(Received 3 August 1987; accepted 28 April 1988)
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A nondestructive procedure has been developed using microstructural examination to predict the Charpy impact value at −46°C (−50°F) of installed normalized flanges (Grade LF2) made to ASTM Specification A 350/A 350M (minimum impact requirement of 20 J at −46°C). V-notch Charpy impact specimens were cut from a number of flanges and tested at −46°C. The absorbed energies were correlated with microstructural measurements obtained from the Charpy specimens resulting in the equation
Impact energy absorbed, J, at −46°C = 37 d−1/2 − 2%P − 226 where P = volume pearlite, and, d = grain diameter, mm.
The relationships between the pearlite volume fraction and grain size at the surface of a flange to that measured at the corresponding Charpy position were then established, so that this equation could be adjusted to predict the impact energy from small slivers taken from the sides of installed flanges (an operation which would not affect the integrity of a flange).
The predicted impact energies from microstructural examination of small surface slivers taken from a large number of flanges were then compared to the values obtained from Charpy testing the same flanges. Statistical analysis of the results showed that to be 95% confident in meeting the ASTM A 350/A 350M (Grade LF2) impact requirement of 20 J at −46°C, the value predicted from the impact energy equation must be ≥ 33 J.
Having established the technique and assessed its accuracy, the technique was used in an on-site investigation to identify flanges that would fail to meet the impact requirement of 20 J at −46°C.
Lecturer in Materials Science, The City University, London,
Stock #: JTE11272J