. colorless. Nitric acid is a strong acid that re- acts violently in the presence of strong bases.8361 10. charcoal and alcohol.267 1.% (superphosphoric) and 115 to 118 wt.4826 1. and in the food industry as preservative. hazardous liquid that reacts with most met- als to form explosive hydrogen gas. organic pigments. aluminum. Gas (anTechnical Aqueous hydrous) Grade 22°Be 100 Gas 50 Liquid 33 Liquid Grade Concentration Physical state Color Odor Boiling point °C (760 mmHg) Vapor density (air = 1) Specific gravity (H2O=1) Liquid g/mL density (at 20ºC) Melting point °C Concentrated wt.4048 –41. H3PO4 is the third most important acid in industry. Commercially. it is a poisonous.2 1.994 HNO3 7697-37-2 63. and for operations in the production of iron and steel. Its appearance varies from pale yellow to colorless. reducing materials. soaps. such as coal-burning.5D 20 0. corrosive fuming liquid with an extremely sharp odor. sulfuric acid is obtained after absorption of SO3 in water. it is a highly oxidizing agent. therefore it reacts violently with bases. It is highly corrosive to most common metals and forms a flammable/explosive gas.% of PO3. chlorides. which is highly soluble in water. It easily dissolves in water to form hydrofluoric acid. Sulfuric acid is a strong acid and a strong oxidizing agent. steel and other chemical derivatives. clarifier or flavor enhancer.5533 –4. such as 105 wt. water and organic compounds with the evolution of heat.5 2. forming flammable or explosive gas. non-toxic and a relatively weak acid.87 1. 27 CHEMICAL ENGINEERING WWW. Both liquid and vapor can cause severe burns to all parts of the body. HF forms dense white vapor clouds if released.1 212. Specialized medical treatment is required for all exposures. Hydrochloric acid has many applications in the production of organic and inorganic compounds such as fertilizers.85 151. waxes. it is a colorless to light-brown fuming liquid with an acrid suffocating odor. acidifier. Sulfuric acid is mostly used in the manufacturing of fertilizers.46 Aqueous. Moreover. and the manufacture or production of aluminum. 80.01 HCl 7647-01-0 36. “Pure” or “technical grade” phosphoric acid is usually found at 85 wt. pharmaceuticals.17 1.68E viscosity (at cP 20ºC) Notes: A Liquid Density of phosphoric acid at 75% B Liquid density of sulfuric acid at 80% C Liquid density of sulfuric acid at 70% D Vapor density of nitric acid at 65% E Dynamic viscosity obtained after extrapolation F Boiling point at 38.164 –46.01 HF 7664-39-3 20.55 –36. Nitric acid.98 Dynamic 20.5129 –42 1.%.50 1.2% is manufactured by the combustion of sulfur with dry air to form sulfur dioxide (SO2). When boiling all aqueous solutions. dyes and more.251 Pungent odor 83 1. explosives. phosphate fertilizer.7272B 1. Hydrogen chloride and hydrochloric acid. then sulfur trioxide (SO3) is produced through a catalytic conversion. Nitric acid also reacts violently with organic compounds. PHYSICAL AND CHEMICAL PROPERTIES OF ACIDS [1–5] Units CAS Number Molecular weight H2SO4 7664-93-9 g/gmol 98. Anhydrous hydrogen fluoride (AHF) is a clear.83 1. 75–85 65 SO3 Liquid Solid 100 Liquid 90 Liquid 68 Liquid 48–51 Liquid 40 Liquid Colorless Colorless Colorless Colorless Colorless Colorless Colorless Colorless Colorless Colorless Colorless Colorless Colorless Colorless Odorless Odorless Odorless Odorless Odorless Pungent odor 86 Pungent odor 120.2 1.57 1.62 1. highly corrosive. Nitric acid is the second most important industrial acid. It is used mostly in the production of phosphate fertilizers. steel pickling and metal cleaning. HF is used to manufacture fluoropolymers.4 112.14 1.159 –62 –114 Acrid odor Pungent odor –85 1. explosives and more.24% HCl and boils at 110°C (230°F). 85 and 87 wt.52 2.72 1. fertilizers.03 1. rosive to metals. Occupational Safety and Health Administration (OSHA) regulations: 29 CFR 1910. solution Emergency Guide 157 Guide 157 Guide 125 Guide 157 Guide 125 Guide 157 Response [10] Notes: PEL: Permissible exposure limit REL: Recommended exposure limit IDLH: Immediately dangerous to life or health concentration TWA: Total weighted average STEL: Short time exposure limit ERG: Emergency Response Guidebook high-octane gasoline. 7 mg/m3 ceiling 1 mg/m3 TWA. such as in the following reference for H2SO4: NACE RP0391 — Materials for the Handling and Storage of Concentrated (90 to 100%) Sulfuric Acid at Ambient Temperatures. fuming. fuming. This guidebook is available in printed form. alkalis. brass. liquid.5 mg/m3 TWA. powdered metals.CHE. including applications for smart phone that allow for quick searches of the chemicals and their associated guides. Reacts with water to produce metals.Cover Story TABLE 2. solid.S. nitric acid. as well as any lining or internal coating requirements should be determined by a materials expert based on the acid.000 mg/m3 50 ppm Organic materials.55 and 29 CFR 1915. HF: NACE 5A171 — Materials for Storing and Handling Commercial Grades of Aqueous Hydrofluoric Acid and Anhydrous Hydrogen Fluoride. water or steam. including toxicity levels. only properly trained personnel such as firemen and policemen (or properly trained plant personnel) should be involved in the emergency response and containment of the product. Other toxicity levels.. alcohol. refrigerated liquid 1789: hydrochloric acid. 6 ppm. fuming.S. such as the Recommended Exposure Limit (REL) and Immediately Dangerous to Life and Health Concentrations (IDLH) are published in the U. chlorates. electronics (microchips and printed circuit board cleaning) and uranium isotopes. spent Guide 137 2796: sulfuric acid. sulfuric acid. zinc. The Emergency Response Guidebook 2008 (ERG2008) provides guidelines for managing emergencies when hazardous chemicals are involved. metallic powders. hydrogen sulfide. 