News & Views, Volume 49 | Materials Lab Featured Damage Mechanism - Soot Blower Erosion

News & Views, Volume 49 | Materials Lab Featured Damage Mechanism: Soot Blower Erosion

News & Views, Volume 49 | Materials Lab Featured Damage Mechanism - Soot Blower ErosionBy:  Wendy Weiss

Soot blower erosion (SBE) is caused by mechanical removal of tube material due to the impingement on the tube wall of particles entrained in the “wet” blower steam. As the erosion becomes more severe, the tube wall thickness is reduced and eventually internal pressure causes the tube rupture.

Mechanism

SBE is due to the loss of tube material caused by the impingement of ash particles entrained in the blowing steam on the tube OD surface.  In addition to the direct loss of material by the mechanical erosion, SBE also removes the protective fireside oxide. (Where the erosion only affects the protective oxide layer on the fireside surface, the damage is more properly characterized as erosion-corrosion.) Due to the parabolic nature of the oxidation process, the fireside oxidation rate of the freshly exposed metal is increased. The rate of damage caused by the steam is related to the velocity and physical properties of the ash, the velocity of the particles and the approach or impact angle. While the damage sustained by the tube is a function of its resistance to erosion, its composition, and its operating temperature, the properties of the impinging particles are more influential in determining the rate of wall loss.

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News & Views, Volume 48 | Metallurgical Lab Case Study – Grade 91 Elbows Cracked Before Installation

By:  Wendy Weiss and Terry Totemeier

News & View, Volume 48 | Metallurgical Lab Case Study - Grade 91 Elbows Cracked Before InstallationStructural Integrity (SI) personnel visited a power plant construction site to examine four Grade 91 elbows (ASTM A234-WP91 20-inch OD Sch. 60) that were found to contain axially oriented surface indications. The elbows had not yet been installed. The indications were initially noticed during magnetic particle testing (MT) after one end of an elbow was field welded to a straight section and post weld heat treated (PWHT). Subsequently, three additional similarly welded elbows were inspected and indications were found at both the welded (inlet) and open (outlet) ends of three elbows. The elbow with the most significant indications was selected for SI’s on-site examinations. Figure 1 shows the inlet and outlet ends of the selected elbow.

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