Hazard Analysis with STPA Methods: Application to Mould Level Control Within Continuous Casting Free Stream Operations
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Date
2025-04-30
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International Journal of Safety and Security Engineering Vol. 15, No. 4, April, 2025, pp. 835-846
Abstract
In the continuous casting process, maintaining precise control over the mould level is
essential to ensure product quality, prevent defects, and optimize operational efficiency.
Mould Level Control (MLC) in Free Stream operations presents unique challenges, as it
requires accurate and stable control amidst dynamic process variations and complex
interdependencies between sensors, actuators, and controllers. This paper presents a case
study conducted at a steel plant located in Bellara, El Milia – Jijel, Algeria, which utilizes
a 120-ton Electric Arc Furnace (EAF) operating at a tap temperature of approximately
1630℃. The process is controlled via a Siemens PLC-based automation system.
Continuous casting is performed using a curved-type machine (3BLC 0905), featuring
five strands, a casting section of 150 ×150 mm, and a maximum casting speed of 3.5
m/min. The system includes a ladle turret, 30-ton tundish, mould, and withdrawal system,
and is used to produce low-carbon steel grades (C < 0.13%, Al < 0.006%). SystemTheoretic Process Analysis (STPA) is applied to identify and mitigate hazards in MLC
systems under Free Stream conditions. The analysis highlights unsafe control actions
(UCAs), actuator delays, and sensor inaccuracies, and proposes improvements in control
logic, calibration, and response strategies to enhance system safety and reliability.