10 mg/m3 STEL 25 ppm Combustible materials. Aqueous acid solutions are very corrosive. 3 mg/m3 STEL 3 ppm. solution 3453: phosphoric acid. The chemical safety data for the acids covered in this article. anhydrous 1790: hydro. fuming. health effects and other concerns when handling or storing hazardous chemicals are also given in the NIOSH Pocket Guide.S. It is also used to etch glass or metal. Cor. most water. as well as how to respond in the event of a spillage. Reacts with water to produce heat. hydrochloric acid. respectively. TOXICITY AND EMERGENCY RESPONSE DATA H2SO4 PEL (OSHA) 1 mg/m3 [6–8] REL (NIOSH) 1 mg/m3 TWA [9] H3PO4 1 mg/m3 TWA HNO3 2 ppm. phosphoric acid. Reacts with heat. sulfuric acid. with not more than 51% acid 1805: phosphoric acid. rail tank cars transporting concentrated sulfuric acid should be internally coated according to NACE SP0592 — Application of a Coating System to Interior Surfaces of New and Used Rail Tank Cars in Concentrated (90 to 98%) Sulfuric Acid Service. their toxicity levels and incompatibilities need to be taken into account when storing and transporting them. with more than 51% acid 1831: sulfuric acid. transportation of these acids or other hazardous materials 28 is subject to the U. interior coatings or linings could also be considered. Hydrochloand concrete ric acid is highly corrosive to most metals UN Listing Number 1052: hydrogen fluoride. with not less than 30% free sulfur trioxide 1832: sulfuric acid.1000 for the general. Department of Transportation Pipeline and Hazardous Materials Safety Transportation regulations.Hydroxides. For instance. phosphoric acid. 5 mg/m3 TWA. with less than 30% free sulfur trioxide. sulfuric acid. Materials selection The materials of construction. anhydrous 2186: hydrogen chloride. construction and maritime industries. 2 mg/m3 TWA HCl 5 ppm.1000. Do not mix with solutions containing bleach or ammonia 1830: sulfuric acid.1050: hydrogen fluoric acid chloride. other than red fuming 2032: nitric acid. 5 mg/m3 TWA 2 ppm. Some recommendations are given regarding the correct material selection depending on acid. its concentration and storage conditions. pipeline or tank cars) is subject to Title 49 of the Code of Federal Regulations (49 CFR). Transportation of hazardous materials in various forms (bulk. solid Guide 154 Metals. Corrosive to metals 2031: nitric acid. Permissible exposure limits (PEL) for hazardous materials are given by the U. Attacks glass copper. A new version of the Emergency Response Guidebook is scheduled for release this year (2012). 29 CFR 1926. amines. 2. Safety and emergency response Because acids are mostly hazardous chemicals. and can also be downloaded in convenient electronic form. In the event of spills of these acids or other hazardous materials. carbides. phosphoric acid. CHEMICAL ENGINEERING WWW. fulminates. 5 mg/m3 (15 min) ceiling 30 ppm 5 ppm. Strong caustics. red fuming HF 3 ppm.S. transport or process conditions. National Institute of Occupational Safety and Health (NIOSH) Pocket Guide to Chemical Hazards. 4 ppm. Depending on the acid and storage. Corrosive to metals metals to form H2 gas. incompatibilities and emergency response guides are summarized in Table 2.COM OCTOBER 2012 . 7 mg/m3 ceiling IDLH 15 mg/m3 (NIOSH) [9] Incompatibilities & Reactivities 1. In the U. The chemical incompatibilities. carbides. and usually require special materials depending on the temperature or phase. acid concentration. or from professional associations. because the acid that remains on the surface establishes a vapor-liquid equilibrium in which toxic and corrosive gases are released.COM OCTOBER 2012 . such as particular corrosion allowances or nozzle design. High-silicon cast irons are ideal to manage phosphoric acid in all concentrations at any temperature. Low Pressure Storage Tanks: for vertical tanks with flat bottoms and operating pressures between 0. are also considered in acid storage tanks — either by special company or supplier criteria. and Inspection of Storage Tank Systems for Concentrated Fresh and Process Sulfuric Acid and Oleum at Ambient Temperatures.14 barg (2. Welded. and offer an appropriate facility for sampling. no presences of fluoride ions (F-) are allowed Copper and copper alloys can be used to manage pure phosphoric acid solutions in heatexchanger tubes. along with their general acceptable use ranges (concentrations and temperatures) for each of the acids covered in this article. such as white. corrosion rates increase at higher temperatures. high corrosion rates or vaporization. System impurities can accelerate the rate of corrosion more than acid concentration It is extensively used in the manufacture of phosphoric acid.14 barg and 1. CLADDING & LINING [12] Materials of construction H3PO4 Aqueous solutions of phosphoric acid with concentration of 5 to 85% are highly corrosive for alloys 1100. Consequently this material is not recommended for phosphoric acid handling All cast irons can be considered to handle phosphoric acid.CHE. concentrated sulfuric acid tanks design should follow NACE SP0294 — Design. so a recirculation system is recommended. and can also resist higher stresses or impacts. Fabrication.5 psig and 15 psig) • ASME BPV Code. so acids should be stored at the lowest possible temperature without freezing the acid. Sect VIII. pipes and fittings.03 barg (2. Periodically. iron content and flowrates Alloys with 14. For