Velocity for CS transporting 98%H2SO4 2

[kootheBUNNY]

Hello,

Can anybody tell me what's the max velocity or acceptable range for carbon steel, sched 80 transporting 98% sulfuric acid at 40C? some states that it should be around 0.9 m/s, while other sources states around 1.2-1.5 m/s Thank you!

 

[shvet]

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]); for some restrictions, see Paragraphs 2.1.4 and 3.3.6. The initially high corrosion rate is quickly reduced by the formation of an insoluble sulfate film that is highly protective unless physically disturbed. However, even at nominal flow velocities within the prescribed limits, rapid, localized attack may occur. For example, short-radius elbows or excessive internal protrusion of circumferential welds may cause downstream turbulence resulting in high corrosion rates.
2.1.2 An important form of accelerated localized attack is hydrogen grooving on vertical or inclined walls exposed to the liquid phase in piping or vessels. Hydrogen grooving is caused by evolution and movement of hydrogen bubbles, resulting in deterioration of the protective film.
2.1.3 Anodic protection is effective in minimizing corrosion and preventing hydrogen grooving.
2.1.4 In the 99.5 to 100% concentration range, increased corrosion rates may limit the fitness of carbon steel. The actual corrosion rate is strongly affected by temperature, acid concentration, ferrous and ferric ion concentration, flow conditions, and chloride contamination, because these parameters determine the dissolution rate and stability of the protective iron-sulfate film.
2.1.5 In all steel fabrication, weldments shall be thoroughly inspected to ensure that they do not contain slag, porosity, laps, or other welding defects that may initiate accelerated corrosion. Steel vessels and piping must also be free of mill scale, or serious local attack may occur (see also Paragraph 3.1.7).
2.1.6 Because of a lack of internal smoothness resulting in localized turbulence, threaded or socketwelded piping may cause accelerated corrosion. As an alternative, butt-welded and flanged carbon steel piping have been used successfully (see also Paragraph 3.1.6).
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3.1.6 Especially in cases of higher flow velocities, side-entering nozzles should be austenitic stainless steel with moderate or high nickel content, or nickelalloy solid, lined, clad, or weld-overlay construction to prevent corrosion problems encountered with carbon steel construction (see Paragraph 3.1.3). Alternatively, carbon steel nozzles with an additional corrosion allowance of 6.0 mm (0.25 in.), and designed to limit flow velocities at a maximum of 0.9 m/s (3 ft/s), may be used. By using internal nozzle extensions, turbulent conditions that would otherwise cause localized corrosion or hydrogen grooving problems on adjacent vertical tank walls are minimized.
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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. See Paragraph 2.1.6 for information on potential problems caused by lack of internal smoothness.
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.