Designing A Robust Reaction Furnace

Mike Porter, SOGAT 2016

Sulfur plant reliability is greatly influenced by the reliability of two interconnected pieces of equipment, the thermal reactor (TR) and the waste heat boiler (WHB). Over the past fifteen years, PMI’s engineers have developed performance metrics that must be satisfied to ensure robust WHB operations [1], defined as successful operation between planned turnarounds, without failures. Alongside these metrics is an analysis framework that allows quantification of the metrics through the use of complex numerical models. Rules-of-thumb (lightly defined metrics) for robust TR operation, such as flame shape and stability, O2 enrichment level and reactor retention time, have been developed within the industry, but to this point, most complex numerical models developed to study TR performance metrics have been necessarily limited in scope due to the computing requirements required to study these phenomena. With the knowledge that TR operations can have a significant impact on WHB reliability, the authors set about to develop an analysis framework to allow quantification of TR metrics in engineering rather than research time scales.
This paper introduces a framework for computational evaluation of TR performance metrics to the industry for the first time through the analysis of a TR with known problematic operations. Through a series of analyses, the TR was studied at different rates and in different geometric configurations to investigate possible methods to achieve successful operation. The framework successfully predicted the cause of the problematic operation. The framework is also capable of quantifying the effect of changes on the reactor’s chemical operation, primarily through ammonia destruction. The paper also demonstrates how this analysis framework can be used to not only study problematic TRs, but also to optimize throughput without modifying the reactor’s steel.

Stoichiometric Firing Damage In Claus Unit

Dennis Martens, Mike Porter, 2016 Laurance Reid Gas Conditioning Conference.

This presentation provides examples of how high temperatures resulting from stoichiometric firing can significantly damage thermal protection systems and brickwork of a Claus reactor. Charts showing the relationships between fuel type, fuel-air ratio, and tempering steam level on flame temperature are presented. Steam tempering is identified as an effective method for reducing reactor temperatures to a safe range.

API 521 SRU Reaction Furnace Waste Heat Boiler Evaluation For Overpressure Due To Tube Rupture

Dennis Martens, Alan Mosher, Brimstone 2015

American Petroleum Institute (API) Standard 521, Pressure‐relieving and Depressuring Systems (current edition: 2014), is being revised to include information regarding Sulfur Recovery Unit (SRU) Reaction Furnace Waste Heat Boiler (WHB) tube rupture developed through process side overpressure. The proposed modifications regarding the SRU Reaction Furnace WHB were first balloted in the spring of 2015. Once all of the changes are balloted and approved, a new edition of API 521 will be issued in 2019 at the earliest. The modifications to API 521 that were balloted state that the user should evaluate the system to determine if the system can relieve a rate equivalent to double the cross sectional area of a single tube in the WHB without exceeding the corrected hydrotest pressure of the reaction furnace and other low‐pressure side equipment. The proposed modifications suggest that Steady State analysis be completed first. If the steady state analysis predicts that the corrected hydrotest pressure will be exceeded, it is suggested that other methods such as Dynamic Analysis should be completed. The proposed modifications also state that an alternative to dynamic analysis would be the application of ASME Section VIII, Division 1 UG‐140 Overpressure Protection by System Design. The proposed modifications do not provide any real guidance on how the analysis should be done or suggested scenarios and sequences for the various analyses that should be completed. This paper focuses on the authors’ understanding of how the overpressure analysis should be completed and provides a flowchart with a suggested sequence for the analysis. The bulk of this paper was originally developed and submitted to API for possible inclusion in the modifications to API 521 to provide guidance for engineers that are responsible for evaluation of tube ruptures in new and existing SRU reaction furnace WHBs. After consideration, the information was rejected by the API 521 Task Group from inclusion in API 521 because it was risk-based direction, utilizing ASME Code Case 2211 addressing UG 140 Overpressure Protection by System Design and WRC Bulletin 498 Guidance on the Application of Code Case 2211 ‐ Overpressure Protection by Systems Design. This paper provides guidance for evaluating overpressure scenarios due to a WHB double-ended tube failure, including a suggested sequence for analysis flowchart and examples.

