Steel and coated pumps: a guide to choosing them for processes with aggressive fluids

Steel and coated pumps: a guide to choosing them for processes with aggressive fluids

The safety of a plant is the first aspect to consider when installing a new component. Incorrect technical choices, due to approximation or inattention, expose workers, equipment, and the environment to concrete risks, especially when handling corrosive or chemically aggressive liquids that react with the materials they come into contact with. The selection between steel pumps lined pumps are among these decisions, The pump casing is one of the first elements exposed to the fluid, and any incompatibility can lead to corrosion, weakening of internal surfaces, and leaks that compromise the integrity of the system.

The use of steel pumps with substances like hydrochloric acid or sulfuric acid, for example, can lead to rapid deterioration of surfaces, with the formation of micro-lesions that favor leaks and dispersions, creating situations that put those working on the plant at risk and that can also have consequences on the surrounding environment. In the presence of aggressive fluids, inadequate material clearly becomes a critical point, because the pump cannot guarantee a safe barrier between the liquid and the outside, increasing the probability of failures and urgent interventions.

For this reason The choice between steel and lining must be guided by precise criteria that take into account the chemical nature of the fluid and the characteristics of the process. CDR Pompe It makes its technical expertise and dedicated services for the selection, management, and maintenance of centrifugal pumps available to all its customers, with constant attention to the protection of workers and the environment, especially in contexts where the presence of corrosive substances requires appropriate materials and configurations.

Pumps in AISI 304 steel: characteristics and areas of use

Steel pumps, especially those made of AISI 304, they offer a balanced combination of mechanical resistance, structural stability, and adaptability to different fluid types, characteristics that allow them to handle heterogeneous applications without requiring particularly complex configurations. AISI 304 stainless steel, mainly composed of iron, chromium, and nickel, offers good corrosion resistance in the presence of non-particularly aggressive substances., while maintaining high robustness that allows the pump to work continuously even under significant stress.

Within systems that handle water, industrial oils, or low-aggressiveness chemical solvents, the Steel pumps ensure reliability and stability over time., with surfaces that resist oxidation well and don't require frequent maintenance. This versatility, A common feature of centrifugal pumps, making them suitable for various sectors, including water treatment, some food industry processes, and numerous manufacturing sector processes, where the fluid does not have characteristics that would rapidly compromise the metallic material.

Limits of steel pumps in the presence of aggressive fluids

When the liquids to be moved have more complex chemical characteristics, such as in the case of strong acids or highly concentrated solutions, steel pumps can encounter limitations related to the material's nature itself., which, despite being resistant in many contexts, remains sensitive to specific substances capable of attacking its surface. Hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and concentrated saline solutions, such as those found in seawater or industrial brines, they can generate localized corrosion phenomena, with the formation of micro-cavities and progressive deterioration of the internal walls of the pump.

These phenomena do not necessarily manifest immediately but tend to develop over time, increasing the need for periodic and unscheduled maintenance interventions. It is important to emphasize that this behavior does not depend on the quality of the steel pumps, but on the Compatibility between the material and the treated fluid, an aspect that must be carefully evaluated already during the selection phase to avoid situations that could compromise the reliability of the entire system.

Performance of steel pumps: temperature, pressure, and stresses

One of the elements that makes steel pumps particularly appreciated is their ability to work in a wide temperature range, which can extend approximately from -40°C to about 300°C., allowing its use in systems that handle hot fluids or those subject to significant thermal variations. This feature is complemented by Good resistance to pressure and mechanical stress, which allows for applications where the fluid is moved with intensity or in the presence of significant structural loads.

In complex industrial contexts, where vibrations, flow variations, and harsh working conditions are constant, steel pumps offer a stability that is difficult to achieve with plastic materials.

