Case Studies
KnightHawk Engineering (KHE) has executed hundreds of projects since its inception. Following are several case studies that present a sampling of the type of projects we are traditionally involved with. Please contact us for further information concerning these case studies or our capabilities.
Problem
A client purchased approximately fifty Transfer Line Exchangers (TLE) valued at $18MM. The equipment was designed to operate for over twenty years. Within twelve months after startup the equipment failed. This equipment is used in ethylene facilities to quench cracked gas exiting out of a furnace. The gas side process conditions were approximately 1650 °F and 1 bar. The shell side conditions were saturated water at 616 °F. Each failure caused approximately $1MM in expense and posed a safety hazard.
Solution
KHE developed detailed waterside computational fluid dynamics (CFD) models to investigate the cooling of the inlet tube sheet. CFD also was utilized to determine the aerodynamic conditions of the flow entering the exchanger. The heat transfer and stresses of the heat exchanger were determined by finite element methods. KHE’s work determined that the root cause was a low flow zone that caused superheating and failure. Our work was verified by the client and vendor of the equipment by experimental investigation. Scale models were built and was determined that KHE’s CFD and FEA work matched the experimental model. KHE utilized the same CFD and FEA methods to redesign the equipment.
Result
A major failure root cause was determined. The client saved several million dollars in lost production. The problem was solved by KHE on the first iteration of design and stands as a model in industry today.
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Problem
Pipe ruptures occurred at a major refinery Coker blowdown system. The problem was investigated by the internal engineering group and other consultants. KHE was called in because of our capability to analyze the process and mechanical response of the unit using our Integrated Systems Approach. The failure cost over $1MM in expense and posed a safety hazard.
Solution
KHE field services group instrumented the unit. KHE recorded the pressure, temperature, flow, and vibration during the ten plus operating modes. Pipe stress was performed to analyze large-scale piping response. The process was analyzed and determined that thermal shock occurred during one transient event. Using FEA, we modeled the field data in a structural model of the piping section and determined that the thermal shock created sufficient stress to rupture the line. Our field services group verified this occurrence as part of the process cycle.
Result
A process change with rerouting of two process streams solved the problem. The client has experienced no more problems with this unit.
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Problem
A major petrochemical facility was experiencing failures from a 2000 psi blowdown system. The failures would shut the unit down and cause losses in excess of $1MM. A safety hazard existed for the operators.
Solution
KHE developed a transient pressure and momentum fluid dynamics analysis that incorporated the blowdown valve, upstream piping, and downstream piping. This was manually coupled to a structural dynamics analysis. KHE determined that the root cause was an improperly sized blowdown system. The structural system was redesigned.
Result
The system operates smoothly and the operator confidence in the design of the unit is high. This design now serves as a model design for blowdown systems for the facility.
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Problem
Our client experienced a major fire caused by a rupture of a pipeline. The cause of the failure was unknown and the refinery had a sister unit with the same pipe design.
Solution
KHE personnel performed pipe stress models on site and formulated results within two days. KHE determined the failure was caused by inadequate support system which failed. Recommendations were made to improve the sister unit design.
Result
KHE’s emergency response saved valuable time for the shutdown at the refinery and offered the best solutions to avoid a reoccurrence.
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Problem
A major petrochemical facility experienced a premature corroded tank. To shut the plant down to replace the large diameter tank located in the middle of the process facility would have cost the plant millions in lost profits. KHE was contracted to design a large API tank that could be built along side of the existing system, and then be lifted into place and piped up to the same headers that the corroding tank fit.
Solution
KHE performed extensive structural and lift engineering design to develop a API tank that could be built off the production unit property. The tank was then lifted into place by a large crane and put into service.
Result
The shutdown was only a few days instead of weeks. KHE saved the facility over $1MM in lost income.
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Problem
KnightHawk Engineering was contracted to investigate periodic high vibration in a gas compressor train.
