Considerable interest has developed in the engineering community concerning the damage to the floating roof of oil storage tanks due to liquid sloshing from earthquake loading. Engineering groups in countries bordering the circum-Pacific seismic belt in particular are devoting extensive efforts to obtaining solutions capable of identifying vulnerable roof designs and developing modifications to improve strength. The recent efforts of the Japanese Fire Disaster and Management Authority (FDMA) as a result of 1995 Kobe and the 2003 Tokachi-Oki earthquakes are examples of recent work in this area. This paper focuses on efforts to analyze floating roof structures for stress and stability under typical earthquake velocity spectrums using advanced finite element methods. It employs ideas included in the Japanese FDMA studies, work done as part of the ASCE Committee on Gas and Liquid Fuel Lifelines, and some original methods developed at ExxonMobil. It has been applied to several tank designs and been submitted as a suitable advance analysis method to the Japanese FDMA. The paper provides both the theoretical foundation as well as an example covering typical tank geometry.
Stress intensity factors were calculated for a modified round bend bar (MRBB) using 3-D finite element analysis. The results were compared with published solutions for a rectangular and round bend bars. The stress intensity values for the MRBB are between those for the two other geometries as expected. The stress intensity solutions were non-dimensionalized utilizing limit solution for short and long cracks.
A recent high temperature steam header case study is extended here to include alternate methods of review, including elastic stress and isochronous strain analysis and accompanying limits. The previous creep analysis was formulated to be exactly consistent with the allowable stress basis, such that alternate design analysis methods and criteria could be rigorously compared. In the current work, the selection of the appropriate limits for elastic results is investigated, as discussed in previous literature, which is motivated by stress redistribution characteristics of the primary (and secondary) loading in a typical header. Next, use of isochronous stress-strain curves generated from the same consistent (Omega) creep model are used for analysis and compared to candidate strain limits. The analyses show that both elastic and isochronous analysis have potential for effective creep design in the context of current high temperature design modernization activities. Finally, multiaxial creep behavior and its effect on detailed creep, elastic and isochronous stress-strain analyses and corresponding limits is also introduced.
When exposed to air at elevated temperatures, graphite oxidizes by a reaction between carbon and oxygen forming carbon monoxide and carbon dioxide. Using graphite as a sealing material and exposing it to the aforementioned environment, the reaction consumes graphite which degrades the sealing performance leading to leakage and seal unreliability. As a response to industry needs, graphite and sealing element manufacturers offer “oxidation inhibited” or more simply “inhibited” grades of graphite that show improved resistance to oxidation, however, there is no industry accepted definition that assures the purchaser that these grades of graphite do in fact have sufficient oxidation resistance for their specific application. This paper proposes a performance based definition for oxidation inhibited graphite and a protocol to convert test results to index any graphite resistance to oxidation. Furthermore, the paper provides a methodology to determine temperature limits and/or service life expectations for any graphite grade.
This paper explores torque wrench accuracy, one source of the overall inaccuracy associated with bolted flange joint assembly. The accuracy and repeatability of various pneumatic torque wrenches were tested and analyzed. Pneumatic torque wrenches were benchmarked against a hydraulic wrench which has a lower perceived bolt load scatter. The testing was performed on two mock-up flanges, NPS 8 Class 150 and NPS 16 Class 300 raised-face flanges with spiral-wound gaskets. The analysis compares the accuracy and repeatability of the following: each tool versus its manufacturer’s claims; duplicate models of the same tool; and overall tool type (pneumatic or hydraulic) versus another tool type. Because accuracy is closely related to tool calibration, torque wrench calibration method and frequency are also discussed. There are several methods of applying axial load through torque that have been used within the industrial assembly of Bolted Flanged Joint Assemblies (BFJA’s). The most common tool used within the industry is the manual torque “clicker” wrench which traditionally allows an assembler to reach 600ft/lbs. While companies make wrenches that achieve higher amounts of torque, they are harder on the assembler to use so other tools, such as hydraulic and pneumatic torque wrenches (Powered Equipment), that require less physical strength are used instead. This paper will discuss the accuracy and repeatability of pneumatic and hydraulic wrenches and compare them to the manufacturer’s/industry standards.
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