Views: 0 Author: Kath Publish Time: 2025-02-12 Origin: Site
When stainless steel is welded or heated under high temperature conditions, intergranular corrosion will occur. This is because during the welding or heating process, the chromium in the stainless steel combines with carbon to form chromium carbides, which causes the chromium to be depleted near the grain boundaries, making the grain boundaries fragile and prone to corrosion.
Prevention methods:
(1) Select stainless steel materials with low carbon content: such as 304L and 316L, whose carbon content is below 0.03%, which can effectively reduce the precipitation of intergranular carbides.
(2) Add stabilizing elements such as titanium (Ti) or niobium (Nb): These elements have a stronger affinity with carbon than chromium, and can preferentially combine with carbon to form carbides, maintaining the stability of stainless steel.
(3) Optimize the hot working process: Reasonably control the heating temperature, time and cooling rate to avoid staying in the sensitization temperature range for a long time.
2. Pitting corrosion
Pitting corrosion is a localized corrosion that usually starts at small breaks in the stainless steel passivation film at temperatures above 100°C in the presence of chlorine. Once pitting corrosion is formed, oxygen is isolated from the metal, chromium is prevented from being repassivated, and corrosion quickly spreads to the interior of the stainless steel.
Prevention Methods:
(1) Select High-Chr, High-Mo Stainless Steel Materials: Opt for grades like 316 and 316L, which offer enhanced resistance to chloride ions.
(2)Regular Surface Cleaning: Maintain the cleanliness of the stainless steel elbow's surface to remove dirt and impurities, thereby preventing corrosion due to pollutant buildup.
(3)Avoid High-Chloride Media: Steer clear of using media with high concentrations of chloride ions, such as seawater and saltwater, in the operational environment.
3. Crevice corrosion
Crevice corrosion is localized corrosion that occurs in the crevices, contact surfaces, and other oxygen-rich areas of stainless steel. This type of corrosion is mainly caused by the depletion of oxygen in the crevices or the accumulation of corrosive media.
Prevention Methods:
(1) Avoid Creviced Connections: During design and installation, minimize the use of connections that can create crevices. For example, prefer welding over bolted connections to reduce the risk of crevice formation.
(2) Regular Inspection and Cleaning: Routinely inspect and clean crevices to prevent the accumulation of corrosive media. This includes removing debris, biofilms, and other contaminants that can initiate corrosion.
4. Stress corrosion cracking (SCC)
Stress corrosion cracking is a cracking phenomenon caused by stress on stainless steel in a specific medium. This type of corrosion usually occurs under high stress or high strain conditions, causing cracking or even fracture of the material.
Prevention methods:
(1) Select appropriate materials and designs to ensure that the stress level of the material in the operating environment is lower than its critical stress.
(2) Heat treatment to reduce residual stress.
(3) Regular inspection and maintenance to detect and deal with microcracks in a timely manner.
5. Electrochemical corrosion
When two different metals come into contact and penetrate into an electrolyte solution, the less inert metal becomes the anode and the more inert metal becomes the cathode. The anode metal will continuously produce ions that move toward the cathode, causing the anode metal itself to corrode.
Prevention Methods:
(1) Avoid Contact Between Different Metals: Especially in humid or corrosive environments, prevent different metals from touching.
(2) Use Insulating Materials or Coatings: Apply insulating materials or coatings to prevent contact between different metals.
II. Anti-corrosion measures
(1) Surface treatment: spay anti-corrosion coating, electroplating or hot-dip galvanizing on the surface of stainless steel pipe fittings to form a protective film to prevent corrosion from external media.
(2) Anodic protection: Apply an anodic protective layer on the surface of the stainless pipe fittings to extend the service life through cathodic protection technology.
(3) Alloy addition: Add alloy elments such as Mo, Ni, Chr to improve corrosion resistance and adapt to harsh environments.
(4) Select suitable sealing gasket: Such as rubber or PTFE gasket to prevent leakage.
(5) Regular cleaning: Clean industrial pipe fittings regularly to remove dirt and impurities and prevent corrosion.
(6) Regular inspection: replace damaged parts in time, repair surface coatings, and maintain good anti-corrosion performance.
(7) Control the use environment: control temperature, humidity and gas composition to reduce corrosion risks.