Solution
Using the Integrated Systems Approach, KHE interviewed and gathered information from engineering, maintenance, and operations personnel. KHE also performed field measurements of machine vibration. Shortly after KHE started work on this project the machine was shut down due to high vibration levels. Based on the data KHE submitted a list of recommendations to be acted upon during the short shutdown. During the shutdown most recommendations were completed including piping support repairs, tightening of the anchor bolts, and realignment of the train. After the shutdown the machine did not exhibit the high swings in vibration levels noted before. However, there were higher than desired vibration levels at one bearing which was not inspected during shutdown due to facility constraints. The rotordynamic stability of the system was improved by the repairs and changes made during the shutdown. However, not all problems were eliminated during the shutdown. Subsequent rotordynamic analysis diagnosed specific problems with shaft dynamic unbalance. The dynamic unbalance, the root cause of the high vibration, could not have been diagnosed until the other influences had been eliminated.
Results
The dynamic unbalance was subsequently corrected. The compressor train did not develop the high vibrations.
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Problem
A steam turbine was experiencing excessive vibration. Shutting down the turbine eliminated electrical power to one of the facility’s units. The turbine had recently been reworked. The turbine was not equipped with proximity displacement transducers.
Solution
KHE installed temporary displacement transducers and triaxial accelerometers at each bearing location. Using multi-channel field digital acquisition, KHE performed an orbit analysis of the shaft at the inboard turbine bearing and recorded data from accelerometers located on both turbine bearings. Based on this analysis, KHE informed the client that a rub internal to the machine was the most likely cause of high vibration. Disassembly of the turbine confirmed that the shaft had been rubbing on the internal carbon rings. This rubbing was due to a damaged turbine casing. The damage was most likely caused by excessive pipe loading which was corrected during a previous outage.
Results
The client made the necessary changes to the turbine to assure reliable operation, allowing the affected unit to resume normal operations.
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Problem
KnightHawk Engineering was contracted by an OEM to develop a conceptual design for the inlet cone and connected piping for a Transfer Line Exchanger (TLE) to improve the performance of the system due to existing erosion problems.
Solution
The analysis work for this project consisted of two parts. The first part involved the analysis on the pressure drop of the inlet piping and selecting an optimum pipe size. The second part of the analysis involved the development of a computational fluid dynamics CFD model to determine a desirable inlet cone design. An optimum TLE inlet cone design should have a low-pressure drop and should diffuse the flow entering the cone. KHE evaluated the pressure drop, flow distribution entering the tube bundle, and radial tube velocities at the inlet tubesheet when comparing cone designs. A design with low-pressure drop, an even flow distribution through the tubes, and a low radial velocity at the inlet face tubesheet is considered most desirable. A 10-inch diameter and a 12-inch diameter inlet cone design were analyzed. It was determined the 12 inch diameter inlet cone with specific modifications was the optimal design.
Results
The OEM developed a more efficient cone design with greatly reduced erosion across the tubesheet without having to resort to costly trial and error with multiple prototypes and testing.
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Problem
A paper mill was experiencing inconsistent paper length, resulting in an unacceptably high percentage of waste 35” paper sheets.
Solution
KnightHawk Engineering developed custom instrumentation and software to monitor and record shaft speeds at various points on the folio sheeter drive train. Several shafts were monitored simultaneously. Although no paper length problems were encountered while KHE was measuring and recording shaft speeds, KHE noticed an increase in standard deviation of the cutter and squeeze roll shaft speeds as the feeding paper reels decreased in size. This trend indicates a sensitivity to change in system loading.
Results
The detailed information in the report provided by the multi-point field digital data acquisition proved instrumental to the mill’s maintenance personnel to improving the consistency of the cut paper lengths.
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Problem
KnightHawk Engineering was contracted to investigate the cause of repetitive coupling failures on a steam turbine/refrigeration compressor system. The machine experienced 3 failures in a period of 9 months.
Solution
KnightHawk examined the system and found evidence of high piping loads and high angular misalignment in the vertical direction. Analysis showed the last coupling failure was due to angular misalignment of the machine on the turbine side, caused by high piping loads on the turbine. KHE performed pipe stress analysis and communicated with the turbine manufacturer for their input.
Results
The vibration levels were reduced from .24 in/sec to .17 in/sec. Due to operational difficulties with a portable refrigeration unit, the schedule of the project was greatly accelerated. However, the equipment returned to reliable service with the remainder of the changes scheduled for the next turnaround.
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Problem
A high-speed dual impeller fan, used for process, was experiencing high vibrations.
