Interesting question.

In theory it depends on corrosion environment, material, stress etc.

In practice it depends on how much of the joint was consumed by corrosion. If cross-section of the bolt was oxidized by 10%, than nominal strength of this bolt is reduced by 10%, at least.

Corrosion can have a significant impact on the mechanical properties of both bolted and welded joints, as it weakens the materials involved, reduces the structural integrity, and may lead to catastrophic failure if not properly managed. Here's how corrosion affects these types of joints:

1. Bolted Joints:

a. Reduced Load-Bearing Capacity:Corrosion, especially in the threaded areas, can reduce the ability of bolts to maintain proper tension. This can result in reduced clamping force, which diminishes the joint's load-bearing capacity. The bolts may become more prone to slipping or loosening under stress, leading to failure.

b. Stress Concentration and Crack Propagation:Corrosion tends to concentrate stresses at the localized areas of the corroded surface. These weak spots can act as initiation sites for cracks. Over time, these cracks may propagate, eventually causing the bolt to fail even under lower stress levels than it would have otherwise with no corrosion.

c. Decreased Ductility and Toughness:Corrosion, particularly pitting corrosion or uniform corrosion, can cause localized thinning of the material, reducing the overall cross-sectional area. This leads to decreased ductility and toughness in the bolted joint, which makes it more prone to brittle failure.

d. Thread Damage:Corrosion can damage the threads on both the bolts and nuts. This can make it difficult to achieve proper torque, leading to improper tightening or loosening over time. The threaded interface is also more susceptible to wear, further compromising the joint’s effectiveness.

2. Welded Joints:

a. Decreased Weld Strength:Corrosion can significantly weaken welded joints by degrading the weld material or the heat-affected zone (HAZ) in the surrounding base metal. This can lead to a reduction in the overall strength of the joint, making it more susceptible to failure under tensile or shear loads.

b. Corrosion at the Weld Root or Toe:The areas where the weld meets the base metal, particularly the weld root (inside the joint) and the weld toe (outside the joint), are common sites for corrosion to initiate. These areas are often poorly protected from moisture or corrosive environments, especially if the weld bead is not sufficiently smooth or if there are voids or porosity in the weld.

c. Stress Corrosion Cracking (SCC):Welded joints, especially those made from certain materials (like stainless steel), can be susceptible to stress corrosion cracking. This occurs when a combination of tensile stress and a corrosive environment causes the material to crack. Welds are particularly vulnerable to SCC because the process introduces residual stresses, which can exacerbate the formation of cracks.

d. Loss of Fatigue Resistance:Corrosion can significantly reduce the fatigue resistance of welded joints. Even small pits or cracks that develop due to corrosion can act as initiation points for fatigue cracks under cyclic loading. The loss of material and changes in the surface texture caused by corrosion further degrade the joint’s fatigue life.

3. General Effects on Both Types of Joints:

• Localized Material Loss: Both bolted and welded joints can suffer from material loss due to corrosion, which can reduce the joint’s overall strength, stiffness, and fatigue resistance.
• Reduced Service Life: With continued exposure to corrosive environments, both bolted and welded joints will degrade over time. This means that regular inspections, maintenance, or material protection (e.g., coatings, corrosion inhibitors) are crucial for extending service life.
• Environmental Sensitivity: The extent to which corrosion impacts the joints depends on environmental factors like temperature, humidity, salinity (for marine environments), and the presence of corrosive agents like acids or industrial chemicals.

Mitigation:

To prevent or minimize corrosion-related issues in bolted and welded joints:

• Use corrosion-resistant materials (stainless steel, coatings, galvanized parts).
• Apply protective coatings such as paints, galvanization, or anodizing to prevent exposure to corrosive agents.
• Regular inspection and maintenance (e.g., cleaning, replacing corroded parts) to catch any damage early.
• In environments where corrosion is unavoidable, design the joint to accommodate the potential for material loss (e.g., over-engineering the joint strength).

сильно снижает, а дефекты можно выявить МНК : вибрационными и УЗК.

Corrosion will lower the stress at which fatigue cracking will initiate. Depending upon the environment, other forms of corrosion mechanisms may occur.

Dear Dr. Karimu Muniru

Following my colleagues' valuable answers, I would like to point out the very recent research paper that addresses the gap resulting from the lack of correlation between corrosion-induced joint damage and preload, nor an existing numerical model capable of capturing such effects. I hope the knowledge derived by the research team will be helpful in utilizing guided wave ultrasonic investigation to examine the deterioration of inter-facial contact caused by corrosion in bolted joints. Additionally, a contact modification-based numerical approach is presented to capture the effects of changing inter-facial stress during joint corrosion.

Best regards ....

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