Apparatus for carrying mobile means of inspection in the interior of a tubular body

An apparatus is provided for carrying a mobile inspection assembly in the interior of a tubular body, the assembly of inspection being adapted to emit and receive at least one sweeping radiation beam for inspection purposes. The apparatus includes a pair of carrier assemblies, coupled together by a bridge which has at least two linking pieces and a coupling piece therebetween. The apparatus also has a reflector with at least as many reflection planes as the bridge has linking pieces, each of which reflection planes defines a transmission path. The reflector is rotatable about a longitudinal axis through the carrier assemblies, the reflection planes being so arranged that at least one transmission path extends to the interior of the tubular body at any one time. Part of each transmission path is longitudinal and part is perpendicular to the longitudinal axis. The reflection planes are arranged so as to partially overlap.

BACKGROUND 
The invention relates to an apparatus for carrying mobile means of 
inspection in the interior of a tubular body comprising: a first mobile 
carrier assembly; a second mobile carrier assembly and a bridge for 
coupling together the two carrier assemblies, which means of inspection 
are adapted to emit and receive at least one sweeping radiation beam for 
inspection purposes, and forming part of which means of inspection are a 
transducer which is arranged to adopt a stationary position in relation to 
the said carrier assemblies and is adapted to emit and receive the said 
radiation beam along a longitudinal imaginary axis through the carrier 
assemblies, and a reflector which is fitted at a predetermined distance 
from the said transducer and is rotatable in relation to the said 
longitudinal axis. 
Such an apparatus is known from Dutch patent 181302. With such an apparatus 
ultrasonic sound is sent by the transducer in the direction of the 
reflector which comprises an inclined reflecting plane with which the 
radiation beam is sent in the direction of the interior of the tubular 
body to be inspected. The radiation beam reflected through the tubular 
body follows the same path but in the opposite direction and is detected 
by the transducer. 
A problem of the known apparatus is that a circular and full detection on 
the interior of the tubular body is only possible in one recording pass by 
using at least two apparatuses in accordance with the known state of the 
art series-linked at a certain distance. Apart from the circumstances that 
this is a costly solution, it also gives rise to interference and a 
relative comparison of the measurement results of the series-linked 
apparatus in accordance with the known state of the art is not simple. 
SUMMARY OF THE INVENTION 
The object of the invention is to make possible an all-round recording on 
the interior of the tubular body using a single apparatus according to 
claim 1, whereby a reliable measurement is made available which has low 
susceptibility to interference. 
To this end the apparatus in accordance with the invention is characterised 
in that the bridge for coupling together the carrier assemblies has at 
least two linking pieces adjacent to the longitudinal axis and extending 
longitudinally, as well as a coupling piece extending perpendicularly to 
the longitudinal axis for linking the said linking pieces, and in that the 
reflector has at least as many reflection planes as the bridge has linking 
pieces, each of which reflection planes defines a transmission path of 
which a part extends perpendicularly to the said longitudinal axis. 
In a preferred embodiment of the invention the reflector is arranged in 
such a way that each of the reflecting planes is positioned at the level 
of a linking piece, so that as the reflector is rotated through 
360.degree. during operation, at least one transmission path extends up to 
the interior of the tubular body at any one time. 
In a first embodiment of the reflector, two reflecting planes are used, 
each forming an angle of 45.degree. relative to the longitudinal axis, 
whereby the said reflecting planes form an angle of 90.degree. to each 
other. A preferred embodiment for this is one in which the reflecting 
surface located closest to the transducer partially overlaps the 
reflecting plane that is located behind it viewed in the longitudinal 
direction from the transducer. This prevents undesired reflections at the 
location of the reflecting plane lying behind. 
Each carrier assembly is preferably centred in the tubular body to be 
inspected by a plurality of carrier arms. The carrier arms may have 
rolling elements attached thereto. There are preferably three such carrier 
arms around the circumference of each carrier assembly.

SPECIFIC DESCRIPTION 
The Figure shows an apparatus embodying the present invention for carrying 
mobile means of inspection in the interior of a tubular body. The 
apparatus has a first carrier assembly 1, a second carrier assembly 2 and 
a bridge comprising a linking piece 3 that is coupled to carrier assembly 
1 and extends longitudinally on one side of the central longitudinal axis 
20 of this carrier assembly; the bridge further comprises a linking piece 
4 that is linked to carrier assembly 2 and that is placed on the opposite 
side of the longitudinal axis 20 and displaced relative to linking piece 
3; finally the bridge comprises a coupling piece 5 for coupling linking 
pieces 3 and 4. 
The apparatus is further provided with a transducer 6 which is incorporated 
in carrier assembly 2 and a reflector 7 which forms part of carrier 
assembly 1. Each carrier assembly 1, 2 is further provided with carrier 
arms 8 onto which rolling elements 9 are attached, there being three of 
the carrier arms 8 around the circumference of the respective carrier 
assemblies for centring the two carrier assemblies 1, 2 in the tubular 
body to be inspected. 
Reflector 7 comprises two reflecting planes 10, 11. Reflecting plane 10 is 
positioned at the level of linking piece 4 and defines a transmission path 
that extends partly in the direction of arrow A perpendicular to the 
longitudinal axis 20 of the apparatus. The reflecting plane 11 lying 
behind reflecting plane 10 in the direction of the longitudinal axis 20 
from the transducer 6 defines a further transmission path which extends at 
least partly in the direction of arrow B perpendicular to the longitudinal 
axis 20. The reflecting plane 11 partially overlaps the reflecting plane 
10. 
During operation of the apparatus, the reflector 7 is rotated by motor 12 
about the longitudinal axis and the respective transmission paths defined 
by reflection planes 10 and 11 rotate in such a way that at least one 
transmission path extends to the interior of the tubular body to be 
inspected at any one time. 
The apparatus in accordance with the invention is suitable for applications 
including inspecting the wall thickness of the tubular body, and for 
inspecting for cracks in it.