The Cost of Corrosion in the Aviation Industry

Introduction

For most people, corrosion is nothing more than just rusty metal parts. But when you’re in the airline industry, corrosion could turn deadly real quick. Because lives are at stake, steps must be taken to eliminate the threat of corrosion and maintain the structural integrity of the aircraft and its parts. 

A single aircraft costs millions and if corrosion is left unchecked, it could make the aircraft un-air worthy in just a few years. In a 2000 NACE report, researchers concluded that the US is spending a staggering $276 billion in damages cost by corrosion. The report was the culmination of a 2-year study on the direct costs associated with metallic corrosion in nearly every industry sector in the nation.

The Cost of Corrosion in the Aviation Industry 

The transportation sector, which covers aircraft, ships, railroad, motor vehicles, and HAZMAT transport, are quite vulnerable to metallic corrosion because most of the vehicles and metal components are exposed to naturally corrosive environments. 

Commercial airplanes, jets, and private aircraft are often subjected to humidity, fluctuating temperatures, strong winds, and microbes that cause rust and corrosion. As such, the annual cost of corrosion in the transportation sector amounts to $29.7 billion with more than $2.2 billion spent on the aircraft industry. This amount covers:

· Design and Manufacturing ($0.2 billion)

· Corrosion maintenance ($1.7 billion)

· Downtime Due to Corrosion ($0.3 billion)

The US military spends $10.2 billion in corrosion costs accordingto a 2016 LMI report. 

· Army Corrosion Control ($1 billion)

· Navy/USMC Corrosion Control ($3.4 billion)

· USAF Corrosion Control ($5.7 billion)

There are about 220,000 civil aircraft registered in the United States and 5,000 - 7,000 are commercial airplanes. Generally, airplanes have a 20-year life and those nearing their 20-year design life cause much concern because older models are not as resistant to corrosion as newer designs, which come with better corrosion resistance during engineering and manufacturing. However, even modern designs are not impervious to corrosion.

Corrosion has a way of creeping into a system – even a brand new one. Even if the plane is made with more corrosion-resistant materials, the operators must have a good corrosion control program in place to reduce the threat of corrosion. The corrosion control measures must be observed throughout the life of the aircraft. 

By improving the corrosion inspection and monitoring techniques, operators could detect minor issues and prevent it from affecting the operability of the aircraft. Through continuous corrosion monitoring and mitigating, operators can avoid bigger, more expensive problems down the line. 

Common Types of Corrosion in the Aviation Industry

Because airplanes are subjected to extreme pressures, harsh weather conditions, and naturally corrosive environments, the metal and non-metal parts are vulnerable to different types of corrosion. These are: 

· Galvanic corrosion 

· Exfoliation corrosion

· Pitting corrosion

· Atmospheric corrosion 

· Surface corrosion

· Filiform corrosion

· crevice corrosion

· Inter-granular corrosion

· Stress corrosion

Just like ships and tankers, corrosion control is built into the aircraft. From the moment that the metal parts are manufactured, they are treated to withstand corrosion and harsh weather conditions. These treatments include certain elements that are added to the base metal to create corrosion-resistant alloys. A protective coating (chemical conversion coating, metal or paint) is also applied to protect the metal surface from rust and corrosion. 

Factors that Increase the Risk of Corrosion

Climate

The likelihood of corrosion and rust development often depends on the environmental conditions that the aircraft is subjected to. Airplanes that are stationed near marine environments, for example, tend to corrode much faster due to the extended exposure to sea air and saltwater. Moist air is incredibly damaging to metal surface, even a corrosion-treated one due to frequent electrochemical attacks.

Environment

Corrosive attacks that occur in low-temperature environments happen because of the presence of water. When a metal surface is exposed to water, it conducts electrons and positive ions that pave the way to corrosion. Moisture could also condense in areas of the plane that do not have ample air circulation. The ambient conditions + constant exposure to moisture is the perfect environment for corrosion. This is the reason why corrosion sets in places that are always hidden from view and in some cases, completely closed off. 

In fact, some of the most serious cases of corrosion were found in closed structures of airplanes. Tube assemblies could be corroded on the inside with no external sign of deterioration, which makes inspection even more challenging. 

Airplanes are designed to withstand frequent changes in atmospheric pressure and temperature but no system is 100% corrosion-proof. That’s why all parts of the aircraft, even assemblies that are molded, welded, sealed or closed, could corrode because of the moist air. In some cases, spillage + water/moisture creates a weak acidic solution that eats away at the metal surface with a compromised or inadequate protective treatment.

Foreign Material

Even if airplanes are made with some of the strongest alloys on the planet, the dynamics are different when a plane is up in the air, traveling at great speeds. Foreign materials could adhere to the metal surfaces and cause significant damage to the aircraft. These foreign materials include:

· Atmospheric dust

· Soil, grease, and engine exhaust residues

· Saltwater

· Moisture condensation

· Spilled solutions

· Spilled caustic cleaning solutions 

· Brazing flux residues

To minimize the chances of foreign materials inflicting damage to the aircraft’s body or components, always keep the airplane clean regularly. In the case of spilled solutions, the leaks have to be traced, sealed, and cleaned thoroughly so these do not happen again. 

System Leaks and Spillage

System leaks could seep into the small components of the engine, which could cause corrosion to set in without being detected. If there are leaks, these have to be traced to address the problem quickly. The area where the leaks occur has to be cleaned immediately, along with the surrounding parts. Any corrosion treatment that’s applied to these parts has to be restored because most engine solutions are corrosive. 

For example, hydraulic oils, ester-based oils, coolant fluid, and glycol defrosting fluids are damaging to engine parts. Battery compartments are often plagued by acid corrosion. Battery fluids are incredibly corrosive so an anti-sulphuric protective treatment is a must to maintain the affected areas. The affected area, along with the surrounding parts, has to be cleaned with a washing soda and water solution, rinsed thoroughly with freshwater and then dried completely before being re-assessed for corrosion. 

Mercury leaks are incredibly damaging to aluminum alloys because the chemical could dissolve the normal protective oxide layer of the aluminum material. This leads to rapid and widespread degradation. This is the reason why carrying any item that contains mercury is generally avoided in cargo and passenger planes to reduce the chances of spills.

Spillage usually occurs in the cabin, something that happens frequently in passenger planes. But spillage could happen on the exterior of the plane as well and affect the aircraft’s small parts. Refreshment spillages (coffee, mineral water, juice, wine, etc.) could cause corrosion on the floor structures. 

Exhaust Gasses

Yes, exhaust gasses and noxious fumes could also cause structural damage to an aircraft. Exhaust gasses have traces of sulfur, which could cause corrosion. The fumes produced by the Auxiliary Power Unit or APU are also damaging to the engine and the surrounding parts so the anti-corrosion treatment has to be restored regularly. 

Addressing Corrosion in the Aviation Industry

Routine maintenance checks are also critical in the fight against corrosion. This goes especially for older planes, aircraft operators are mandated to conduct frequent checks and maintenance on airplanes are that nearing the end of their 20 year life.

Once corrosion has been detected, treat the affected area immediately. Thankfully, the extent of the damage is superficial in most cases so the corroded areas are just repaired and then re-treated with anti-corrosion products. But in severe cases of corrosion, the parts have to be removed and replaced right away to contain the problem. There are cases when deeper inspections involving nose to tail assessments and dismantling parts of the aircraft are needed to check for corrosion. 

Applying protective waxes, oils, and paint on the affected areas is a common treatment for corrosion but there are newer anti-corrosion sprays, like Corrosion Zero, that effectively protect from rust and corrosion on airplanes.