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What is Corrosion? - A Definitive Guide 

What is Corrosion?

Corrosion is usually understood as the process of degradation of a metal or alloy that results in the loss of material. Corrosion processes are thermodynamically driven (i.e. the tendency for a material in nature to transform from a high energy state A to lower energy state B) but kinetically controlled (i.e. the rate of transformation depends of the reaction pathway taken). An obvious example is the observation of ‘rust’, formed through the reaction of exposed steel surfaces in ambient moist air and conversion to more stable corrosion products. 

Despite the apparently simple nature of ‘everyday’ corrosion, the process conceals a rich and complex range of phenomena whose causes are varied and whose consequences impact many industries across the globe. For example, corrosion of steel can occur in the presence of hot gases in the absence of water (e.g. high-temperature oxidation, sulfidation and carbonization), through processes that are very different to that for standard ‘wet’ (electrochemical) corrosion. Accordingly, there is no single universally accepted definition for corrosion, but rather different definitions have evolved that reflect the primary concerns of different technology areas and industries. TWI deals with corrosion within many of its industry sectors and, as a Member of The Welding Institute, you can access information and resources specifically related to those sectors. 

Industry sectors and corrosion at TWI:

Renewable Energy 

Corrosion of offshore wind turbines is a challenge that is continuously effected by the constant threat from seawater corrosion. This significantly increases inspection and maintenance costs, thereby affecting the affordability of this renewable energy source. TWI offers a range a range of inspection capabilities to detect corrosion related faults as well as expertise in corrosion protection coatings. Examples of TWI’s work includes the development of a phased array ultrasonic testing procedure to enable the volumetric inspection of welds.

Oil and Gas

There are numerous corrosion related challenges in the oil and gas sector, including corrosion of offshore platforms, pipelines and downhole tools as well as further challenges downstream. TWI looks closely at the mitigation of corrosion and offers a range of corrosion testing capabilities, including corrosion under insulation and sour and sweet service testing at ambient or at elevated temperatures and pressures. 


Corrosion is also an important consideration for medical implants. Corrosion resistance is an important factor in the ability of a product to continue to function throughout the design lifetime. Corrosion damage leads to reduction in mechanical performance and harmful leaching of chemical species into the patient. TWI offers a range of electrochemical testing expertise which can be applied to simulate in vivo environments. 


Power generation can result in highly corrosive conditions such as those produced in biomass power plants from the combustion of variable fuel sources. Typically, damage is experienced on heat transfer surfaces, such as boiler tubes and heat exchangers. TWI has extensive experience in performing tests in aggressive environments such as HCl gas and molten salt. TWI also offers expertise in coating solutions to mitigate the effect of corrosive environments.


Corrosion can present a challenge to the operation of existing bridges and in the design of future structures. Corrosion can result in increased maintenance and inspection costs as well as reduced asset lifetime. TWI offers experience in materials selection, joining and testing to support future construction projects. TWI’s experience with non-destructive testing (NDT) methods and corrosion mitigation technologies provides the opportunity to reduce operational costs and improve asset availability and lifetime.


Corrosion can present a challenge in the automotive industry, due to material performance and aesthetic requirements. TWI offers support to Members through reducing costs, developing innovative solutions and adding functionality to their products/services. More specifically, the improved wear or corrosion performance through coatings and surface modification. Surface engineering affects the chemistry and properties of the surface layer of the asset. Weld hardfacing and other cladding processes are used for wear or corrosion resistance and repairing damaged parts.


For safety critical industries such as aerospace, corrosion risks are particular important. Due to the range of different operational environments experienced by aircraft components, a wide variety of corrosion (and cracking) damage modes can occur. As for the automotive industry, TWI offers services in wear or corrosion performance through coatings and surface modification to help in the aerospace industry. 


TWI Software offers different software products suited to corrosion engineers to analyse the risk of corrosion and the integrity of components impacted by corrosion.

RiskWISE assesses the risk of corrosion occurring in pressurised equipment including pressure vessels, piping, pipelines, tanks, etc. The software calculates the probability of failure (PoF) as well as the consequences of the failure of components/structures. RiskWISE is a risk-based inspection and risk-based-management engineering software. It enables engineers to ensure the continued safe and economic operation of the equipment/plant in line with relevant industry standards. To find out more about TWI RiskWISE software, please click here

IntegriWISE is a plant life management software that assesses the fitness-for-service (FFS) of high pressure equipment, looking at the severity of different damage mechanisms, including pitting and general corrosion. It calculates and records the fitness-for-service of industrial equipment and plant, including ageing pipework, pipelines, storage tanks, and pressure vessels. The software assesses if the component/equipment is suitable for continued use at the specified operating conditions. To find out more about TWI IntegriWISE software, please click here

Membership of The Welding Institute

Membership of The Welding Institute holds many benefits for you as a corrosion engineer. Joining as a Member of The Welding Institute provides you with professional recognition separate to your employment.

As a corrosion specialist, the Institute will be able to support you through your registration process with our different industry sector specialists volunteering as mentors to help new Members.

As a Member of the Institute, you can attend Technical Group Meetings (TGM) where developments in the technology and the practice of specialist areas, such as corrosion, are discussed. Technical group meetings are held throughout the year and are an excellent opportunity to network and gain contacts that can aid your career development. Another benefit of TGMs is the continuous personal development points that you can gain from attending them, whilst gaining valuable industry knowledge.

The Welding Institute also offers other events related to corrosion, click here to find out about the events that The Welding Institute offers.

Other membership benefits that you as a corrosion engineer can benefit from include the ability to access other TWI resources including its Technical Library containing technical information, journals, research papers and more, relating to corrosion.


As a Member of The Welding Institute you can access corrosion related training courses with TWI Training and Examinations, at a 5% discount

Read The Welding Institute's 'Training and Examinations - Corrosion' Insight to find out more about the training courses provided by TWI Training and Examinations.

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