By Aubry Shackelford, Inglenook Engineering, Inc.

In high-velocity gas flows, such as those that may occur within the discharge piping of a pressure-relief or depressurization valve, the temperature experienced at the wall of the pipe through which the gas is flowing can be much higher than the flowing stream’s “static” temperature. In fact, the wall temperature approaches the stagnation temperature, which is the temperature that would be obtained if the fluid were brought adiabatically and reversibly (isentropically) to rest. Recent investigations into the potential for fluid temperatures to exist below the embrittlement temperature of relief-valve discharge piping have shown that low-flowing temperatures can exist for a wide variety of systems, including: flashing liquids or two-phase flow; autorefrigeration and Joule-Thompson cooling in response to pressure drops; and high-velocity gas flow.  »

By Jerry Spindler, Endress + Hauser, Inc.

Typical discussions of flowmeter selection address specifications, technologies, accuracies and performance, but there are many other steps that are not normally considered. This article focuses on these often overlooked criteria, which inevitably have far-reaching and costly implications over the life of the flow-measurement instrument chosen. Every aspect of a flowmeter that impacts an organization’s bottom line must be given consideration, even if it does not appear to affect the original purchase price. There are several less-than-obvious issues to review with any supplier you are doing business with that have cost-saving implications. Failing to pay attention to these factors early in the discussion could lead to greater costs in the long run. It pays to take the time up front to ensure you have made the proper selection. »