Analysis of the causes of pipe elbow fracture or rupture

Analysis of the causes of pipe elbow fracture or rupture:

1. Excessive working pressure leads to elbow fracture
Elbow pipe fittings are subject to huge pressure in industrial pipeline systems, and pipe elbows of different specifications have their bearing capacity limitations when used. If the working pressure exceeds its bearing capacity, it will cause deformation, plastic deformation and fracture of the pipe elbow.

2. Poor material quality leads to elbow fracture

The quality of the material of elbow pipe fittings directly affects its compression, tension and bending resistance, and is also one of the key factors for whether the elbow can work stably for a long time. If the material quality does not meet the standard, or after poor processing or manufacturing, the elbow will have cracks, interlayers, pores, delamination and other defects, which will lead to its fracture.

3. Manufacturing process defects lead to elbow fracture
Improper manufacturing process of pipe elbows is also an important reason for elbow fracture. If the welding quality of the elbow is poor, the interface of the elbow is not fully strengthened, and the elbow has cracks or bulges during the manufacturing process, the strength, toughness and corrosion resistance of the elbow will be damaged, which will affect its service life and eventually lead to elbow fracture accidents.

4. Residual stress causes elbow fracture
The residual stress of the pipe elbow has not been eliminated. In addition to the working stress generated by the load, more stress comes from the residual stress generated during the manufacturing process. The elbow of the shell and tube heat exchanger will have a certain level of tensile stress conditions under the action of internal pressure, thermal stress, welding residual stress, etc.

Under the combined action of stress and corrosive media, stress corrosion cracking will occur in the elbow. For example, in a corrosive environment containing sulfur elements, factors such as poor welding quality of the weld and large residual stress will cause the elbow to crack.

5. Environmental problems cause elbow fracture
Steel elbow pipe fittings will be affected by environmental factors during use. For example, in harsh environments such as high temperature, high pressure, and corrosion, the corrosion and oxidation rate of the elbow will accelerate, making it easy to crack. In addition, under the influence of natural disasters such as earthquakes and sandstorms, the elbow may also crack or break.

For example:
‌Alkali corrosion‌: In some cases, such as the low-temperature superheater connection elbow of the waste heat power generation boiler, the alkali enters the elbow and gathers and concentrates at the weld, which will cause alkali embrittlement cracking under the action of multiple stresses.

‌Corrosive environment‌: In some corrosive environments, such as chloride ion environments, elbow materials are prone to stress corrosion, leading to cracking. For example, the pipe material of the shell and tube heat exchanger is prone to stress corrosion in a chloride ion environment, leading to transgranular fracture‌.

6. Pipeline maintenance and management
Pipelines are also prone to problems during daily maintenance and management. During the use of the pipeline system, maintenance personnel are required to perform regular maintenance, but some units do not perform maintenance on the pipeline according to regulations, resulting in aging and disrepair of the pipeline, and the elbow will leak.

Preventive measures‌:
‌1. Regular inspection and maintenance‌: During use, elbows should be inspected and maintained frequently to ensure that they are of good quality and can work safely and stably.
‌2. Select high-quality materials‌: Select materials that meet the standards to ensure that the materials' compression, tension, bending and other capabilities meet the requirements.
‌3. Optimize the manufacturing process‌: Ensure good welding quality and sufficient reinforcement of the interface to avoid problems such as cracks or bulges during the manufacturing process.
‌4. Avoid stress corrosion environment‌: During the design and use process, try to avoid the elbow in a stress corrosion environment, or take appropriate anti-corrosion measures.
Under the combined action of stress and corrosive media, stress corrosion cracking will occur in the elbow. For example, in a corrosive environment containing sulfur elements, factors such as poor welding quality of the weld and large residual stress will cause elbow cracking.

Conclusion: 

Excessive working pressure, poor material quality, residual stress, manufacturing process defects, use environment, and maintenance and management of the pipeline system are the main reasons for the fracture and rupture of elbow pipe fittings. In order to prevent the occurrence of fracture accidents, before using the pipe elbow, it is necessary to carefully check the important factors such as the material, pressure resistance, manufacturing process and appearance of the elbow to ensure its good quality and safe and stable operation. At the same time, it is also necessary to frequently check and maintain during use, and replace aging and degraded elbows in time to ensure the safe production of pipelines.

Read more: American standards for pipe elbows or Pipe elbow size selection