Choice of Probe-Couplant combination in Phased Array UT


Michele, C.; NDT ITALIANA; Italy

ID: ECNDT-0249-2018
Session: Applied PAUT 2
Room: G2
Date: 2018-06-14
Time: 15:20 - 15:40

Phased array inspections are performed on a wide variety of surfaces, from flat to curved, from smooth to rough and irregular, from horizontal to vertical.

The purpose of this paper is to investigate the best combination of probes, couplant gels and phased array instrument settings in order to obtain the most reliable and productive ultrasonic testing even in difficult working conditions.

Different probes and couplants gels have been used throughout the tests carried out for this paper. Gain has been set on 100% FSH on known reflector, to compare different coupling agents and evaluate results about:

– Gain: the lowest gain to obtain 100% FSH as indicator of performance and reliability of the phased array inspection;
– Time of effective coupling performance
– Resolution of the indications
– Possibility to work on non-flat/vertical surfaces

Surfaces tested:

– Flat and smooth surface (UT test blocks)
– Flat and rough surface (Weldings)
– Curved and irregular surface (Oil&Gas Pipes irregularly grinded)

Manual and automatic applications have been investigated. Probes have been selected with different frequencies, wedge size and shape, to optimize inspection results. With the same purpose, different coupling agents have been tested: water, water with UT additives, glue, different UT couplant gels.

Results have been fit into a matrix to help PAUT operators have a reference guide of the best combinations of instrument settings, probes, couplant gels to obtain the most reliable and fast inspection in any type of situation in the NDT inspection field.

Results show that the use of a specific couplant on PAUT is even more critical compared to conventional UT because:
– Contact surfaces of PA’s probes wedges are wider compared to conventional UT
– It’s more critical to ensure a constant wetting ability
– PAUT inspections are mostly recorded and coupling consistency has to be guaranteed