Fracture tests for welder qualification

Fracture tests are conducted to qualify a welder by the examination of fracture surfaces of a weld metal rather than using expensive macroscopic examination. The procedure is applied in order to assess the quality of test weld made by a welder. Although standards elucidate the test procedure, test location, technique, dimensions and type of specimen. There are two types of fracture tests; Fillet weld fracture and Butt weld fracture in which a notch is machined on the weld metal that enables the specimen to fracture easily. Following are the critical points regarding these tests.
  • Nature and dimensions of Test specimens
  • Number of tests
  • Location of test
  • What is the method and technique for making fracture
  • Weld defects that ought to be detected
  • Job description of an inspector


Butt Weld Fracture
The procedure is applied to observe the fracture piece of groove weld in order to detect the weld imperfections. Common problems like solid inclusion (slag, flux, and oxide), porosity and lack of fusion which have severe effects on groove weld, can be detected by simply breaking the test weld. No other technique like radiography is used that may be expensive.  

Also See How to reduce concentration of weld porosity?

Test specimens taken from the groove weld are notched in order to take fracture path from the middle of the weld. That is why it is also known by a term ‘Nick Break Test’ in industries. The techniques that are used to cause fracture are; three point bending and hammering. You can split the weld parts by simply hammering or on the other, if the test piece is supported on two points and the load is applied from the above, required breakage is obtained.

Fillet Weld Fracture
With the same procedure and objective as in butt weld fracture, fillet weld fractures are used to qualify a welder for fillet test welds. Fracture is made to find out the weld imperfections that may harm fillet weld. Defects like porosity, lack of penetration, solid inclusion are observed on fracture surface of split parts.
Dimensions and nature of test piece are specified by the standards and codes and required specimen is obtained accordingly. A notch of specific profile is indented on the weld. Normally the shapes of notch are;
  • V-shaped
  • Square profile
  • U-shaped

Specimen are placed in specific direction or clamped is special tools to achieve the required fracture through throat. After placement, hammering or pressing is applied and the split parts are ready for examination.

What is the job of Inspector?
Inspector must have a close examination throughout the procedure. After observing the splitting/ breakage, he must identify the weld defects with great care. It is essential that he has work experience about determining the imperfections on the fracture surface and assisting others to conduct the procedure in right way. Moreover he should give a systematic report containing meaningful information about;
  • The shape of fracture
  • Imperfections and their types
  • Position of imperfections on Butt/Fillet weld surface
Also Learn Visual Welding Inspection

Last comments
Fracture tests are conducted as a second choice for welders’ qualification in place of other examination techniques as it serves for the same purpose of visualizing the weld defects deep inside or at the root of the weld. 

Comments

  1. Is charpy and izod test also used forbthe same?

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    Replies
    1. yes both are used for the same job but with different placement of sample and striking method. In case of izod, hammer strikes the notched side of vertically placed sample while in charpy test, hammer strikes opposite to notched side of horizontally supported sample.

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  2. In charpy impact test both U and V type notches are used. In izod the specimen has only V type notch.

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  3. This comment has been removed by a blog administrator.

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