Tank corrosion and its prevention – why is acid-resistant steel not always sufficient?
When it comes to transporting demanding chemicals, the industry standard has long been "acid-resistant steel" (RST/HST). The name conjures up images of eternal durability. However, the truth is harsher: under the right conditions and with sufficiently aggressive substances, even the best steel grades will succumb to corrosion. The truth is harsher: under the right conditions and with sufficiently aggressive substances, even the best steel grades will succumb to corrosion.
Tank corrosion is not just a cosmetic problem. It is a safety risk, an environmental threat, and a significant cause of premature removal of equipment from service. In this article, we will explore why steel corrodes and how composite construction completely eliminates this problem.
The myth of stainlessness: pitting corrosion and weld seams
Even if steel is classified as acid-resistant (e.g., AISI 316L), it is not immune to everything. The weakest link in steel tanks is often their structure and manufacturing method.
The most common problems are:
- Pitting: Substances containing chloride (such as hydrochloric acid or iron chloride) in particular can "pierce" the protective oxide layer on steel. This leads to deep, needle-sharp pitting, which can cause leaks surprisingly quickly.
- Weld fatigue: Steel tanks are assembled by welding. The constant vibration of road transport and pressure fluctuations in the tank place stress on these welds. When combined with corrosion, this can lead to stress corrosion cracking in the weld.
The Myth of Stainless Steel: Pitting Corrosion and Weld Seams
Even if steel is classified as acid-resistant (e.g., AISI 316L), it is not immune to everything. The weakest link in steel tanks is often their structure and manufacturing method.
The most common problems are:
- Pitting: Substances containing chloride (such as hydrochloric acid or iron chloride) in particular can "pierce" the protective oxide layer on steel. This leads to deep, needle-sharp pitting, which can cause leaks surprisingly quickly.
- Weld fatigue: Steel tanks are assembled by welding. The constant vibration of road transport and pressure fluctuations in the tank place stress on these welds. When combined with corrosion, this can lead to stress corrosion cracking in the weld.
Composite: Chemistry that does not react
Why is a composite tank the superior solution for corrosion prevention? The answer lies in chemistry. Unlike metals, composite materials (plastic matrix reinforced with fibers) are electrically non-conductive and chemically inert.
In practice, this means two things:
- No electrochemical corrosion: Since the material does not conduct electricity, galvanic corrosion or pitting corrosion cannot occur, regardless of how acidic or alkaline the transported medium is.
- Seamless construction: Admor composite tanks are manufactured using a process that produces a uniform structure without welded seams. No seams means no weak points that would fatigue from vibration.
What materials does the composite withstand better?
Composite tanks are often the only sensible option when transporting substances that are toxic to metals. Examples of substances where composite offers superior durability:
- Ferric chloride and ferric chloride: Used in wastewater treatment, highly aggressive to steel.
- Hydrochloric acid (HCl): Rapidly corrodes most metals.
- Hypochlorites: Bleaching and disinfecting agents that cause pitting corrosion in steel.
Summary: safety without compromise
Tank corrosion is a problem that does not have to be accepted as part of everyday life. By selecting the material of the transport tank according to the chemical properties of the substance being transported, the service life of the tank can be extended by years or even decades.
A composite tank not only withstands chemicals – it ensures that hazardous substances remain where they belong: inside the tank, safely isolated from the environment.
Do you transport hazardous chemicals?