This paper deals with the stress analysis of a pipe flange connection with a spiral wound gasket under an internal pressure using the elasto-plastic finite element method taking account the hysteresis and the non-linearity in the stress-strain curve of the gasket. The effects of the different nominal diameter of the pipe flange connections from 2”to 20”on the contact gasket stress distributions, the hub stresses and the load factors are examined. As a result, it is found that the variations in the contact gasket stress distributions are substantial due to the flange rotation in the pipe flange connections with the larger nominal diameter. It is observed that a difference of the hub stresses between the initial clamping state and the internal pressure application is small in the pipe flange connections. It is also found that the value of the load factor of the connections decreases as the nominal diameter of the pipe flange increases. The results by the analysis are fairly consistent with the experimental results concerning the variation in the axial bolt force. By using the contact stress distributions and the results of the leakage tests, the new gasket constants are evaluated. In addition, a method to determine the bolt preload for a given tightness parameter is demonstrated. The bolt preload obtained by PVRC is found to be smaller than that obtained using the load factor.

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Prevention of large-scale brittle fracture inducing hull breakage is extremely important in order to secure the safety of vessels. Meanwhile classification societies specify the arrangement of grades E or EH steel plates as crack arrestor to critical hull structural members such as sheer strake, deck stringer etc. However, the clear arrestability requirement for the crack arrestor is not necessarily specified in the rules of the classification societies.
In this paper, the arrestability requirements for the crack arrestor, which intends for vessels under “normal operation” and “emergency situation” such as collision and stranding, are examined by fracture mechanics (K-concept) . Moreover based on the above examination, the first-ever crack arrestor concept to secure hull structural integrity under “emergency situation” is developed by the classification society.
Then this paper comes to the following conclusions:
(1) For vessels under “normal operation”, it is possible to arrest extremely long brittle crack where Kca value of crack arrestor plate at minimum service temperature (-10°C) secures 6000N⁄ mm^1.5and over.
(2) For vessels under “emergency situation”, it is possible to arrest extremely long brittle crack where Kca value of crack arrestor plate with 10% plastic strain at minimum service temperature (-10°C) secures 6000N⁄mm^1.5 and over.
(3) As the first-ever crack arrestor concept corresponding to “emergency situation”, the classification society (ClassNK) developed the innovative institution to identify and register the vessels with Descriptive Note “H-ARST” which denotes applying the higher crack arrestor to the specific hull structural members.

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A new methodology to guarantee the structural integrity of ceramics component has been proposed. This methodology consists of following three stages; (a) Crack-healing at the best conditions, (b) Proof test and (c) In-situ crack-healing. Above (a) is suitable to heal the surface cracks those were introduced by machining. Above (b) is necessary, because embedded flaws such as cracks and pores can not be healed at the present stage. For the flaw-healing, oxygen is necessary. If, crack initiated during service, structural integrity maybe reduced considerably depending on crack size. However, if material has in-situ crack-healing ability and heal the crack during service, it would be desirable for the high structural integrity. Using the past studies related to crack-healing, bending and fatigue strength of crack-healed member at elevated temperature, in-situ crack-healing behavior and proof test theory, usefulness of this new concept has been explained concretely.

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Monotonic four-point bending tests were conducted using tee pipe specimens having local wall thinning. The effects of local wall thinning on the fracture behaviors of tee pipe were investigated. Local wall thinning was machined on the inside of pipes in order to simulate erosion⁄corrosion metal loss. The configurations of the eroded area were l =100mm in eroded axial length, d⁄t=0. 5 and 0. 8 in eroded ratio, and 2θ=90°in eroded angle. The area undergoing local wall thinning was subjected to either tensile or compressive stress. Fracture behaviors of the tee pipes were compared with those of straight pipes. It was found that fracture type could be classified into ovalization, local buckling, and crack initiation, depending on pipe shape, eroded ratio, and stress at the eroded area. Three-dimensional elasto-plastic analyses were also carried out using the Finite Element Method, which is able to accurately simulate fracture behaviors.

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H-II launch vehicle, the large Japanese launcher placing a 4000kg class satellite into GTO, failed in the two flights of No. 5 and No. 8, after the successful 29 flights from N-I to H-II. Both failures were caused by malfunction of the cryogenic engine, the second stage engine LE-5A or first stage engine LE-7, respectively. The incidents, the causes, and the corrective actions of these failures are reported in detail in this paper. The failures brought us the precious experiences and a lot of lessons and learn.
Important lessons are related with small amount of products such as a launch vehicle, which happen to fail for uneven quality by handcraft. To solve this problem, it is noted that critical manufacturing process should be distinguished to control very important characteristics of products, and that all specifications on critical processes should be determined on well-grounded technical data. In development phase, the design margin of important characteristics should be assured by testing the varied nature within defined specifications.
H-IIA flew successfully in its maiden flight on August 29, 2001 to put LRE (laser Ranging Experiment) into GTO precisely. The author believes that this success results from great efforts of many engineers and researchers who learned the precious lessons of H-II failures. Rocket technology will make progress to be matured by a lot of lessons and learn from failure.

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