Solution
The original vibration on the fan at running speed was 1.93 inches per second (ips) and the vibration after initial field balancing was 0.41 ips at running speed. Further balancing was attempted with no success in decreasing vibration amplitude. A resonance test of the rotor indicated the first critical was near the running speed which amplified the vibration problem. KHE performed an analysis of the rotor and wheels in order to predict the effect of a heavier wheel on the rotor and it’s dynamics response. This analysis indicated the critical speed would decrease approximately 11%. Heavier fasteners would be required in construction of the new wheels to maintain an acceptable factor of safety for the vane’s attachment to the front and rear wheels.
Results
The fan was modified according to KHE recommendations, resulting in reliable operation.
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Problem
KnightHawk Engineering was contracted to determine the root cause of an unacceptably high rate of ethylene furnace coil tube failures and provide an assessment of the entire processside of the furnace system.
Solution
KHE began this process by using the Integrated Systems Approach and developing a pipe stress model of the coil system, analyzing an initial heat and mass transport model, reviewing the process procedures, and developing a 2-D Computational Fluid Dynamics model of the firebox and tube. This provided a comprehensive view of the process, mechanical, and material interactions and established a baseline for subsequent work. Review of the process procedures indicate changeovers and decoking did not specify ramp conditions with detailed control parameters. The coil counterweight system, modified from original design, could allow accelerated creep to occur with the elevated temperatures being the driving factor. The decoke procedures needed to consider more control variables for changeovers and decoking. The coil had high sensitivity to the process flow rate, to the coke layer, and to the coke layer conductivity. Computational Fluid Dynamics results indicated that the circumferential temperature differences along the coil may affect the structural stability. These factors combined to increase the likelihood of tube failure during operation. Detailed recommendations were given to improve performance and reliability.
Results
New operating procedures were developed and implement, resulting in more efficient and reliable production.
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Problem
KnightHawk Engineering was contacted to assist a service contractor in the evaluation of repair options to a four stage, reciprocating compressor cylinder for CO2 service. The compressor was critical to the contractor client’s process. The fourth stage cylinder was having a cast iron sleeve replaced at the contrepair Option for actor’s facility when a crack in the cylinder forging was found. Delivery of a new forging was estimated to require over 5 weeks.
Solution
KHE conducted a finite element analysis of the forging and of the recommended installation of a sleeve. The interference of the sleeve was designed to produce enough compressive strain at the crack to prevent any leakage or further crack propagation. After the repair was made, the compressor was returned to service.
Results
The compressor was put back on-line with the minimum of downtime. No further problems were reported.
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Problem
A process reactor’s support structure was vibrating excessively and disrupting production. The client contracted KHE to evaluate proposed structural modifications.
Solution
A finite element static and dynamic analysis was conducted of the existing structure and the proposed modification. Analysis verified the modification’s cold spring in the main columns reduced the loading in the W8X31 columns within acceptable design limits. In the dynamic analysis, the first mode natural frequency with the new tangential strut design is over 6.5 Hz. compared with the original design of 1.21 Hz. The design modification provides a dramatic increase in the stability of the structure. This modification is cost effective when compared to rebuilding and redesign of the entire structure for the loadings. The strut loads induced upon the building structure as defined in the static section are less than 1000 lbf for the worst case.
Results
The client was able to verify their diagnosis of the original design and predict the response of their proposed changes to ensure reliable future operations.
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Problem
A contractor had incorrectly cut a door in the bottom course of a 500,000 barrel petroleum storage vessel. The door was too close to the longitudinal welds as specified in API 650 and 653. Code required the vessel be hydro tested, which would result in unscheduled costs and extend the vessel’s downtime.
Solution
As with ASME and ANSI, API codes often allow for properly executed detailed engineering analysis to supersede the letter of the code providing the original intent was observed. KHE developed a FEA model of the tank with a sub-model of the area of interest. The tank model incorporated settlement surveys and ultrasonic test data, then was subjected to the required design conditions specified in code (hurricane winds with the vessel empty and full.) The model’s response was transferred to the submodel, which in turn showed the stresses and deflections in the area of interest. The results indicated the improper repair did not jeopardize the vessel’s reliability.
Results
The storage tank was put back into service on schedule. The analysis provided an estimated 25:1 return on investment compared to the direct cost of the hydro test.
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Problem
KnightHawk Engineering was asked to examine failed components of a two cylinder, two-stage reciprocating compressor in recycle gas service.
