Method For Detecting Cracks In A Tubular Pipe

A method for detecting and characterizing a stress corrosion crack in a steel tubular pipe at an inspection region extending from a welded joint between two portions of the steel tubular pipe by means of an ultrasonic measurement probe, comprising:

• a) for a plurality of measurement positions distributed circumferentially around the steel tubular pipe on an external surface of the steel tubular pipe at the welded joint:
• a1) positioning the ultrasonic measurement probe against the external surface at the measurement position, the ultrasonic measurement probe having a transmission surface forming an angle comprised between 10° and 30° relative to a plane tangent to the external surface of the steel tubular pipe supporting the ultrasonic measurement probe,
• a2) successively transmitting and receiving at least two bursts of ultrasound of the same frequency to obtain a plurality of measurement signals, the at least two bursts of ultrasound comprising a first, direct-mode, plane-wave burst being configured to scan a first region of interest encompassing the inspection region and the welded joint with a beam axis scanning an angular scanning range at least 10° greater than an angular range of interest occupied by the first region of interest relative to the plane tangent to the external surface of the steel tubular pipe supporting the ultrasonic measurement probe, and at least one second, indirect-mode, burst scanning the angular range of interest,
• b) constructing a first representation on the basis of the first-, direct-mode, plane-wave bursts at a plurality of measurement positions distributed circumferentially around the steel tubular pipe in which a region characteristic of the welded joint appears, and constructing a second representation on the basis of the at least one second-, indirect-mode, bursts at a plurality of measurement positions distributed circumferentially around the steel tubular pipe, the first representation and the second representation being two-dimensional data sets associating an amplitude with a location in a two-dimensional space,
• c) identifying a trace, of the stress corrosion crack that appears as a localized variation in amplitude in the first representation and the second representation, the trace having two amplitude peaks, in the first representation constructed from the first, direct-mode, plane-wave bursts,
• d) determining a height of the stress corrosion crack on the basis of a distance between the two amplitude peaks, of the trace in the first representation constructed from the first, direct-mode, plane-wave bursts, the height of the stress corrosion crack extending from an internal surface of the steel tubular pipe.