Primary Membrane Stress Research Articles

Stress Classification for Elevated Temperature Service

The paper presents two procedures which can be used to classify the stresses originating at the structural discontinuities of pressure vessel and piping components designed for elevated temperature service. The stress classification is based upon the definitions of primary and secondary stress intensities which are provided in the ASME Boiler and Pressure Vessel Code, Sections III and VIII. The intent is not to reclassify primary stresses, but to provide a designer with practical guidance in evaluating the primary characteristics of thermal and structural discontinuity pressure stresses. Two objectives for an appropriate classification of stresses are: (a) to reduce undue conservatism in elevated temperature Code Case N-47 design rules when primary stress is only a small fraction of secondary stress, and (b) to provide a sufficient margin of safety for extreme (Level D) loadings when the primary local and general membrane stress levels are close to the yield point of the material at structural discontinuities.

Thermal Ratcheting Criteria and Behavior of Piping Elbows

A thermal ratcheting test was performed using an elbow model test specimen subjected to sustained primary load and cyclic thermal transient strains. Under severe loading conditions incremental longitudinal strains are observed in the region where a circumferential angle is around ± π/9 from the side of the elbow, while the elbow cross section was ovalized cycle by cycle causing large circumferential bending strain at around φ = π/2. It was shown by the test and analyses that the maximum primary membrane stress in an elbow is an essential parameter for thermal ratcheting behavior of elbows. Direct application of thermal ratcheting criteria in the ASME Code Case N-47 showed considerable conservative estimation and an improved thermal ratcheting criterion for elbows is recommended.

Design and related experiments of JT-60 divertor coils.

The JT-60 divertor coils produce a separatrix configuration in divertor operations of JT-60. A suitable separatrix configuration was obtained for a plasma current of 2.1 MA with coil ampere turns of ± 0.755 MAT. A high primary membrane stress of 52 MPa was permissible at the welded joints of the copper conductor made on the site. The mechanical strength of the joints welded in a factory was also improved by means of a press treatment. Electric insulation materials were selected considering a degradation of with stand voltage characteristics due to high cyclic mechanical strain. Vacuum-tight coil cases were composed of rigid rings and U-shaped bellows made of Inconel-625 alloy, and designed to withstand plasma disruption with a current decay time constant of 3 ms. The maximum temperature of the conductor in the periodic operation of divertor discharges was below 155°C which was the allowable temperature of the coil insulation. Molybdenum armor plates coated with titanium carbide and Inconel-625 bellows cov...

Increased Allowable Stresses for Earthquake and Wind Loads in Section VIII, Division 1

Abstract There has been a need for some time to provide rules for allowable stresses for short-time and infrequent loading such as earthquake and wind loads in Section VIII, Division 1 of the Boiler and Pressure Vessel Code. Such rules exist in Section VIII, Division 2, in Section III, and in many other Codes. Division 1 has been silent on the subject. This has caused some manufacturers to make their own rules, and some to overdesign their hardware. Neither situation is without problems. Therefore, in 1979 the Boiler and Pressure Vessel Committee undertook to develop rules for Section VIII, Division 1. This work resulted in the addition of paragraph UG-23(d) to the Code, in the Summer, 1983 Addenda. The paragraph permits an increase in general primary membrane stress of 20 percent for earthquake and wind loads for temperatures below the creep regime.

The Integrated-Blanket-Coil Concept Applied to the Poloidal Field and Blanket Systems of a Tokamak Reactor

A novel concept is proposed for combining the blanket and coil functions of a fusion reactor into a single component. This concept, designated the integrated-blanket-coil (IBC) concept, is applied to the poloidal field and blanket systems of a Tokamak reactor. An examination of resistive power losses in the IBC suggests that these losses can be limited to less than or equal to 10% of the fusion thermal power. By assuming a sandwich construction for the IBC walls, MHD-induced pressure drops and associated pressure stresses are shown to be modest and well below design limits. For the stainless steel reference case examined in this paper, the MHD-induced pressure drop was estimated to be approx. 1/3 MPa and the associated primary membrane stress was estimated to be approx. 47 MPa. The preliminary analyses presented in this paper indicate that the IBC concept offers promise as a means for making fusion reactors more compact by combining blanket and coils functions in a single component.