IJ: How many ultrasonic (UT) sensors are necessary on the Intelligent Pig to ensure adequate inspection coverage when inspecting coils in fired heaters?
RR: The diameter of the heater coil should ultimately dictate the number of ultrasonic (UT) sensors the intelligent pig should have designed into it. For example, a 3-inch diameter heater coil should have a minimum of forty-eight (48) ultrasonic readings acquired around the coil circumference, while a 12-inch diameter should have one hundred sixty-eight (168) ultrasonic readings taken around the coil circumference. Additionally, the intelligent pig should be acquiring a minimum of four (4) samples for every one inch (25mm) of axial length.
IJ: What is the maximum diameter of the ultrasonic (UT) sensor on the Intelligent Pig instrument to ensure both adequate inspection resolution and sensitivity?
RR: The physical dimension of damage mechanisms such as pitting, isolated corrosion and mechanical fretting can be small and in locations where it is impossible to access externally using manual NDE. Intelligent pigs applied from the interior surface should have a maximum of ¼” diameter (or smaller) ultrasonic (UT) sensors in order to ensure adequate resolution and sensitivity to reliably detect these flaws. Both of these key elements are compromised if the UT sensor is larger in diameter.