Radiography examination of Welds (RT)

All welded joints subjected to RT shall be examined in accordance with Article 2 of ASME Sec. V

RT examination personnel shall be qualified and certified in accordance with employer’s written practice, as per SNT-TC-1A

The requirements of ASME Sec. V Article 2 Clause T280 are used as a guide.

Final acceptance of radiographs shall be based on the ability to see the prescribed penetrameter (IQI) image and the prescribed hole, or the designated wire of wire type penetrameter.

Evaluation of Radiographs (RT)

All radiographs shall be free from mechanical, chemical or other blemishes to the extent that they do not mask and or confused with the image of discontinuity in the area of interest of the object being radiographed.

Such blemishes include, but are not limited to:

Fogging

Processing defects such as streaks, water marks or chemical stains.

Scratches, finger marks, crimps, dirtiness, static marks, smudges or tears.

False indications due to defective screens

Requirements of Radiography

Density limitations: The transmitted film density through the radiographic image of the body of the appropriate hole penetramenter or adjacent to the designated wire of a wire type penetrameter and the area of interest shall be 1.8 minimum for single film viewing for radiographs made with an X-ray source and 2.0 minimum for radiographs made with gamma ray source.

The maximum density shall be 4.0 for either source.

Density variations: If the density of radiograph anywhere through the area of interest varies more than minus 15% or plus 30% from the density through the body of hole type penetrameter or adjacent to the designated wire of wire type penetrameter, within the e maximum/minimum allowable density specified above. Density variations shall be calculated based on T282.1 of Article 2

IQI Sensitivity

RT Shall be performed with a technique of sufficient sensitivity to display the hole pernetrameter image and the specified hole, or the designated wire of a wire type penetrameter, which are essential indications of the image quality of the radiograph. (Refer ASME Sec. V Table T-233.1; T-233.2 and T276 for IQI Selection)

Excessive Backscatter: If a high image of the “B” Described in T-233 appears on a darker background of radiograph, protection from back scatter is insufficient and radiograph shall be considered unacceptable. A dark image of the “B” on lighter background in not a cause for rejection

Geometric unsharpness shall be calculated as Article 2 of ASME Sec.V

Evaluation: The manufacturer is responsible for the review, interpretation, evaluation and acceptance of the radiographs to assure compliance with the code requirements.

Acceptance Criteria (RT)

The following imperfections are unacceptable.

Any indication characterized as a crack or zone of incomplete fusion or penetration

Any other elongated indication on the radiograph which are greater than

 ¼” for t up to ¾”

1/3 t for t from ¾” to 2 ¼”

 ¾” for t over 2 ¼” Where, t is the thickness of the weld excluding allowable reinforcement

For a butt weld joining two members having different thickness at the weld, t is the thinner of those two thicknesses.

Any group of aligned indications that have an aggregate length greater than “t” in a length of 12t, except when the distance between the successive imperfections exceeds 6L, where, L is the length of the longest imperfection in the group.