Solution
Using the Integrated Systems Approach, KnightHawk conducted an overall system assessment and failure analysis that consisted of a site visit, examination of maintenance records, interview of maintenance personnel, machine and structural calculations, visual observation of failed machine, and visual inspection of fracture surfaces. Analysis work indicated a maximum cylinder to frame tension of 26,000 lbs. Interaction load calculations contained allowables for the normal condition. The bolts used in service would yield under normal circumstances. Data and analysis suggest that most likely incompressibles were introduced into the system causing the bolting to stretch leading to fatigue failure. The factor of safety of the bolted joint in operation was reduced by utilization of an improper washer.
Results
The client examined the upstream process to eliminate incompressible fluid introduction to the flow. Maintenance procedures were reviewed and updated. The compressor was repaired and put into reliable service.
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Problem
Due to changes in regulations, expansion joints in process transport piping needed to be replaced with hard piping. KnightHawk Engineering was contracted to design a new piping system to mate with the existing tanks and pumps while providing sufficient flexibility for reliable operation.
Solution
KHE conducted a series of site visits to develop “as-built” drawings of the various runs of pipe. Pipe stress analysis was used to analyze the existing piping with the expansion joints simply removed. Pipe stress analysis was then used to develop pipe modifications to incorporate the required flexibility while insuring the equipment loadings were within acceptable limits. Working with facility personnel, piping isometrics were developed to not only reliably replace the expansion joints but to improve operations and equipment access. Detailed drawings were provided to the client.
Results
The client’s emission exposure was greatly reduced, complying with the new federal and state regulations. Equipment reliability and accessibility was improved, reducing the long-term cost of ownership.
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Problem
A baggasse conveyor, suspended from an overhead crane system, needed replacement. The original system’s OEM was no longer in existence. The new system had to be fabricated and installed overseas and be robust enough to provide years of operation under heavy service. KnightHawk Engineering was contracted to design the new system and provide fabrication and installation drawings.
Solution
KHE obtained detailed drawings of the existing overhead crane system and the structure of the building the conveyor was to be installed in. The conveying system was designed using commercially available parts. The design included the conveyor, the lifting system, the control system, and a specially designed switching mechanism to prevent likely operator errors. A 2-D finite element model of the building’s structure was used to analyze the worst-case loadings and verify longterm integrity.
Results
The conveyor was fabricated, installed, and successfully put into operation, allowing the sugar mill to resume full operation.
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Problem
A hydraulically-operated clam shucking and packaging facility had excessive utility bills. Additionally, the facility had difficulties maintaining the required climate control. The process machinery was suspected of being the root cause.
Solution
KHE performed a design audit of the hydraulic system. Custom software was developed to account for different operation conditions. It was determined the main hydraulic lines were constructed and maintain for too high of a pressure, wasting a great deal of energy and contributed to the numerous equipment malfunctions and failures. KHE recommended modifying the system to operate at a lower main pressure with an additional pump to operate the few high-pressure equipment items.
Results
The facility saw an immediate reduction in their utilities and maintenance costs.
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Problem
A major producer of polyethylene had pellet quality problems with the operation of a pelletizing die. The client was not sure if the problem was the pelletizing die or the process. Down time due to these problems resulted in over $50,000 in losses each time the train had to be shut down. Since KHE has experience in analyzing many of the major pelletizing dies KHE was asked to troubleshoot this problem.
Solution
KHE characterized the pellets and reviewed the train operation on site. A computational fluid dynamics model was built of the die. The process was modeled and the response experienced by production was duplicated numerically. Proposed changes by KHE were also modeled to determine possible solutions. It was determined that the vendor’s die was not ideally suitable for the application; however, the process could be changed to produce an acceptable pellet until a new die could be put in service.
Results
The client implemented the KHE recommended changes and was able to stay on line and produce acceptable pellets. A new die was ordered that was better suited for the application.
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(Section VIII, Division 2, Appendix 4, Paragraph 4-136)
Problem
A vendor was asked to design a selective linear exchanger in accordance with ASME Section VIII, Division 2, Appendix 4. This exchanger was to be used for quenching cracked gas as it exits out of an ethylene cracker. The result of quenching the cracked gas on the tube side with saturated high pressure water on the shell side is steam. The vendor’s design was optimized and standard elastic analysis procedures would not satisfy the code. The vendor required an elastic-plastic analysis to be in accordance with paragraph 4-136.