dilute acid alloys 20Cb-3 and 825 are recommended. usually chemically inert. such as plate coils mounted on the outside of the tank wall. short storage times. Corrosion resistance depends on temperature. MATERIALS OF CONSTRUCTION.5 psig) • API STD 620 — Recommended Rules of Construction of Large. Higher corrosion rates could also result from heating of the metal surfaces due to sun radiation. It is highly resistant to corrosion Nickel alloys are appropriate for handling phosphoric acid. Storage tanks Usually aboveground storage tanks (ASTs) are used to store acid as they facilitate accessibility to tanks and ancillary equipment for inspection and maintenance. it is necessary to homogenize the contents of the tank. so the tank exterior should be painted with a radiation reflecting color. although the presence of contaminants must be previously evaluated since it can provoke severe cases of corrosion. or external heat exchangers connected to 29 CHEMICAL ENGINEERING WWW. In places where the storage temperature could be below the acid freezing point.5% content of silicon have shown best resistance to corrosion for sulfuric acid handling in all concentrations at temperatures up to the boiling point Copper and copper alloys are not suitable for sulfuric acid handling It has shown high resistance to corrosion in sulfuric acid handling up to 70% concentration. for concentrated acid at high temperatures alloy B-2 offers the highest corrosion resistance Resistant to corrosion for handling acid at temperatures below 100°C in all concentrations Resistant to corrosion for handling acid at temperatures between 160 and 200°C in all concentrations Resistant to corrosion for handling acid at temperatures up to the boiling point in all concentrations in absence of fluoride ions (F–) Conventional austenitic stainless steel has shown elevated corrosion resistance for all concentrations of phosphoric acid up to 65°C (150°F) Aluminum Cast Iron Copper Lead Nickel Niobium Silver Tantalum Stainless Steel Tables 3–8 list some common metal alloys used in the CPI. Metal tanks offer a higher durability. CLADDING & LINING [12] Materials of construction Aluminum H2SO4 Aluminum alloys may be used to handle dilute (concentration below 10%) and concentrated acid (above 98%). Special attention should be given to the acid physical properties in storage to prevent freezing. MATERIALS OF CONSTRUCTION. whereas FRP tanks are economical. It suffers corrosion for handling sulfuric acid in a range of concentration of 40–95 % It can be used to handle concentrated sulfuric acid at ambient temperatures under static and low-velocity condition. Another regular measure to maintain acids at an appropriate temperature is coating the tank with an adequate material such as vinylbased materials. storage tanks and vessels should be provided with heating facilities. For instance. The conventional austenitic grades show good resistance in dilute or highly concentrated acid at moderate temperatures It is slowly dissolved by dilute sulfuric acid. Although. Tanks for acid storage are usually built of either metal (lined or nonlined). and can be a good alternative for low-volume. The storage tank should be sized for at least 50% more volume than required. this material is not recommended for pumps or valves Nickel 200 demonstrates good tolerance to sulfuric acid when it is handled at low or moderate temperatures It can be used for handling sulfuric acid at concentrations below 95% under oxidizing conditions Exhibits excellent resistance to sulfuric acid up to 250°C (480°F) and is used when no corrosion can be tolerated Resists sulfuric acid in all concentrations and temperatures It is attacked by sulfuric acid in the presence of air In wrought or cast form rhodium is not recommended for handling sulfuric acid Concentrated sulfuric acid turns extremely corrosive in presence of 316 and 304 stainless steels. or fiber reinforced plastic (FRP). The mechanical design of tanks for acid storage usually follows either of the following codes: • API STD 650 — Welded Steel Tanks for Oil Storage: for vertical tanks with flat bottoms and operating pressures less than 0. Div 1: for other operating pressures Special design criteria. corrosion resistance depends on the concentration of the acid and the purity of the metal Carbon steel Cast Iron Copper Lead Nickel Niobium Gold Platinum Palladium Rhodium Stainless steel Zinc TABLE 4. Tanks should allow access to the top nozzles and the vent system. In general.TABLE 3. are suitable. but it is not recommended for handling hydrofluoric acid in aqueous solutions Unsuitable for handling hydrofluoric acid Unsuitable for handling hydrofluoric acid Unsuitable for handling hydrofluoric acid Unsuitable for handling hydrofluoric acid Pumps The design basis should be set before selecting a pump. The system must ensure the acid is transported safely and efficiently. On the other hand stainless-steel type 316 can be used for handling dilute acid at low temperatures The use of copper alloys is affected by aeration and velocity. this is an advantage regularly offered by vertical submerged pumps over horizontal pumps.891 — Mineral Acid Storage Tank Requirements. Complex reaction occurs Appropriate for handling nitric acid at any concentration in temperatures below the boiling point. gate valves or plug valves are regularly used. A primary issue that must be taken into account while pumping acids is safety. type of flow.COM OCTOBER 2012 . Corrosion attacks when handling dilute nitric acid For concentrations of 0 to 65%. In order to maintain a low velocity of the