Centrifugal Pumps and Corrosive Acids: Material Compatibility According to CDR

Introduction

Handling corrosive acids in industrial processes requires reliable technical solutions and a deep understanding of the materials used in centrifugal pumps. Sulfuric acid and hydrofluoric acid, although widely used in sectors such as chemicals, energy, surface treatment and advanced materials manufacturing, exhibit very different levels of aggressiveness that strongly depend on operating conditions.

This article analyzes the central role of material compatibility in the selection of centrifugal pumps designed to handle these fluids, highlighting how concentration, temperature and contact time can significantly affect component durability and reliability. The chemical characteristics of sulfuric acid and hydrofluoric acid are examined in detail, emphasizing application challenges and the risks associated with improper material selection.

Special focus is placed on materials that are truly compatible, with particular attention to engineering polymers such as PP, PVDF, PTFE and PFA, as well as the limitations of traditional metallic solutions. The article concludes with an overview of CDR Pompe’s approach, based on technical consultancy, application experience and engineered solutions designed to ensure safety, operational continuity and long-term reliability in the most demanding applications.

Material Compatibility in Centrifugal Pumps: Understanding the Fluid Before the Pump

When discussing material compatibility, it is essential to evaluate how a specific fluid interacts with all wetted surfaces within a centrifugal pump. In the case of corrosive acids such as sulfuric and hydrofluoric acid, this interaction may lead to chemical attack, oxidation, embrittlement or structural degradation.

Material compatibility is not an absolute parameter. A material that performs adequately at a certain concentration may become unsuitable as temperature increases or operating time is extended. For this reason, selecting materials for centrifugal pumps handling aggressive acids requires careful analysis of actual operating conditions and possible process fluctuations over time.

CDR addresses this aspect through a method based on real application experience and validated technical data, prioritizing plastic and fluoropolymer materials capable of guaranteeing chemical stability and reliability even in harsh environments or prolonged continuous operation.

Sulfuric Acid (H₂SO₄): A Common Yet Unpredictable Fluid

Sulfuric acid is one of the most widely used industrial reagents and is applied in sectors such as basic chemicals, fertilizer production, metal surface treatment, refining, energy and numerous synthesis processes. Its widespread use often leads to an underestimation of its complexity from a process engineering perspective.

Its aggressiveness varies significantly depending on concentration and temperature. At lower concentrations it may appear relatively manageable, while at higher concentrations and temperatures it becomes strongly oxidizing, capable of rapidly attacking many metals and alloys. In continuous processes, dosing lines or recirculation systems, these characteristics can result in progressive corrosion that is difficult to detect and control.

For centrifugal pumps used to transfer sulfuric acid, such as CDR’s DTN-L series, this means materials must be selected not only based on nominal conditions, but also considering potential operating variations. Material compatibility thus becomes a dynamic parameter tied to the entire lifecycle of the system, not to a single operating point.

Sulfuric Acid and Material Compatibility: CDR Selection Criteria

Selecting materials for sulfuric acid handling requires a technical approach based on chemical data, application experience and in-depth knowledge of operational limits. CDR adopts differentiated solutions tailored to real operating conditions, avoiding generalizations that may lead to medium- or long-term issues.

• PP (Polypropylene)
  Polypropylene offers good chemical resistance to sulfuric acid up to high concentrations, generally between 80% and 90%, provided temperatures remain moderate. It is suitable for systems with well-controlled parameters and limited process variability. However, resistance decreases significantly as temperature increases.
• PVDF
  PVDF provides superior chemical resistance compared to PP and maintains good performance even with concentrated sulfuric acid. Its stability makes it suitable for more demanding applications involving higher temperatures or where increased long-term reliability is required.
• PFA / PTFE
  These materials represent the most comprehensive technical solution for sulfuric acid. Their excellent chemical stability allows them to handle high concentrations and severe operating conditions without significant degradation. For this reason, PFA is the material most strongly recommended by CDR for critical applications where material compatibility must remain stable over time.
• AISI 316 Stainless Steel
  AISI 316 stainless steel can only be used at low concentrations, typically below 40%. Beyond this threshold, corrosion becomes rapid and difficult to control, making it unsuitable for continuous sulfuric acid service.

