MP I Machine Operation

4.2.7.8.2 Coi 1.

l Magnetization (Test piece as per figure 13 of BS 6072).

Place the coil test piece at the bottom of the test coil.

2. Energize the machine with 300A (AC) or 430 A (DC).

3. Observe the strong transverse hole indications shows at the middle of the test piece.

4. The indication shows that the coil magnetization is good condition.

5. Record the results.

4.2.7.9 MP I Machine Operation

1. Local instructions for MT machines at HAN [TBD].

a. User’s care and instructions for Magwerks.

4.2.7.10 Magnetization (As per ASTM E 1444)

The current shall produce a peak tangential-field strength in the range of 30 to 60 gauss (2.4 to 4.8 kAm-1) or in the range of 80 to 160 gauss according to manufacture requirement in all areas to be inspected.

Gauss meter readings shall take precedence over calculated current requirements.

4.2.7.10.1 Circular magnetization

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1. Direct Circular Magnetization. The current shall be from 300 to 800 A/in of part diameter (12 to 32 A/mm)

2. Central Conductor Circular Magnetization.

a. Centrally Located Conductor. The current as per para 7.10.1 (1) shall be applied.

b. Offset Central Conductor. The current as per para 7.10.1(2) shall be applied except that the diameter shall be considered the sum of diameter of the central conductor and twice the wall thickness.

4.2.7.10.2 Longitudinal magnetization

Longitudinal magnetization shall be used for those parts that are at least two times as long as they are wide (i.e. L/D ≥ 2)

The peak current for longitudinal inspection shall be calculated as follows: For parts positioned at the bottom of the coil:

NI = 45,000 ( L ) ( D )

For parts positioned at the center of the coil:

Where:

NI = 43,000 R ( 6L ) - 5

( D)

I = Coil peak current to be used (amperes) N = Number of turns in the coil R = Coil Radius L = Part length

D = Part diameter

* NOTE: If a part is longer than 18 inches, L/D shall be calculated using a value o L

= 18, and D = Actual Diameter. If the resulting value of L/D is between 2 and 15, that calculated value will be used in the equations located on the preceding page.

If the resulting value of L/D is greater than 15, a value of 15 shall be used in the equations located on the preceding page.

If the resulting value of L/D is less than 2, the part will be inspected using an alternate approach.

When calculating the L/D ratio for a hollow part, D shall be replaced with an effective diameter,

Deff' calculated using:

(At

-

Deff' = π \

PART 4 – NDT SPECIFIC PROCEDURES & WRITTEN INSTRUCTIONS – AESC/NDT/PR/MT02

Where: At = the total cross-sectional area of the part

Ah = the cross-sectional area of the hollow portion of the part.

For cylindrical parts, Deff is equivalent to:

Deff =

√

Where: OD = the outside diameter of the cylinder ID = the inside diameter of the cylinder

Separate magnetizing operations shall be used for both circular and longitudinal magnetization when parts contain changes in sections that differ by more than 30 percent. In such cases, the sequence of magnetization shall begin with the lowest current level and proceed in the direction of higher currents. For circular magnetization, the peak field strength of each section shall be maintained in the range of 30 to 60 gauss. Proper care shall be taken to avoid damage to smaller sections from overheating.

Residual magnetization shall be used when required by Drawing or program document 4.2.7.11Magnetization (As per BS 6072)

4.2.7.11.1 Current Flow

The effective value of current in MPI is the peak value. However, it is impractical to use ammeters which are responsive to the peak value, hence it necessary to use instruments which response either to root mean square (rms) or to the mean value, and to calculate the peak from the known or estimated waveform.

The following table shall be used to determine indicated current values for the various methods of magnetism. Each machine in use shall be clearly marked with correction factors allowing conversion from peak to indicated and vice versa.

Current Waveform DC Source (Amp)

For Threading Bar application, where the bar is concentric with the part, the current value shall be calculated from the above table, based on the outside diameter of the part. In cases where the Threading Bar cannot be mounted concentric with the part, it shall be positioned away from the axis. The current value shall be calculated from the above table by taking the diameter of the circle centered on the Threading Bar with the outer surface of the part on its circumferences. In such cases the part shall be tested in stages to ensure 360°C coverage

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The central conductor used shall be covered with an insulating material, or non- conductive spacers to ensure that components do not touch the threading bar to avoid a danger of burning

To test parts of varying diameters some compromise is necessary regarding the current used. When the largest diameter exceeds the smallest diameter by 50% or less, then the average of the currents normally required may be used to test the whole part (e.g. a part having diameters of 100mm and 75mm could be given are shot to test the whole length) calculated as follows:

100.0 at 20 amps AC per mm = 2,000 amps AC 75.0 at 20 amps AC per mm = 1,500 amps AC

3,500 amps

Average current = 3,500 = 1,750 amps AC 2

Where the largest diameter exceeds the smallest diameter by more than 50% then more than one shot is required. A higher current than that required for test may be passed through the smaller diameter, in order to test the larger diameter providing due precautions are taken against burning and overheating and that defect indications are evaluated at the correct testing amperage for each diameter (e.g. a part made up of 25mm, 50mm and 100mm diameters would require three separate testing shots of current flow):

4.2.7.11.2 Coil

Shot 1: 25 at 20 amps AC per mm = 500 amps AC Shot 2: 50 at 20 amps AC per mm = 1,000 amps AC Shot 3: 100 at 20 amps AC per mm = 2,000 amps AC

The peak current shall be calculated from the formula:

NI = K

Where the part length diameter L/D ratio is less than 5:1, extenders shall be used to extend the length of the flux path. If the L/D ratio is greater then 20 then the value 20 shall be substituted for L/D.