Are your mill's thermowells safe?Application: Mills can use the proposed method to help in the selection and application of thermowells. Published thermowell design standards Design standards Specifications of materials, physical measurements, processes, performance of products, and characteristics of services rendered. Design standards may be established by individual manufacturers, trade associations, and national or do not cover corrosive environments or account for observed modes of failure. By adopting a more comprehensive stress model, mills and engineers can identify design limitations that are consistent with experience even where corrosion, corrosion fatigue Corrosion fatigue is fatigue in a corrosive environment. It is the mechanical degradation of a material under the joint action of corrosion and cyclic loading. Nearly all engineering structures experience some form of alternating stress and are exposed to harmful environments , or embrittlement Embrittlement A general set of phenomena whereby materials suffer a marked decrease in their ability to deform (loss of ductility) or in their ability to absorb energy during fracture (loss of toughness), with little change in other mechanical properties, such processes are active. Unlike previous models, this work recommends a principal stress model of the thermowell. This permits the simplest possible assessment of thermowell design limitations and insures that it is compatible with the design requirements of the adjacent piping. The model considers hydrostatic hy·dro·stat·ic or hy·dro·stat·i·cal adj. Of or relating to fluids at rest or under pressure. hydrostatic pertaining to a liquid in a state of equilibrium or the pressure exerted by a stationary fluid. , fluid drag, and vortex shedding Vortex shedding is an unsteady flow that takes place in special flow velocities (according to the size and shape of the cylindrical body). In this flow vortices are created at the back of the body and periodically from both sides of the body. forces acting on a flexible beam model of the thermowell. It consistently predicts likelihood of failure in both powerhouse and process applications. The model is suited to simplified spreadsheet estimates of thermowell velocity ratings or more precise calculations based using dynamic analysis methods, and it drastically improves the quality and mechanical reliability of the thermowell selection. Bartran and Yee are with Monsanto Enviro-Chem Systems; Frikken is with Solutia Inc., Chesterfield, Missouri, USA. Contact Bartran by email at david.s.bartran@monsanto.com. |
|
||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion