I need to procure a sulphuric acid( Strength 98%) centrifugal pump. But the problem is that as per API 610 8th edition Table - G.1 and Table H-1, for sulphuric acid strength > 85% , the pump material class is S-1,(i.e. CS pressuer casing, CI impeller, CI inner case parts etc) and for acid consentration 85%-<1% the pump material class is A-8( AUS 316 base parts).
 In short, I want to point out that for higher acid concentration pump materlals class suggested in API 610 is of lower metallurgy, while for lesser acid consentration pump material class is of higher metallurgy.

The size of the pump (flow required) will influence the type of pump selected, as well as the acid strength and temperature influencing the selection of material of construction. Chris0164 is correct in pointing out the need for alloy material for lower concentrations.  I would reserve the use of PTFE lined pumps for weak acid services.

The 98% sulphuric acid could be handled in carbon steel tanks and piping, if it is ambient temperature.  Once the acid temperature gets above 100 deg F the corrosion rate is increasing to a point where other materials are used.

The Charles Lewis Pump Co. (WEIR Group-ball valve) has a range of vertical pumps for large flows of sulphuric acid and molten sulphur.  Large flows would be in the acid plants of 3500 tons/day and more.  Their standard pump casing is a process iron.  Pump impellors are hardened alloy.

In Europe the vertical pumps from Friatec Rheinhutte and from Ensival are commonly used in those large acid plants.  

Small flow pumps for neutralization / pH control service could be mag-drive pumps of Alloy 20 casing and impellor.  The mag-drive pump and the vertical pump both avoid the leak problems of packing or mechanical seals.

The Lewis Pump casing material is a somewhat proprietary cast iron recipe.  The grain structure has a compacted graphite structure that is between that of grey iron's flake graphite, that of ductile iron's spheroidal graphite, and that of the pearlitic grains of tempered(?) steel.  Their line of Lewmet alloys are used for impellors, flow orifices, and valves where the higher velocities result in severe errosion even for Alloy 20.  The alloys range up in hardness to where the parts are not weldable, and shaping is done by grinding, not by conventional machine tools.  If you check the Friatec Rheinhutte pump materials, they seem to have a couple of dozen alloys of optional materials.
 The use of carbon steel for tanks and piping is possible where flow velocity does not remove the suphate film that provides protection to the metal. If the velocity goes higher than 2 ft/sec or 0.6 m/sec, then erosion does increase.  Stainless steel can tolerate some higher velocity, but temperature usually is limiting parameter and the problems of packing / mechanical seal temperatures with severe weak acid corrosion at the stuffing box / mechanical seal face will force the pump material selection to Alloy 20 or higher.

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