Page 282 - Handbook of Structural Steel Connection Design and Details

Welded Joint Design and Production

Welded Joint Design and Production 267

side of the joint. X-rays are produced by high-voltage generators while
gamma rays are produced by atomic disintegration of radioisotopes.
Whenever radiographic inspection is employed, precautions must be
taken to protect workers from exposure to excessive radiation. RT
relies on the ability of the material to pass some of the radiation
through, while absorbing part of this energy within the material. The
absorption rate is a function of the material. As the different levels of
radiation are passed through the material, portions of the film are
exposed to a greater or lesser degree than the rest. When this film is
developed, the resulting radiograph will bear the image of the cross
section of the part. The radiograph is actually a negative. The darkest
regions are those that were most exposed when the material being
inspected absorbed the least amount of radiation. Porosity will be
revealed as small dark round circles. Slag is generally dark and will
look similar to porosity but will have irregular shapes. Cracks appear
as dark lines. Excessive reinforcement will result in a light region.
Radiographic inspection is most effective for detecting volumetric
discontinuities such as slag or porosity. When cracks are oriented per-
pendicular to the direction of a radiographic source, they may be
missed with the RT method. Radiographic testing has the advantage
of generating a permanent record for future reference. Effective inter-
pretation of a radiograph and its implications requires appropriate
training. Radiographic inspection is most appropriate for butt joints
and is generally not appropriate for inspection of corner or T joints.
Applications for NDT methods. Visual inspection should be appropri-
ately applied on every welding project. It is the most comprehensive
method available to verify conformance with the wide variety of issues
that can affect weld quality. In addition to visual inspection, nonde-
structive testing can be specified to verify the integrity of the deposited
weld metal. The selection of the inspection method should reflect the
probable discontinuities that would be encountered and the conse-
quences of undetected discontinuities. Consideration must be made to
the conditions under which the inspection would be performed such as
field versus shop conditions. The nature of the joint detail (butt, T, cor-
ner, etc.) and the weld type (CJP, PJP, fillet weld) will determine the
applicability of the inspection process in many situations. Magnetic
particle inspection is generally preferred over dye penetrant inspec-
tion because of its relative simplicity. Cleanup is easy, and the sensi-
tivity of the process is good. PT is normally reserved for applications
where the material is nonmagnetic and MT would not be applicable.
While MT is suitable for surface or slightly subsurface discontinuity
detection only, it is in these areas that many welding defects can be
located. It is very effective in crack detection and can be utilized to

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