Use of Acoustic Emission for Studying Ratcheting Behavior of 304LN Stainless Steel Elbows

Acoustic emission technique (AET) has been used for studying ratcheting behavior of elbows made of AISI type 304LN stainless steel. High pressure piping and elbows in nuclear power plants are subjected to large amplitude reverse cyclic loading during an earthquake and the stresses are likely to exceed the elastic limit. A strong possibility for the accumulation of plastic strain by ratcheting thus exists in such components. Monitoring cyclic strain and ovality are normally done to predict damage in pressurized components during ratcheting. The novelty of the present work is the use of acoustic emission (AE) for getting information about the damage and formation of cracks during the ratcheting tests in elbow specimens. The tests were carried out under steady internal pressure and cyclic bending. During the ratcheting tests, the first significant increase in AE signal occurred at around 214 cycles and 103 cycles for the two elbows, and this has been attributed to crack initiation. Higher AE generated beyond that has been attributed to crack growth. Different parameters of the AE signal have been used to substantiate the results. Keywords: Ratcheting, AISI type 304LN stainless steel, crack initiation, piping, elbow, acoustic emission