Lined pumps: structure and materials used

Lined pumps are designed to meet specific needs related to the management of highly corrosive fluids. They feature an external metal structure, responsible for mechanical resistance, and an internal lining made of high-chemical-resistance plastic materials, which prevents the fluid from coming into contact with the metal parts.. This solution overcomes some limitations of steel pumps, especially in contexts where the fluid's composition can quickly attack surfaces.

Among the most commonly used materials for cladding are polypropylene (PP), PVDF (polyvinylidene fluoride), ETFE (ethylene tetrafluoroethylene), and PFA (perfluoroalkoxy), each with specific characteristics that make it more or less suitable for certain substances and temperatures. The lining creates a continuous barrier that protects the pump from the corrosive effects of the fluid, while maintaining a solid structure thanks to the external metal support—a combination that makes it capable of handling particularly demanding applications from a chemical perspective.

Advantages of coated pumps in highly corrosive processes

When handling chemically aggressive fluids, the choice of pumping technology requires particular attention because direct contact between the liquid and metallic materials can lead to very rapid degradation phenomena, with consequences that affect, as we have seen, the plant's sealing and safety. lined pumps,Featured in the CDR Pompe catalog, offering a targeted solution thanks to an internal barrier designed to withstand the action of highly reactive substances.

• High chemical resistance Coatings made of materials like PVDF, PTFE, ETFE, or PFA are designed to withstand a wide range of strong acids, concentrated bases, and aggressive solvents, allowing for the safe transfer of substances such as HCl, H₂SO₄, and NaOH without degradation of the internal surfaces.
• Fluid and metal structure separation The coating creates a continuous barrier that prevents liquid from coming into contact with the pump's metal parts, thus avoiding direct corrosion phenomena that, in steel pumps, occur when the material is not compatible with the fluid.
• Reduction of contamination phenomena: The absence of interaction between the fluid and the metal limits the release of particles or residues, a relevant characteristic in chemical processes and in the treatment of sensitive substances.
• Greater stability of internal surfaces: The coating maintains its characteristics even in the presence of particularly reactive substances, ensuring continuity of operation without significant surface alterations.
• Performance vs. Investment Balance: Compared to the use of special metal alloys, lined pumps represent a technically effective solution with a lower cost, especially in applications where chemical aggressiveness is the dominant factor.

When to choose steel pumps

The steel pumps They have robustness and the ability to work in the presence of significant mechanical and thermal stresses on their side. The selection of this solution must be based on a careful evaluation of the nature of the fluid and the characteristics of the system, favoring applications where the material can best express its properties without being exposed to substances that compromise its integrity.

• Low chemical aggressiveness fluids Steel pumps are suitable for transferring water, industrial oils, and non-reactive solvents, where the corrosion resistance of AISI 304 stainless steel is sufficient to ensure the stability of internal surfaces.
• High-temperature applications: thanks to the ability to work up to about 300°C, the steel pumps they are indicated for processes involving hot fluids or significant thermal variations.
• Presence of elevated pressures: The metal structure allows for handling conditions where fluid pressure requires materials with high mechanical strength.
• Structural Stresses and Vibrations In systems where the pump is subject to dynamic loads, steel provides a stability that plastic materials cannot offer with the same effectiveness.
• Systems with complex configurations: The versatility of steel pumps makes them suitable for complex systems, where it is necessary to maintain continuous operation even in the presence of flow rate variations or demanding operating conditions.

When to Choose Lined Pumps

The choice of lined pumps becomes a priority when the fluid being handled has chemical characteristics that rapidly attack metallic surfaces., making it necessary to use materials capable of creating a stable and continuous protective barrier. In these situations, chemical compatibility is the main criterion on which to base pump selection, with the goal of ensuring plant safety and reliability.