Solution
KHE developed an elastic plastic model of the system. It included all the non-linear effects of the material. The designed proved to be in accordance with ASME, Section VIII, Division 2, Appendix 4, Paragraph 4-136.
Results
The vendor’s client accepted the design and the client claims cost savings were realized. The most advanced structural analysis techniques were employed by KHE to make this project a success.
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Problem
A major ethylene producer was putting in a new cracking furnace design. The ethylene producer determined potential long term problems with creep of the furnace coils due to design and support problems. The ethylene producer turned to KHE to develop non-linear creep finite element analysis of the coils.
Solution
KHE performed a comprehensive non-linear finite element model of the furnace coil system with supports. Creep equations for the material were incorporated into the analysis. The analysis determined overstress problems after relaxation of the coils and load transformations. This would lead to excess bowing and buckling of the coils. The design was changed based on the model.
Results
The facility implemented the design. The model was verified by measuring deflections in the cracking furnace after a period of time in operation. The ethylene producer avoided shutdowns and repairs by taking care of this problem before it could occur.
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Problem
A major refinery was experiencing vibration problems with a high temperature furnace coil used in a cracking process. The flow-induced vibration shook the coil and failures were experienced. Differential thermal growth and the need for heavy constraint caused conflicting design issues. KHE was contracted to design the coil to handle the driving forces of the flow and allow for the thermal expansion.
Solution
KHE developed a structural dynamics model of the coil using CAESAR II pipe stress tool. With custom software KHE determined the driving forces from the flowinduced vibration. Supports were strategically placed that reduced harmful dynamic effects while allowing for differential thermal growth.
Results
The design was implemented and the furnace performed as designed.
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Problem
A major refinery had a contract to process sour crude. The material required for the piping was stainless steel. The existing pipe in the operation was carbon steel. KHE was contracted to perform a rush analysis of the piping system within only five days. A routine schedule would be four weeks.
Solution
To accomplish this task KHE sent a team consisting of engineers and designers to perform this work on site. KHE developed CAESAR II models of the entire system that consisted of vessels, pumps, and heat exchangers. ANSYS finite element models were built to evaluate locations of high stress on several of the vessels. After completion of the work on site concurrently with construction, KHE completed a check of the calculations at KHE offices.
Results
KHE finished the project on site on time. The plant started up with the new system and it is operating as expected.
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Problem
A major petrochemical facility was experiencing vibration problems with a steam bypass valve. The valve is used when a steam turbine is taken out of service. KHE was contracted to perform a vibration analysis of the valve, which included fieldwork and analytical work.
Solution
KHE conducted a field survey with data acquisition equipment. KHE also performed calculations to evaluate the performance of the valve. The calculations indicated the valve would experience destructive shock waves that could damage the valve under some operating conditions. Working in a team environment with the client, KHE made recommendations on process changes for the valve. It was also recommended the valve should be replaced or upgraded for the service.
Results
The results of the evaluations indicated the plant should reduce load on the valve during the by-pass operation until the valve could be replaced or modified. The plant was able to complete the by pass operation under reduced operating condition.
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Problem
A major petrochemical facility was experiencing vibration problems with a piping system. The piping system consisted of piping, pumps, a static mixer, and a heat exchanger. KHE was contracted to perform a mechanical and process analysis of the vibrating system. The client was willing to accept a process solution if it was the most economical as long as the quality of the product being produced could be maintained.
Solution
KHE developed a structural dynamics model of the piping system using the CAESAR II pipe stress tool. The results of this analysis indicated extensive supporting would be required to solve the problem. A FLUENT computational fluid dynamics model was created of mixer area. The model contained several species that were reacting. An assessment of all data suggests flashing flow was occurring in a local area. The mixer was redesigned.
Results
The problem was solved at minimum cost. The plant started the unit up and product quality improved and the vibration was within acceptable limits.
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Problem
A major petrochemical facility was experiencing vibration problems with a shaker
structure. The shakers used in the process service caused destructive vibration levels of the building containing the equipment. KHE was contracted to design a fix for the problem.
