Now that the nasty, cold weather is well out of sight on its annual migration to somewhere south of the equator, attending to outside maintenance ought to be much easier, safer and higher on the priority list. No doubt, you already have a backlog of maintenance tasks that Mother Nature dropped on your doorstep. If one of them has anything to do with freeze protection or heat tracing, you’re in luck. That’s because this month we’re going to take you on a hunt through the digital morass we call the Web in search of practical, zero-cost, noncommercial, registration-free resources that you can use to optimize your heat tracing systems and improve their reliability well before that endless migration reverses direction. Remember, we search the Web so you don't have to.
How much do you need?
The cost of operating your heat tracing system is a function of temperatures, geometry and insulation properties, among other relevant variables. If you’re designing a new system, you want to match supply to demand the first time because it’s too expensive to change it later. Or, if you’re evaluating an existing system, you might be interested in knowing how well your predecessor matched them. But, to do this, you should have a basic knowledge of heat transfer and the Web has much info on heat and tracing. For an example, warm up that pesky desk rodent and send it to www.process-heating.com to scroll down and click on “Archives” at the left side. Then, click on the link to the January 2006 issue, after which you should select the article titled “Calculating Heat Loss” by Mark Crombie. This is a primer for calculating heat transfer via conduction, convection and radiation on cylindrical surfaces. Be sure to perform the search that Crombie suggests at the end of his article. You’ll find that worthwhile, too.
Don’t stress out
The linear coefficient of thermal expansion is a physical variable that defines the relationship between piping dimensions and temperature. Thermal stresses that arise when temperatures vary from the design value can impose huge loads on pipe racks, tank nozzles, pumps, inline equipment and fittings. Imagine, for example, the thermally-induced stress that can afflict the standby pump in a pair that handles any high-temperature fluid. Or, consider the stresses that arise when you leave the steam tracing running while the flow through the process pipe is stopped or the line drained. Both these situations are addressed in “Piping Design Considerations to Control Loads on Load Sensitive Equipment (Part I).” Check out this brief article by Carmagen Engineering, Inc., Rockaway, N.J. by tossing a hot mouse at http://carmagen.com/newsletter/news1.htm and read all about it.
From the subcontinent
The Department of Chemical Engineering at the University of Engineering and Technology in Lahore, Pakistan, offers a brief piece titled “The Maximum Heat Loss through Pipe Insulation,” by Asim Umer and Muhammad Adeel Zia. It points out that with flat insulation, heat loss is inversely proportional to insulation thickness, but with curved insulation on pipe, the loss-thickness relationship isn’t linear because the surface area through which heat flows isn’t constant. Based on economic measures only, it’s possible to calculate the proper thickness to wrap around your pipe, and the authors give you the calculations. Start by going to www.uet.edu.pk/ht2, which apparently is a subdirectory related to one of the heat transfer classes at the school. Anyway, scroll down the list and click on the first of two entries labeled “insulation optimizat...” when the page loads, be aware that some of the links at the left are dead.
Holding it in
After you fire up heat tracing of any type, you’ll need to keep buying energy to make it operate. With the industrial pressure to be a cheapskate who cuts costs and the social pressure to be a greenie who cuts carbon dioxide emissions, you might as well wrap thermal insulation around those traced lines and tanks. Having made this decision, I know you’re going to want to use an optimum amount of optimum insulation. A resource that can help guide your struggle to be a cheap greenie is available at www.insulation.org/articles. Pop in for a visit and enter the phrase “mechanical insulation systems” in the title/intro keyword slot. Then, use the quick search feature to find the link to “Specifying for Mechanical Insulation Systems,” an article by Michael J. King. It explains the reasons we insulate something, reveals 18 considerations for developing a prioritized list of important selection factors, details the organization and content you should use when writing a spec for insulation, offers tips for communicating your expectations about material and workmanship, shows the information that should appear on your construction drawings, and gives you an outline specification that wraps it all up in a neat bundle.
Making the jump
If you’re going to use steam, the tracing lines must necessarily accommodate both steam and condensate. How you route the tracing around flanges, valves and other non-pipe line elements makes a difference in system performance. So argues Andrew Sloley in an article, “Make jacketing your strong suit,” that appeared in the December 2006 issue of Chemical Processing. This one-page piece is available at www.chemicalprocessing.com/articles/2006/181.html. Read and take heed.
