Chemical Processing - May 2008 - (Page 27)

“TWENTY-TWO WEEKS AFTER RECEIPT OF APPROVED drawings.” How often do you see this in a quote and don’t understand why it takes so long to fabricate equipment. With the loss of in-house fabrication-savvy personnel over the last two decades, many owner/operators and engineering companies often write purchase specifications that can add unnecessary time and cost to a project. So, in this second article in our series (see sidebar), we’ll provide pointers on how to avoid delays and achieve savings in the fabrication process. Moreover, we’ll cover techniques that, if schedules permit, can improve vessel reliability and thus forestall costly repairs down the road. 1. Know your fabricator’s limitations. Nearly all ASMEstamp-holder fabricators are qualified to weld carbon steel and stainless steel; some are qualified for high nickel. But when ordering vessels in an exotic alloy (e.g., titanium, tantalum or zirconium), another niche material (e.g., copper, aluminum or chrome-molys), or made via a specialized process (such as clad overlays), do your homework. Welding is a skill and all metals don’t weld in the same manner or require the same skill level to produce a quality weld. If a welder hasn’t used a specific welding process in the last six months, the ASME Code requires the welder to requalify. Therefore, strive to find fabricators that regularly weld the material you need. Call around before making your bidders’ list and request references or a rundown on recently fabricated equipment. This will eliminate “no bids” and less qualified fabricators. Additionally, it’s a mistake to view a heat exchanger as just another vessel. Heat exchangers are “performance” vessels and “mechanical only” fabricators don’t have the necessary thermal performance software to appropriately analyze your process data to provide an optimum design. It may seem safe to award mechanical only fabricators “replace in kind” orders without performing a new thermal analysis but you may have missed an opportunity to improve your plant’s performance. Also, heat exchanger fabrication requires special processes such as tube-to-tubesheet welding and tube rolling, which depend upon acquired skills and knowledge. So, fabrication should be left to those companies well versed in manufacturing and analyzing heat exchangers. 2. Be aware of wide loads. A wide load is a generic term for over-the-road shipments whose width exceeds 8 ft. or height exceeds 13.5 ft. (Length and weight restrictions also apply.) Western U.S. states have a legal height limit of 14 ft. When exceeding these limits, state (and sometimes city) “wide load” permits must be obtained — requirements vary by state — and driving restrictions such as dawn-to-dusk curfews are imposed. It’s always easier to obtain permits for excess width; states usually require at least one escort vehicle. When height limits are exceeded, utility company involvement and police escort become the rule rather than the exception. www.chemicalprocessing.com May 2008 • 27 http://www.chemicalprocessing.com

Table of Contents Feed for the Digital Edition of Chemical Processing - May 2008

From the Editor ChemicalProcessing.com Field Notes In Process Energy Saver Compliance Advisor WirelessHART signals a change at plants Avoid costly fabrication mistakes Watch out with variable speed pumping Hot cutover boosts control system migration Plant InSites Process Puzzler Equipment & Services Product Spotlight/Classifieds Ad Index End Point

Chemical Processing - May 2008

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