Solution
For this task KHE developed a finite element model of the structure using ANSYS. KHE was able to match the actual response numerically and determined the root cause of the problem. It was determined that there was inadequate vibration isolation between the shakers and the structure. KHE de-tuned the structure using the computer simulation to choose appropriate vibration isolators that were implemented in a new design.
Results
The new design eliminated the problem.
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Problem
A power plant facility determined a new piece of equipment was required to add to the process to crush a product so that it could be processed. This equipment was required so the plant could start-up this new unit. KHE was contracted to design this equipment.
Solution
To accomplish this task KHE assembled a team of engineers and designers and work 7 days per week at 16 hours per day. As preliminary designs were being developed fabrications started. During final fabrication and machining detailed calculations were being checked. Part of the design and drawing was conducted at the machine shop that built this equipment. This equipment was designed and built in a phenomenal 32 days. Normal delivery for such equipment is 26 weeks.
Results
The equipment performed in accordance with design specifications.
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Problem
A gasification plant was experiencing plugging in a pneumatic conveying system designed to transport ash generated in the gasifier, preventing plant start-up. During start-up, the ash was found to include particles as large as 3” diameter, which were plugging the conveying system. KHE was contracted to design an ash grinder to crush the larger particles.
Solution
A single roll grinder was designed for installation into a custom designed pressure vessel. To accomplish extremely fast turn around on the design and fabrication cycle, KHE personnel located temporary offices in the client selected fabrication shop for concurrent design and fabrication efforts.
Results
The grinder was shipped from the fabrication shop within 38 days of receipt of initial purchase order from the client. Installation of the grinder eliminated large particle plugging.
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Problem
A paper plant was experiencing shaft and bearing failures on the non-drive end bearing on the breast roll of a paper machine. Several shaft design modifications were previously implemented by the plant, but were unsuccessful in eliminating the shaft and bearing failures. KHE was contracted to analyze the shaft and bearing application the determine the allowable wire loading for several shaft design options, and the determine the sensitivity of the bearing to support misalignment.
Solution
Initial field evaluation of the installation helped identify modifications of the bearing housing to allow for bearing alignment inspection during installation. Next, a finite element model was generated for each shaft design using ANSYS. Fatigue stress analysis was used to determine the wire loading limit for each design. An additional finite element model was used to determine the deflection of the bearing support due to the asymmetric loading inherent in the design.
Results
Purchase of an expensive forged journal was prevented since an existing design was adequate for the wire loading capability of the machine. Bearing design was found to be adequate with appropriate installation methods.
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Problem
A petrochemical plant had experienced two major failures of a centrifugal compressor during start-up. Plant concerns were that the compressor was surging during the start-up process due to modification of the control system during starting. KHE was contracted to evaluate for the potential for surge and make recommendations that could be implemented to assure successful startup of the compressor.
Solution
An integrated surge model was developed for the compression system including two compressor cases, intercoolers, suction and discharge piping as well as the dump valve used to prevent surge during start-up.
Results
The surge analysis identified that under certain start-up conditions the 1st compression stage was likely to surge. In addition, review of the start-up practice identified several drain valves and an additional vent that if open during a throttled start, would increase the likelihood of surge. Recommendation were made, resulting in a successful startup.
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Problem
A petrochemical plant had identified metal particles and debris in the oil sump of a vertical agitator gearbox. KHE was contracted to evaluate the casing vibration of the unit to determine if bearing or gear damage was evident.
Solution
Three-axis vibration measurements were conducted to assess the mechanical condition of the gearbox. Evaluation of vibration velocity spectra and acceleration time waveforms did not identify evidence of bearing or gear damage.
Results
A major overhaul of the gearbox was postponed.
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Problem
A petrochemical plant had experienced multiple failures of an open-faced impeller on a multistage centrifugal compressor. Either a piece of a blade or an entire blade would break loose causing major damage to the compressor and result in significant down time and repair costs. KHE was contracted to perform an independent study of the latest failure.
Solution
An in depth study of the process, process controls, upstream and down stream equipment as well as the compressor itself was conducted. Field Measurements were taken to determine dynamic conditions for vibration, pressure pulsation and natural resonant frequencies of the compressor and impeller. It was determined that under specific process conditions and rotor speeds, the 2nd mode of the impeller tuned in and resulted in catastrophic failure of the impeller.