fluid. However. stem and seat) should be selected according to the acid concentration and operating conditions. State of Florida has specific requirements as given by Rule 62-762. Alloy 617 offers an excellent performance and corrosion resistance for handling nitric acid at high temperatures in the catalyst-support grids in high pressure plants It is completely resistant to nitric acid in all concentration at temperatures below 100°C It is resistant to nitric acid in concentrations up to 50% above that it is attack by corrosion It is vulnerable to attack from corrosion when nitric acid is in presence of air In wrought or cast form rhodium is resistant to corrosion produced by concentrated nitric acid at 100°C Not suitable for use in nitric acid Not suitable for use in nitric acid. Pressurized storage is required when the vapor pressure exceeds the atmospheric pressure at the storage temperature. releas- CHEMICAL ENGINEERING WWW. suction pressure. Piping and fittings Selecting pipe material and designing the pipe system is a very important issue in a plant. transport temperature. Common guidelines for acid storage tank design are summarized in Chem. As temperatures exceed 80°C (175°F). For control. Internal heating coils are not recommended. for instance. globe or butterfly valves Acid handling Sulfuric acid. Corrosion depends on temperature and concentration of the acid. 30 Valves Valves are used for various functions. they can be manually operated or be fitted with actuators. so the chance of having leaks becomes negligible. fluid velocity. most AISI 300-Series stainless steel has shown great corrosion resistance for temperatures up to the boiling point Not suitable for use in nitric acid It can be used for concentration between 52 and 70% Not suitable for use in nitric acid Nickel alloys are widely used in the production of nitric acid. containment is also an issue. Materials for different parts of the valves (disk. and so on. a bigger pipe diameter is suggested. Also. May 2008. Nickel Niobium Tin Titanium Zirconium In order to select the piping material. Sulfuric acid must be stored separately from combustible and reducing substances in a wellventilated environment at temperatures below 23°C (73. by consulting the valve manufacturer. or less provided there is adequate drainage to an acid neutralization pit. high-pressure steam is not recommended as a heating medium since heat exchange surfaces could exceed 100°C. impurities in the acid and solids presence. especially while handling acids. to ensure proper valve operation.TABLE 5. acid concentration.CHE. because excess temperature in the coil walls accelerates corrosion and could cause leaks. Eng.S. CLADDING & LINING [12] Cover Story the tank. causing severe corrosion. its corrosion resistance depends on the concentration and temperature Fair corrosion resistance in a wide range of concentration and temperatures for handling hydrofluoric acid. MATERIALS OF CONSTRUCTION. or double walled. Not recommended for handling dilute acid It offers great corrosion resistance to aqueous and anhydrous hydrofluoric acid with concentrations up to 50%. MATERIALS OF CONSTRUCTION. Facts at your Fingertips: Acid Storage. phase. the selected pump for the system cannot leave place for leakage. Piping should have as few flanges as possible. the operating conditions such as temperature. to contain spills. plug valves are preferred for this service. Corrosion is often related to an acid’s velocity. Tanks should be properly diked. the U. it has poor resistance to dilute or concentrated hydrofluoric acid. below 100°C (212°F) Nickel 200 is ideal for handling hot anhydrous hydrogen fluoride vapor. Concentrated acid needs to be isolated from water. Also. the following aspects have to be defined: acid concentration. Materials of construction Aluminum Cast iron Stainless steel Copper Lead Molybdenum Nickel Niobium Gold Palladium Rhodium Silver Tin Titanium HNO3 Aluminum alloys commonly used for nitric acid services are 1100 and 3003. Some common materials according to the acid to be handled are presented in Tables 9–13. In general. that is. with blockage valves accessible to operators. so. Local code requirements should also be addressed when designing acid-tank containment. Aluminum alloys are compatible with nitric acid at temperatures up to at least 71°C (160°F) when it is inhibited by hydrofluoric acid Cast iron can be used for handling concentrated nitric acid under control conditions such as low temperature and low velocity. CLADDING & LINING [12] Materials of construction Aluminum Stainless steel Copper Lead Molybdenum HF Unsuitable for handling hydrofluoric acid Stainless-steel type 304 has a good performance for handling anhydrous hydrogen fluoride up to 200°C (390°F). including the following: For blocking. Titanium alloys can’t be used for red fuming nitric acid due to a violent reaction that can take place in the system TABLE 6. impeller or other internals damage.4°F). containment should be at least for one tank volume (if not properly drained). corrosion becomes stronger depending on nitric acid purity. as it may react violently. material selection guidelines shall be followed to avoid casing. When storing acids above ground. 10. CLADDING & LINING Materials of construction Aluminum Unalloyed cast iron systems are unsuitable for handling HCl. G. Chemical Safety Handbook. Dept. rhodium has excellent corrosion resistance to handle concentrated hydrochloric acid in temperatures up to 100°C (212°F) It is very susceptible to aeration when concentration and temperature are high It has shown excellent corrosion resistance to handle HCl at any concentrations under atmospheric pressure and temperatures up to 90°C (195°F). 