Within the reforming stages of conventional ammonia production, critical metallic components are exposed to high temperatures and aggressive process environments for prolonged periods. Although these components are manufactured from carefully selected high-temperature alloys, environmental degradation can still become a limiting factor in their useful service life.

Metal dusting, carburisation and high-temperature oxidation can progressively attack susceptible surfaces, potentially increasing maintenance requirements and contributing to premature component replacement.

For operators, the challenge is therefore not simply preventing corrosion.

It is protecting high-value reformer components for as much of their intended operating life as possible.

Diffusion Alloys provides diffusion aluminising for components used in demanding reformer environments, creating an aluminium-rich, metallurgically bonded surface designed to increase resistance to high-temperature degradation.

The Challenge Inside an Ammonia Reformer

Ammonia production begins with the generation of hydrogen-rich synthesis gas.

In plants using natural gas or other hydrocarbon feedstocks, reforming plays a central role in this process.

Equipment within these systems must withstand combinations of:

• High temperature
• Carbon-containing process gases
• Reducing and oxidising environments
• Thermal gradients
• Long operating periods
• Start-up and shutdown cycles

These conditions place considerable demands on component materials.

High-temperature alloys are selected to provide the required mechanical performance, but the surface of the material remains the first point of interaction with the process environment.

Where that environment promotes aggressive degradation, surface condition can become critical to overall component longevity.

When Environmental Degradation Limits Component Life

Reformer equipment represents a significant investment.

Components may be manufactured from specialist heat-resistant alloys specifically selected for demanding long-term service.

If environmental attack causes those components to deteriorate prematurely, the impact can extend beyond the damaged surface.

Operators may face:

Shortened Component Service Life

Environmental degradation may contribute to components reaching replacement criteria sooner than anticipated.

Additional Inspection and Maintenance

Progressive degradation can require closer monitoring and intervention.

Replacement of High-Value Components

Specialist alloys and engineered components can be costly to manufacture and replace.

Associated Plant Intervention

Replacement may need to be incorporated into maintenance and shutdown planning.

The engineering objective should therefore be to identify what is limiting component life and whether that degradation route can be reduced.

Metal Dusting in Ammonia Reformer Applications

Metal dusting is one of the most aggressive high-temperature corrosion mechanisms encountered in carbon-rich process environments.

Under susceptible conditions, interaction between carbon-containing gases and the metallic surface can cause progressive breakdown of the alloy.

Rather than producing conventional uniform corrosion alone, the affected material can deteriorate into a mixture of carbon, carbides and fine metallic particles.

This can lead to significant localised material loss.

For ammonia reformer equipment operating within susceptible temperature and process conditions, metal dusting can therefore present a serious threat to long-term component integrity.

Protecting the Surface Against Metal Dusting

Diffusion aluminising creates an aluminium-rich surface capable, under appropriate conditions, of developing a protective alumina scale.

This barrier helps isolate the underlying alloy from the carbon-rich process environment and can significantly increase resistance to metal dusting.

Related: Metal Dusting in Reformer Systems: Causes, Consequences & Prevention

Protecting Against Carburisation

Carburisation presents a different but related challenge.

At elevated temperatures, carbon can diffuse into susceptible alloys and react with alloying elements to form carbides.

Over prolonged exposure, this can alter the microstructure of the material and affect its properties.

For components expected to operate over extended periods, limiting carbon ingress can therefore be an important part of protecting the underlying alloy.

An aluminium-rich diffusion layer can provide a barrier to carbon transfer, increasing resistance to carburising environments.

Related: Carburisation in Reformer Tubes: Protecting High-Value Alloys

High-Temperature Oxidation

Oxidation is another important consideration for equipment exposed to elevated temperatures.

When a metal reacts with an oxygen-containing environment, an oxide scale forms at its surface.

The effectiveness of this scale depends on its composition, growth rate, adherence and stability.

If the oxide provides insufficient protection — or repeatedly cracks or spalls — fresh metal can become exposed and further oxidation can occur.

Diffusion aluminising is designed to create an aluminium-rich surface capable of forming a stable, slow-growing alumina (Al₂O₃) scale under appropriate operating conditions.

This provides an additional protective barrier between the component and its environment.

Related: High-Temperature Oxidation in Reformer Systems

Why Surface Engineering?

High-temperature alloy selection requires engineers to balance numerous properties.

The material may need to provide:

• High-temperature strength
• Creep resistance
• Mechanical stability
• Fabricability
• Weldability
• Appropriate environmental resistance
• Long-term metallurgical stability

No single alloy property exists in isolation.