Hydrofluoric Acid (HF): When Material Choice Is Critical

Hydrofluoric acid is used in highly specialized industrial applications, such as chemical and petrochemical processing, fluorinated compound production, metal treatment and etching, glass processing, microelectronics and certain energy-sector processes. In all these fields, HF is considered one of the most critical fluids to handle.

Its danger lies not only in its toxicity, but above all in its ability to attack a wide range of materials. Unlike other strong acids, hydrofluoric acid also reacts with silicates, making glass, ceramics and many commonly used industrial materials highly vulnerable. It also rapidly attacks many metals, leading to fast degradation with effects that may occur in a very short time.

For centrifugal pumps designed for HF transfer, such as the XTN-BL series, material selection becomes a non-negotiable step. In these applications, material compatibility directly determines whether safe and continuous operation is even possible, strongly affecting plant reliability and operator safety.

Hydrofluoric Acid and Material Compatibility: Mandatory Choices

For hydrofluoric acid, the number of truly compatible options is very limited and must be applied within clearly defined concentration and operating limits.

• PTFE / PFA
  These materials provide reliable compatibility with hydrofluoric acid up to concentrations of approximately 50%. Their chemical inertness makes them the reference choice for HF applications, especially where long-term safety and operational continuity are required. PFA is widely used by CDR in centrifugal pumps designed for HF service.
• PVDF
  PVDF can only be used at low HF concentrations, generally below 30–40%. Beyond these levels, material resistance is no longer adequate and the risk of degradation increases significantly.
• AISI 316 Stainless Steel
  Not compatible with hydrofluoric acid. Chemical attack is rapid, making it unsuitable for any continuous HF application.
• PP (Polypropylene)
  Not compatible with hydrofluoric acid and therefore not usable. HF rapidly compromises the integrity of the material.

For these reasons, CDR solutions for hydrofluoric acid applications are primarily oriented toward PFA-based configurations, ensuring safe fluid handling and accurate evaluation of material compatibility under real operating conditions.

CDR Centrifugal Pumps and Corrosive Acids: Applying Theory to Practice

From an application standpoint, a clear guideline emerges:
for sulfuric acid, CDR centrifugal pumps are made of PP, PVDF and, above all, PFA; for hydrofluoric acid, PFA becomes the reference solution.

These choices result from detailed process analysis and extensive experience on real industrial systems. Material compatibility is treated as an integral part of pump design, helping to reduce risk and increase overall system reliability.

Technical Expertise as an Operational Guarantee

Handling corrosive acids requires solutions engineered around the fluid and operating conditions. In this context, the compatibility between materials and the pumped liquid is the foundation on which the safety and lifespan of centrifugal pumps are built.

CDR supports its customers through analysis, informed material selection and long-term technical assistance, including post-sales support, pump alignment and maintenance. This provides tangible value for companies operating with aggressive fluids and seeking solutions designed to perform reliably without interruptions.

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Frequently Asked Questions

Why do sulfuric acid and hydrofluoric acid require different design approaches?

Sulfuric and hydrofluoric acids exhibit fundamentally different chemical behaviors, which directly influence material selection in centrifugal pumps. Sulfuric acid varies in aggressiveness based on concentration and temperature, while hydrofluoric acid can attack materials generally considered resistant, such as silicates. This requires distinct design strategies and fluid-specific compatibility assessments.

What are the main risks of incorrect material selection?

Improper material selection can lead to accelerated corrosion, leaks, component failure and unplanned downtime. With corrosive acids, degradation may occur rapidly and go unnoticed in early stages. Proper compatibility analysis prevents these scenarios, ensuring production continuity and reducing extraordinary maintenance costs.

How does CDR support the selection of the most suitable centrifugal pump?

CDR supports customers by analyzing real process conditions, including fluid properties, operating parameters and system constraints. The service goes beyond product supply and includes technical evaluation to identify the most suitable materials based on chemical compatibility and required performance.

Why is PFA often the preferred solution for highly corrosive acids?

PFA (perfluoroalkoxy) is one of the most chemically stable fluoropolymers. Its molecular structure provides high inertness against aggressive agents, including concentrated sulfuric acid and hydrofluoric acid within defined limits. This stability translates into higher operational reliability and reduced maintenance needs, making PFA a reference material in critical applications.