Abstract: Two big explosions,many leakages and bulges appeared on SA-213 T22 hanging tubes at the same outer ring of hanging screen in front wall of 660 MW subcritical boiler during running.And the failure reasons were analyzed by means of macroscopic examination,chemical compositions analysis,mechanical properties test and metallographic examination.The results show that local longtime overheating running caused several bulges and leakages of the hanging tubes,local steam-water flow inadequate in downstream of the leakages led to short-time overheating tube burst,and then the neighboring leakage was ripped into big diamond-shaped rupturing.