High Temperature Corrosion on Knowledge Library

Carburization

Mon, 01 Jan 0001 00:00:00 +0000

General Information

Carburization is a form of metallurgical failure/degradation commonly observed in environments containing carbon at elevated temperatures. This type of degradation is frequently associated with metals and alloys exposed to carburizing conditions, where carbon diffuses into the material at high temperatures, leading to the formation of carbides.¹ This process can compromise the material’s mechanical properties and structural integrity. Furthermore, it may escalate to metal dusting, particularly when carbon activity exceeds unity, resulting in highly localized carburization and causing catastrophic damage.² ⁴ Carburized steel tends to become brittle and may exhibit spalling or cracking .² Notably, carburization is of significant concern in industries such as refining, petrochemicals, and power generation.

Creep and Stress Rupture

Mon, 01 Jan 0001 00:00:00 +0000

General Information

Under applied or internal stress and at elevated temperatures, the polycrystalline structure of metal tends to dislocate along the grain boundaries, resulting in the formation of grain boundary voids. These voids weaken the metal’s overall structure, leading to a reduction in its strain properties. This deterioration in mechanical properties can occur even when the stress levels are below the material’s elastic yield stress. The elastic yield stress is the point at which a material begins to deform plastically and will not return to its original shape when the applied stress is removed. When grain boundary voids form, the metal can no longer withstand the same level of stress without deforming, compromising its integrity and performance. Temperature plays a critical role in determining the creep rate, and below a specific level – which varies for different materials – it is generally assumed that creep will not progress, or its rate can be neglected. Table 1 shows some creep threshold temperatures for popular materials.¹

High Temperature H2-H2S Corrosion

Mon, 01 Jan 0001 00:00:00 +0000

General Information

High-temperature H₂-H₂S corrosion represents a more aggressive form of traditional sulfidation. In this process, various sulfur species directly interact with the metal surface, forming corresponding sulfide scales. While H₂-H₂S corrosion also results in the formation of metal sulfide scales, the presence of hydrogen distorts this process, ultimately leading to higher corrosion rates compared to sulfidation without H₂. For details on sulfidation, please refer to the Sulfidation Chapter.

It is worth noting that H₂-H₂S corrosion has not been the subject of as extensive research as sulfidation without H₂. The primary investigations into H₂-H₂S corrosion were conducted over 50 years ago, leading to the formulation of what is known as the Couper-Gorman curves.¹ ² ³ These curves, following subsequent adjustments, establish correlations among H₂S concentration, temperature, and the corrosion rate of diverse materials. While the Couper-Gorman curves reasonably predict corrosion rates in specific scenarios, in others, particularly at very low H₂ concentrations, the predicted rates are lower than those observed in practical settings.⁶ ⁷

High Temperature Hydrogen Attack

Mon, 01 Jan 0001 00:00:00 +0000

General Information

At high temperatures and elevated partial pressures, hydrogen can attack carbon and low-alloy steels by reacting with carbon and/or carbides to form methane. These reactions may occur either on the metal surface or within the metal lattice, leading to decarburization (surface reactions) and the formation of microcracks or blisters (internal reactions). Internal defects like cracks, blisters, or voids can significantly weaken the steel’s mechanical properties, potentially resulting in catastrophic failure. ¹ ^,²

Naphthenic Acid Corrosion

Mon, 01 Jan 0001 00:00:00 +0000

General Information

Historically, the term ’naphthenic acids’ referred to organic acids featuring saturated aliphatic rings with a carbon atom count ranging from 6 to 20, primarily found in crude oil and distillation side cuts. However, its definition has evolved to encompass all types of organic acids, including those with both saturated and unsaturated rings, some with structures containing up to 50 carbon atoms (see Figure 1). The molecular weight (MW) of these acids varies approximately from 100 to nearly 600-700 atomic units (au).

Sulfidation (w/o H2)

Mon, 01 Jan 0001 00:00:00 +0000

General Information

High temperature sulfidation, or simply sulfidation, results from reactions between various sulfur species and metallic materials, typically occurring at temperatures above 230°C (446°F). Sulfidation has been a presence in the refining industry since its inception; however, over the last 30 years, intensified processing of sour crudes has amplified the scale of the problem. Often exacerbated by naphthenic acid corrosion, sulfidation is considered a key and active damage mechanism that critically impacts refinery operations.