Effective Thermal Fatigue Cracking Characterization in Pipeline Branch Connections
Published on 23rd November 2020
To maximize productivity in an economy that demands efficiency, Non-Intrusive Inspection (NII) is necessary to determine Fitness-For-Service (FFS) of these online assets.
Ensuring the smooth operation of pipelines responsible for transporting contents throughout different areas of a process plant depends on regular assessment of the pipework including all branch connections. Because pipelines and other factory components are exposed to cyclic thermal stresses like those incurred from extreme temperatures or condensate and steam system contact, they are more susceptible to fatigue cracking. To maximize productivity in an economy that demands efficiency, Non-Intrusive Inspection (NII) is necessary to determine Fitness-For-Service (FFS) of these online assets.
Deliver better data results from examination of the typically difficult-to-access inside surface of branch connections.
Thermal Fatigue Cracking
Thermal fatigue cracking, or TFAT, damage is a real threat to branch connections, and conventional A-scan ultrasonic techniques are the current NII method for detecting this defect. The traditional Non-Destructive Testing (NDT)approach uses a tangential ultrasonic technique with a conventional search unit to locate the bore of the main pipe, the crotch corner area of the bore, and the bore of the branch pipe. An operator uses an array of single angle probes to locate cracking emanating from the regions of interest. Although this technique has proven to be successful in detecting damage, the geometry of certain branch connections adds complexity to this inspection region and can restrict full coverage. Furthermore, accurate sizing of damage can be difficult.
Overview of the typical inspection area
Inspection coverage of a typical branch connection
Phased array ultrasonic testing technology improves upon current non-intrusive methods of inspection.
Sectorial scan from 0/180 position with phased array response
Tangential scanning showing phased array response with no reflectors present
Optimized tangential scanning showing maximized phased array response from an EDM notch reflector
Phased Array Ultrasonic Testing (PAUT) technology uses a linear array of piezo elements individually mounted in one complete probe housing. Each element can be individually pulsed with an accurate timing sequence (focal law). The phasal interference of wave fronts from each adjacent element can be used to form a bulk wave that is steered or focused based on the time delays of the voltage pulses between each element. The use of multiplexing and PAUT probe technology allows for numerous inspection angles and focal laws to be collected simultaneously.
The resulting bulk wave can take two forms: sectorial or linear. In a linear scan, all focal laws employ a fixed angle beam, whereas sectorial scans use fixed apertures and steer through a sequence of angles.