For the sake of uniformity and reliability, your plant ought to have some control over the components and systems that get installed. If you don’t have construction standards, you might be courting trouble. You could do worse than to follow the lead of the Facilities Division of the University of Alabama at Birmingham, the group responsible for the buildings and grounds at the university. To help meet its vision — to become the international leader in university and medical center facilities — the Facilities Division put in place quite a few design standards that apply to new and retrofit projects. One of them applies to electric heat tracing. You can find this three-page document by climbing the Ivory Tower at www.fab.uab.edu/Standards.ASP, scrolling down to Facilities Standard 16690 and clicking to get your very own PDF.
Playing with Ohm’s law
Heat tracing comes in two varieties; steam and electric. It’s the latter option that is so well showcased in the “Heat Tracing Products Training Manual” by Adam Heiligenstein and Gary Ozegovich of Chromalox Industrial, E. L. Wiegand Division of Emerson Electric Co., Pittsburgh. This 76-page document, found at www.chromalox.com/literature/PJ324.pdf , is an in-depth exploration of electric heating as it applies to tracing pipes and tanks, warming floors and melting snow on gutters. The content covers the fundamentals of heating, types of electric heating cable, cable design guidelines, circuit layout, controls and hazardous area considerations. It’s a real educational opportunity, not just for heat tracing, but basic electricity as well. Commercial content is rare throughout about the first 50 pages, so it isn’t too blatant a violation of our guidelines to present it here as a site worthy of your consideration. What I found curious is that this online document is clearly marked “For internal use only.” Someone in Pittsburgh might read this and pull the piece from the big, nasty Web, thereby denying you the benefit of a bit of the collective wisdom of this venerable company. So, I recommend you hustle and download the entire manual, just in case.
While you’re there capturing those binary digits, there are other pages you should investigate. A good example is the material behind www.chromalox.com/technical. The page has plenty of white space, with only five main links. But those give you access to a surprising amount of technical material. Space constraints prevent me from even listing the topics. Go explore on your own. You’ll probably find it rewarding.
You can do this at home
Your computer most likely has a copy of Excel, the spreadsheet application that came out of Redmond, Wash. It’s capable of doing some pretty amazing mathematical acrobatics, even those associated with keeping things warm. That’s a good thing because some of the other Web citations mentioned in this column involve computations you probably never expected to see again. Fortunately, Andre de Lange, from South Africa, managed to tie it all up into a neat bundle called “Steam Tracing with MS Excel.” This work of art is available for your use if you make the effort to visit www.cheresources.com/steam_tracing.shtml, which is operated by the Chemical Engineers' Resource Page, Midlothian, Va. The spreadsheet template you download is a steam tracing simulation for determining a process fluid’s temperature. The painstakingly detailed theoretical calculations that de Lange provides certainly give a user the sense that the numbers coming out of the digital cruncher have some finite probability of being accurate. Be warned —— the spreadsheet uses macros, so you’ll need to reduce your computer’s security level if you want to run a simulation.
Nobody really wants to do the heavy math involved with specifying your heat tracing. All you want is a pipeline that remains at a temperature within alarm limits. Renegade, a free “manufacturer independent” heat tracing design software package, is available to do the heavy lifting. Launched in 1994 by Serge Baril & Associates in Quebec, it’s supposed to be able to work with any heat tracing technology from any manufacturer. It’s still available for your convenience and the fastest way to get your hands on this material is to go to www.baril.ca/frmpr_en.htm and look for the download link at the bottom of the left-hand frame.
Hot tips from your peers
An online forum is a digital mechanism that allows one to post a question on the Web for all to see and, hopefully, post a cogent, to-the-point answer. Given human nature and technical capability, though, each such response elicits another response from someone else [i]ad infinitum[i] and, voila, a forum comes to life. I’d guess there’s a forum for any topic you can name but, this month, the focus is on heat tracing. Who better to participate in a technical-topic forum than engineers with too much time on their hands? Get a sense of how this works by dressing your mouse in its royal toga and sending it to Eng-Tips Forums at www.eng-tips.com . Enter the phrase “heat tracing” in the search box on the right side and you’ll access more than 650 postings related to heat tracing. The quality of the individual entries varies widely, but the point is that you’re not alone in having questions about tracing and many other technical issues that arise in the plant environment. Besides, you might even get a cogent answer to your own question.