11. 2008.htm 18. 2002.gov/cgi/t/ text/text-idx?c=ecfr&tpl=/ecfrbrowse/ Title49/49cfrv2_02.1000 (Maritime): www. C-276 and 686 are recommended. 5.tpl Cast Iron Stainless steel Copper Lead Nickel Niobium Gold Palladium Rhodium Silver Tantalum Titanium TABLE 8. DKL Engineering.. 650. Technical Manual..inchem.show_document?p _table=standards&p_id=10286 9. 2012.S.htm 4. Inconel alloys 625. “Emergency Response Guidebook 2008 (ERG2008)”. Perry. Efficient Handling of Acids. Safe. 12. and Inconel alloy G-3 are used for dilute hydrochloric acid handling..S. Inc..com/publishedliteratureDOWCOM/dh_0131/0901b80380131028. “Sittig’s Handbook of Toxic and Hazardous Chemicals and Carcinogens”.1000 (General Industry): www. & Maloney. Occupational Safety and Health Administration (OSHA). NIOSH Publications. Retrieved July 6. 2012. The lower the concentration the higher can be the temperature of the system. face shield and full suit shall be used.show_ document?p_table=Standards&p_id=10628 8.. Monel alloy 400 is appropriate in the absence of air for temperatures up to boiling point for concentrations below 15%.gov/ pls/oshaweb/owadisp. Other alloys like Hastelloy C-2000 and Hastelloy G-30 are also recommended for handling hydrofluoric acid H2SO4 HNO3 H3PO4 HCl HF ing heat. A high-silicon iron alloyed with small amounts of molybdenum. Hastelloy alloys B-3 and G-30 stand phosphoric acid in all concentrations and temperatures.” McGrawHill. D.sulphuricacid. U. 15. 2012. . without air presence. 2012. Sulfuric Acid Properties. Inconel alloys 625.S. from Hydrogen Chloride: www. Retrieved May 16. Nickel alloy 200 is commonly used.gpoaccess. Inc. Hastelloy alloy G-35 was especially designed for phosphoric acid wet processing in fertilizers manufacture Incoloy alloys 25-6MO. a vapor respirator when ventilation is inadequate. 65% MSDS. April 2000. C-2000 and G-30 are also suitable for handling sulfuric acid Chromium enhances corrosion resistance in alloys while handling nitric acid. HCl at 0.TABLE 7. from Strong Acid System — Piping.org/documents/icsc/icsc/ eics0163. The Dow Chemical Company. at all concentrations and temperatures The formation of fluoride films is key on engineering materials in order to offer good corrosionresistance rates while handling hydrofluoric acid. Retrieved July 9. U. Hastelloy G-30 alloy and G-35 offer excellent corrosion resistance for this same reason When handling phosphoric acid. National Institute of Occupational Safety and Health. For dilute HF and temperatures up to 70°C (158°F) Inconel alloy 600 can also be used. Technical information bulletin. Elsevier. 88–98. 3. J. sulphuric-acid. In Sulfuric Acid Manufacture: Analysis. MATERIALS OF CONSTRUCTION. If sulfuric acid needs to be diluted or combined with water. Hastelloy B3. Dept. it has no resistance to corrosion References 1.osha.show_document?p_ table=Standards&p_id=9991 7.. of Labor. J. from Regulation: 29 CFR 1915. Transportation. Dept. Inconel alloys 625. Stanley S. 020 and Inconel alloy G-3 have shown excellent corrosion resistance for temperatures up to 50 °C (120°F). W. Handbook of Corrosion Data. When handling aggressive acid. 287–291. 825 and 020. N. C-276 and 686 are recommended. DKL Engineering. For environments that contemplate the presence of oxidizing contaminants and hot hydrochloric acid.com/techmanual/Properties/proper ties_acid_properties. from Chapter I Pipeline and Hazardous Materials Safety Transportation regulation: http://ecfr. December 20. It is unsuitable for concentrated acid at higher temperatures Pure nickel and nickel-copper alloys can be used for handling hydrochloric acid below 10% concentration. C-276 and 686 are suitable. Nitric acid. International Program on Chemical Safety. alloy 690 has shown better corrosion resistant because its chromium content is higher. from Sulfuric Acid Properties: www. of Transportation. 2006. “NIOSH Pocket Guide to Chemical Hazards”.13. 19.osha. 20. aeration and oxidizing impurities It exhibits tolerance to corrosion at 24°C (75°F) and concentrations up to 15%. Dept. For storage of H2SO4. 2008. 6.S. Monel alloy 400 is widely used for this purpose. and King.htm 17. API Std. “Perry’s Chemical Engineers’ Handbook. for example. 2003. Control and Optimization. Eng. To manipulate sulfuric acid.S. due to the fact that it has shown excellent corrosion resistance for all hydrofluoric acid services in all concentrations and temperatures up to (and even above) the boiling point. For reducing conditions. It can be used to handle acid with concentrations below 25% up 190°C (375°F) Unsuitable for handling hydrochloric acid HCl It is not appropriate for handling HCl. of Labor. Incoloy alloy 800 and 825 are adequate for nitric acid at all concentrations for temperatures up to the boiling point. Monel alloy 400 can be used at room temperatures up to 80% concentration. ASME Boiler and Pressure Vessel Code Sec.. ASM International. Nickel alloy 200 can be used at room temperature for concentrations up to 30% as well. CLADDING & LINING ACIDS COMMON ALLOYS For dilute and intermediate sulfuric acid (between 40 and 80% concentration) Incoloy alloys 256MO. pdf?filepath=productsafety/pdfs/noreg/23300312. of Labor. April 12. Hastelloy alloys B-3. chromium and copper can be used to handle hydrochloric acid up to 95° C (200°F) at all concentrations Corrosion attacks stainless steel (316) and stainless steel (304) when handling HCl at any concentration or temperature Copper can be used to handle dilute hydrochloric acid only. 2008. www. June 2008. 