One of the effective approaches to the retardation of cracks in pipes is based on thermal reinforcement of rolled sheet. For the manufacture of pipes it was proposed to use thermally reinforced steel sheet with periodic strengthened strips. These barriers in the crack path reduce the rate of its propagation and change its trajectory. The direction of crack propagation may be controlled by the configuration of these barriers. This paper presents experimental and theoretical results concerning the direction of crack propagation near the boundary of a strengthened part of a steel sheet depending on the angles of inclination of this boundary with respect to the initial crack trajectory. The competition between deflection and penetration at the interface is investigated for different ratios of the strength limits of the strengthened material and the matrix. The problem is studied using known expressions for the stress components in the vicinity of crack tips with non-singular terms associated with load biaxiality, and the generalised maximum tensile stress criterion.