Steam Blanketing | Materials And Corrosion Control
Damage Mechanism |
Steam Blanketing |
Damage Description |
· In steam generation, when heat flow balance is disturbed, individual bubbles join to form a steam blanket.
· Form of Short Term Overheating in steam generating units leading to rapid tube rupture. · Failure occurs as a result of the hoop stress in the tube from the internal steam pressure at elevated temperature. · Flame impingement from misdirected or damaged burners can provide a heat flux greater than the steam generating tube can accommodate. · Heat flux and fluid flow are critical factors. · On the water side, anything that restricts fluid flow (for example, pinhole leaks lower in the steam circuit) will reduce fluid flow and can lead to Steam Blanketing conditions. |
Affected Materials |
Carbon steel and low alloy steels. |
Critical Factors |
· Heat flux
· Fluid flow rate |
Affected Units or Equipment |
· Steam boilers
· Generating tubes |
Appearance or Morphology of Damage |
· Similar to short-term overheating, fish-mouth tube rupture |
Prevention/Mitigation |
· When steam blanketing condition has developed, tube rupture will quickly follow. Proper burner management should be practiced to minimize flame impingement. · Proper Boiler Feedwater (BFW) treatment can help prevent some conditions that can lead to restricted fluid flow. · Tubes should be visually inspected for bulging. · Undertake Boiler Condition Assessment |
Inspection and Monitoring |
· Burners should be properly maintained to prevent flame impingement. · Perform Boiler Condition Assessment |
Inspection Frequency |
As determined by OSI |
Key Performance Indicators (KPIs) |
· # Tube failures attributed to steam blanketing
· # % of boiler tubes inspected by conventional/advanced NDT (IRIS, Eddy Current) |
Plant Integrity Windows (PIWs) |
· Not Applicable |
Competencies and Training |
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Reference Resources (Standards/GIs/BPs) |
· API RP571 (DM #61) |