622.osha. Material Safety Data Sheet. 2007..Y. 622. 14. Inconel alloy 600 and C-276 also offer good corrosion resistance to nitric acid for concentration over 20% at room temperature. as well as Inconel alloy G-3 are suitable and regularly used. Occupational Safety and Health Administration (OSHA)..COM OCTOBER 2012 31 . 2012. Purified Phosphoric Acid.gov/pls/oshaweb/owadisp. VIII Div 1. Nitric acid must be stored separately in a corrosion resis- CHEMICAL ENGINEERING WWW. 2012. from Regulations: 29 CFR 1910. M. Green. from Regulation: 29 CFR 1926.5% can stand temperatures up to 200°C before corrosion attacks the alloy It has shown excellent corrosion resistance to handle HCl at any concentrations and temperatures up to 100°C (212°F) It can be used for handling hydrochloric acid at any concentrations and atmospheric pressure up to the boiling point Unsuitable for handling hydrochloric acid In cast or wrought form. 020 and 25-6MO. P. For anhydrous hydrogen fluoride up to 82°C (180°F). Retrieved May 16. Davenport. U. pp. Chemical Safety Information from Intergovernmental Organizations. especially if high velocities are involve. due to its sensitivity to velocity. Elsevier. 2012. U.pdf&fromPage=GetDoc 21. Retrieved May 14. 2005. then it has to be added to water carefully.gov/ pls/oshaweb/owadisp. Retrieved May 14.dow. Electronic Code of Federal Regulation. Potash Corp. 825. Dept. MATERIALS OF CONSTRUCTION. Chem. 2012. Another alloy that offers good corrosion resistant in concentrations below 10% with aerated conditions at room temperature is Monel alloy 400. R. PCS Sale — Industrial Products. U. 2. API Std. Incoloy alloys 825.. Retrieved July 6. Southerm States Chemical A Dulany Industries Co. July 1998. from Product Safety Assessment: Nitric Acid: http// msdssearch. at low temperatures... such as gloves. Nitric acid. 2005. Occupational Safety and Health Administration (OSHA). O. 620. pp. 2012. Technical Manual.com/techmanual/strong%20 acid/sa_piping.CHE. R. 2002. 622. Retrieved May 12. due to this fact. Pohanish. (2002). proper personal protective equipment.55 (Construction Industry): www. 16. W. For extreme conditions such as high temperature and high amount of impurities or halides contaminants. Grossel. C-2000 and G-30 are also suitable for handling hydrochloric acid. and the container must remain dry and locked up.6°C (40. Impervious rubber or polyvinyl chloride gloves with gauntlets covering forearms should be used. therefore the pump suction pipe should be placed above the tank bottom to avoid pumping solid residues that can compromise pump well-functioning. SPECIFIC EQUIPMENT. The seat should be made of PVF. Phosphoric acid. storage tanks must provide a facility to clean the tank bottom. sulfide. for concentrations lower than 75% at low temperatures Alloy 20 and Hastelloy have also been used. because it can accelerate corrosion. even though the piping material can be the same used for storage When using stainless steel. When vapor or mist concentrations exceed applicable standards. Phosphoric acid can be described as a stable chemical. Common seat materials include: PVF. the fittings and valves should be welded or flanged. Under the same line. Impervious gloves and aprons are recommended.000-L ISO containers. When boiling all aqueous solutions. HCl must be stored in a corrosion resistant location. engineering controls (instrumentation: detectors.%.% and 40 wt. emergency dump systems). the use of air is not recommended. Along the same lines it is important to mention that nitric acid’s storage requires special conditions. HF is delivered commercially in concentrations of 98 wt. However. carbides. Viton or EPT Properly fitted chemical goggles and protective clothing should be worn. not only this measure needs to be taken into account but also workers should be aware of the risks arising from management of nitric acid. in a manner preventing drainage of acid to gloves or boots.%. Acid-proof clothing should be fitted snugly at neck and wrists.VALVES AND PROTECTIVE CLOTHING GUIDELINES Equipment H3PO4 Heating coils should be provided in order to maintain the phosphoric acid above its freezing point. Nitrogen can be used for such purposes Valves Butterfly Valves: Lead is an adequate stem and disk material for sulfuric acid at all concentrations. with Monel also showing fair results. submerged type Pumps For handling sulfuric acid at 93. PIPING. because heat may cause containers to burst and result in escape of poisonous gases.1°C (70. when it is heated hydrochloric acid fumes are released. so. Alloy 20 plunger.5°C (0.5°F) at 75%. avoiding contact with powders. It can cause severe burns. Alloy 20 and Hastelloy C are good stem and disk materials for phosphoric acid at various concentrations. with Viton and Hypalon also been used Properly fitted chemical safety goggles.000 mL for analytical products. both in liquid and vapor phase.35°C (231.COM OCTOBER 2012 . No special respiratory protection is required under ordinary conditions of use. Such measures include administrative controls (for example. to 10. CHEMICAL ENGINEERING WWW. which may not be immediately painful or visible. Usually iron sulfate precipitates. Sulfuric acid also promotes hydrogen gas formation. approved respiratory protective equipment must be used Protective Clothing skin and generates destruction of tissue and severe bone damage. Due to HF’s nature. SPECIFIC EQUIPMENT. Unlike other acids. because it is not subject to thermal decomposition. relief valves. depending on ambient conditions and acid concentration. face shield (8-in.1°C All fittings should have wetted parts of 316 L stainless steel. the severity of the damage is related to the time of contact or exposure and the acid concentration.19% (66 °Bè) usually horizontal centrifugal pumps with mechanical seals are used Common materials of construction are: cast iron or Alloy 20 wetted ends. HF acid is a very hazardous material. tetrafluoroethylene plastic chevron packings For sulfuric acid service.01°F) at 85%. it is a consequence of interaction between the tank’s surface and the acid. pumps used for sulfuric acid handling are usually horizontal centrifugal pumps or heavy duty vertical.CHE. phosphoric acid does not react violently with metals. Neoprene.2°F) at 80% and 21. 