Surface engineering provides an opportunity to separate some of these requirements.

The base alloy can provide the required structural properties while the surface is engineered specifically for environmental resistance.

This means the complete component does not necessarily need to be replaced with a different material simply because the operating environment presents a surface-related degradation problem.

Instead, the existing high-value alloy can potentially be protected.

How Diffusion Aluminising Works

Diffusion aluminising is a thermochemical surface-engineering process.

During treatment, aluminium is introduced at elevated temperature and diffuses into the substrate.

Rather than simply depositing a separate coating onto the surface, aluminium reacts with elements within the base material to create a metallurgically bonded aluminide diffusion layer.

This aluminium-rich surface can subsequently develop a protective alumina scale during high-temperature exposure.

The combination of the diffusion layer and protective oxide can increase resistance to environmental degradation.

Depending on the application and operating conditions, this may include improved resistance to:

• Metal dusting
• Carburisation
• High-temperature oxidation
• Other relevant forms of high-temperature corrosion

The coating specification can be developed according to the component material, geometry and required service conditions.

Protecting More Than Reformer Tubes

Although reformer tubes are critical assets, degradation challenges are not necessarily limited to the tubes themselves.

Different components within reforming systems experience different combinations of temperature, atmosphere and mechanical loading.

Depending on the plant and identified degradation mechanism, diffusion aluminising may be considered for selected:

Reformer Tubes

Where environmental degradation contributes to loss of tube life, aluminising can provide additional surface protection while retaining the mechanical properties of the underlying high-temperature alloy.

Burner Components

Components operating within combustion environments can experience prolonged high-temperature exposure and oxidation.

Appropriate diffusion coatings can provide additional environmental resistance.

Headers and Collectors

Depending on their position and process conditions, headers and collector systems may encounter environments in which additional surface protection is beneficial.

Tube Supports and Associated Hardware

Supporting components may also experience high-temperature oxidation or other environmental attack during prolonged service.

Other Process Components

Diffusion Alloys can assess additional components individually according to material, geometry, operating environment and degradation mechanism.

From Component Protection to Lifecycle Value

The immediate technical purpose of aluminising is to increase resistance to environmental degradation.

For an ammonia producer, however, the potential value is broader.

Extending Useful Service Life

Where environmental degradation is one of the mechanisms limiting component performance, improved surface resistance can help support longer useful service.

The actual life of any reformer component will depend on the complete combination of thermal, mechanical, metallurgical and process conditions.

Surface engineering addresses one important part of that equation.

Maximising the Value of Specialist Alloys

High-temperature components contain significant value in their materials and manufacture.

Premature replacement due to surface degradation means some of that value may never be fully realised.

Protecting the surface can help operators obtain greater service from the material already installed.

Supporting Maintenance Planning

Identifying and mitigating known degradation mechanisms can help operators take a more informed approach to inspection, maintenance and component lifecycle planning.

Reducing Replacement Demand

Where component life can be extended, the frequency with which replacement equipment must be manufactured, procured and installed may also be reduced.

This has both economic and resource-efficiency implications.

Long-Term Operating Experience Matters

For critical reformer applications, theoretical corrosion resistance alone is not enough.

Operators need confidence that the protection technology has experience in relevant industrial environments.

Diffusion Alloys has extensive experience applying diffusion coatings to components used in demanding process industries, including long-term service experience within ammonia reformer applications.

This operating history provides valuable evidence when considering diffusion aluminising as part of a component-lifecycle strategy.

Rather than treating every component identically, the Diffusion Alloys technical team considers factors including:

• Substrate material
• Component geometry
• Surfaces requiring treatment
• Operating temperature
• Process chemistry
• Identified degradation mechanism
• Existing service history
• Required coating characteristics

This enables the proposed coating to be evaluated against the actual operating requirement.

Protecting Existing Assets in Ammonia Production

Improving plant economics does not always require replacing existing equipment with entirely new technology.

There can also be significant value in extending the useful life of the assets already installed.

Where environmental degradation is limiting the performance of high-value reformer components, surface engineering provides an opportunity to protect the underlying material rather than relying solely on increasingly expensive alloy solutions.

For ammonia producers, that creates a straightforward lifecycle objective:

Protect critical components. Extend useful service life. Maximise the value of the reformer.

Discuss Your Ammonia Reformer Application

If components within your ammonia reformer are experiencing metal dusting, carburisation, oxidation or another high-temperature degradation mechanism, Diffusion Alloys can review the component, substrate material and operating environment to determine whether diffusion aluminising may provide an appropriate protection solution.