4.5 Isolated white etching layer (WEL)
Isolated patches of white phase or WEL can occur if wheelslip has been insufficient to cause a wheelburn or stud. These may appear opposite one another on both rails. At present it is not known if these are the origin of a more substantial defect, such as a stud, but they do represent a measurable irregularity.
Discontinuous patches of WEL are often the first sign of corrugation.