PHASED ARRAYS FOR WELD INSPECTION

The concept of weld inspection is shown below. A probe is selected that illuminates the weld as shown below. In the first leg, only the bottom half of the weld is illuminated. However, with reflection from the ID surface the entire weld is illuminated and the complete weld volume can be inspected. For example, the indication ‘a’ in the weld is detected by the reflected sound and displayed as the mirror image ‘a-’ in the second leg. Similarly other flaws are displayed in the image.

Concept of phased arrays for Weld Inspection. Indication ‘a’ detected by the reflected beam is displayed as a mirror image ‘a-‘ in second leg

Examples of defects images detected in welds are shown below.

Root detected in first leg.	Image shows a strong ID crack signal

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What are Ultrasonic Phased Arrays?

What are Ultrasonic Phased Arrays?

Ultrasonic phased arrays use a multiple element probe whereby the output pulse from each element is time delayed in such a way  so as produce constructive interference at a specific angle and a specific depth. These time delays can be incremented over a range of angles to sweep the beam over the desired angular range. For example, 40 to 75 degree beam sweep would be produced by calculating the time delays to produce constructive interference at 40, 41, 42 ...75 degrees. This NDT technology is also referred as Swept Beam Ultrasonic testing.

The main advantages of phased array in NDE are:
1. Ability to sweep a range of angles
2. Ability to display the image in real time for the swept angles
3. Ability to focus

The above figure displays the concept of phased arrays. Time delays to the eight elements control focusing and beam sweep. Focal spot size (shown by the shaded orange area) is controlled by beam spread. Checking Phased Array Probe Resolution. Resolution determines flaw definition and sizing accuracy. Instrument: Phasor

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Brief Description of ASME P-Numbers

ASME P-Numbers

To reduce the number of welding and brazing procedure qualifications required base metals have been assigned P-Numbers by the ASME BPVC.  Ferrous metals which have specified impact test requirements have been assigned Group Numbers within P-Numbers.

These assignments have been based on comparable base metal characteristics, such as:

            Composition

            Weldability

            Brazeability

            Mechanical Properties

Indiscriminant substitution of materials in a set of P-Numbers or Group Numbers may lead to problems or potentially failures.  Engineering assessment is necessary prior to a change in materials.

When a base metal with a UNS number Designation is assigned a P-Number, then a base metal listed in a different ASME material specification with the same UNS number shall be considered that P-Number.

The table below is a guide and is for instructive purposes only.  Anyone specifying materials or requirements should refer directly to the ASME Boiler and Pressure Vessel Code to specify materials, P-Numbers,  procedures, or other requirements and not rely on the table below.  The table below is only a rather incomplete and approximate summary of ASME data. 

P-Numbers	Base Metal (Typical or Example)
1	Carbon  Manganese  Steels (four Group Numbers)
2	Not Used
3	Half Molybdenum or half Chromium, half Molybdenum (three Group Numbers)
4	One and a quarter Chromium, half Molybdenum (two Group Numbers)
5A	Two and a quarter Chromium, one Molybdenum
5B	Five Chromium, half Molybdenum or nine Chromium, one Molybdenum (two Group Numbers)
5C	Chromium, Molybdenum, Vanadium (five Group Numbers)
6	Martensitic Stainless Steels (Grade 410, 415, 429) (six Group Numbers)
7	Ferritic Stainless Steels (Grade 409, 430)
8	Austenitic Stainless Steels             Group 1 - Grades 304, 316, 317, 347             Group 2 - Grades 309, 310             Group 3 - High Manganese Grades             Group 4 - High Molybdenum Grades
9A, B, C	Two to four Nickel Steels
10A, B, C, F	Various low alloy steels
10H	Duplex and Super Duplex Stainless Steel (Grades 31803, 32750)
10I	High Chromium Stainless Steel
10J	High Chromium, Molybdenum Stainless Steel
10K	High Chromium, Molybdenum, Nickel Stainless Steel
11A	Various high strength low alloy steels (six Group Numbers)
11B	Various high strength low alloy steels (ten Group Numbers)
12 to 20	Not Used
21	High Aluminum content (1000 and 3000 series)
22	Aluminum (5000 series - 5052, 5454)
23	Aluminum (6000 series – 6061, 6063)
24	Not Used
25	Aluminum (5000 series - 5083, 5086, 5456)
26 to 30	Not used
31	High Copper content
32	Brass
33	Copper Silicone
34	Copper Nickel
35	Copper Aluminum
36 to 40	Not Used
41	High Nickel content
42	Nickel, Copper - (Monel 500)
43	Nickel, Chromium, Iron - (Inconel)
44	Nickel, Molybdenum – (Hastelloy B2, C22, C276, X)
45	Nickel, Chromium
46	Nickel, Chromium, Silicone
47	Nickel, Chromium, Tungsten
47 to 50	Not Used
51, 52, 53	Titanium Alloys
61, 62	Zirconium Alloys

   

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