Which of the following factors can affect the accuracy of ultrasonic testing results?

The accuracy of ultrasonic testing (UT) results is significantly influenced by the material's surface condition and grain structure. A smooth and properly prepared surface facilitates better sound transmission and helps to minimize signal loss, ensuring that more accurate data is collected. Conversely, a rough or contaminated surface can scatter the ultrasonic waves, leading to misleading readings.

Additionally, the grain structure of the material can affect how ultrasonic waves propagate. Different materials and their specific grain arrangements can influence the velocity and attenuation of sound waves, thus impacting the measurements obtained during testing. Variations in grain size and orientation within a material can also lead to differences in wave behavior, resulting in variations in the detection and characterization of flaws.

The other factors mentioned, while important, do not have the same level of direct impact on the accuracy of the readings. The temperature of the testing environment can affect the speed of sound in the material, but it is typically a manageable variable if accounted for. The angle of the transducer is crucial for optimal sound wave entry and flaw detection, yet it is within the operator's control during testing. Lastly, the type of flaw present is important for evaluating the integrity of the material but may not specifically influence the measurement accuracy itself like surface condition and grain structure do.