Angle Probe Calculation for UT


There are three methods for selecting a probe angle, these are:

  1. Based on groove angle:

            Probe Angle (Ø) = 90 – α/2

Where, α – Groove angle and Ø- Probe Angle

  1. As per AWS:
  • 0 – 30 mm Thickness – 700 Probe
  • 30 – 40 mm Thickness – 600 Probe
  • > 40 mm Thickness – 450 Probe
  1. As per approved procedure:

    Third way of selection of Probe angle is as per the procedure approved by any competent person/client.



  1. Skip distance calculation:

(Abbreviations: HSD – Half Skip Distance, FSD – Full Skip Distance)

Tan Ø = Perpendicular (BG)/ Base (AG) = AC (or HSD)/THK

Hence, Tan Ø = HSD/T

Or, HSD = T X Tan Ø

Similarly, FSD = 2T X Tan Ø

And, 1-1/2 Skip Distance = 3T X Tan Ø

  1. Beam Path calculation:

(Abbreviations: HBP – Half Beam Path, FBP – Full Beam Path)

Cos Ø = Base (AG) / Hypotenuse (AB) = THK/HBP

Or, HBP = T / Cos Ø

Similarly, FBP = 2T / Cos Ø

And, 1-1/2 Beam Path = 3T / Cos Ø

NOTE: 1. Scanning area should be 1-1/2 Skip Distance i.e. 3T X Tan Ø

              2. Probe Travel Speed shall not be more than 150 mm/S

Read more: How to write a Welding Procedure Specification (WPS)

Read more: Welding Positions

Read more: Preheating – How, When and Why

Read more: Welder Qualification test

Read more: Thickness range as per ASME Section IX


About Auther:

I am a Mechanical Engineer with more than ten years of work experience in the field of welding and NDT.

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