What is the wear and tear of stainless steel seamless elbows?
The wear reasons of stainless steel seamless elbows can be divided into four categories: mechanical wear, corrosion wear, processing defects, and environmental factors.
1. Mechanical wear and tear
Material erosion and wear: When the medium (such as fluids containing coal ash and sediment) flows through the elbow, it is subjected to centrifugal force, and particles repeatedly collide with the outer inner wall of the elbow to form pits, manifested as both frictional wear and impact wear. When the flow rate is greater than 15m/s, wear significantly intensifies, and penetrating damage may occur in high particle concentration environments within months.
Typical wear area: The groove like wear is most likely to occur in the 1/3 area of the outer inlet of the 90 ° elbow.
Two phase flow erosion corrosion: The synergistic effect of mechanical erosion and electrochemical corrosion caused by solid-liquid mixed fluids (such as seawater containing sand) far exceeds the sum of simple wear or corrosion. For example, the erosion corrosion rate of 304 stainless steel in salt spray environment can reach three times that of dry environment.
2. Corrosion accelerates wear and tear
Chloride ion pitting corrosion: Cl ⁻ penetrates the passivation film to form corrosion pits, weakening the substrate’s resistance to erosion. Honeycomb shaped corrosion holes are present around the worn area.
Stress corrosion cracking: intergranular cracks are induced by tensile stress and corrosive media (such as acidic solutions). The crack area rapidly peels off under fluid impact.
Microbial corrosion: Bacterial metabolites (such as organic acids) promote localized electrochemical corrosion. Wear and tear surfaces adhere to mucous biofilms.
3. Processing and material defects
Surface treatment defects: deep scratches (>0.05mm) left by polishing or abrasive contamination (mixed with iron filings), which become the starting point of wear; During the cold bending process of elbows, uneven wall thickness (such as outer thinning rate>10%) can lead to a decrease in local resistance to erosion.
Insufficient material properties: Poor quality stainless steel (such as pseudo 304 with insufficient chromium content) has poor passivation film stability and accelerated wear rate in corrosive environments.
4. Environmental and operational factors
High temperature accelerated failure: An environment above 80 ℃ reduces the toughness of stainless steel, and particle impact is more likely to cause material peeling. At the same time, high-temperature oxidation leads to thinning of the wall thickness.
Vibration and stress concentration: Pipeline system vibration or installation stress causes continuous micro friction in the elbow weld area, inducing fatigue wear.
Chemical media erosion: Strong acid/alkali environments dissolve metal substrates, significantly reducing surface hardness (such as a 20% decrease in 316L hardness when pH<2).
What is the wear and tear of stainless steel seamless elbows?
The wear reasons of stainless steel seamless elbows can be divided into four categories: mechanical wear, corrosion wear, processing defects, and environmental factors.
1. Mechanical wear and tear
Material erosion and wear: When the medium (such as fluids containing coal ash and sediment) flows through the elbow, it is subjected to centrifugal force, and particles repeatedly collide with the outer inner wall of the elbow to form pits, manifested as both frictional wear and impact wear. When the flow rate is greater than 15m/s, wear significantly intensifies, and penetrating damage may occur in high particle concentration environments within months.
Typical wear area: The groove like wear is most likely to occur in the 1/3 area of the outer inlet of the 90 ° elbow.
Two phase flow erosion corrosion: The synergistic effect of mechanical erosion and electrochemical corrosion caused by solid-liquid mixed fluids (such as seawater containing sand) far exceeds the sum of simple wear or corrosion. For example, the erosion corrosion rate of 304 stainless steel in salt spray environment can reach three times that of dry environment.
2. Corrosion accelerates wear and tear
Chloride ion pitting corrosion: Cl ⁻ penetrates the passivation film to form corrosion pits, weakening the substrate’s resistance to erosion. Honeycomb shaped corrosion holes are present around the worn area.
Stress corrosion cracking: intergranular cracks are induced by tensile stress and corrosive media (such as acidic solutions). The crack area rapidly peels off under fluid impact.
Microbial corrosion: Bacterial metabolites (such as organic acids) promote localized electrochemical corrosion. Wear and tear surfaces adhere to mucous biofilms.
3. Processing and material defects
Surface treatment defects: deep scratches (>0.05mm) left by polishing or abrasive contamination (mixed with iron filings), which become the starting point of wear; During the cold bending process of elbows, uneven wall thickness (such as outer thinning rate>10%) can lead to a decrease in local resistance to erosion.
Insufficient material properties: Poor quality stainless steel (such as pseudo 304 with insufficient chromium content) has poor passivation film stability and accelerated wear rate in corrosive environments.
4. Environmental and operational factors
High temperature accelerated failure: An environment above 80 ℃ reduces the toughness of stainless steel, and particle impact is more likely to cause material peeling. At the same time, high-temperature oxidation leads to thinning of the wall thickness.
Vibration and stress concentration: Pipeline system vibration or installation stress causes continuous micro friction in the elbow weld area, inducing fatigue wear.
Chemical media erosion: Strong acid/alkali environments dissolve metal substrates, significantly reducing surface hardness (such as a 20% decrease in 316L hardness when pH<2).