Lloyds Gr.a Steel Plate

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OFFSHORE TECHNOLOGY REPORT - OTO 2000 001 FRACTURE PROPERTIES OF GRADE 'A' SHIP PLATE Prepared by British Steel Limited Swinden Technology Centre Moorgate Rotherham S60 3AR Date of Issue: January 2000 Health and Safety Executive This report is made available by the Health and Safety Executive as part of a series of reports of work which has been supported by funds provided by the Executive. Neither the Executive, nor the contractors concerned assume any liability for the reports nor do the
  FRACTURE PROPERTIES OFGRADE 'A' SHIP PLATE Prepared by British Steel LimitedSwinden Technology CentreMoorgateRotherhamS60 3ARDate of Issue: January 2000Health and Safety Executive OFFSHORE TECHNOLOGYREPORT - OTO2000 001  This report is made available by the Health and Safety Executive aspart of a series of reports of work which has been supported byfunds provided by the Executive. Neither the Executive, nor thecontractors concerned assume any liability for the reports nor dothey necessarily reflect the views or policy of the Executive.Reports in the OTO series can be obtained from Research Admin,OSD, Bootle, Merseyside, L20 3DLFax: 0151 951 3098ii  SUMMARY A programme of work was undertaken to generate fracture property data, including a measureof the degree of scatter, from as rolled ship plate material, nominally Lloyd's Grade 'A',representing the lower end of the Charpy toughness spectrum. This was in response toconcerns regarding the safety of sea going vessels, particularly when an extension of the servicelife is envisaged or a change of use, for example to offshore production or storage vessels, isconsidered which would require structural integrity assessments.Seven plates, which were not necessarily certified Grade A plates but were offered by stockistsas suitable alternatives, were examined. The selection was dictated by the desire to includeplates at the lower end of the toughness spectrum. These, therefore, srcinated from a numberof steel suppliers and had widely differing chemistries.The test certificates did not always reflect the actual chemistries or mechanical properties.Some of the plates exhibited strength levels which were outside the limits for Grade A. All of the plates were homogeneous and the material properties were not influenced by samplingpositions.In general there is no minimum Charpy impact energy value specified for Grade A, although the1997 amendments to the Lloyd's Register rules and regulations for Classification of Ships nowinclude a Charpy impact energy requirement for Grade A plates of 27 J in the longitudinaldirection and 20 J in the transverse direction at +20°C. The Charpy impact energy for theplates in this current test programme exceeded 27 J at +20°C in both orientations.Pellini Drop weight tests were carried out on some of the plates, fully recognising that three of the four plates were less than the minimum plate thickness covered by the Drop Weight teststandard thus yielding non-standard specimens.The fracture toughness of four plates was measured using high loading rate and resultscompared with the criterion, proposed by Sumpter, that the toughness K mat must exceed a valueof 125 MPa √ m at a loading rate of 10 4 MPa √ m/s or higher at a test temperature reflectingoperating conditions for ships. Three plates with thickness up to 15 mm had adequatetoughness such that K mat exceeded the minimum stated above at a test temperature of -10°Cwhich is the minimum operating air temperature for the North Sea. The only 20 mm thick platein this study failed to meet the minimum toughness level as described above.The effect of strain ageing treatment on toughness properties was measured on one plate andthe Charpy toughness of strain-aged specimens was, as expected, worse than the correspondingparent plate material with the 50% FATT approximately 50°C higher.The effect of welding on HAZ toughness was studied by applying thermal simulation treatment.The coarse grained HAZ was simulated by using single cycle thermal treatments correspondingto nominally 1.5 and 5.0 kJ/mm heat input welds and the toughness was characterised by theCharpy impact toughness test. 50% FATT increased by up to 15°C for the lower heat input and40°C for the higher heat input welds for the two plates studied. It is likely that this will be theworst case view of the toughness compared to this region in a real weld because the thermallysimulated specimens contain uniform microstructure of low toughness through the specimencross-section. A specimen taken from a real weld is likely to contain a mixture of microstructure ranging from low to relatively high toughness.iii  CONTENTS Page1.INTRODUCTION12.BACKGROUND33.MATERIALS54.TEST PROGRAMME75.RESULTS AND DISCUSSION95.1Grades and Chemical Composition95.2Mechanical Properties95.3Charpy Impact Energy95.4Pellini Nil Ductility Transition Temperature105.5High Rate Fracture Tests105.6HAZ Thermal Simulation125.7Strain Ageing126.CONCLUSIONS13ACKNOWLEDGEMENTS15REFERENCES17TABLES19FIGURES23iv
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