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Featured Projects

Coke Drum Replacement

Coke Drum Skirt Replacement - No Downtime

drumwithconcreteA major refinery in the Middle East requested Becht Engineering to evaluate the problem of their coke drums walking and tilting, and the baseplate/skirt/anchor bolts corroding. After an initial site visit by Trevor Seipp, Division Manager of Becht Engineering Canada Ltd., we determined that the lower portion of the skirt as well as the entire baseplate needs to be replaced for all eight coke drums. In addition, some of the coke drums needed to be re-leveled, and all needed to have shims and slide plates installed. Finally, all of the anchor bolts need to be replaced. And all of this needs to be done without any downtime. Building on the success of our world’s first in Texas, Becht Engineering developed a window methodology to complete the work whereby after we temporarily jack and re-level the drums and place them on temporary shims and slide plates, entire windows of the skirt (~1m x 1m) would be cut out and replaced with new material. While the window is cut out, however, we will have excellent access to the concrete deck to enact the anchor bolt replacement. What will make this project especially challenging is that all of this work needs to be completed while the drum remains in operation. Plus, there are 24 windows per drum and eight drums. All of this work needs to be developed using first-class engineering skills. Since the internal pressure, high temperature, and widely fluctuating weight due to the hydrocarbons, coke, and quench water all have to be evaluated during the repair process, Becht Engineering applied its expertise in finite element analysis (FEA) to the task. Our analysts are among the best in the business, and have performed evaluations on some of the most challenging problems.

Pressure Vessel Fitness for Service

Pressure Vessel Fitness for Service

A major oil company revitalizing an Iraqi oil field called on Becht Engineering to review several hundred pressure vessels containing thinned regions to determine their fitness for service (FFS) per the API-579-1/ASME-FFS-1 Part 5 process for analyzing Local Thin Areas (LTAs).PVD1 Using ultrasonic testing (UT) and visual inspection data, Becht Engineering customized its proprietary API-579-1/ASME-FFS-1 compliant General Metal Loss and Local Thin Area evaluation software to create a program capable of evaluating the maximum allowable working pressure (MAWP) of these pressure vessels in an efficient manner. The software  is very easy to use and presents the results in a user-friendly format for evaluation by engineers and managers. PVD2Because of the extensive nature of the corrosion, large files containing UT scan data needed to be evaluated, and the software was enhanced to parse and analyze the LTAs in the large datasets. This highly efficient process allows rapid evaluation of LTAs, and most vessels were completed in less than one week’s time. Becht’s software modification has also included the COMPRESS vessel design software output as an input to these FFS assessments. Becht has performed Level 1 and Level 2 LTA analyses on various vessels, evaluated sections of vessels for total replacement, analyzed external damage caused by shrapnel from previous wars, and developed repair procedures within the means of the maintenance team for this remote oil field.

 

Computational Fluid Dynamic (CFD) Analysis Resolves Deaerator Cracking

Becht Engineering recently reviewed a utility company's deaerators which experienced a through-wall, circumferential crack at the toe of the fillet weld attaching the saddle to the shell and a through-wall crack was found at the head-to-shell junction at the steam inlet end of the drum.

The saddle to shell cracking was attributed to restrained axial thermal expansion of the shell at a tightly bolted sliding saddle support. The crack was ground out, welded and the support modified to permit sliding.

The head to shell crack cause was attributed to corrosion fatigue, a common occurrence in deaerators. The crack was most likely initiated at a weld surface defect on the I.D. of the drum and grew with time. The daily operating cycles of the drum during periods of reduced steam demand and thermal stresses which we attributed to a poorly designed steam inlet nozzle were the main contributors to the crack growth.

A large diameter superheated steam inlet nozzle extended through the head of the drum terminating 18” into the vessel. The steam exited through a rectangular shaped slot opening on the underside of the pipe which directed the flow of superheated steam directly into the condensate on the bottom of the drum near the shell-to-head weld.

Becht’s computational fluid dynamics model (CFD) indicated that there was little dispersion of the steam exiting the nozzle and that the velocity of the steam mixing with the condensate was relatively high. The superheated steam contact with the cooler condensate resulted in a violent reaction with localized heating and cooling of the vessel shell. This cycling can cause thermal stresses which can result fatigue cracking. Generally, fatigue cracking occurs at welds and heat affected zones adjacent to the weld. Notably no such weld cracking occurred at the opposite end drum where there is no steam inlet nozzle. Figures 1a and 1b demonstrate that the flow trajectory of the incoming steam acts more like a high velocity jet of steam directed at the condensate in the bottom of the drum.

To provide better dispersion, Becht recommended that the inlet pipe be modified with multiple and wider distributed holes. In this configuration, the nozzle acts as a sparger which better disperses the steam in all directions and at lower velocities as can be seen in Figures 2a and 2b.

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Corrosion – Risk-Based Inspection (RBI) Program

Focus on Corrosion – A Refinery-Wide Risk-Based Inspection (RBI) Program

Becht Engineering has completed development of a Refinery-wide Risk Based Inspection Program (RBI) at a Caribbean Refinery with a focus on corrosion damage mechanisms. The Refinery has observed accelerated corrosion in recent years, resulting in a higher than expected equipment replacement rate and commissioned the study in order to develop a plan to mitigate the corrosion.

Becht Engineering - RBI Corrosion ProjectBecht used its proprietary Risk-Based Equipment Reliability Planning work process which is embedded in the our software program STIER© (Strategy Tool for Improving Equipment Reliability) to develop the Risk-based Inspection and Maintenance Plan to address corrosion-related failure scenarios for fixed equipment, rotating equipment and piping circuits. Our work process is compliant with API RP 580, Risk-Based Inspection and ASME PCC-3-2007 Inspection Planning Using Risk-Based Methods.
The subject matter expert (SME) based approach was employed to develop failure scenarios. Once the relevant equipment data were collected and loaded into STIER, a Senior Metallurgists, James McLaughlin, reviewed the information and pre-developed damage mechanisms and failure scenarios for each item. Becht also employed the advice of a Senior Furnace SME, Robert Dubil, to develop failure scenarios, and inspection and maintenance plans for the furnaces. The facilitation team for the RBI Work Process was Dr. Eileen Chant and James McLaughlin.

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Flow Induced Vibration

Becht has been involved in a number of flow induced vibration problems. The problems typically occur in heat exchangers, boilers, flue gas coolers and piping downstream of bypass valves used for pressure letdown. Vendors typically design their equipment to operate outside the range of fluid flows to avoid the problems. However, problems can occur at off design conditions, e.g., process upsets, and outages where more flow is diverted through a piece of equipment than  the design rates   or unit capacity "creep" where  the flow has increased flow beyond original design throughput. The driving forces are fluid phenomena such as vortex shedding, acoustic resonance, and fluid elastic instability. These phenomena can cause vibration and failures in tubes, tube banks, large diameter, thin-wall piping and small branch connection attached to larger diameter piping. Vibration amplitude is magnified if the exciting force is +/- 20% of a component's natural frequency. There are a number of industry criteria to evaluate the potential for vibration. One such criterion we have used to evaluate instability in tube banks in flue gas coolers is shown on the chart. Published industry data on the regions of Stable (low probability) and Unstable (high probability) regions of tube bank instability are shown. Overlaid on the data are the data for a superheater (SH) and high pressure section (HP1) of a flue gas cooler on the back end of a Fluid Catalytic Cracking Unit. The 1250F flue is used to generate steam. The data is shown for two mass flow rates, normal operating and   a higher flow rate when one of the units is offline for repair. At the higher flow rates the SH and HP1 sections move into the lower end of the Unstable region.