Dealing with corrosive media: material selection for canned motor pumps
Jul 17, 2025
The chemical industry is full of corrosive and hazardous chemicals. Although these media play a key role in the relevant industries, they pose a serious challenge to pump equipment. The more corrosive the process fluid is, the greater the wear on mechanical parts, which in turn leads to more frequent maintenance, higher cost of ownership, and even potential safety hazards. Therefore, pump manufacturers must fully understand the specific characteristics of the fluids they handle to ensure that the right materials are selected for the pump.
First, it should be clear what kind of fluid is being handled
This question seems simple, but it is often overlooked in actual applications. Different fluids have very different corrosive properties (for example, the materials required to transport water are far less demanding than those required to transport hydrochloric acid).
Second, it is necessary to confirm whether the fluid contains solid particles
As these particles will increase the corrosion rate.
Third, consider the concentration of the fluid
This parameter has a significant impact on corrosiveness. Using hydrochloric acid as an example, 100% hydrochloric acid is less corrosive than 36% hydrochloric acid due to the higher reaction rate at the lower concentration.
The fourth and final critical factor is fluid temperature
Temperature changes can significantly alter the reaction rates in the fluid, accelerating the corrosion process. Knowing these characteristics and accurately communicating them to the manufacturer helps users obtain a canned motor pump that is suitable for their specific conditions while avoiding unnecessary material investments. Table 1 lists three examples that cover the potential range of corrosivity.
Minimally corrosive
Corrosive
Highly corrosive
Fluid
Water
Anhydrous hydrochloric acid
Hydrochloric acid
Temperature
Normal temperature (75°F)
Normal: -14°F, Operating: 100°F
200°F
Concentration
100%
100%
36%
Solid particles
Contains
Contains
Contains
Table 1: Examples of potential corrosive ranges
Once the above parameters are determined, the end user can provide the information to the pump manufacturer, who can then make key material selections. The selection of wet-end components is particularly critical. The so-called "wet-end" refers to those parts that are in direct contact with the process fluid. Some wet-end components corrode at a higher rate than others, which is related to the fluid flow rate they are subjected to (for example, the impeller, as the component that transmits rotational energy to the fluid, usually has a higher flow rate than parts such as bearings or rotors). Therefore, the selection of wet-end materials is the most complex and needs to be adjusted according to the actual corrosiveness of the process fluid.
Another important decision that the pump manufacturer needs to make is the selection of "tank" material. The tank is the main pressure boundary component that contains the process fluid and must be strong enough to withstand the operating pressure while allowing the electromagnetic field to be transmitted from the stator to the rotor. The electromagnetic field is generated by the stator and drives the rotor to rotate, which is the basis for the operation of all induction motors. Therefore, nickel-chromium-molybdenum alloy (also known as C-276 alloy) has become the first choice for tank material due to its excellent strength and corrosion resistance. Although this material is critical, since most canned motor pumps are made of this material, the material selection is relatively uniform and less restrictive.
Now that we have identified the fluid information that the end user needs to provide and why it is necessary, we can analyze specific real-life application cases with the help of the three fluid situations in Table 1.
The first example is water without solid particles at room temperature (75°F)
This fluid is extremely non-corrosive and has a wide range of wet-end materials to choose from. The most common material for canned motor pumps is 304 stainless steel, which is an economical and durable metal material. Some manufacturers even recommend the use of plastic materials such as nitrile rubber or polypropylene. As mentioned earlier, the tank body is generally made of C-276 alloy, which is also the standard configuration of most canned motor pumps.
The second example is 100% anhydrous hydrochloric acid, which has a wide operating temperature range (-18°F~68°F)
Although hydrochloric acid itself is highly corrosive, its overall corrosiveness is relatively low due to its extremely high concentration and low temperature. Therefore, the selection of 316 stainless steel can effectively deal with the corrosion risk under this condition.
The most corrosive liquid mentioned in Table 1 is hydrochloric acid at a concentration of 37% at 200°F. This condition combines the two factors of high temperature and low concentration that aggravate corrosion, posing a great challenge to the material. For most alloys, high-temperature hydrochloric acid will not only accelerate the corrosion of the metal, but also further induce secondary corrosion of the metal by water.
Under such extreme conditions, it is difficult to find a standard metal material that can meet the corrosion protection requirements. Therefore, manufacturers often choose special materials such as armor with excellent corrosion resistance. In addition, in order to protect the motor components, a clean water flushing circulation system is also used to prevent damage to the C-276 tank and bearing materials. Although such applications require higher material costs, they are necessary investments to ensure the long-term stable operation and safety of the pump.
Material selection may seem complicated, but it is actually a key step in maximizing pump performance. For the end user, although the task seems simple, it is crucial. A deep understanding of your application requirements and full communication with the pump manufacturer are the first steps to a successful selection. If this step is not performed properly, resulting in distorted information about fluid properties, the design basis of the entire pump will be biased. As a pump manufacturer, it is necessary not only to fully understand the user's actual application environment, but also to clearly understand the interaction between these conditions and the existing materials. The key is to ensure that the selected materials can handle the most severe operating conditions while taking into account the economical design.
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