which are being carried out around

which are being carried out around the area in which the radiographic
test is taking place must be halted so that the staff
members responsible for undertaking such tasks are not exposed
to radiation. Thus, given this fact, it is a common place for
radiographic tests to be carried out in the shift where there is
less industrial activity (usually the night shift), which, in its turn,
compromises the productivity of the inspection service. Besides, to
use the tangential radiographic technique, the distance between
the source and the detector must be around three times the
external diameter of the pipe, to minimize the diffusive effect
generated by the divergence of the radiation beam. In this way, for
large diameters, this distance can be quite big, which is a
complicating factor for sites with restrictions of access.
A good alternative to radiography is the gamma transmission
technique. This technique employs a low-activity monoenergetic
gamma ray source and a high-efficiency detector. Both devices are
placed on the same horizontal plane and positioned at 1801 from
each other. The transmitted intensities are logged by the electronic
components associated with the detector. The system consists of
simultaneously moving the source–detector apparatus perpendicularly
to the inspected pipe so as to obtain a density profile of the
inspected section.
Among the advantages of employing this kind of system are the
low dose of radiation issued, the precision of the identification and
quantification of deposit layers and the small space required for
performing the inspection.
The purpose of this study is to develop and apply a gamma
transmission system capable of detecting and quantifying the
thickness of the scale layer on the inside of in-service pipelines.