Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)
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Centrifugal Pumps Design and Application 2nd ed - Val S. Lobanoff, Robert R. Ross (Butterworth-Heinemann, 1992)

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Slurry Pumps 231 Table 13-2 Alloys for Abrasion Resistance (Properties Sensitive to Carbon Content Structure) Alloy Tungsten carbide composites High-chromium irons Martensitic iron Cobalt base alloys Nickel base alloys Martensitic steels Pearlistic steels Austenitic steels Stainless steels Manganese steel Properties Maximum abrasion resistance. Worn surfaces become rough. Excellent erosion resistance. Oxidation resistance. Excellent abrasion resistance. High compressive strength. Oxidation resistance. Corrosion resistance. Hot strength and creep resistance. Corrosion resistance. May have oxidation and creep resistance. Good combination of abrasion and impact resistance. Inexpensive. Fair abrasion and impact resistance. Work hardening. Corrosion resistance. Maximum toughness with fair abrasion resistance. Good metalto-metal wear resistance under impact. pumped and the particle size is limited to fines below 7 mesh in size. At velocities above 35 ft/sec the rubber may not have sufficient time to flex and absorbs all the impact, and as result, wear will increase. Natural rubber is limited in temperature to 150°F or less. Where oils are present, a synthetic rubber such as neoprene should be used; however the addition of fillers will have a detrimental effect on wear resistance. Elastomer materials generally have good corrosion resistance, but care must be exercised to prevent the slurries from penetrating behind the casing and causing corrosive damage. Natural rubber-lined pumps with a durometer hardness of 40 shore A are usually limited to about 120 feet total head. Higher heads can be generated if fillers are added to increase hardness.

232 Centrifugal Pumps: Design and Application Castable urethanes in the 90 shore A hardness range exhibit good tear strength and elongation properties and in certain applications have out performed both rubber and metal. Ceramic materials in castable form have excellent resistance to cutting erosion but because of their brittle nature are unsuitable for direct impact. Silicone carbide refrax liners and impellers in the 9,5 original Moris hardness range are commonly used for pumping fines where the impeller tip velocity is limited to less than 100 ft/sec. Slurry Pump Types There is no specific demarcation point where one pump design ceases to be effective and another takes over. Figure 13-3 shows a classification of pumps and materials according to particle size. It is important to note that the selection of the pump type and its materials of construction depend also on the abrasivity of the slurry and the total head to be generated. The abrasivity of slurries can be divided into five distinct classifications to which limits on pump selection can be applied, lable 13-3 shows a pump selection guide for wear resistance. Specific Speed and Wear The majority of centrifugal pumps are conventionally designed to achieve the desired hydraulic performance at the highest efficiency and lowest cost when handling clear fluids in reasonably clean environments. Manufacturing limitations are not imposed on the configuration of the pump, since conventional materials such as cast iron, bronze, and stainless steel are used. Since wear is not a major consideration, the highest possible specific speed is chosen. When a centrifugal pump is designed for a slurry service, the factors that predominantly influence the pump design are wear and materials of construction; efficiency is of lesser importance. To achieve these objectives the pump has to operate at a lower rotational speed and the impeller is typically a radial-flow type. This suggests that the pump must be of a low specific speed design in the range 600 to 1,800. Specific speed is defined in Chapter 2. Since wear is a function of velocity it can be shown that for a given head and capacity, wear will increase with increased N s .

Slurry <strong>Pumps</strong> 231<br />

Table 13-2<br />

Alloys for Abrasion Resistance<br />

(Properties Sensitive to Carbon Content Structure)<br />

Alloy<br />

Tungsten carbide<br />

composites<br />

High-chromium<br />

irons<br />

Martensitic iron<br />

Cobalt base alloys<br />

Nickel base alloys<br />

Martensitic steels<br />

Pearlistic steels<br />

Austenitic steels<br />

Stainless steels<br />

Manganese steel<br />

Properties<br />

Maximum abrasion resistance.<br />

Worn surfaces become rough.<br />

Excellent erosion resistance.<br />

Oxidation resistance.<br />

Excellent abrasion resistance.<br />

High compressive strength.<br />

Oxidation resistance.<br />

Corrosion resistance.<br />

Hot strength <strong>and</strong> creep resistance.<br />

Corrosion resistance. May have<br />

oxidation <strong>and</strong> creep resistance.<br />

Good combination of abrasion <strong>and</strong><br />

impact resistance.<br />

Inexpensive. Fair abrasion <strong>and</strong> impact<br />

resistance.<br />

Work hardening.<br />

Corrosion resistance.<br />

Maximum toughness with fair<br />

abrasion resistance. Good metalto-metal<br />

wear resistance under impact.<br />

pump<strong>ed</strong> <strong>and</strong> the particle size is limit<strong>ed</strong> to fines below 7 mesh in size. At<br />

velocities above 35 ft/sec the rubber may not have sufficient time to flex<br />

<strong>and</strong> absorbs all the impact, <strong>and</strong> as result, wear will increase. Natural rubber<br />

is limit<strong>ed</strong> in temperature to 150°F or less.<br />

Where oils are present, a synthetic rubber such as neoprene should be<br />

us<strong>ed</strong>; however the addition of fillers will have a detrimental effect on<br />

wear resistance.<br />

Elastomer materials generally have good corrosion resistance, but care<br />

must be exercis<strong>ed</strong> to prevent the slurries from penetrating behind the casing<br />

<strong>and</strong> causing corrosive damage.<br />

Natural rubber-lin<strong>ed</strong> pumps with a durometer hardness of 40 shore A<br />

are usually limit<strong>ed</strong> to about 120 feet total head. Higher heads can be generat<strong>ed</strong><br />

if fillers are add<strong>ed</strong> to increase hardness.

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