48–51 wt. eyes and respiratory tract. turpentine and strong bases. with tops being covered by the trousers. Centrifugal pumps are also used for phosphoric acid handling Tanks Pumps Piping and Fittings Stainless steel 316 is regularly used for piping because it has shown excellent results in corrosion resistance for all concentrations of phosphoric acid.Cover Story tant location. and personal protection equipment (appropriate clothing). for this reason it is necessary to avoid pressure buildup by venting the line In case of draining the pipe. Package sizes range from 500–1. hydrogen. work permits). 85% H3PO4 freezes at 21. provided that adequate ventilation is maintained. reaction occurs slowly and progressively with hydrogen as a product. Hypalon. caution should be exercised because the vapors formed are flammable. screwed fittings are not recommended because they may allow leakage Valves Butterfly valves: 316 SS. 4.6% (by weight) HF and boils at 111. Hydrofluoric acid. The most important issue about this acid is the variation of its freezing point according to its concentration. the design criteria for its handling should be based on the acid concentrations and operating temperatures. with mechanical seals rather than packing. Head protection via hard hat or full cover acid hood should be worn. such as adequate ventilation and especially low temperatures to ensure a cool environment for the solution. as well as a respirator for protection against fumes Tanks Piping and fittings Protective clothing TABLE 10. these pipes should be kept full of acid to minimize corrosion attacks.4°F). The fluoride ion easily penetrates the 32 TABLE 9. Every process that involves nitric acid handling or storage must contemplate an adequate ventilation system that ensures airborne levels below the safety exposure limits allowed. the freezing point of standard concentrations are –17. HF is a strong irritant to the skin. therefore it becomes necessary to heat phosphoric acid at high concentrations in order to maintain the acid as a liquid solution. Boots made of the same material should be worn.VALVES AND PROTECTIVE CLOTHING GUIDELINES Equipment H2SO4 Iron sulfate is produced in storage tanks of sulfuric acid. Hydrochloric acid. The tank’s maintenance should be performed periodically according to the laws of the state and the company policies According to the plant requirements. high minimum) and protective clothing should be worn.8 °F). PIPING. strict measures shall be taken when handling the acid in industrial facilities. For instance. Nitric acid and its vapors can cause severe damage during its handling to persons who have contact with it. so it should not be stored above 23°C (73. Even though the acid is nonflammable. welded pipe lines with schedule 80 are commonly used. HF forms an azeotropic constant boiling mixture that contains 35. oil and gas industries. 2011). for low concentrations at low temperatures.%. Vents should be routed to a scrubber Pumps similar to those used for H2SO4 and H3PO4 can be used.VALVES AND PROTECTIVE CLOTHING GUIDELINES Equipment HCl Outdoor tanks are preferred for storing hydrochloric acid. 15-A. for higher concentrations. She has a degree in chemical engineering from Universidad Metropolitana (Venezuela). proper ventilation has to be ensured in order to maintain the acid concentration in air below the permitted limit of exposure. in renewable energy development at Heriot-Watt University (Scotland). international associations and academic institutions. Tanks Pumps Piping and Fittings Valves Protective Clothing the following compounds: chromate. Electronic-grade HF can be transported in unplasticized PVC pipe Butterfly valves: Hastelloy C is the best material for the stem and disk. SPECIFIC EQUIPMENT.CHE. petrochemical. ■ Edited by Gerald Ondrey TABLE 12. and has published a work on the effects of microbial contamination in diesel fuel used for thermal power generation. respectively. email: mcoronado@ecotekgrp. oil and gas industries. He has a Master’s Diploma in water treatment management from Universidad de León (Spain. Other grades of HF can be stored in tanks made of CS with natural rubber lining. Phone: +507-203-8490. PVC or FRP piping have also been used. they should be made of titanium (with a water content higher than 1. and chemical industries. Common seat materials include: PVF. She has experience in the development of conceptual and basic engineering projects for the oil and gas. He is also professor of project management at Universidad Latina de Panamá. PIPING. Vent piping should be designed taking into consideration possible corrosion from contact with moisture Wetted parts should be made of 304L stainless steel for concentrations lower than 95 wt. Hypalon and Viton. Hydrogen corrosion may occur in steel tanks. and of aluminum for higher concentrations. glove change is necessary before 8 hours Authors Alberto Baumeister is the CEO and co-owner of the Ecotek group of companies. and a degree in chemical engineering from Universidad Metropolitana (1987). FEP or glass linings (up to certain temperatures) can also be used for all grades. Fax: +507203-8491.