Designing a Robust Waste Heat Boiler

Dennis Martens, Michael Porter, Laurance Reid Gas Conditioning Conference 2015

The reliability of Sulfur Recovery Units (SRUs) is ever more important for maintaining acceptable environmental discharge criteria. The SRUs used in gas conditioning and refining applications are typically based on the Claus process, employing a reaction furnace (RF) and fire tube type waste heat boiler (WHB).

The reliability of the WHB is a significant factor in the overall SRU reliability. Understanding the root causes for WHB failures provides the basis for establishing the parameters necessary for a robust WHB design and also operating guidelines needed for reliable operation.

Typically, WHB failures are due to three factors: excessive temperatures, excessive mass flux (process through-put), and excessive water- or process-side fouling. Each of these three factors can independently or in combination cause a WHB to fail. This paper discusses these factors, the need to learn from prior failures, the corresponding considerations necessary for designing a robust WHB, and the necessary considerations for operational parameters and procedures to improve the reliability of this critical equipment.

Why do Waste Heat Boilers Fail?

Dennis Martens, Mike Porter, Lon Stern, Sulphur Magazine 2014

Why do waste heat boilers in sulphur plants fail? We can look to the auto racing industry to find the answer. Engine size in Formula 1 race cars has continually reduced over the years as engineers have found ways to make the cars go faster and faster with a given engine size. On its super speedways, NASCAR places restrictor plates below the carburettor to limit engine output. Similar efforts take place in almost all types of racing. Why? Because the limiting factor is the ability of the driver to react quickly enough to safely control the car. Waste heat boilers fail because we try to operate them at levels beyond which we can adequately design and safely control them to provide reliable operation. Typically waste heat boilers (WHBs) fail due to three factors: excessive temperature, excessive mass flux rate, and excessive water-side fouling. Similar to the racing industry, the sulphur industry has increased temperatures and mass flux (process flow) rates to obtain greater unit capacity. However, this push has exceeded reasonable bounds, to the extent that reliability of a unit can be and has been compromised. To maintain acceptable discharge environmental criteria, often the sulphur recovery units (SRUs) must operate with significant variance in acid gas flow rates – variances that are not controllable by the SRU operators. Water side fouling is potentially affected by these same parameters and becomes a significant factor for reduced reliability.

Designing to proposed API WHB Tube Failure Document

Dennis Martens, Lon Stern, Brimstone 2014

This paper highlights the current API “TASK FORCE ON HRSG OVERPRESSURE” design considerations for WHB tube failure and provides information and comments for consideration for inclusion within API STD 521/ISO 23251 for the protection against the potential overpressure of a Claus Unit resulting from tube failure in the Waste Heat Boiler.

The results of Amine Best Practices Group’s 2014 SRU industry survey update to Years of SRU Operation and Fatalities/Injuries Resulting from a WHB Tube Failure are presented to focus on actual operational experience of WHB tube failures which resulted in loss of containment due to overpressure rupture. We discuss past WHB tube failures reported in the public domain.

The use of Layers Of Protection Analysis (LOPA) is discussed for addressing the probability of a tube failure occurrence, associated loss of containment occurrence and risk quantification. A summary table provides examples of LOPA application for various tube failure scenarios. The 2013 ASME Section VIII Div 1 UG-22 Loadings and UG-140 Overpressure Protection by System Design refers to utilizing the overpressure scenarios in API 521 and HAZOP procedures to determine credible failure scenarios.

The use of an alternate allowable pressure design methodology is presented. This paper provides a suggested pressure design approach for consideration by the SRU community and the API Task Force.

The Use of Porous Media Models and CFD for Sulfur Treating Applications

Sean McGuffie, Michael Porter, Dennis Martens, Brimstone 2013

Packed beds are used in numerous applications in sulfur recovery. During typical design processes, the flow through these beds is usually assumed to be uniformly distributed throughout the bed. Unfortunately, such is not always (or even mostly) the case. We will look at several different bed configurations and examine the flow conditions that typically exist and see what could be done to improve the flow.

