Method of suppressing grain noise in ultrasonic waveform data by 3D filtering

A method of ultrasonically inspecting a metal object formed from a plurality of grains wherein grain noise arises at interfaces between the plurality of grains during the ultrasonic inspection of the metal object, the method comprising the steps of:

• ultrasonically scanning the metal object with sound wave energy;
• detecting waveform signals reflected from the metal object;
• determining data values from said waveform signals which define a 3D waveform data set U(x,y,t) having both spatial (x,y) and temporal (t) ultrasonic data values which map directly to a third spatial dimension from the scanned metal object, the 3D waveform data set U(x,y,t) corresponds to a 3D volumetric region in the metal object;
• converting the 3D waveform data set U(x,y,t) into a 3D filtered waveform data set V(x,y,t) by performing a 3D filtering operation thereon, wherein for each data value in said 3D waveform data set U(x,y,t), a filtered data value is obtained by taking into account data values which are adjacent in 3D space;
• suppressing grain noise arising at the interfaces between the plurality of grains within the metal object with the 3D filtered waveform data set V(x,y,t);and
• generating a full volume 3D image of the 3D filtered waveform data set V(x,y,t).