Cause analysis of common quality problems in some pipeline connections

Leakage at the threaded connection of the pipe


After the pipeline is watered and ventilated, there is moisture and air leakage at the threaded connection for the following reasons.

  • (1) The processing of the pipe’s fillet does not meet the requirements, and the fillet is too deep and worn, causing leakage at the threaded connection.
  • (2) When the threaded joint is installed, the connection between the fillet and the fitting is too loose, and the filler of the fillet connection is not installed in place or the quality of the material does not meet the requirements, resulting in leakage at the connection.
  • (3) After the pipeline is installed in place, not all pressure and tightness tests are conducted, and cracks in the pipeline, sand holes in the fittings, and construction at the interface are not found and dealt with in a timely manner.
  • (4) Improper setting of bracket spacing and elevation deviation of pipelines, uneven overall force after installation of pipelines, resulting in the presence of pick and carry situation at joints; pipeline reducers using small and large heads and short wire lengths too long, leakage occurs due to uneven force.
  • (5) The underground pipeline involves improperly compacted foundation, the force at the pipeline joint is concentrated or large, and the joint is fractured.

Leakage at the flange connection of pipeline

After the pipeline is watered and ventilated, the flange connection piece has moisture return and air leakage for the following reasons.

  • (1) When welding the pipe and flange, the end face of the flange is not perpendicular to the center line of the pipe, resulting in two pieces of flange face has a slant, the piece between the warped edge, thus causing leakage at the connection.
  • (2) The quality of the gasket is not up to standard, resulting in leakage.
  • (3) The thickness of the gasket is not uniform, resulting in leakage.
  • (4) The bolts of the flange are installed in an unreasonable order or not tightly fastened, resulting in leakage.
  • (5) Poor quality of welding between flange and pipe, resulting in slagging and leakage at the weld opening.

Leakage at the socket of metal pipes

After the pipeline is watered and ventilated, there is moisture return and leakage at the interface of the pipeline for the following reasons.

  • (1) Cracks at the socket of the pipe, resulting in leakage.
  • (2) The interface is not cleaned during operation, and the connection between the filler and the pipe wall is not tight, resulting in leakage.
  • (3) The interface does not meet the requirements, resulting in a poor connection, resulting in leakage.
  • (4) The filler is not qualified or the ratio is not allowed, resulting in leakage at the interface.
  • (5) improper operation, resulting in the interface is not dense leakage.
  • (6) poor maintenance of the interface after connection, resulting in leakage.
  • (7) Inappropriate location of underground pipe pier or improper backfill tamping method, resulting in uneven stress on the pipe and damage to the pipe or parts, resulting in leakage.
  • (8) No serious water pressure test, parts or pipes with defects such as sand holes and cracks, and poor interfaces are not found, thus causing leakage.

 

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