Is HPMA a stable corrosion inhibitor?

Yes, HPMA (Hydrolyzed Polymaleic Anhydride) is considered a highly stable corrosion inhibitor, particularly in terms of its thermal and chemical stability. However, its performance can be influenced by specific environmental conditions.

Here is a breakdown of HPMA's stability and performance based on the search results:

✅ Stability Strengths

HPMA exhibits excellent inherent stability due to its polymeric structure:

High Thermal Stability: It has a very high decomposition temperature, above 330°C . It performs well even at temperatures up to 350°C in alkaline conditions .

Long-Term Effectiveness: It can maintain its scale inhibition effect for up to 100 hours at 300°C .

Chemical Robustness: It is stable across a wide pH range (typically effective between pH 6-9) and is suitable for use in alkaline water systems .

🛡️ Corrosion Inhibition Performance

Regarding its role as a corrosion inhibitor specifically:

Moderate Alone, Excellent in Combination: By itself, HPMA has a "good" or "certain" corrosion inhibition effect . However, its performance is significantly enhanced when used in a formulation. It is particularly effective when combined with zinc salts to protect carbon steel from corrosion .

Primary Role: While it provides corrosion inhibition, HPMA is primarily renowned as an excellent scale inhibitor (with up to 98% inhibition rate) . Its high stability allows it to function as a reliable multifunctional agent (scale inhibition and corrosion inhibition) in demanding environments like low-pressure boilers and industrial cooling systems .

⚠️ A Critical Caveat: Stability Under Corrosion Conditions

A recent academic study (2023) provides an important nuance regarding HPMA's performance stability:

Performance Degradation Mechanism: The study found that while HPMA is chemically stable, its anti-scale performance can degrade in the presence of active corrosion .

The Cause: This is because the Fe²⁺ ions released by the corrosion of carbon steel preferentially chelate with the carboxylic acid groups in HPMA . This disrupts the inhibitor's ability to bind with and control scale-forming ions like calcium, leading to reduced efficacy at the metal-water interface .

Conclusion: The research emphasizes that HPMA's full anti-scale (and by extension, its anti-corrosion) potential is best realized when the underlying corrosion process itself is inhibited .

Summary

HPMA is a thermally and chemically stable polymer that serves as an effective corrosion inhibitor, especially when combined with zinc salts. However, its performance can be compromised if the system already has significant active corrosion, as the resulting iron ions can interfere with its function.