Failure Analysis of Bank-Wall Side Boiler Tube in a Petrochemical Plant

Abstract

Failure analysis of the petrochemical plant’s bank-wall side boiler tube has been conducted to determine the root cause of tube failure. The tube material is low carbon steel ASTM A178 grade A. Visual examinations of the cracked surface revealed that the fractured surface is flat, without plastic deformation, and several longitudinal and transverse fissures are present. The SEM and optical microscope examinations show that the cracks were intergranular and transgranular. A hydrogen attack caused the intergranular crack, and thermal fatigue produced the transgranular crack. Boiler tube failure was caused by a steam blanket on the sloping tube’s top inner diameter that induced iron oxide deposition and accumulation. Hydrogen was produced after a chemical reaction at the deposit-metal interface between the iron oxide deposit and ingress steam. Local temperature variation on the top part of the sloped tube occurred during the splashing and evaporation of water, promoting thermal fatigue.

Keywords

• bank-wall side boiler tube
• low carbon steel
• under deposit corrosion
• hydrogen attack
• thermal fatigue