In the first example, we see how a bed with non-uniform geometry can be modeled with a discrete particle geometric model to determine the porous media constants. Without sacrificing accuracy, the porous media model allows the analysis of large beds with much less computational overhead than models that include geometric complexity. In the second example, the analysis of a Tail Gas Unit (TGU) reactor will be demonstrated. This analysis shows how Computational Fluid Dynamics (CFD) can be used to analyze packed beds and as a design tool to optimize piping configurations. In this case, the CFD analyses were able to make much more effective use of the catalyst bed, which has resulted in extended service life and significantly reduced operating costs for the reactor. In the third example, a CFD analysis performed on an amine filter bed demonstrates how the existence of more complicated features, such as bed voids, can be included to bracket the expected performance envelope of a bed. This example also demonstrates the use of species wash-out tracking to determine the percent of bed utilization.

It is expected at the end of the presentation that conference attendees will understand the basics behind the incorporation of porous media models to model packed beds, their limitations, and how these models can be used to model specific processes. While the accompanying paper contains all theoretical details related to the porous media models, it is expected that the presentation will focus on examples, with the understanding that the paper will provide a solid framework to begin independent research if attendees are interested in the “nuts and bolts” of the models.

Reduction Of Stack Vortex Induced Vibrations

Mike Porter, Sean McGuffiePVP2013-97995

A stack installation experienced vortex-induced vibrations (VIV) while in-service. The vibration magnitudes were severe enough that cracking in the welds at the base of the stacks was experienced shortly after installation. Initially, straight strakes were placed on the stacks, per API 560, based on field serviceability. The strakes proved ineffective and it was determined that the stacks would be uninstalled for repair. During the repair process, design steps were required to reduce or eliminate the VIV experienced in-service. Due to a flaw in the initial design and the ineffectiveness of the straight strake solution, the end client required verification of any proposed design changes before their implementation. Additionally, there was a very short time frame for the investigation of solutions.
Initially, tuned mass dampers were explored for the design modification. It was determined that they could not be constructed of suitable materials for the environmental operational characteristics of the stacks. It was then agreed that aerodynamic modifications of the stacks should be explored to reduce VIV. ASME STS I specifies the design and installation of helical strakes on stacks, but does not indicate the magnitude of vibration reduction that can be expected [3]. Therefore, numerical models were used to determine if the strakes would reduce or eliminate the service vibration.
A baseline analysis was first conducted to validate that the tools – a combination of computational fluid dynamics (CFD) and finite element (FE) methods – could capture the in-service behavior. To perform this analysis a baseline CFD model was constructed of the as-built stack. Using detached eddy simulation (DES) methods, the model was analyzed at several wind speeds to determine the magnitude and frequency content of the VIV-forcing functions. Information from the flow simulation was then used to perform a dynamic analysis using an FE model of the stack. The model accurately predicted the correct wind speed corresponding to VIV and the amplitude of the stack’s vibration. A second model was then constructed of a stack with helical strakes, using a novel modeling methodology, and this model was analyzed over a variety of wind speeds using DES methodologies. The forcing functions predicted with the helical strake model were then used to determine the stack’s in-service response. This paper contains the complete methodologies and results associated with these analyses.

A Robust SRU Waste Heat Boiler Design

Sean McGuffie, Dennis Martens, Michael Demskie, Brimstone 2012

It is well known in industry that sulfur recovery unit waste heat boilers (WHBs) can fail due to a wide variety of reasons. The primary modes of reported failure include departure from nucleate boiling (DNB) and sulfidation corrosion. From experience, there are several design variables that must be considered when developing a robust design. For example, limiting the mass velocity limits the peak heat flux and the driving potential for gas bypass in tubesheet ferrule and refractory systems. While general design guidance for WHBs exists, it is the authors’ experience that few boilers represent genuinely robust designs.

