Design Conditions and Criteria

Design conditions in ASME B31.3 are specifically intended for pressure design. The design pressure and temperature are the most severe coincident conditions, defined as the conditions that result in the greatest pipe wall thickness or highest required pressure class or other component rating. Design conditions are not intended to be a combination of the highest potential pressure and the highest potential temperature, unless such conditions occur at the same time.

Enhanced Boost Factor for Three-Level Quasi-Switched Boost T-Type Inverter

A new modulation strategy has been introduced in this paper in order to enhance the boost factor for the three-level quasi-switched boost T-type inverter (3L-qSBT2I). Under this approach, the component rating of power devices is significantly decreased. Moreover, the use of a larger boost factor produces a smaller shoot-through current. This benefit leads to reducing the conduction loss significantly. Furthermore, the neutral voltage unbalance is also considered. The duty cycle of two active switches of a quasi-switched boost (qSB) network is redetermined based on actual capacitor voltages to recovery balance condition. Noted that the boost factor will not be affected by the proposed capacitor voltage balance strategy. The proposed method is taken into account to be compared with other previous studies. The operation principle and overall control strategy for this configuration are also detailed. The simulation and experiment are implemented with the help of PSIM software and laboratory prototype to demonstrate the accuracy of this strategy.

Multi-Stage Cascaded Quasi Z-Source Inverter System for Renewable Energy Applications

Multi-stage cascaded quasi Z-source inverter (qZSI) features a lesser shoot-through duty ratio for the same boost factor of the input voltage, but the traditional qZSI has the disadvantage of possessing increased shoot-through ratio and very high component stress at the same voltage boost factor. The whole idea of this work is to present a multi-stage cascaded quasi Z-source inverter for application to photovoltaic power system. Three-stage cascaded qZSI is obtained by adding two diodes, two inductances and three capacitances to the traditional quasi Z-source network. Due to the cascaded structure and qZSI topology, the proposed system acquires all the advantages of impedance inverter that can realize boost/buck function in a single-stage with improved reliability, lower component rating, constant DC current from source and good power quality. Besides, the three-stage cascaded solution the shoot-through duty cycle by 25% at the same voltage boost factor. The topological characteristics of three-stage cascaded qZSI system is analysed and operating principles are discussed. An experimental prototype is built to test the three-stage cascaded qZSI module. Simulation and experimental results are presented to demonstrate the validity of the proposed system.

Bolted Flange Joints Under External Moments: An Analysis Using the Compound Gasket Approach for Spiral Wound Gaskets

It is common to rate a piping system to its weakest component to maximize flexibility for future operations. In many situations, the bolted flange joint is the lowest rated component. Rating a system for its full flange rating reduces the flange’s capacity to carry external bending moments. In the past, moments on flanged joints have been evaluated by using the concept of equivalent pressure, first presented in the Kellogg Design of Piping Systems. Operating moments are converted to an equivalent pressure. This equivalent pressure is added to the design pressure and compared against a limit. According to conventional practices, the design pressure plus the equivalent pressure must not exceed the rating pressure. Consequently, designing up to the flange rating pressure presents an issue, since no margin is left for the effects of external moments on flange joints. Depending on the circumstances, many designers have compensated by permitting the combined design pressure and equivalent pressure to be as high as twice the flange rating. In this paper, the authors demonstrate a robust methodology to define an appropriate limit for operating moments on bolted flange joints. Using the calculation methodologies of EN-1591-1, the authors calculate the maximum external moment that various classes of standard ASME B16.5 flanges (for Group 1.1 materials) can tolerate over a range of temperatures and present a representative sample. Conclusions are drawn about appropriate limits for moments on flanges and are compared to results using the equivalent pressure method.