PAUT Validation/Demonstration Blocks

PAUT - Phased Array Ultrasonic Testing

Phased array ultrasonic (PA) is an advanced method of ultrasonic testing that has applications in medical imaging and industrial nondestructive testing. Common applications are to noninvasively examine the heart or to find flaws in manufactured materials such as welds.

Validation/Demonstration Blocks:

A Qualification demonstration on the qualification block is essential. The qualification targets (Surface and embedded notches) are used to prove the technique. Side drilled holes can also be made and provided in the same block and these targets will be used to set the system sensitivity. Therefore, one single block can also be used at times for qualification work as well as calibration purposes.

General:

The following Article 4 paragraphs apply to demonstration blocks: T-434.1.2, T-434.1.3, T-434.1.4, T-434.1.5, T-434.1.6, and T-434.1.7.

Preparation:

A demonstration block shall be prepared by welding or, provided the acoustic properties are similar, the hot isostatic process (HIP) may be used.

Thickness:

The demonstration block shall be within 25% of the thickness to be examined. For welds joining two different thicknesses of material, demonstration block thickness shall be based on the thinner of the two materials.

Weld Joint Configuration:

The demonstration block's weld joint geometry shall be representative of the production joint's details.

Flaw Location:

Unless specified otherwise by the referencing Code Section, the demonstration block shall contain a minimum of three actual planar flaws or three EDM notches oriented to simulate flaws parallel to the production weld's axis and major groove faces.

The flaws shall be located at or adjacent to the block's groove faces as follows:

1. One surface flaw on the side of the block representing the component O.D. surface
2. One surface flaw on the side of the block representing the component I.D. surface
3. one subsurface flaw

When the scan plan to be utilized subdivides a weld into multiple examination zones, a minimum of one flaw per zone is required.

Flaw Size:

Demonstration block flaw sizes shall be based on the demonstration block thickness and shall be no larger than that specified by the referencing Code Section

1. maximum acceptable flaw height for material less than 1 in. (25 mm) thick, or
2. 0.25 aspect ratio acceptable flaw for material equal to or greater than 1 in. (25 mm) thick based on the demonstration block thickness.

Levels of Demonstration Blocks

Low Level:

Qualification blocks shall be fabricated similar to a calibration block in accordance with Article 4, T-434, or Article 5.

Intermediate Level:

Qualification blocks shall be in accordance with T-434.1.2 through T-434.1.6. The procedure shall be demonstrated to perform acceptably on a qualification block (or blocks) having welds, or alternatively, having flaws introduced by other processes that simulate the flaws of interest.

The block shall contain a minimum of three axial flaws oriented parallel to the weld's fusion line as follows:

1. One surface flaw on the side of the block representing the component OD surface
2. One surface flaw on the side of the block representing the component ID surface
3. One subsurface flaw.

Qualification block flaws shall be representative of the flaws of concern, such as, for new construction, slag, cracks, or zones of incomplete fusion or penetration, and, for post-construction, flaws representing the degradation mechanisms of concern.

If the inside and outside surfaces are comparable (e.g., no overlay or cladding present, similar weld joint details and welding processes, etc.) and accessible, one surface flaw may represent both the ID and OD surface flaws.

Qualification blocks shall include flaws having a length no longer than the following, with flaw height no more than 25%t or 1/4 in. (6 mm), whichever is smaller:

I. For surface flaws, 1/4 in. (6 mm) in blocks having thickness t up to 4 in. (100 mm)

II. For subsurface flaws
a. 1/4 in. (6 mm) for t up to 3/4 in. (19 mm)
b. One-third t for t from 3/4 in. (19 mm) to 21/4 in. (57 mm)
c. 3/4 in. (19 mm) for t from 21/4 in. (57 mm) to 4 in. (100 mm)

III. For blocks over 4 in. (100 mm) thick, the blocks shall include flaws having a size no greater than a flaw acceptable to Table II-1434-1 or Table II-1434-2 for the thickness being qualified. Figure II-1434 identifies dimensioning of surface and subsurface flaws.

High Level:

Qualification test specimens shall be provided representative of the weld to be examined. A sufficient number of test specimens shall be evaluated to effectively estimate sizing error distributions, and determine an accurate probability of detection (POD) for specific degradation mechanisms or flaw types and sizes. The number, size, orientation, type, and location of flaws in the specimens shall be as specified by the referencing Code Section or the Owner/User (if the referencing Code does not address) based on POD and confidence level requirements.


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