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Becht Engineering Blog

In this section of the site contributing authors submit interesting articles relating to the various services, industries and research & development efforts of Becht Engineering.

Statistical Analysis of Non-Destructive Examination Data

Statistical Analysis of Non-Destructive Examination Data
In 2008, Becht Engineering was awarded a project by the Materials Technology Institute (MTI) to develop an inspection guideline document and software tool for the collection and analysis of inspection data for piping, piping components and pressure vessels. Dr. Eileen Chant , as project manager, collaborated with Bob Sims of Becht, Dr. Mark Stone of Sonomatic Ltd., the ultrasonic inspection technology company affiliated with Becht, and Dr. William Meeker, a statistics expert at Iowa State University. MTI was founded in 1977 and is a not-for-profit technology development organization serving the needs of its members in key processing industries such as Refining, Mining, Energy production, Chemical production and other manufacturing industries for which safe and reliable fluid storage is critical. A typical refinery or chemical plant may have hundreds of miles of piping and hundreds of pressure vessels that require regular inspection to permit their safe and reliable operation. The inspection document...
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Why Do Coke Drums Tilt Over Time?

Why Do Coke Drums Tilt Over Time?
Background Refinery coke drums experience fatigue induced issues which can be attributed to the coke drum operating cycle; rapidly heating the drum with hot coking feed, and, following the completion of coking process, rapidly quenching of the drum contents with water prior to cutting.  Rapid temperature changes as the drum transitions between steady state temperatures impart a measurable stress gradient on the drum wall and through the skirt and baseplate resulting in long term effects which will cause coke drums to tilt. The tilting of the drum will cause misalignment of the top nozzle and cutting tool. In some cases the misalignment may prevent the drilling operation. The cause of the tilt can be attributed to these uneven temperature distributions which result in the failure of the base plate, grout, construction shims, anchor bolts and drum bulging as noted below: Base Plate, Grout, Shim and Bolt Failure A mechanism which will...
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Designing Elevated Temperature Equipment with Internal Pressure

If the behavior of discontinuity stresses due to pressure is not properly understood in elevated temperature design, unconservative designs can result. One particular issue with pressure stresses is the behavior of the discontinuity bending stresses. An example of discontinuity stresses would be with a pipe welded to a flange. When pressured, the pipe will radially displace (balloon) Pr 2 /Et (neglecting longitudinal stress effects) and the radial displacement of the flange will be very much less than the pipe (considering the massive flange ring). Since they are welded together, the radial displacements must be the same where they are joined, that is, the pipe must be pulled in by the flange to mate. Looking at it as two steps, the pipe expands due to internal pressure, and is pulled back by the constraint of the flange which prevents the expansion where they are joined. This results in through-wall, discontinuity bending stresses...
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Estimating Creep Life of Fluid Catalytic Cracker Internals Using FEA

Estimating Creep Life of Fluid Catalytic Cracker Internals Using FEA
How long will the cyclone system in a Cat Cracker reactor or regenerator last? Cyclones systems in Fluidized Catalytic Cracker units (FCC) are typically designed to a creep allowable stress, where the stress field at various locations of the system has been determined by linear elastic analysis. The basic allowable stress for such internal structures (not on the pressure boundary) is commonly taken from B31.3 or API RP-530, where the allowable stress is dependent on the design life, often 100,000 hours, approximately 11 years. Such analyses may take into account stress classification to give an allowance for elevated stresses of secondary nature (self-equalizing stresses), but this practice often under-estimates the actual stress redistribution that takes place as the structure permanently deforms from creep. Once the time in operation has surpassed the design life, it would seem that the creep life of the structure should be consumed and that the cyclone system...
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