4. CONCLUSIONS
Considering the result from notched angular distorted wide cross joint tensile test for steal plate having thickness 40mm, 50mm and 60mm, followings can be concluded;
1) At test temperature -10℃, which is lower 10℃ than design temperature for actual pressurized LPG tank, all test specimens were fractured with bottle fracture by high stress over not only design_ allowable stress but also yield point of steel without unstable fracture by low stress.
2) Comparing critical COD with required COD which is decided from assumed defect and strict design condition, occurrence of unstable fracture on low stress can be considered not to be occurred.
3) In case of steel plate having thickness 50mm without PWHT, it has enough fracture toughness as same as PWHT carried out.
Accordingly, usage of high strength quench and tempered rolled steel plate, which has tensile strength more than 700N/mm2 having thickness more than 40mm below 50mm without PWHT for pressurized LPG tank is considered to be permitted.
Since class NK has admitted exemption of PWHT for steel plate having more than 40mm from 1990, 37 of the mentioned pressurized LPG carriers classified by Class NK have been on voyage. And any damages caused by fracture of steel plate have not found so far.
ACKNOWLEDGEMENTS
This paper summarizes some studies which have been carried out with the corporation by the following manufacturers.
IZUMI STEEL WORKS LTD.
FUJI CAR MFG. CO. LTD.
KAWASAKI HEAVY INDUSTRIES, LTD.
KAWASAKI STEEL CORPORATION
SUMITOMO METAL INDUSTRIES LTD.
NIPPON STEEL CORPORATION
The authors would like to express their sincere appreciation to the party concerned.
REFERBNCES
[1] T. Kubo, Y Senda, K. Ikezoe & others, "Result of Experiments about Pressurized LPG Tank using 74 kgf/mm2 High Strength Steel without PWHT Journal of High Pressure institute of Japan (HPI), May 1992
[2] T. Kanazawa & others. "Effect of Notch Acuity on Critical COD", Journal of the Society of Naval Architects of Japan. Vol. 148, 1980
[3] Y. Imura & others, "Development of New Steel and Welding Procedure for Hull Structure of Ice Breaking Vessels (2nd Report)", Journal of the Society of Naval Architects of, Japan, Vol. 157, 1985
[4] H. Kihara & others, "Effect of Notch Size, Angular Distortion and Residual Stress on Brittle Fracture Initiation Characteristics of Welded Joints for High Strength Steel (The 1st Report)", Journal of the Society of Naval Architects of Japan Vol. 125, 1969
[5] WES2805-1980, "Method of Assessment for Defects in Fusion Welded Joints with respect to Brittle Fracture", The Japan Welding Engineering Society
[6] H. Kashiwagi & others, "Condition and Study of Crack Occurrence for Spherical Tank using High Strength Steel", Journal of The Japan Society of Mechanical Engineers, Vol. 80, N0.703, June 1977
[7] T. Yada, "On Brittle Fracture Initiation Characteristic to Welded Structures", Journal of the Marine Engineering Society in Japan, Journal of the Society of Naval Architects of Japan Vol. 119, June 1966
[8] WES3003-1990, "Evaluation Criterion of Rolled Steels for Low Temperature Application", The Japan Welding Engineering Society
[9] Stanley T. Rolfe, John M. Barson. "Fracture and Fatigue Control in Structures", Prentice-Hall, Inc., 1977
