CAT (Crack Arrest Temperature) Test Method Using Local Temperature Gradient System for Estimate of Fracture Toughness With Shipbuilding Steel
- Gyubaek An (Chosun university) | Hong-Yeol Bae (POSCO) | Boyoung Jeong (POSCO) | Youngho An (POSCO) | Hongchel Jeong (POSCO)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- crack arrest temperature (CAT), brittle crack arrest (BCA), fracture toughness, local temperature gradient (LTG), Brittle fracture
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- 8 since 2007
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The evaluation of brittle crack arrest temperature have two different methods. First one is isothermal crack arrest test, and the other Local Temperature Gradient (LTG). Concept of CAT by isothermal crack arrest test was proposed by C. Wiesner (Wiesner, 1994; Smedley, 1989; Sumi, 1990) for application of low temperature steels for LPG tanks. The proposed test method was double-tension type brittle crack arrest with EB (Electronic Beam) melt-run which acts as crack initiator and as crack runway. There are several disadvantages to the method of evaluating the CAT value by starting the brittle crack from the electron beam welding (EBW) part. However, the LTG method doesn’t need additional EBW to make a brittle. Recently brittle crack arrest (BCA) steels are used in upper deck or hatch side coaming of large container ships to prevent fatal brittle fracture accident. International Association of Classification Societies (IACS) defined BCA steels for container ships using Kca requirement or CAT requirement in the unified rule (UR) S33 (IACS, 2013). Therefore, when shipyard uses the BCA steel to construct large container ship, CAT or Kca will be evaluated.
In this study, LTG test method will be introduced to evaluate brittle crack temperature. Also both test methods were compared on the same specimens to verify LTG method.
Container ships have increasingly become larger to achieve economical transportation (i.e., above 22,000 twenty-foot equivalent units (TEU)); hence, the demand for stronger and thicker steel plates has recently been increased in the shipbuilding industry. Accordingly, EH47 or higher-grade steels with 80-100 mm thickness have been introduced into the construction of real ship structures. With containerships becoming larger, the steel plate fracture toughness has become an important factor for the integrity of ship structures. It is a challenge to construct the large ship structure without considering unstable fracture.
Previous researchers carried out the studies about brittle crack arrest problems (Inoue, 2007, An, 2014). Steel manufacturers have developed brittle crack arrest steel (BCA steel) to avoid brittle fracture. Classification society has published several guidelines and rules for brittle crack arrest design, i.e. “Guideline for brittle crack arrest designh„ (Class NK, GL, 2008) which defines the required brittle crack arrest toughness, Kca for BCA steels in Hatch Side Coaming (HSC) and Upper Deck (UD). Brittle crack arrest concept for recent container ships is an internationally focused issue. International Association of Classification Society (IACS) also prescribed the unified requirement (UR) for brittle crack arrest design and brittle crack arrest design. IACS UR defines BCA steel plates for HSC and UD with either Kca value or CAT. The Kca value is a kind of fracture toughness parameter, and it can be evaluated by temperature gradient ESSO test. The recent edition of IACS UR prescribes Kca not to be less than 6,000 N/mm3/2 at −10°C for plate thickness up to 80 mm. Also BCA steel was defined with Kca value. However brittle crack arrest parameter can be described with CAT value. The Kca test method has a typical procedure (WES2815, 2014) in spite that CAT test method has no formal procedure.
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