NACE RP0391-2001 Materials for the Handling and Storage of Commercial Concentrated (90 to 100%) Sulfuric Acid at Ambient Temperatures said:
Section 2: Specific Materials
2.1 Carbon Steel
2.1.1 Carbon steel is satisfactorily resistant to concentrated sulfuric acid at ambient temperatures under static or low-velocity conditions (less than 0.9 m/s [3 ft/s]); ...
2.2 Cast Iron
2.2.1 Gray cast iron and ductile cast iron are both more resistant to corrosion by concentrated sulfuric acid than is carbon steel. ...
2.2.2 Gray cast iron has lost favor in recent years because of its brittle nature. Catastrophic ruptures have occurred in piping as well as pressure vessels. Ductile cast iron has been used successfully for thickwall piping and is recommended over gray iron. Gaskets used with ductile iron piping should match the pipe bore to minimize acid turbulence.
2.2.3 High-silicon cast irons (UNS(2) F47003 with 14.5% Si) are resistant but are seldom used for simple handling and storage because of their inherent brittleness.
2.3 Stainless Steel
2.3.1 The conventional austenitic stainless steels of the Cr-Ni and Cr-Ni-Mo type are generally resistant to ambient-temperature, concentrated acid because they have a naturally formed passive film. ...
2.3.2 The molybdenum-bearing grades (e.g., UNS S31600/S31603 or UNS J92900/J92800) are recommended for improved resistance to velocity enhanced corrosion or impingement in valves in the entire concentration range.
2.3.3 Duplex stainless steels have found successful applications in ambient-temperature concentrated acid, in the form of valves and pumps cast from copperbearing UNS J93370 and fabricated components from wrought UNS S31803 material. ...
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2.3.5 Four to six percent silicon-containing stainless steels (UNS S30600, UNS S30601, and UNS S32615) perform very well in ambient-temperature, concentrated sulfuric acid, but are more typically used for hightemperature, turbulent applications found in sulfuric acid production plants.
2.4 High-Nickel Stainless Steels and Nickel Alloys
2.4.1 Nickel chromium-iron-copper-molybdenum alloys or their cast versions (see Appendix A) perform better and are more resistant to concentrated acid than 18Cr-10Ni-Mo stainless steel under the increased velocity conditions found in pumps and valves.
2.4.2 Alloys of the nickel-chromium-molybdenum type, such as UNS N10276, UNS N06625, UNS N06022, UNS N06455, UNS N06985, UNS N06059, UNS N06200, and UNS N06686 or their cast versions, offer excellent resistance to concentrated acid and are especially useful for applications in which high temperatures and significant acid strength variations are possible.
2.5 Other Alloys and Metals
2.5.1 Nonferrous metals such as zinc, tin, copper, and nickel are not resistant to sulfuric acid and therefore have no useful applications in its handling and storage. Aluminum grades UNS A91100, UNS A93003, and
UNS A93004 have been used successfully for handling sulfuric acid in the concentration range of 98 to 100%, but are not generally recommended.
2.5.2 Chemical lead is resistant to sulfuric acid but the protective sulfate film is increasingly solubilized above about 95% concentration and 25°C (77°F). ...
2.5.3 Of the reactive metals, titanium and zirconium must not be exposed to concentrated acid. Tantalum is resistant to concentrations up to 97% acid and thus finds some application, especially as an electroplated coating for orifice plates.
2.5.4 Of the noble metals, gold and platinum are resistant to sulfuric acid but of very limited applicability. Gold is used to condense and cool reagent-grade acid. Silver is not resistant to sulfuric acid.
2.6 Nonmetallic Materials
2.6.1 Organic
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2.6.1.1 The fluorinated plastics listed below are resistant to concentrated acid at the temperatures covered by this standard:
• polytetrafluoroethylene (PTFE);
• perfluoroalkoxy (PFA);
• ethylene chlorotrifluoroethylene (ECTFE);
• fluorinated ethylene propylene (FEP); and
• ethylene trifluoroethylene (ETFE).
2.6.1.2 Polyethylene (PE) and polypropylene (PP) are subject to environmental cracking. ... Polyvinylchloride (PVC) and polyvinylidene chloride (PVDC) have been used successfully as piping materials for concentrated sulfuric acid, but should not be used for acid strengths greater than 96%. ... Polyvinylidene fluoride (PVDF) is resistant to sulfuric acid up to 98% concentration.
