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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.

Basics of Design By Analysis in ASME Section VIII, Division 2

fea-pressure-vessel-nozzl_20181115-174743_1
How hard can it be?  I’ve heard from several (unnamed) analysts that because they have access to an FEA program and have successfully applied FEA in other fields, that FEA for pressure vessels should be a snap.  What is it about FEA for pressure vessels that makes it unique? I was recently discussing with another blogger regarding some distinctive aspects of performing Design By Analysis for pressure vessels.  We generated several questions, and so I decided to post this in a Question & Answer format. When do I have to use FEA in my pressure vessel design? The short answer here is that for most situations, you probably should not be using FEA to design your pressure vessel.  The rules for designing pressure vessels in ASME Section VIII, Division 1 and ASME Section VIII, Division 2 have a long history of successful application.  So, wherever possible, I would recommend that you...
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How To Quantify And Evaluate Oil Storage Tank Annular Plate Corrosion

annular_plates_cover-imag_20181008-172036_1 Failure of Oil Storage Tank Annular Plate
In the past ten years, there have been a few oil storage tank annular plate failures due to soil side corrosion and fatigue loading (filling and emptying) which has led to large spills. The corrosion tends to be localized in a groove fashion and the size of the flaw could vary from 3 feet to 12 feet in the circumferential direction. The location of the corrosion is also where the highest bending stress will occur during filling and emptying of tanks. See Figures 1 and 2 for the location of the failure on the annular plate.   Since the location of failure is under the tank, the corrosion flaws cannot be detected easily from the outside of the tank. It can only be detected if an internal inspection is done which would require the tank to be emptied and cleaned and this is very expensive. However, with UT shear wave technology...
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Identifying Gaps in Risk Based Inspection Programs (RBI) That Impact Reliability

heater-tube-bundle
Risk based inspection (RBI) is a powerful tool to identify and manage mechanical integrity risks in fixed equipment and piping but is only one part of a robust reliability program.  RBI informs inspection decision making on where, when and how to inspect most of equipment but is frequently misinterpreted as a “Silver Bullet” that covers all necessary inspection activities in a refinery.  Most RBI programs have significant gaps that can result in costly reliability issues or unjustified maintenance costs.  RBI gaps can exist where risk assessments require input from outside of an inspection department or mechanical integrity group.  Examples of these gaps are when failures have process consequences but not mechanical integrity concerns, such as tube leaks in shell and tube heat exchangers and cyclones in an FCC Unit.  Another example is when mechanical integrity is dependent upon other systems functioning per design, such as fired heater tubes.  Quantitative RBI Programs...
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Dimensional Accuracy – What is Achievable in the Field?

Measure_cove_20181022-144453_1 Accuracy and Precision Are Not The Same
When I am asked to speak about dimensional accuracy, I often refer to a personal story that happened to me when I began my career as a young structural designer. At that time, I was eager to impress the design checker with my ability to accurately dimension structural rebar spacing in a spread footing foundation. I wanted to make sure the rebar was evenly spaced based on design criteria and clearance. Without even considering the practicality of what I was doing, I placed the rebar spacing dimension of #5 rebar at 7 7/16” on center spacing. As I proudly handed over the drawing to the checker, he looked over the work, and a few minutes later he told me that we were going to the field to do some field measurements the next day. The next day, we proceeded to the site, and the checker was looking for some foundations that...
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