Results
The compressor was immediately limited in speed to avoid the 2nd mode frequency, while a new impeller could be manufactured that would allow increased process throughput at lower speeds and different 2nd mode natural frequency.
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Problem
A petrochemical plant was experiencing cracks in the rotor of a liquid ring compressor and the OEM could not help in resolving the problem. KHE was contracted to perform a failure analysis of the compressor to determine the cause of the rotor cracks.
Solution
KHE conducted field measurements of the natural frequencies of the rotor, two axis vibration of the compressor and dynamic pressure pulsation on the suction and discharge chambers of the compressor. It was determined that during specific transient operating conditions the acoustic conditions allowed amplification of the positive displacement pressure pulses and over loaded the rotor leading to the fatigue cracking.
Results
The controls of the compressor were modified to avoid running the compressor during the problematic transient operating conditions.
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Problem
A multistage Integrally Geared centrifugal compressor experienced a failure of an impeller causing major damage to the compressor, expensive down time of the plant and costly repairs. In addition, the compressor had not been able to perform as designed since its installation. KHE was contracted to participate as a member of a failure analysis and troubleshooting team, consisting of personnel from the OEM, Operating Company and Engineering Company.
Solution
An investigation was conducted of the operating history, conditions, performance test results, events leading up to the failure, changes made during several outages, the damage to the compressor components, and changes implemented during the rebuild. KHE performed a critical speeds assessment, process analysis, surge/stall analysis, aerodynamic review of the impeller metallurgical review, corrosion assessment of all affected components, and a review of the inter-stage cooler design. It was determined that the blade failed due to surging of the failed stage, as a result of failed inlet guide vanes, caused by corrosion of the control linkage, resulting from excessive water carry over and improper materials selection on some critical components. The performance shortfall was determined to be caused principally by poor design of the inter-stage coolers; however, inaccurate speed control, and fouling were also identified as part of the performance problem. Not all the performance shortfall was accounted for, other lesser contributing factors could not be identified without additional analysis and research.
Results
The materials of all critical components were re-specified to a material suitable for the application, the inter-stage coolers were redesign to eliminate of the water carry over, and the compressor speed was raised to increase throughput.
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Problem
A polymers production plant was experiencing a severe shortage of throughput of a polymers double gear pump. KHE was contracted to determine the cause of the shortage and to determine what changes were needed to increase the throughput to acceptable levels.
Solution
KHE performed a general assessment of the pump design and operating conditions in addition to collecting field data from dynamic pressure transducers mounted on the inlet and discharge transition pieces and the inlet and discharge pump chambers. KHE also performed leakage calculations based on the clearance tolerances and a CFD analysis of the suction chamber and compression zone of the pump. It was determined that leakage due to clearance tolerances was higher than originally specified by the pump manufacturer, but most of the performance loss was caused by incomplete fill of the gear teeth due to inappropriate design geometry of the compression zone. KHE worked with the OEM to redesign the compression zone geometry, using CFD methods to evaluate the performance of design changes.
Results
A new design of the compression zone resulted in an improvement of the pump performance that would meet the designed minimum requirements for throughput. In addition, shims were added to reduce the leakage caused by clearance issues.
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Problem
A chemical plant experienced a major failure of a high-speed chlorine compressor. They had been experiencing many operational problems with the compressor since its installation. The failure resulted in significant damage to the compressor and a significant outage of the process line. KHE was contracted to perform a failure analysis to determine the root cause of the failure.
Solution
KHE performed process, process control, mechanical, and metallurgical reviews of the application and interviews with operational and maintenance personnel. KHE performed analysis to determine the possibility of liquid slugging the compressor, fatigue failure of the high speed shaft, bearing failure, seal failure, and seal pressure control system failure. It was determined that the seal system between the gear box and compressor including the controls for the pressurized seal zone were inadequately designed to prevent manual override of the system. Operator personnel unwittingly lowered the nitrogen supply to an insufficient level, causing chlorine gas to leak from the compressor through the seal zone to the gearbox. The gas contaminated of the lubricant causing the bearings to fail from which provided adequate heat to initiate a chlorine metal fire that consumed aluminum and carbon steel components including a portion of the shaft.
Result
The controls to the supply of buffer gas for the seal system were modified to assure appropriate supply of seal gas, with a train shut down on low pressure in the seal zone.
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