Characteristics of skid pipe failure in walking beam reheating furnace of an integrated steel plant. (January 2020)

• Record Type: Journal Article
• Authors: Sahoo, G.; Kumar, P.; Sarkar, B.; Dhua, S.K.; Kumar, S.
• Is Part Of: Engineering failure analysis. Volume 107(2020)
• Publication Date: 2020-01
• Subjects: Skid pipe -- Hard water -- Widmanstatten ferrite -- Oxidation -- Wustite; System failures (Engineering) -- Periodicals; Fracture mechanics -- Periodicals; Reliability (Engineering) -- Periodicals; Pannes -- Périodiques; Rupture, Mécanique de la -- Périodiques; Fiabilité -- Périodiques; Fracture mechanics; Reliability (Engineering); System failures (Engineering); Periodicals; Electronic journals; 620.112
• DOI: 10.1016/j.engfailanal.2019.104212
• Languages: English
• ISSNs: 1350-6307

Abstract

Highlights: Frequent failure of skid pipe in walking beam reheating furnace was major problem of an integrated steel plant. The scale deposits and increased temperature of the skid pipe before failure lead to the sever oxidation of metal into wustite and thinning of the pipe. The microstructure of the affected region changed to ferrite pearlite away from the rupture and pearlite towards rupture, which was originally spherodized annealed microstructure consisting of dispersed carbides in ferrite matrix and degenerated in the unaffected region of pipe. High temperature dynamic transformation of widmanstatten ferrite occurred at the tip of rupture attributed to overheating and cyclic stress. Preventing overheating and dosing of water decreased failure significantly. Abstract: Moving beam of S355J0 grade seamless steel pipe of EN 10025 specification was failing frequently particularly below the retainer ring of skid pipe, which is located under the hearth level of walking beam furnace in an integrated steel plant. The pipe samples both at unaffected and affected regions were examined using scanning electron microscopy (SEM) and light optical microscopy. The oxidized layer and scale deposits were analyzed using X-ray fluorescence spectrometer (XRF) and X-ray diffractometer (XRD). The microstructure of the affected region changed to ferrite pearlite away from the rupture, degenerated pearlite towards rupture and widmanstatten ferrite at the tip of the rupture. The dynamic transformation of ferrite has been attributed to overheating coupled with cyclic stress. On the other hand, the unaffected region of pipe revealed original spherodized annealed microstructure consisting of dispersed carbides in ferrite matrix. The scale deposit constituents were inferred as oxides of Ca, Mg and Si from XRF study, which were confirmed as CaMgSi2 O6 and (Mg, Ca)CO3 and the oxidized scales consisted of FeO, Fe2 O3 and Fe3 O4 . While the hardness of makeup water (89.0 mg/L) was moderately soft and well suited for industrial use, the re-circulating water in skid pipe showed much higher hardness (142.4 mg/L). The oxidation of metal and increase in hardness of water resulting in scale deposits have been attributed to the exposure of skid pipe to high temperature, which finally led to its rupture.