2.6.1.3 Chlorosulfonated polyethylene has been successfully used for hoses handling up to 93% acid. ...
2.6.1.4 High-temperature baked phenolic coatings are routinely used in storage tanks and rail tank cars containing 90 to 98% sulfuric acid in which iron contamination must be minimized and/or corrosion protection is required. At acid concentrations greater than 98%, some types of baked phenolic coatings slowly carbonize. ... High-temperature baked phenolic coatings have provided many years of satisfactory service in concentrated sulfuric acid when properly applied, cured, monitored, and maintained.
2.6.1.5 Polyester, vinyl ester, nylon, and epoxybased materials are attacked by concentrated sulfuric acid.
2.6.2 Inorganic
2.6.2.1 Carbon and phenolic-impregnated impervious graphite are resistant to sulfuric acid up to 96% concentration.
2.6.2.2 Glass, glass-lined steel, and acid-brick ceramics all have satisfactory resistance to all concentrations of sulfuric acid.
Section 3: Specific Equipment
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3.3 Piping
3.3.1 Materials selection for concentrated sulfuric acid piping depends on a number of factors including size, velocity, pumping schedule, contaminants, desired life, and potential dilution.
3.3.2 Carbon steel piping may be used at ambient temperature and low flow velocity (i.e., maximum 0.9 m/s [3 ft/s]). Flow velocities of up to 1.5 m/s (4.9 ft/s) may be allowed if the pumping schedule is brief (e.g., a few hours per day). Good-quality welds are essential, and multipass welds should be used. ...
3.3.3 Carbon steel piping in intermittent service can experience accelerated corrosion because of hydrogen grooving or dilute acid attack. Consideration should be given to drainage and blowing carbon steel lines free of acid using dry air or inert gas.(9) Crevices caused by threaded or socket-welded piping can make the draining or blowing out of acid difficult.
3.3.4 Ductile cast iron pipe has an increased tolerance for higher velocities when compared with steel. Ductile cast iron is preferred to gray cast iron, because it offers better ductility in addition to comparable corrosion and erosion resistance in the acid strengths covered by this standard (see Paragraph 2.2).
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3.3.7 UNS N08020 has been successfully used for small-diameter piping, especially when flow velocities exceed 1.8 m/s (5.9 ft/s).
3.3.8 Plastic-lined piping with PVDF or PTFE liner has also been used successfully. However, PVDF shall not be used for acid concentrations above 98%. Experience with PP-lined concentrated acid piping has been mixed ...
3.3.9 When solar heating is extreme or when heat tracing is required, UNS S31603, high-nickel stainless steels, or nickel alloys are favored (see also Paragraph 3.8.1).
3.3.10 Solid thermoplastic piping should only be used in concentrated sulfuric acid service after a detailed engineering review. (Also see Paragraph 2.6.1)
3.4 Valves
3.4.1 For simple shut-off valves, molybdenum-bearing stainless steel should be used. The industry standard is UNS J92900; UNS J92800 is an acceptable alternative. Copper-bearing UNS J93370 valves are sometimes available at little additional cost and offer greater resistance to dilute acid if it is formed (see footnote 9). UNS J95150 and nonmetallic-lined valves have also been successfully used for this type of service.
3.4.2 For throttling valves with higher velocities and turbulence, UNS J95150 has been used successfully. This alloy is also appropriate for use in stock-tank plug valves employed to protect against inadvertent localized dilution effects. PTFE-lined valves have alsobeen successfully used in this service.
3.4.3 PTFE-based packings and PTFE (filled or unfilled) and fluoroelastomer nonmetallic parts are acceptable for service in concentrated sulfuric acid valving.
3.4.4 A proprietary cast Ni-Cr-Co-Mo-Fe-Cu-Si alloy has been used successfully for valve seats and trim in concentrated acid service at ambient and higher temperatures. This alloy is also used for piping orifice plates.
3.6 Gaskets
3.6.1 Compressed sheet asbestos gaskets and asbestos-filled, spiral-wound gaskets have been used successfully for decades. However, their use has been curtailed because of personnel exposure concerns. Suitable alternatives to asbestos are listed below and should be utilized when required:
• PTFE-, silica-, or aluminum silicate-filled PTFE
• Stainless-steel spiral-wound PTFE
Fluoroelastomers are also appropriate.
3.6.2 Envelope gaskets are satisfactory if the elastomeric or other compressible material within is effectively shielded by a fluorinated plastic envelope.
