Long Range Ultrasonic Testing (LRUT)

Introduction

LRUT is basically an Ultrasonic Testing screening tool use for detection of corrosion. LRUT employs low frequency guided waves, operating just above audible frequencies, propagated from a ring of transducers fixed around the pipe. Guided wave (longitudinal, torsional and flexural) generated by the system travel along the length of pipe to give 100% inspection. In a one shot (single contact point) full circumference of pipe is inspected over the length of 350 meter and applicable up to temperature of 240 ℃.

LRUT indications were primarily categories 1, 2 & 3 as ‘Minor’, ‘Moderate’ and ‘Severe’, in terms of amplitude respectively. Distance amplitude curves (DAC) were superimposed on the LRUT indications for comparison purpose.

Category 1 (Green): Responses lower than -26dB line, Estimated cross sectional area wall loss in the range of 3% to 9% (formerly Minor).

Category 2 (Red): Responses above the -26dB line, but are lower than blue line at -20dB (formerly Moderate), Estimated cross sectional area wall loss in the range of 9% to 15%.

Category 3 (Blue): Responses exceeding -20dB blue line, Estimated cross sectional area wall loss > 15%.

Application

LRUT is applicable for the pipe line of long length for fast and reliable inspection. LRUT have following applications:

Tank farm pipework

• Insulated line
• Bund wall penetrations
• Road crossings

Refinery pipework

• Corrosion under Insulation
• Flare line inspection
• Jetty pipe work

Offshore Applications

• Riser inspection
• Splash zone inspection
• Caisson inspection

Other inspections

• Insulated Sphere legs
• Air-soil interface
• River Crossings

Benefits

This system can be utilized either as an in-service tool or as an initial baseline survey to assist in integrity.
• Internal and external corrosion are detected simultaneously and the complete pipe circumference is inspected.
• Long length of pipe inspected in single contact point shot.
• No need to remove insulation or to fully excavate the buried line.
• No need for scaffoldings.