% and electronic-grade HF.VALVES AND PROTECTIVE CLOTHING GUIDELINES Equipment HNO3 For acid grades lower than 95 wt. The rating and schedule should be selected according to the operating pressure and corrosion allowance. He is a certified project management professional (PMP).%. Hypalon and Viton For concentrations up to 40% neoprene and fluoroelastomer gloves are recommended for handling hydrochloric acid.%.COM OCTOBER 2012 33 . He has experience as coordinator and senior process consultant in engineering projects for the chemical. and in project planning and control. with fumes collected at a disposal system and sent to a scrubber. and is currently a student of the M. Mayhell Coronado is a process engineer of the Ecotek group of companies (same address as above. since the metal is passivated with an iron fluoride film when the fluid is in contact with the metal. Mechanical seals of carbon and ceramic faces with TFE or fluoroelastomer secondary seals. PIPING. SPECIFIC EQUIPMENT. therefore storage tanks need proper venting that shall be directed to a safe location and treatment facility. Email: sgiardeinella@ ecotekgrp.% and electronic-grade HF. PVDF. tanks should be designed for slight pressure and vacuum. for pure (100%) HF. or constructed of TFE. [11] Butterfly valves: 316 SS. Neoprene. For concentrated acid. Undesirable reactions can take place between hydrochloric acid and CHEMICAL ENGINEERING WWW. as well as in support to company management. Alloy 20 and Hastelloy C are good stem and disk materials for nitric acid at various concentrations. Derakane or polypropylene lining is frequently used for HCl. Centrifugal pumps lined with. refining. Vinylidene chloride (VC)-lined steel for 70 wt.34% to prevent spontaneous combustion). CS with VC.% HF up to 66°C. are also recommended [11] CS piping with TFE. Seats made of Viton can handle various concentrations up to 70%. Piso 15. Panamá.% up to 38°C. 1990).VALVES AND PROTECTIVE CLOTHING GUIDELINES Equipment HF Anhydrous and 70 wt. Panama (Calle 60. SPECIFIC EQUIPMENT. refining. When storing hydrochloric acid. PVDF of Derakane are commonly used. He has experience as process leader.com). Rep. Sebastiano Giardinella is the vice president and coowner of the Ecotek group of companies (same address as above. which is located in the City of Knowledge. and a degree in chemical engineering from Universidad Simón Bolívar (Venezuela. or HF between 60 to 70 wt. in engineering projects for the chemical. depending on fluid temperature. a specialization in management for engineers at Instituto de Estudios Superiores de Administración (Venezuela. 70 wt. permanganate and sulfate. where she taught thermodynamics. PH Obarrio 60. butyl gloves are suitable Tanks Pumps Piping and fittings Valves Protective clothing which can compromise the safety and toxicity levels allowed. petrochemical. A subsequent reaction occurs with metal peroxide forming its corresponding chloride. with Alloy 20 also exhibiting fair results. The tank must be provided with a vent so acid fumes do not accumulate in the tank and a drainage system so maintenance can be performed periodically. and Pentonlined steel or solid Penton for electronic grade HF [11] Anhydrous and 70% wt HF can be transported in seamless CS piping. Such reactions generate chlorine gas as a result. polyethylene or unplasticized PVC [11] Diaphragm pumps with TFE or polychlorotrifluoroethylene (CTFE) diaphragms can handle anhydrous. PIPING. transport phenomena and general chemistry as professor assistant. Neoprene. Tanks Pumps Piping and fittings Valves Protective Clothing TABLE 13. Operators handling hydrochloric acid must wear protective equipment and it is advisable for them to take a shower and gargle with sodium bicarbonate after manipulating the acid in order to avoid teeth corrosion in other activities performed by the operator. and has written technical publications for Chemical Engineering magazine. only PVF or Viton should be considered Neoprene and natural rubber gloves are excellent for handling hydrofluoric acid in all concentrations. 2009). Email: abaumeister@ecotekgrp. some common measures of protection when tank is placed indoors are coating the floor with asphalt or another corrosion resistant material to prevent several damages in case of leaks or spills. graduating summa cum laude. Centrifugal pump materials depend on grade: Ni-Cu alloy of Alloy 20 is used for anhydrous HF.com). Ofc.Sc. has Master’s Degree in project management from Universidad Latina de Panamá (Panama.com). silicon iron or 3003 aluminum alloy [11] Piping made of 304L stainless steel is frequently used for HNO3 up to 95 wt. De. TFE and FEP lining is also used. with Sch 80 and Sch 160 commonly used for both grades. Carbon steel (CS) piping with TFE. Obarrio. depending on fluid pressure Butterfly Valves: common stem and disc materials include: lead or Hastelloy C. Common seat materials include: PVF.TABLE 11. Hypalon and EPT have also been used Neoprene or natural rubber latex gloves are acceptable for handling nitric acid. 2006). Panamá. He has been a professor of the Chemical Engineering School at Universidad Metropolitana between 1995 and 2007 and has written several technical publications for international associations. and Hastelloy C metal parts. can be stored in carbon steel (CS) tanks. graduating first of his class.