TPT March 2011

response times than ever before in applications that call for a wake frequency calculation. Chris Chant, business development manager at Okazaki Manufacturing Company (OMC) commented, “To- day, petrochemical plants tend to use smaller diameter pipelines but with higher fluid velocities. This means that the design of the thermowell is critical. For example, the original ASME standard did not provide guid- ance on liquid mass, as the standard was originally developed for steam applications. However, for oil and petrochemical pipeline applications, Okazaki has always taken liquid density or mass into account when siz- ing thermowells. In fact, we are the only thermowell supplier who can provide customers with credible design alternatives to standard tapered, straight and stepped thermowells.” Many thermowell suppliers incorporate a velocity collar on a thermowell in order to move the point of vibration or resonance. But adding a velocity collar means the thermowell needs to be manufactured to a very high tol- erance (on the collar OD) and that the corresponding nozzle is similarly machined to suit. This tolerance must be an interference fit so that no resonance can occur. If supplied and fitted correctly the collar only moves the point of resonance and does not solve the problem. While this seems to work, the extra costs incurred by the thermowell manufacturer and installation contractor are passed on to the buyer, increasing the overall cost. The addition of the collar also increases the need for stocking specific spares for a single measuring point. “Velocity collars are not always the answer,” said Mr Chant. “In effect, by adding a collar, you’re simply moving the problem somewhere else. What customers need is a genuine alternative, and that is why we’ve devel- oped the VortexWell, a unique design of thermowell that incorporates a helical strake design, rather like on a car aerial or cooling tower fins.” After extensive R&D using the latest CFD software, as well as independent evaluation, OMC was able to visualise and accurately compare the flow behaviour of the VortexWell helical strake design with a standard tapered thermowell. In the analyses, the standard tapered thermowell showed classic shedding behaviour as expected, whereas the VortexWell demonstrated no signs of regular flow behaviour. The VortexWell helical strake design disturbed the flow sufficiently to interrupt the regular formation of vortices. Whilst a small vortex was observed in the wake of the VortexWell this was a localised stagnation point and didn’t shed. However, the most significant comparison made was with regard to the pressure fields. For the standard ta- pered well design, an oscillating pressure field was observed around the structure. The VortexWell displayed a constant and stable pressure field, presenting no dynamic variations. As this pressure is the source of vortex-induced vibrations, it can be assumed that the VortexWell would experience a significant improvement in practise compared to the standard thermowell design. In further tests, this time using FEA, OMC found that the ASME calculations used by thermowell manufac- turers could be placing significant limitations on the safety of petrochemical applications. Using the ASME calculations gave the lowest natural frequency of vibration for the standard tapered thermowell to be 68.5Hz. However, OMC’s own FEA results showed a corresponding value of 90.3Hz, a difference of more than 30%. This highlights that the ASME calculations design rules include assumptions that can lead to considerable inaccuracies when designing thermowells for petrochemical applications. The risk of a thermowell failing due to under-engineering, or the extra costs incurred by the end user because of an over-engineered thermowell, can both be avoided if the buyer works with an experienced thermowell supplier. Mr Chant concluded: “Okazaki has been providing technical support and design services to the oil, gas and petrochemicals industry for many years now, working to Japanese standards, which are often more stringent than the ASME equivalent. Therefore, for Okazaki, the new standard simply reinforces that what we’ve been providing our customers with for many years is the best approach.” Okazaki Manufacturing Company designs and manufactures a wide range of high accuracy temperature measurement products. All of OMC’s temperature products can be fully certified for use in potentially explo- sive atmospheres to international standards and to country-specific variations. OMC temperature assemblies are certified by FM for NEC (USA) standards, BASEEFA for IECEx Product Approval and for type approval in compliance with EU ATEX directives. Country-specific approvals include GOST K, GOST R, NEPSI (China) and KOSHA (Korea). Стандарт РТС 19.3 ASME (Американское общество инженеров-механиков) на каналы для ввода термопар претерпевает значительные изменения Компании, которые используют измерительные каналы для ввода термопар в нефтегазовой и нефтехимической промышленности, теперь должны будут соблюдать требования нового пересмотренного стандарта ASME PTC 19.3 (2010), претерпевшего свой первый за более чем 35