Fatigue Failure of 321 Stainless Steel Superheater Tubes from a Thermal Incinerator |
| |
Authors: | F Elshawesh K Abusowa O ElRagei F El Haddad H Mahfud |
| |
Affiliation: | (1) Libyan Petroleum Institute, P.O. Box 6431, Tripoli, Libya |
| |
Abstract: | Several boiler superheater tubes showed circumferential cracking at weld seams after 2 years in noncontinuous service (several
shutdowns). On-site inspection revealed that several tubes were cracked and leaked; while many others were cracked, however,
the severity was less pronounced. Two types of superheater tubes samples were collected: one with butt-welded tubes and the
other with fillet-welded sleeve. The latter was found to be out of the boiler fireplace, and the sleeve was used as tubing
support to the boiler shell. Detailed investigation showed that the butt-welded tubes contained circumferential fatigue cracks
that initiated from the internal surface. The cracks initiated in the heat-affected zone and propagated as a result of tube
vibration. The variations in the tube internal diameter and tube wall thickness are expected to play a role in tube fatigue
failure. On the other hand, tubes with fillet-weld sleeve showed circumferential cracking as a result of fatigue crack initiation
from weld defects on the tube external surface. The high vibration during several unscheduled shutdowns in addition to several
other factors such as variations in tube inside diameter, wall thickness, and weld defects resulted in the initiation and
propagation of fatigue cracks and premature failure. White deposits, similar to those observed when boiler tubes failed by
caustic exposure, were seen in the vicinity of the tube cracks. Therefore, it was difficult to confirm whether the boiler
tubes failed because of the fatigue cracks or because of the caustic salts (pH control chemical). |
| |
Keywords: | 321 Stainless steel Superheater tubes Thermal incinerator Fatigue |
本文献已被 SpringerLink 等数据库收录! |
|