Destructive and No-destructive Testing of Butt Weld Pipe Fittings

Why and how often are butt weld pipe fittings tested ?

  • Butt weld pipe fittings are tested to assure conformity with standards and performance in their applications.
  • Standard, commodity butt weld pipe fittings are tested by sampling during manufacturing process, with both destructive and non-destructive approaches.
  • Custom-made butt weld pipe fittings are regularly tested during manufacturing process with non-destructive approaches, as required for the application or as specified by end-users.

What is the difference between a destructive and a non-destructive test ?

  • After a destructive test, fittings can no longer be used in the field, because they were bent, pulled or abused until breakage point. For this reason, destructive tests can only be performed on a small sample of fittings; otherwise, all fittings would be destroyed during tests.
  • non-destructive test measures performance for regular operating conditions, or by means that do not destroy the fitting.

What are most frequent destructive tests for butt weld pipe fittings?

  • Bending: butt weld pipe fittings are bent until deformation appears on their side, face or root.
  • Charpy impact: named after Georges Charpy who developed it, this test measures toughness of a fitting by determining the amount of energy absorbed during its fracture from impacts.
  • Corrosion: butt weld pipe fittings are exposed to corrosive fluids or materials until corrosion appears.
  • Metallographic: this test studies physical structure and components of metal samples, typically by microscopy. Samples are taken from actual fittings.
  • Tension: butt weld pipe fittings are stretched until deformation appears; measures are taken for strength, yield, elongation.

What are most frequent non-destructive tests for butt weld pipe fittings?

  • Dye or liquid penetrant: low-cost test to detect surface hairline cracks or porosity in fittings, by applying a special liquid to its surface.
  • Ferrite content: ferrite content in Duplex, Super Duplex and stainless steel has to be just right to achieve yield strength, fracture toughness and corrosion resistance. Ferrite content is measured in weld seams by magnetic induction.
  • Hydrostatic: a butt weld pipe fitting is filled with a liquid, often colored water, and pressure is applied; measurements are taken to see if there is pressure loss due to any defects.
  • Magnetic particles: uses a magnetic field to detect surface or slightly subsurface discontinuity or weakness in a fitting.
  • Macrography: makes photographs, sometimes in 3 dimensions, of items visible to naked eye.
  • Micrography: uses microscopes to make photographs of metal and obtain information about its properties.
  • Pneumatic pressure: a fitting is filled with pressurized air; measurements are taken to see if there is pressure loss due to any defects.
  • Positive material identification: analysis of a metal alloy by identifying percentage for each of its elements. Uses specialty equipment, including X-ray fluorescence or optical emission spectrometry.
  • Radiography: uses X-rays or gamma rays to detect any weakness in fittings.

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