Chemical Processing - May 2008 - (Page 31)

Such difficulties teach an important lesson. Be sure when purchasing vessels to include any special information (e.g., company purchase order, equipment number, special heat treatment or nondestructive evaluation) somewhere on the drawing because 20-plus years from now, a drawing may be all your successor is able to locate. Also, register and archive your vessel with the National Board — most states require registration [1], but it’s good practice even where not mandated. The cost is typically less than $50 and your fabricator will handle the registration. 7. More (radiography) is less (metal). The continuing climb in alloy prices necessitates a paradigm shift in thinking. It’s becoming more economical to specify more radiography (i.e., X-raying), not so much for joint quality but to reduce wall thicknesses. Vessel data sheets require the engineer to specify the amount of radiography required for the service. Typically the choices are “full,” “spot” or “none.” This tells the fabricator how much X-raying it should estimate for Include any special information on the drawing because 20 years from now it may be all that can be located. the job but, more importantly, it affects the required shell and head thicknesses based on ASME code rules. The ASME Code recognizes two types of “full” radiography, RT-1 and RT-2. RT-2 vessels provide the best balance in terms of risk and design economy [2]. “Full radiography” indicates to the fabricator that “all” pressure-retaining butt joints in the main vessel (excluding small diameter and thin wall nozzles) are to be X-rayed. This can be costly but actually can provide substantial savings when fabricating vessels from expensive materials by avoiding any penalty in vessel shell/ head thickness. In ASME Code terms, this amount of Xraying is referred to as “RT-1” (Figure 2) and is stamped as such on the code nameplate. Full radiography often is confused with 100% radiography, with the later requiring X-raying of all butt welds, including small diameter and thin wall nozzles. Lethal services require 100% radiography. A savvy designer knows the difference and may specify 100% in nonlethal services where process reliability is crucial (e.g., continuous processes vs. batch) or where accessibility to certain joints will be restricted and hamper future repairs (e.g., jacketed designs). “Spot radiography” is a common choice in the chemical industry for normal service fluids. It involves a 6-in. www.chemicalprocessing.com Meet your plant’s performance objectives with Chesterton® high reliability sealing Depend on the sealing experts at Chesterton to design a detailed plant-wide sealing program that meets the sealing priorities for your facility. Our knowledgeable and experienced specialists and application engineers can help you meet goals for emissions control, increased Mean Time Between Repair, and reductions in total maintenance costs. We offer a comprehensive line of seals, from high technology gas barrier models to cost-saving cassette designs, all backed by Chesterton’s engineering expertise. Our unique combination of innovative seals and services can be tailored for maximum impact to meet your plant’s performance objectives for high reliability sealing. Please visit our website at www.chesterton.com/ms to find your local service office. © A.W. Chesterton Company, 2008. All rights reserved. 21789 http://www.chesterton.com/ms http://www.chesterton.com/ms 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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