• Presence of strong acids and concentrated bases: Lined pumps are suitable for transferring substances like hydrochloric acid, sulfuric acid, and sodium hydroxide, which can quickly damage steel pumps.
• Management of aggressive industrial effluents: In chemical waste and wastewater treatment processes, the coating protects the pump from complex and highly reactive mixtures.
• Prioritize chemical compatibility: When the fluid represents the main risk factor, the coating completely isolates the liquid from the metal structure.
• Risk Reduction of Losses: The protection of internal surfaces limits the formation of corrosion and micro-lesions that could lead to leaks.
• Applications in critical chemical environments: Sectors such as the chemical industry, electroplating, and the production of reactive compounds require solutions capable of ensuring operational continuity even in the presence of particularly aggressive substances, where steel pumps are not adequate without the use of special materials.

Chemical compatibility and mechanical resistance: the driving factors in selection

The choice between steel pumps and lined pumps begins with the fluid's behavior in contact with the material, because the stability of surfaces, pump sealing, and the safety of the entire system depend on this interaction. Steel pumps guarantee robustness, resistance to high temperatures, and the ability to withstand significant mechanical stress, making them suitable for handling fluids with a low level of corrosiveness that is compatible with stainless steel.

When substances like hydrochloric acid, sulfuric acid, or concentrated bases come into play, chemical compatibility becomes the determining factor, because these substances can directly attack metal surfaces. In these cases,Lined pumps offer a solution based on an internal barrier that isolates the fluid, avoiding contact with metal and reducing the risk of deterioration and leaks.

The distinction between these two solutions therefore lies in mechanical resistance versus chemical protection, with a choice that requires attention to technical details and the nature of the substances being handled, avoiding inadequate configurations that could become critical issues for the plant.

For this reason, rely on CDR Pompe means having technical support that accompanies every phase, from the selection of the most suitable pump to its management and maintenance, with the goal of ensuring configurations consistent with the process characteristics and minimize risks associated with handling even highly corrosive fluids.

 

Frequently Asked Questions

What is the difference between a steel pump and a pump coated to resist aggressive fluids?

The difference lies in the contact between the fluid and the material. In the steel pump, like those in AISI 304, the liquid touches the metal directly. In the coated pump, an external metallic structure provides mechanical strength, while an internal plastic coating creates a continuous chemical barrier that isolates the fluid from the metal parts.

Which fluids cannot be pumped with AISI 304 steel pumps?

Steels AISI 304 should not be used with hydrochloric acid (HCl), sulphuric acid (H₂SO₄) or concentrated saline solutions such as sea water and industrial salt solutions. These substances cause localized corrosion with microcavities and progressive deterioration of the internal walls. The limit depends on the compatibility between the material and the fluid, not on the quality of the pump.

What coating materials are used in lined pumps strong acids and bases?

The most commonly used coatings are polypropylene (PP), PVDF, ETFE and PFA, each suitable for different substances and temperatures. They resist a wide range of strong acids, concentrated bases and aggressive solvents, allowing the transfer of HCl, H₂SO₄ and NaOH without degrading the internal surfaces. The material should be chosen based on the fluid.

What temperatures and pressures do steel pumps withstand compared to those coated?

The steel pumps operate at approximately -40°C to about 300°C and withstand high pressures and mechanical stresses well. They lined pumps handle high temperatures, but within lower limits, which depend on the coating polymer. Before selecting the material, it is necessary to check the specifications of the chosen material.

When is it advisable to choose a coated pump instead of an steel pump in a system chemical?

It is advisable to choose a coated pump when the fluid attacks the metal quickly: strong acids, concentrated bases such as sodium hydroxide, aggressive industrial effluents, and galvanic processes. The coating reduces corrosion, micro chemical -damage, and the risk of leakage. Compared to special metal alloys, it also offers a lower cost.

In which applications is an stainless steel pump preferable to a coated one?

The steel pump is preferable for low-aggressive fluids such as water, industrial oils, and non-reactive solvents. It also adapts to high temperatures up to approximately 300°C, high pressures, vibrations, dynamic loads, and complex systems with flow rate variable parameters, where plastic materials provide less stability. It finds use in water treatment and in some food processing applications.