NDE Magnetic Testing (MPI) Standard and Criteria

The ASME V is the guideline to make an NDE procedure, how to evaluate the report or defect is defined by Construction as below for your quick reference:

1. ANSI/ASME B31.1 Power Piping
The following relevant indications are unacceptable:
1.1. Any cracks or linear indications.
1.2. Rounded indications with dimensions greater than 3/16 inch (4.8mm).
1.3. Four or more rounded indications in a line separated by 1/16 inch(1.6 mm) or less edge to edge.
1.4. Ten or more rounded indications in any 6 square inches (3,870 mm²) of surface with the major dimension of this area not to exceed 6 inches (150 mm) with the area taken in the most unfavorable location relative to the indications being evaluated.

2. ASME B31.3 Chemical Plant and Refinery Piping
Any cracks or linear indications are unacceptable.

3. ASME Section VIII, Division 1
3.1. Indications with any major dimension greater than 1/16 inch (1.6 mm) shall be considered relevant. All surfaces to be examined shall be free of:
3.2. Relevant Linear Indications
3.2.1. Relevant rounded indications greater than 3/16 inch (4.8 mm).
3.2.1. Four or more rounded defects in a line separated by 1/16 inch (1.6 mm) or less (edge to edge) except where the specification for the material establishes different requirements for acceptance so far as defects are concerned.

4. API STD 1104 Welding of Pipelines and Related Facilities
Any indication with a dimension greater than 1/16 inch (1.6 mm) shall be considered relevant. Relevant indications shall be unacceptable when any of the following conditions exist:
4.1. Linear indications evaluated as crater cracks or star cracks which exceed 5/32 inch (3.96 mm) in length.

​4.2. Linear indications evaluated as cracks other than crater cracks or star cracks.
4.3. Linear indications evaluated as incomplete fusion (IF) and exceed 1 inch (25.4 mm) in total length in a continuous 12 inch (304.8 mm) length of weld or 8% of the weld length.
4.4. Individual or scattered porosity (P) shall be unacceptable when any of the following conditions exists:
4.4.1. The size of an individual pore exceeds 1/8 inch (3.17 mm) or 25% of the thinner of the nominal wall thicknesses joined.
4.4.2. Cluster porosity (CP) in any pass except the finish pass shall be unacceptable when any of the following conditions exist:
4.4.3. An individual pore within a cluster exceeds 1/16 inch (1.6 mm).
4.4.4. The CP diameter exceeds ½ inch (12.7 mm).
4.4.5. The aggregate length of CP in a continuous 12 inch (304.8 mm) length of weld exceeds ½ inch (12.7 mm).

5. API RP2X Recommended Practice
For Ultrasonic and Magnetic Examination of Offshore Structural Fabrication and Guidelines for Qualification of Technicians:
5.1. All relevant indications must be reported.
5.2. All relevant indications, as determined by MT (typically cracks or incomplete fusion) are rejectable regardless of length otherwise specified by the owner.

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