Abstract: Thereactor material of the MTO plant of a petrochemical company is 347H and the plant was completed and put into use in October 2011. In September 2017, cracks were first found near the circumferential weld of the reactor head. On May 2, 2018, the company stopped production for overhaul. Larger cracks were found again at the position of the circumferential weld of the head, and micro-cracks appeared in many places. Through expanded test, defect removal and fitness-for-service assessment and formulating strict operational monitoring measures, the smooth operation of the device has been ensured.This paper analyzes and explores the causes of the weld cracking from various aspects, and makes relevant recommendations.

Key words: 347H, austenitic stainless steel, stress relaxation crack, reheat cracking, welding quality