Corrosion can drive expensive and dangerous equipment failures in chemical processing. A corroded reactor that fails mid-process or a heat exchanger that springs a leak can trigger unplanned downtime, emergency repairs and serious safety incidents.
Understanding corrosion helps you make smarter purchases, especially when evaluating used equipment. Assessing a machine’s previous application and calculating its remaining service life separates reliable investments from costly mistakes.
What Is Industrial Corrosion?
Corrosion is an electrochemical reaction where metal reacts with its environment and gradually breaks down. The metal oxidizes when exposed to moisture and oxygen. The same process happens in chemical processing equipment, except the reactions can be far more aggressive depending on what the equipment handles.
This degradation causes material loss and reduces wall thickness over time. Some corrosion is visible, such as rust or pitting on a surface. Other forms happen internally or at the microscopic level, making them harder to detect.
The 8 Common Types of Corrosion Affecting Your Equipment
Several forms of corrosion can attack the same piece of equipment simultaneously. Corrosion behaves differently depending on the material and environment. When you learn to recognize these patterns, you can better evaluate the threats to your equipment.
- General corrosion: Metal loss occurs evenly across the entire exposed surface, creating a predictable thinning pattern that you can measure and monitor.
- Pitting corrosion: Small, localized cavities form on the metal surface, often penetrating deep into the material while leaving the surrounding area intact.
- Crevice corrosion: Corrosion concentrates in tight spaces, such as under gaskets, bolts or deposits, where stagnant solution creates aggressive, localized conditions.
- Galvanic corrosion: When two different metals contact each other in the presence of an electrolyte, the more active metal corrodes faster while the other remains protected.
- Stress corrosion cracking: Tensile stress combined with a corrosive environment causes cracks to propagate through the material, often with little visible surface damage.
- Intergranular corrosion: Corrosion attacks along grain boundaries in the metal structure, weakening the material without obvious surface deterioration.
- Erosion corrosion: High-velocity fluids or suspended particles wear away protective surface films, accelerating metal loss in areas of turbulent flow.
- Sour gas cracking/sulfide stress cracking: Hydrogen sulfide exposure causes brittle cracking in susceptible metals, particularly in oil and gas processing applications.
How to Determine Corrosion Allowance
Corrosion allowance is the extra thickness added to equipment walls to compensate for metal loss over the expected service life. This value accounts for anticipated degradation so the equipment maintains structural integrity throughout its operational lifespan. Steel corrosion allowance, copper corrosion allowance and glass-lined corrosion allowance all vary based on the specific application and operating conditions.
Why Standard Calculations Don’t Always Apply
Codes such as ASME B31.3 establish a framework for process-piping design, but they don’t dictate specific corrosion allowances. The code outlines materials, components, design rules and fabrication requirements — yet actual corrosion rates depend on each system’s unique chemistry, temperature, flow conditions and operating history.
Because of this variability, engineers draw on experience, industry norms and data from similar operations to determine corrosion allowances. There’s no universal table that applies to every situation. The correct allowance for your equipment depends on what the system handles, how it operates and what historical degradation data you can reference.
Historical Data and Corrosion Rate
The most reliable way to predict corrosion is to look at how similar equipment has degraded over time. Engineers track wall-thickness measurements at regular intervals and use those data points to calculate an actual corrosion rate for the specific service environment. Once you know how quickly the material is thinning, you can estimate remaining service life by comparing the current thickness to the minimum allowable thickness and dividing the difference by the corrosion rate.
While corrosion allowance calculators exist, their accuracy depends entirely on historical data. If you don’t know the equipment’s operating conditions, load cycles or maintenance history, any estimate of its remaining life is essentially an educated guess.
Factors Influencing Corrosion Allowance
Three primary factors influence the final corrosion allowance an engineer selects.
- Chemical service: The specific chemicals and substances that contact the metal determine how aggressively corrosion attacks it.
- Operating temperature: Higher temperatures accelerate reaction rates, speeding corrosion and increasing metal loss. A reactor handling moderately corrosive chemicals at high temperature for 20 years needs more allowance than the same reactor running cooler for 10 years.
- Design life: The required lifespan dictates how many years the equipment must last, which directly affects the extra thickness you need to add.
How Equipment History Impacts Degradation Rate
Information about used equipment’s previous service is often patchy or unavailable. Understanding what the equipment handled before becomes critical to assessing its remaining life.
Cosmetic Plant Reactor vs. a Waste Water Tank
A used cosmetic plant reactor and a waste water tank might be similarly sized stainless steel vessels, but their degradation patterns can be completely different. Cosmetic reactors typically handle relatively pure chemicals such as acetone, focusing on preventing contamination and maintaining product quality. They tend to operate in controlled environments with consistent chemical compositions and cleaning protocols.
A waste water tank treats a mixture of pollutants, biological matter and treatment chemicals. It must contain hazardous substances while handling aggressive and variable chemical exposures, including chlorine and bleach. These harsher conditions accelerate degradation in ways that cosmetic processing doesn’t.
Even if the reactor and tank are nearly identical, the reactor from the cosmetic plant will have experienced far less aggressive corrosion. This difference in service history directly affects the equipment’s useful life.
Assessing Remaining Life in Used Process Equipment
Inspections and appraisals help you understand the condition of used equipment. Fitness-for-service methodologies, degradation modeling and data analysis provide a clearer picture than visual inspection alone. Qualified engineers and inspectors can measure current wall thickness, identify corrosion patterns and estimate remaining service life based on the equipment’s known history.
Choosing the Right Corrosion-Resistant Materials
Different materials respond differently to chemical exposure. Here are some commonly used materials in chemical processing.
Carbon Steel
Carbon steel is economical and widely used, but it can be problematic in aggressive chemical environments. Its corrosion rate increases significantly with salt concentration. Temperature and acid molarity are also influential. Corrosion accelerates rapidly in hydrochloric acid as temperature and concentration increase.
Stainless Steel
Stainless steel offers better corrosion resistance than carbon steel across many applications. However, corrosion rates in sodium hydroxide solutions are highly temperature-dependent. Some organic acids can cause measurable mass loss, while others have a mild inhibiting effect. The specific grade matters, as different alloy compositions perform differently in various chemical services.
Nickel Alloys
Nickel alloys such as Inconel 625 offer versatile resistance to localized corrosion and stress-corrosion cracking. Alloy 22 demonstrates extremely low corrosion rates, measured in nanometers per year in some conditions. These premium materials can significantly extend equipment life in highly corrosive environments.
Titanium
Titanium excels in oxidizing acids, seawater and wet chlorine environments. It resists many aggressive chemicals that rapidly attack other metals. However, titanium is not resistant to pure sulfuric acid and hydrochloric acid, which limits its use in certain applications. Matching titanium to the appropriate service is critical to realizing the value of this premium material.
Find Quality Used Process Equipment at Louisiana Chemical Equipment Company
Selecting used process equipment involves more than checking corrosion rates — you also need to match materials to your application and analyze service history. Louisiana Chemical Equipment Company specializes in chemical processing equipment of all scales, from individual heat exchangers to complete plant systems. With inspected inventory ready to ship, you can secure a single vessel or an entire setup without waiting months for your order to arrive.
Let us help you find equipment that fits your process and timeline. Submit a purchase request to get started or give us a call at +1-866-289-5232.
