Significance and Control of Lamellar Tearing of Steel Plate in the Shipbuilding Industry

摘要

Lamellar tearing is a separation in the parent or base metal caused by through-thickness strains. These strains are usually induced by weld metal shrinkage under conditions of high restraint. This manual provides specific recommendations for controlling lamellar tearing in the types of steels used in the construction of ships and offshore platforms. A briefdescription of the characteristics and mechanism of lamellar tearing shows that for lamellar tearing to occur there must be a critical combination of material susceptibility, and welding procedures and joint design which permit the development of high through-thickness strains. Tee (T) and corner joints, used extensively in ships and offshore structures, are the two basic joint configurations most susceptible lamellar tearing. However, the incidence of lamellar tearing has been extremely rare in shipbuilding. The problem of lamellar tearing is considerably more significant in mobile and fixed offshore drilling platforms which use thick plates in highly restrained T-and cruciform joints. The factors which contribute to and influence lamellar tearing are grouped into three categories: joint design, material selection and fabrication procedures. For each parameter recommendations are presented for reducing the risk of lamellar tearing. Inquiries made to the major ship classification societies indicate that the most successful and cost-effective method of preventing lamellar tearing is the use of steels with improved through-thickness (Z-direction) properties at susceptible connections. Methods for the post-welding detection and repair of lamellar tears are reviewed as are the test procedures developed to date for determining the susceptibility of steel plates to lamellar tearing. (Author)