Use of magnetic non-destructive testing to evaluate thickness of concrete protective layer for enclosing and bearing structures at NPP

Introduction. This article discusses methods and means of controlling the diameter and position of reinforcement and the thickness of the concrete protective layer, along with the contemporary techniques and devices for diagnostic and non-destructive testing of concrete. A comparative analysis of the applicability of contemporary devices was carried out.

Aim. In this work, magnetic non-destructive testing was used to assess the thickness of the concrete protective layer, along with establishing the location of the upper row of rod reinforcement and embedded parts. Based on analyzing the interaction between the electromagnetic field of the sensor and the electromagnetic field of eddy currents induced by the source coil of the sensor in rebar, this method allows the diameter of the latter to be approximately estimated at an unknown protective layer.

Materials and methods. As an example, the thickness of the concrete protective layer of enclosing structures (walls, floors) at power unit № 1 at the Kalinin Nuclear Power Plant (NPP) was measured using the POISK-2.6 device.

Results. The analysis of design and as-built drawings for buildings and structures of the main facility of power unit № 1 at the Kalinin NPP was carried out. The state of passive fire protection equipment at the power unit (fire doors, cable penetration seals, and ventilation fire dampers) was evaluated. The actual thickness of the concrete protective layer and the location of the reinforcement of concrete elements at the facilities of the Kalinin NPP power unit were measured as per GOST 22904-93 using electromagnetic NDT. The applicability of the magnetic NDT for determining the thickness of the concrete protective layer was shown during the inspection of building structures.

Conclusions. During the inspection of the facilities, it was established that the average thicknesses of the concrete protective layer, including the thickness of the reinforcement, range from 38 to 85 mm, with the diameter of the reinforcement of 12–20 mm. During the measurements, the applicability of the method was shown; it was also confirmed that the examined structures exhibit fire endurance of at least 90 minutes, which meets the requirements of regulatory documents.

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