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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.

Very Unusual Motor Vibration Issue Resolved with Innovative Vibration Analysis & Solution

Background and The Problem 24 new 3600 RPM, 440 volt AC induction motors were replaced at a large refinery as a result of flooding during hurricane Ike. The motors were inundated by 6 ft to 12 ft of floodwater. The new motors were from three of the major industrial motor manufacturers. Horsepower ratings ranged from 40 hp to 100 hp. After the motors were installed, they were checked for soft foot and aligned to the driven equipment. They were then connected electrically and soloed with couplings removed so that vibration data could be collected to insure they met specification. All of the motors had excessive 2X line frequency (7200 cpm) vibration amplitudes ranging from 0.2 ips-pk to 0.6 ips-pk. For each of the 24 motors, when one or more of the motor feet were released, the 2X vibration dropped to 0.08 ips-pk or below. When re-tightened, the vibration immediately returned. All...
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Changes In the 2012 Edition of ASME B31.3

In addition to the many clarifications, updated references to codes and standards, updates to basic allowable stresses, and added listed materials, there are several substantive changes to the 2012 Edition of ASME B31.3, Process Piping. These changes are: Category D Fluid Service The definition was revised to include piping with design minimum temperatures below -29⁰C (-20⁰F) if the cause of the lower temperature is from ambient conditions. Allowable Displacement Stress Range The allowable displacement stress range was limited to 60,000 psi (414 MPa) in the 2012 edition. High strength steels have higher yield and tensile strengths and thus higher allowable stresses. Therefore, they also have higher calculated allowable displacement stress ranges when calculated using the old formula. However, these materials have fatigue strengths similar to the more common steels, which is why the limit was added. Flexibility Stress Equation The axial stress was added to the flexibility stress equation. While axial...
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Recent Comments
Byron Laird

Allowable Displacement Stress ...

Dear Don, Thanks for your article, very informative. Referring to your comment on the allowable displacement stress range. I can ... Read More
Wednesday, 11 September 2013 18:16
Don Frikken

MPa Stress table - response

The ASME B16.5 ratings are based on data supplied by the B&PV Code Section II Committee. In some cases, the MPa values are derived... Read More
Tuesday, 10 December 2013 11:31
Don Frikken

RE:withstand

I'm not familiar enough with ASME B&PV Code Section IX to know if there is an exception to the rule you describe. If the material ... Read More
Friday, 06 February 2015 09:17
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Demister Pads—A simple device until they don’t work

Demister Pads—A simple device until they don’t work
A demister pad is similar to an air filter except instead of removing dust particles from a stream of air for example, it removes micron-size liquid particles from a liquid/vapor stream often found in many industrial processes. An air filter prevents dust particles from entering downstream equipment; similarly a demister prevents liquid droplets from entering downstream equipment where they may affect operation or cause damage. In general, a duty specification is prepared by the process designer and given to demister vendors to recommend a demister that meets the duty requirements. Or today, knowing the required duty you can select a demister from the vendor's online catalog. The demister is installed, performs as intended and is never heard about again. On occasion, problems arise as the case in which Bob Fiocco, a Becht Sr. Advisor, provided technical support to a refining client on demister design and selection. An existing demister installed in...
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Risk-Based Work Selection - Key to Optimized Turnaround Workscopes

Risk-Based Work Selection - Key to Optimized Turnaround Workscopes
Operations and Maintenance Practices in refineries focus on maximizing safety, reliability and profitability, in a highly competitive industry, with tight margins. A key consideration is to effectively manage annual maintenance costs which can be as high as 40-50 MM$/year for a medium size refinery. These costs can escalate to several hundred million dollars, if unplanned shut downs occur, resulting in loss of production. Risk-based work selection (RBWS) is used to plan, schedule and execute maintenance work and is an industry Best Practice for improved reliability. The result is a risk-justified, optimized work list which uses maintenance resources cost effectively while mitigating unacceptable business and S/H/E risks. For TAs which require 200,000 to 1,000,000 person-hrs, the process has identified potential savings of 15-30% on estimated direct costs for the planned work scope. RBWS is used for task prioritization for turnaround (TA) work scopes and routine maintenance work. Rigorous use of RBWS enables...
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