Low Temperature Corrosion on Knowledge Library

Amine Corrosion

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

General Information

Removal of acidic compounds (H₂S, CO₂, COS etc.) from hydrocarbon streams, both liquid and gaseous, is a critical aspect of refinery operations. The purification of hydrocarbon streams from acidic compounds is commonly achieved through the absorption-desorption process, employing various alkanolamine-based solvents.

Figure 1 illustrates a typical amine unit configuration with a simple absorber/contactor – regenerator setup. However, variations of this arrangement are also possible, depending on factors such as treatment type, the solvent used, or the type/concentration of acid compounds.

Ammonium Bisulfide Corrosion

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

General Information

Ammonium bisulfide corrosion, also known as alkaline sour water corrosion, is a prevalent issue in hydroprocessing units, which encompass hydrocracking (HC), hydrotreating (HT), and hydrodesulfurization (HDS). Catalytic hydroprocessing involves desulfurization and denitrification reactions (see Equations 1 and 2), resulting in the production of ammonia (NH ₃) and hydrogen sulfide (H₂S). These compounds readily react to form ammonium bisulfide, or formally, ammonium hydrosulfide (NH₄HS), through a simple, reversible reaction as shown in Equation 3.

Ammonium Chloride Corrosion

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

General Information

NH₄Cl corrosion is virtually present at any refinery process unit where gaseous HCl and NH₃ are stream components. Table 1 shows most common areas affected by NH₄Cl corrosion.

Table 1 Potential locations for NH₄Cl corrosion in process units.¹ ² ³ ⁴ ⁵

Process Unit	Affected Area
Crude Distillation Unit (CDU)	Atmospheric tower top Atmospheric tower overhead (OVHD pipelines and commonly 1st stage exchangers)
Catalytic Reforming Unit (CRU)	Product separator Debutanizer section (OVHD)
Fluid Catalytic Cracking (FCC)	Main fractionator top section and OVHD system Stripping columns
Hydroprocessing Hydrotreating/Hydrocracking	REAC and surrounding pipelines (inlet, REAC tubes, outlet manifold) HP/LP separators Recycle Hydrogen lines
Delayed Coking Unit (DCU)	Fractionator OVHD section Coke drums blowdown system

The primary effect of NH₄Cl is deposition, which leads to fouling or plugging. This issue significantly impacts process operations by increasing pressure drops across the exchangers and disrupting heat flux. The secondary problem arises as a consequence of the first; when the solid deposit (which is virtually noncorrosive - if dry) becomes wet. In this scenario, the area beneath the deposit becomes “enriched” with Cl^- and H⁺ from the dissociation of NH₄Cl and water. As a result, under-deposit HCl corrosion is initiated, leading to the rapid degradation not only of carbon steel but also a wide range of corrosion resistant alloys (CRAs).

Corrosion Under Insulation

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

General Information

Corrosion under insulation (CUI) stands out as a widely acknowledged issue across various industries; paradoxically, it remains one of the most inconspicuous challenges. This problem manifests beneath the layers of insulation, making it elusive and often undetected until substantial damage has occurred.

The primary driver of CUI is the presence of water – essentially, where there is no water, there is no CUI. Unfortunately, it is nearly impossible to prevent water ingress into the insulation. Even seemingly dry hot insulation systems may experience moisture ingress, for example, during equipment cooldown, physical damage to insulation jacketing, or joint caulk seal failures. The severity of Corrosion Under Insulation (CUI) is influenced by several factors, including the duration of moisture exposure, the insulation’s capacity to absorb and retain moisture, the cyclic nature of moisture, and the temperature of the substrate.¹ ² ³ ⁴ ⁵

Hydrochloric Acid Corrosion

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

General Information

Hydrochloric acid finds widespread use across various industries, serving as a crucial component in chemical manufacturing, food production, pharmaceuticals, rubber manufacturing, metal cleaning, and well activation (acidizing), among others. In the refining industry, HCl typically emerges as a by-product during the decomposition reactions of both inorganic and organic chlorides in the crude distillation process, impacting the integrity of the overhead (OVHD) section of the atmospheric distillation tower. Additionally, HCl is present in reforming and isomerization units where it either emanates from Cl-containing catalysts or forms during the regeneration of catalysts through the addition of chlorinated compounds. Moreover, HCl is also employed as a bulk chemical, serving as a neutralizing agent in tasks such as water treatment plants or within caustic treatment units.

Hydrofluoric Acid Corrosion

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

General Information

Hydrofluoric acid (HF) finds application in diverse industrial processes, serving as a crucial component in the production of fluorinated compounds. Moreover, it plays a key role in the electronics industry, where it is employed for the precision etching of glass and silicon. Additionally, HF is instrumental as a catalyst in specific chemical reactions, particularly in the alkylation process. The following chapter is mostly oriented to refining applications (alkylation), however some information is common for other process industries.

Sulfuric Acid Corrosion

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

General Information

Sulfuric acid has been well-known for centuries, with the earliest documented information dating back to the Sumerian period (2000-3000 years BC). Its significance in modern times, particularly during the 19th and 20th centuries, led to numerous extensive studies on its chemical properties, such as reactivity in processes like electrophilic aromatic substitution, as well as its corrosion reactions with common construction materials such as carbon steel, stainless steels, and high chromium and molybdenum alloys.