Chemical Processing - May 2008 - (Page 28)

The impacT of radiography level Joint Location Long seam Round seam Large nozzles Total number of shots Cost @ $75/shot Resulting shell thickness Linear Feet of Weld 16 75 5 Case A RT-1 (Full) 16 75 4 95 $7,125 ½-in. Case B RT-2 (Full) 16 3 0 19 $1,425 ½-in. 5 Case C RT-3 (Spot) 1 3 0 4 $300 /8-in. Case D No RT 0 0 0 0 $0 ¾-in. Table 1. The level of X-raying directly affects the necessary thickness of material, as illustrated here for an 8-ft. diameter, 16-ft. long shell vessel with the same design pressure and temperature and with internal pressure governing the design. (Note: costs are approximate and can vary greatly depending on set-up costs, wall thickness (i.e. exposure source/time) and film type/length.) Shipping arrangements are handled by the fabricator but it’s useful to know where the break points are for permits when developing your design. In general, a vessel 12-ft. diameter (or less) can be shipped with minimal permitting and attendant costs. This accounts for the deck height of a trailer and can mean the trailer must occasionally bypass an overpass. For larger diameters, the permit process gets more involved. A “stick trip” (travel of the entire route by a vehicle with a mounted stick to verify clearance prior to actual shipment) often is involved and the design of the equipment (i.e., location of nozzles and other external attachments) will impact the permit. If possible, orient attachments to minimize the load height. Purchase vessels of this size and magnitude from fabricators knowledgeable about handling wide loads. Experienced personnel will recognize if a vessel can be shipped in large sections (Figure 1) and then welded together and tested in the field. As the vessel’s diameter, weight or length increase, shipping costs can become an overriding factor on which fabricators you invite to bid. Vessels more than 16-ft. diameter can only be trucked a short distance economically; hauling by either rail, barge, or shop fabricated in pieces and field assembled becomes the norm. Between 12-ft. and 16-ft. diameters, it becomes very situational, so chose your bidders wisely. Moving a large vessel from the fabricator’s shop through a city to a major interstate or river can cost $10,000/ mile and usually the most direct route can’t be taken. Factor in geographic location. It’s easier to ship wide loads in Western U.S. states than in the more congested Northeast. 3. Move carefully with used and relocated vessels. Several suppliers specialize in used equipment; check the classified ads in Chemical Processing and other magazines. Such vessels can be purchased at a discount and are available for your inspection if desired. Also, some operating companies often consolidate opera28 • May 2008 tions into a single location, which can lead to relocating vessels and other major equipment across state lines. When relocating a used ASME-code vessel to your state, first check with the office of the Chief Boiler Inspector in your state capital. Many state laws require pre-approval and inspection by that office before a vessel can enter the state. Failure to comply with state law carries monetary penalties. 4. Pay attention to internal coils. Internal coils can be included as part of an ASME vessel but aren’t required to be code stamped. It’s good practice to include internal coils in the pressure vessel scope so that strict quality control procedures are followed and third party inspections are performed. Internal coil failure can lead to forced shutdown, off-spec product quality and possibly safety concerns. For internal coils, specify butt-type joints with 100% radiography and avoid internal flanges, threads, couplings and socket-type joints. Fillet welds, which >> Wide load Figure 1. This wide load represents only one section of a large vessel that will require field assembly. www.chemicalprocessing.com 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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