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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.

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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Crane Mats of the Future – Timber, Composite or Steel

crane_mats_fig4
Where will crane mats be in 10 years, 20 years, 50 years? It takes approximately 90 years to grow a 12-inch by 12-inch oak timber twenty feet long. High quality hardwood timbers are becoming harder to find. This is widely known but rarely discussed. The shortage of wood timbers is a national problem. Timber Mats Crane mats have typically been constructed using oak or other select hardwood timbers.  In recent years, as supply dwindles, timbers do not measure a full 12-inch cross section. As they are milled, we often see one or more sides are not square but rounded due to the smaller diameter of the raw cut logs. In some cases, we are seeing timber mats made from mixed wood species, and some with combined hard and soft woods. Ground bearing pressure and load distribution calculations for timber mats are based on a full cross section of matched hardwood with...
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