• Author / Uploaded
• Grin Nikiforov

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7.3. Choose a suitable material of construction for the following duties: 1. 98% w/w sulfuric acid at 70⁰C; CPVC (Schedule 80 Type 1 -Gray) is a good low cost material that can withstand all concentrations of sulfuric acid. With a maximum service temperature of 200 ºF, CPVC can withstand some heat of dilution, for injectors or diffusers that are adding small amounts of acid. Silicon cast iron also has excellent resistance to sulphuric acid in all concentrations to 100% up to the atmospheric boiling point. 2. 5% w/w sulfuric acid at 30⁰C; PVC (Schedule 80 Type 1 -Gray) is a good low cost material that can chemically withstand all concentrations of sulfuric acid. PVC has relatively low temperature resistance (a maximum working temperature of 140 ºF), and should not be used for the diffuser components such as the injector or quill that are near the dilution or diffusion of the acid, as the heat of reaction can damage the pipe. Silicon cast iron also has excellent resistance to sulphuric acid in all concentrations to 100% up to the atmospheric boiling point. 3. 30% w/w hydrochloric acid at 50⁰C; PVC would be the cheapest. It must be adequately supported. It must have some room for thermal expansion! It should be protected from sunlight and from fluorescent light for longest service. The UV makes it brittle over time. Clear PVC is available from companies like Harvel. It costs more and has a lower tolerance for UV light. PVDF (Kynar®) is also a tough liner. It has excellent resistance to Halogens and high strength acids. It can withstand temperature to 275°F (135°C), Abrasion Resistant, and has a High Thermal Expansion Coefficient. 4. 5% aqueous sodium hydroxide solution at 30⁰C; Use a flanged steel pipe with a polypropylene lining if maintaining low iron concentration in the caustic soda solution is important. Because of the hazardous properties of caustic soda solution, unsupported plastic pipe should not be used, and fiberglass reinforced plastic (FRP) pipe should not be used.

5. Concentrated aqueous sodium hydroxide solution at 50⁰C; Type 304 stainless steel (or better) is the recommended pipe MOC for 50% caustic up to 95⁰C and 175 psig. Both 304 and 316 stainless steel types are resistant to a wide range of concentration and temperature. Below 80 degC they can be considered resistant to any concentration of sodium hydroxide, up to the limit of solubility. 6. 5% w/w nitric acid at 30⁰C; Generally stainless steels are resistant to corrosion in nitric acid over a wide range of concentration and temperature. The 'helpful' oxidising properties of nitric acid are used in the chemical 'passivation' of stainless steels. The 304 types can be used over a wide range of concentration and temperature, up to 95%, for storage applications. The 304 types are preferable to 316 types for nitric acid applications however. This is an exception to the 'general rule' for stainless steels where the 316 types are normally found to be more corrosion resistant than 304 types.

7. Boiling concentrated nitric acid; Over 95% concentration, aluminium alloys should be considered OR 4% silicon stainless steels. Any additional chlorides or fluorides in nitric acid may increase corrosion rates by pitting. To avoid the risk of localised corrosion, especially where post weld heat treatment is impractical, the low carbon, 304L types should be considered. Solution heat treatment (1050 -1100 degC followed by fast cooling) on the standard carbon 304 type can be considered as an alternative. These treatments should also re-dissolve any sigma formed.

8. 10% w/w sodium chloride solution; We have been using HDPE tanks and pipes for brine solution (saturated NaCl solution) for water softening application. uPVC / cPVC may be used. Avoid stainless steel. Other options can be MS with rubber or FRP lining.

9. A 5% w/w solution of cuprous chloride in hydrochloric acid; Super austetic, high nickel stainless steel containing between 29-30% nicel and 20% chromium have a good resistance to acids and acid chlorides. 10. 10% w/w hydrofluoric acid. PVC-U-, PVC-C- or PVDF pipes exhibit very good resistance to sulfuric acid, hydrofluoric acid or hydrochloric acid. PVDF offers superior chemical resistance to many solvents, acids, bases and halogens. It is designed for extra tough applications where plastic may not have been considered before. It has been certified to meet ASTM E-84 and UL 723 standards for flame spread and smoke generation. The certification means that for the first time PVDF piping systems, when approved, can be used safely in areas such as air plenums where typically local codes have prohibited use of plastic pipe due to fear of fire. PVDF is able to maintain much of its strength and chemical resistance within a broad temperature range of -40°F to 285°F. 7.4. Suggest suitable materials of construction for the following applications: 1. A 10,000m3 storage tank for toluene; For benzene and toluene, PVDF, a special plastic tanks resin, is often specified. PVDF plastic tanks are exceptionally resistant to inorganic acid solutions. 2. A 5:0m3 tank for storing a 30% w/w aqueous solution of sodium chloride; Fiberglass reinforced plastic (FRP) and cross-linked polyethylene (XLPE) are the storage tank material options for brine storage. In comparing these two materials, cross-linked polyethylene offers the following advantages over fiberglass: o Faster turnaround time - Lead times for a poly tank are 4-5 weeks versus 8-10 weeks for a fiberglass tank. o Superior warranty - Fiberglass offers a 1-year warranty; cross-linked polyethylene offers a 5-year warranty. o More robust product - Crosslinked Polyethylene is less prone to damage and will have a greater useful life. o More cost effective - In general, a XLPE tank will be 20-30% less than a fiberglass tank.

3. A 2m diameter, 20m high distillation column, distilling acrylonitrile; Stainless steel or carbon steel are recommended for tank construction. Carbon steel tanks are usually cleaned either by chemical or physical means before initial use to remove rust. If the tank is cleaned by chemical means, further cleaning with water, according to an acceptable procedure, is mandatory in order to prevent a potential chemical reaction. 4. A 100m3 storage tank for strong nitric acid; Aluminum Tanks are used for storage of highly corrosive fuming nitric acid & other chemicals such as acetic acid, acetic an-hydride etc. These aluminium tanks are made in high purity aluminum material (bis 19500 grade, 99. 5% purity) and fabricated by adopting advanced tig & mig welding technology. 5. A 500m3 aqueous waste hold-up tank. The wastewater pH can vary from 1 to 12. The wastewater will also contain traces of organic material; Carbon steel construction with the convenient choices of tough, high-solids epoxies, polyurethanes, rubber, PVC and other sheet linings can be used for this. Stainless steel HDWWST are also available. These tanks withstand the wider range of temperatures, chemicals and pH factors encountered in industrial applications. 6. A packed absorption column 0.5m diameter, 3m high, absorbing gaseous hydrochloric acid into water. The column will operate at essentially atmospheric pressure. Super austetic, high nickel stainless steel containing between 29-30% nicel and 20% chromium have a good resistance to acids and acid chlorides. Titanium coatings also improve resistance to HCl.