Published on 31-Mar-2022

Defect Size That Is Accepted In Ultrasonic Testing

Defect Size That Is Accepted In Ultrasonic Testing

In reference to the standards, indications that get identified by using any of the NDT methods are accepted or rejected. " Acceptance criteria" here means the standards that are followed by us in the process of production or the standards that are accepted by the clients. In this blog, we are going to describe some of the important ASME acceptance criteria for ultrasonic testing, we all should know. So let's begin! 

ASME Acceptance Criteria for Ultrasonic Testing

1)ASME Section VIII Division 1 – Pressure Vessel Construction – Ultrasonic Testing Inspection Services -

This particular standard should be applied unless & until the other standards are determined for certain applications within this region. Drawbacks that create a response of more than 20℅ of the reference level have to be investigated to the degree so that the operator can ascertain the identity, shape and location of all the imperfections & drawbacks to evaluate them in terms of acceptance standards listed below : 

If the indications are characterised by unsatisfactory penetration, lack of fusion, and cracks is unacceptable; still, the other imperfections are unacceptable. If the indications will surpass the level of reference amplitude and the lengths that also exceeds : 

a) 6mm(1.4  in.) for t up to 19mm(¾ in.)

b) 1/3t for t from 3/4 in. to 21/4 in. (19 mm to 57 mm); (3) 3/4 in. (19 mm) for t over 21/4 in. (57mm).

Where t is referred to the thickness of the weld apart from any permissible reinforcement. A butt weld, when joined by two members, has different thickness levels at the weld, t is the thinnest out of the other two thicknesses. The thickness of the throat of the fillet should be included in t only if the full penetration weld does include a fillet weld. 

2)ASME B 16.34 – Valves – Ultrasonic Testing 

Here, there are two types of beam examination, one is straight, and the other one is angle beam examination. Let's read about the two of them! 

Straight Beam Examination - Indications that are equal to or exceed which is obtained from a 6.4 mm diameter flat bottomed whole in a calibration test piece of thickness that is equal to the depth of the defect is totally unacceptable. 

Angel Beam Examination - Indications that are equal to or surpass that is obtained from a 60 deg V-notch, 25 mm long and which have a depth that is not greater than 5℅ of the nominal thickness of the wall in a test piece are totally unacceptable. 

3)ASME B 31.1 – Power Piping – Ultrasonic Testing

 Shown by ultrasonic examination, welds will have discontinuities that produce an indication that is greater than 20℅ of the reference level should have to be investigated to the extent so that the operator who has done ultrasonic examination can signify the shape, location and identity, which will help in evaluating each and every discontinuity for acceptance following (B.1) and (B.2) given below : 

(B.1) Regardless of the length, It is unacceptable if the discontinuities are determined as lack of fusion, incomplete penetration and cracks. 

(B.2) The other discontinuities are not acceptable if the indication will exceed the level of reference and if their length surpasses the points given below : 

(B.2.1) ¼” (6.0 mm) for t up to ¾” (19.0 mm).

(B.2.2) 1/3 t for t from ¾” (19.0 mm) to 2 ¼ “ (57.0 mm).

(B.2.3) ¾”. (19.0 mm) for t over 2¼” (57.0 mm)

Here, t refers to the thickness of the weld that is being examined. t is the thinnest of the two thicknesses if the weld will join the two members, which have different thicknesses at the weld. 

4)ASME B31.3 Process Piping – Ultrasonic Testing 

Assessment of the weld joints is carried out as per the ASME Section 5 of Article 4. 

Pipe and Tubing

ASME acceptance criteria for ultrasonic testing - An indication greater than what is being produced by the calibration notch representation. 

Pipe and tubing have to go through ultrasonic testing and also have to pass with 100℅ for longitudinal defects according to the ASTM E213 ultrasonic testing of the tube and the metal pipe. Longitudinal reference notches should be there on the outer & inner surfaces of the calibration standard, which should be to a depth of not greater than 0.1 mm or 4℅ of thickness. The length should not exceed the notch depth, i.e. 10 times. 

As the procedure given in the ASME Sec 5 of article 4, welds having thickness over 6 mm can be tested ultrasonically. Using the applicable techniques, indications should be in size in reference to the given procedure for the examination. Indications that have to be assessed for the ASME acceptance criteria for ultrasonic testing are given below : 

Indications which are specified as cracks, incomplete penetration and lack of fusion are absolutely not acceptable regardless of the factors - 

a) Indications that exceed 3 mm in length are probably considered appropriate and are not acceptable when the length surpasses : 3 mm for t up to 10 mm, 1/3t for t from 10 mm to 57 mm and 19 mm for t over 57 mm. 

There is referred to as the thinnest out of the two thicknesses when a butt weld joins two members having different thicknesses at the weld. The thickness of the throat of the fillet should be included in t only if the full penetration weld does include a fillet weld. 

5)API 1104 Welding of Pipelines & Related Facilities – Ultrasonic Testing – Acceptance level  

Standards accepted with 9.6.2.1 indications are determined as cracks should be considered. 

LS stands for Linear Surface, indications other than cracks if interpreted to be open to the D. or O.D surface should be considered defected if any of the following conditions prevail: 

a) If the aggregate length of the Linear Surface indications in any continuous 300 mm length of the weld surpasses 1, i.e. 25 mm.

b) If the length of the Linear Surface transcends the weld by 8℅.

LB, i.e. Linear Buried indications interpreted to be the subsurface within the weld and not in the I.D & O.D surface-connected should be contemplated as defected if any of the following conditions prevail : 

a) If the aggregate length of the Linear Surface indications in any continuous 300 mm length of the weld surpasses 1, i.e. 25 mm.

b) If the length of the Linear Surface transcends the weld by 8℅.

Talking about the Transverse indications, it should be considered as volumetric and be examined utilising the measures for volumetric indications. 

VC stands for Volumetric Cluster, here indications shall be considered defects if the ultimate dimension of Volumetric Cluster indications overrun 13 mm.

VI stands for Volumetric Individual, here the indications should be considered as defects when the ultimate dimension of VI surpasses 6 mm in both length and width. 

VR stands for Volumetric root; this indication interprets to be open to the D. surface and should be considered defected if the following conditions exist :

a) The maximum dimension of VR indications surpasses 6mm.

b) The total length of VR indications exceeds 13 mm in any continuous 300 mm.

Accumulation of relevant indications(AR) should be considered defective if any of the following conditions prevail:

a) If the length of the indications above examining level exceeds 8℅ of the weld.

b) The length of the indications level exceeds 50mm in any 300mm of length. 

Conclusion:

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