1、 Corrosion related causes (one of the most common causes)

1. Internal corrosion:

   Fluid corrosiveness: The medium being transported (acid, alkali, salt water, sulfur-containing oil and gas, wet carbon dioxide, etc.) is inherently corrosive.

   Turbulence accelerates corrosion: The direction of the fluid changes at the elbow, generating strong turbulence and eddy currents, destroying the protective film and accelerating corrosion (especially pitting and groove corrosion). The higher the flow rate, the greater the impact.

   Phase change/cavitation corrosion: Fluid pressure changes at the elbow may cause cavitation or flashing, and the impact force generated by the collapse of bubbles may damage the metal surface.

   Electrochemical corrosion: A primary cell is formed between the pipeline material and the medium, or at the connection between different metals (such as different materials between the elbow and the straight pipe section).

   Microbial corrosion: Certain bacteria breed metabolic products (such as acid) in the pipeline, causing corrosion.

    

2. External corrosion:

   Environmental corrosion: Soil corrosion (electrochemical corrosion) of buried pipelines, atmospheric corrosion (rain, salt spray, industrial waste gas) of overhead pipelines.

   Corrosion under insulation: If the elbow has an insulation layer, moisture will not evaporate easily after entering the insulation layer, and will accumulate on the metal surface for a long time, causing severe corrosion (CUI). This is a common cause of external corrosion on overhead pipeline elbows.

   Stray current corrosion: Stray current from nearby electrical equipment (such as subways and electric welding) flows through the pipeline, causing electrolytic corrosion.

2、 Erosion/wear related causes (especially in systems with solid particles or high flow rates)

1. Solid particle erosion: When hard particles such as sand, catalyst powder, welding slag, and oxide scale carried in the fluid flow through the outside of the elbow at high speed, they repeatedly hit and cut the metal surface, causing the wall thickness to thin. The outside of the elbow is the area with the most serious erosion.

    

2. Droplet/bubble impact: In gas-liquid two-phase flow, droplets or bubbles hit the pipe wall at the elbow and cause damage.

    

3. High flow wear: Even if there are no solid particles, the extremely high flow rate itself will cause wear on the pipe wall, especially at the elbow.

3、 Causes of mechanical stress and fatigue

1. Stress concentration: The sudden change of the elbow geometry causes the internal pressure, thermal stress, and external load to be highly concentrated here, exceeding the yield strength or fatigue limit of the material.

    

2. Thermal stress fatigue: The pipeline system is frequently started and stopped or the temperature fluctuates violently, and the thermal expansion and contraction stress caused by the constraints at the elbow acts repeatedly, resulting in the initiation and expansion of fatigue cracks.

    

3. Vibration fatigue: Mechanical vibration (pumps, compressors, fluid pulsation, wind loads, etc.) is transmitted to the pipeline, inducing fatigue failure at the stress-concentrated elbow.

    

4. Installation stress: Forced assembly during pipeline installation, or unreasonable support/hanger setting (such as lack of necessary support or limit near the elbow), causes the elbow to bear excessive residual stress or improper load.

    

5. Water hammer/pressure shock: The pressure wave shock caused by the rapid opening and closing of the valve or the start and stop of the pump generates huge instantaneous stress at the elbow.

4、 Elbow pipe leak solution

According to the detailed leakage analysis of pipelines on site, different pipelines have different requirements for elbow pipe repair clamps due to their different connection methods, including but not limited to the following types, which can all be solved by Changzhou Baoshuo Pipe Fittings elbow pipe repair clamp.