Can someone please explain this?
ASTM E1444 states that "Magnetic Field Strength may be determined by using notched shims (ASTM E1444, 18.104.22.168.).
ASTM E1444 states that "Magnetic Field Directions may be determined by using flexible laminated strips (ASTM E1444, 6.2.5)
What is the difference between laminated strips and notched shims. Why laminated strips cannot be used for both checks or vise-versa?
In reply to Ledon Watkins:
Thanks for the reply, however couldn't find the answer in SAE AS-5371. Fortunately, I met a Magnaflux guy in October, while attending an NDT Forum organised by NANDTB Australia. Then I got a better answer and I thought I should share this with everyone.
"Notched shims can be used to determine both direction and strength. Laminated strips should not be used to determine strength.
Notched shims (QQI, or AMS 5371 shim) have intimate contact with the part and can conform to the part geometry. This intimate contact means the field they receive is as close to the actual field in the part as possible with an artificial flaw. Therefore, if the technique can find the notches on a QQI, then there is enough magnetic strength to find indications on the part at that location. Because the notches are circular, they can show the field direction in any orientation without changing position.
Laminated strips (Burmah-Castrol strips) have a core of ferrous steel and are laminated with either brass or stainless steel. They are much thicker than QQIs, are not as flexible, and normally cannot conform to the part geometry. So the magnetic field they receive is external to the part being tested. For that reason, technically they do not show the strength of the field in the part, so they cannot demonstrate that sufficient field is available to find indications. "
ASNT 107643, PCN 205373.
Responsible NDT Level 3 & Radiation Principal Licensee
Air New Zealand
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