The 8 most common types of corrosion
Corrosion weakens tanks, pipelines and steel structures and is a common cause of repairs and unplanned shutdowns. From pitting to crevice corrosion – the different types of corrosion call for different countermeasures. Here you will find the 8 most important types of corrosion and learn what drone inspections can reveal – and where other test methods are needed.
Detecting corrosion damage early: inspection by drone without scaffolding
Corrosion is particularly dangerous where access is difficult: on tank roofs, inside vessels or on elevated pipelines. Conventional inspections there require scaffolding, rope access technicians or man entry. With the ELIOS 3 drone for internal inspections and underwater drones for filled tanks, visible corrosion damage can be captured and located safely. What the drone does not show, such as loss of wall thickness, is measured by your inspector specifically at the points marked in our inspection report.
Christian Engelke
1. Uniform corrosion: the most common type of corrosion
Uniform corrosion attacks metal surfaces evenly over large areas. This widespread type of corrosion shows up as typical rust formation and dull discolouration. Exposed metal surfaces in industrial plants are particularly at risk:
Critical areas:
- External steel structures
- Unprotected metal cladding
- Exposed piping systems
Effective prevention:
- Industrial protective coatings
- Galvanising
- Use of corrosion-resistant materials
Drone inspection:
- Uniform corrosion is easy to see: rusty areas, discolouration and peeling coating show up clearly in photos and video. The ELIOS 3 captures it with its camera and its own lighting, even in dark vessels. Repeated flights show how the affected areas develop. The remaining material loss is measured by the inspector, for example by ultrasonic wall thickness measurement.
2. Pitting corrosion: localised attack with great depth
Pitting corrosion is one of the most dangerous forms of corrosion. It develops at individual points and eats deep into the material – often unnoticed from the outside. Stainless steel is particularly at risk if its protective layer is damaged.
Danger zones:
- Chemical plants with chloride exposure
- Marine industrial facilities
- Process vessels with aggressive media
Prevention strategies:
- Special anti-corrosion coatings
- Installation of sacrificial anodes
- Systematic monitoring of vulnerable areas
Drone-based detection:
The ELIOS 3 enables detailed inspections of tanks and vessels. Its high-resolution camera and lighting make pits on the surface visible – often recognisable by rust pustules or small craters. The images show where the pits are located; their depth cannot be measured in the image and is measured specifically by the inspector.
3. Crevice corrosion: hidden damage at joints
Crevice corrosion develops in narrow gaps, where a lack of oxygen creates aggressive corrosion conditions.
Joints and overlaps in industrial plants are particularly critical.
Risk areas:
- Bolted pipe connections
- Flange connections
- Overlapping metal structures
- Sealing areas
Targeted prevention:
- Design that avoids narrow gaps
- Use of special sealing materials
- Regular cleaning of crevices
Drone inspection:
The crevice itself cannot be seen from outside. The consequences, however, are visible: rust streaks on flanges, corrosion products at overlaps and sealing areas. The ELIOS 3 captures such joints at close range, and the 3D point cloud shows where they are located in the plant. Whether the crevice needs to be opened and examined more closely is decided by the inspector.
4. Intergranular corrosion: danger in the microstructure
Intergranular corrosion destroys metals along their grain boundaries and thus jeopardises the structural integrity of industrial plants. This form of corrosion takes place within the microstructure and is barely detectable from the outside.
Main risks:
- Welds on stainless steel structures
- Heat-treated metal components
- Highly stressed aluminium structures
Preventive measures:
- Optimised heat treatment processes
- Stabilised steel alloys
- Regular material testing
Drone-assisted detection:
Intergranular corrosion can only be detected by camera once it becomes visible on the surface – for example as fine cracks or grain disintegration along welds. The ELIOS 3 documents welds and heat-affected zones across the whole surface and shows the inspector where to apply penetrant or metallographic testing.
5. Stress corrosion cracking: when stress and corrosion combine
Stress corrosion cracking (SCC) results from the interaction of mechanical stress and corrosive attack. This combination can lead to sudden material failure – particularly critical in pressure vessels and pipelines.
Installations at risk:
- High-pressure vessels
- Chemical process plants
- Stressed piping systems
- Load-bearing structures
Preventive measures:
- Stress-optimised design
- Use of SCC-resistant materials
- Corrosion protection
- Coatings
- Regular stress measurements
Drone-based monitoring:
Stress cracks are often very fine and only become visible late. The ELIOS 3 captures surfaces and welds at close range, so that visible cracks are documented and located in the 3D point cloud. Reliable detection and assessment require test methods such as magnetic particle, penetrant or ultrasonic testing carried out by the inspector.
6. Galvanic corrosion: when dissimilar metals meet
In a damp environment, contact between different metals leads to galvanic corrosion. The less noble metal becomes the ‘sacrificial’ one – a process that can severely weaken components within a short time.
Critical combinations:
- Aluminium–steel connections
- Copper–zinc contacts
- Stainless steel–structural steel transitions
- Metallic flange connections
Protection strategies:
- Electrical insulation between metals
- Targeted installation of sacrificial anodes
- Coating of vulnerable contact points
Drone inspection:
Galvanic corrosion typically appears directly at the point of contact between two metals: the less noble component corrodes more heavily there. The ELIOS 3 camera records such transitions – for example bolts, brackets or flanges made of different materials – and the inspection report shows where they are.
7. Microbiologically influenced corrosion: biological attack on industrial plants
Microbiologically influenced corrosion (MIC) is caused by the metabolic products of microorganisms. It mainly affects installations with standing water or moist deposits.
Main risk areas:
- Oil and gas pipelines
- Industrial water systems
- Tank farms and vessels
- Marine installations
Targeted prevention:
- Systematic cleaning concepts
- Biocide treatment of vulnerable areas
- Antimicrobial coatings
- Regular biofilm monitoring
Drone-assisted early detection:
Visible signs of MIC are biofilms, slimy layers, deposits and tubercles with pits underneath – often on the tank bottom and in the splash zone where the water level changes. The ELIOS 3 captures them in emptied vessels, an underwater drone in filled tanks. Whether it really is MIC is clarified by laboratory sampling.
8. Erosion corrosion: wear and corrosion at the same time
Erosion corrosion combines mechanical wear with chemical attack. Especially in high-velocity flow systems, this combination leads to rapid material loss.
Areas at risk:
- Turbines and pump systems
- High-pressure pipelines
- Valves and control fittings
- Heat exchangers
Effective countermeasures:
- Flow-optimised design
- Wear-resistant coatings
- Reducing velocity at risk points
- Regular wall thickness measurement
Drone-based inspection:
Erosion corrosion leaves characteristic traces: bright, wavy or grooved surfaces in the direction of flow, often at bends, inlets and downstream of fittings. The ELIOS 3 captures such areas in large pipes, ducts and vessels. The inspector then measures the remaining wall thickness at the points shown using ultrasound.
Visible corrosion located – your expert assessor makes the assessment
Corrosion takes many forms – from clearly visible uniform corrosion to hidden stress corrosion cracking. Drones such as the ELIOS 3 systematically capture even hard-to-reach areas and show where visible damage is located. The assessment and any further testing are carried out by expert assessors on the basis of our inspection report. Learn more on our page on the inspection of tanks and silos.
If you would like to read further on the subject, the book “Principles of Corrosion Engineering and Corrosion Control” by Zaki Ahmad provides a detailed overview.