This paper explores a robust WHB design that has been in service for almost a decade without significant corrosion or unscheduled outages. The authors first describe general design rules that were incorporated in the subject WHB that should be considered in all WHBs where reliability is a major consideration. By examining the results of computational fluid dynamics (CFD) analyses performed to study this WHB’s historical operation and to determine limits for future operation, the authors will demonstrate how incorporating design results affects the WHB’s performance.

The paper will conclude with a discussion of how complex, state-of-the-art CFD analyses can be used to determine, with a high degree of certainty, operational limits for existing WHBs and to evaluate designs of proposed new WHBs.

Use of CFD in Design – A Tutorial

Sean McGuffie, Mike Porter, Thomas Hirst, ASME PVP Conference 2012

Recent advances in computational resources have made the use of computational fluid dynamics (CFD) to support industrial design activities more commonplace. Though large and small organizations have adopted the technology, it is still considered to be “black magic” by many engineers. The purpose of this tutorial is to provide the design engineer with an understanding of the fundamental concepts related to successfully performing CFD analyses and how CFD analyses can be incorporated into design processes.

Molten Sulfur Fire Sealing Steam Requirements

Alan D. Mosher, Sean M. McGuffie, Brimstone 2011

National Fire Protection Association (NFPA) 655, Standard for Prevention of Sulfur Fires and Explosions (current edition: 2012), Chapter 5, Handling of Liquid Sulfur at Normal Handling Temperatures, Section 5.5, Fire Fighting, states that protection of covered liquid sulfur storage tanks, pits and trenches shall be by one of the following means: (1) inert gas system, (2) steam extinguishing system capable of delivering a minimum of 2.5 pounds per minute [lb/min] (1.13 kilograms per minute [kg/min]) of steam per 100 cubic feet [ft3] (2.83 cubic meters [m3]) of volume, or (3) rapid sealing of the enclosure to exclude air. The NFPA snuffing steam rate stated in the standard results in a large steam rate being fed to sulfur tanks and sulfur pits that typically have a low design pressure. The sulfur tanks and sulfur pits are typically designed with air sweep systems to prevent the accumulation of hydrogen sulfide (H2S) in the vapor space, thereby eliminating the flammable mixture. The air intake and exhaust systems are typically designed with very low pressure drops for normal operation. If snuffing steam is fed to sulfur tanks and sulfur pits at the rate specified in NFPA 655, the built‐up back pressure typically far exceeds the design pressure of the enclosure. For these reasons, the refining and gas plant industry has tended to choose not to follow the NFPA 655‐specified snuffing steam rate. Actual operating data from sulfur fires in sulfur tanks and sulfur pits indicate that a lower sealing steam rate is adequate to extinguish the fire by sealing the sulfur tank or sulfur pit from air ingress and purging some of the air as the fire is extinguished by lack of oxygen. Some computational fluid dynamics (CFD) modeling has been completed that supports the field data showing that a lower steam rate is adequate to extinguish the fires. This paper focuses on the potential problems caused by the current NFPA 655 snuffing steam rate, analysis of actual field data for fires in sulfur tanks and pits, and a recommendation for the NFPA 655 committee to consider regarding a steam rate to seal the enclosure and extinguish the fire in a sulfur tank and sulfur pit. The paper also includes comments on good engineering practice resulting from the calculations and CFD analyses that were completed. NFPA 655 is currently being updated and will be reissued in 2017. This paper was initially prepared to document issues with the current NFPA 655 snuffing steam rate for molten sulfur and to recommend a reduced rate to NFPA during the first public comment period that ended on January 5, 2015.

Burner Flame Temperature During Warm Up And Hot Standby

Alan D. Mosher, Brimstone 2011

Typically, more damage occurs in an SRU during startup and shutdown than any other time. The “hot standby” condition is another thermal reactor and WHB killer. One of biggest concerns is operating the Thermal Reactor Burner at stoichiometric natural gas and air flame temperatures. The best available refractory cannot withstand the temperature of a stoichiometric flame. An understanding of the potential flame temperatures is critical since one cannot fully trust the temperature measurement devices instrumenting a reactor. These flame temperature concerns can be successfully addressed by using a proper flow rate of tempering media (steam or nitrogen) whenever natural gas or other fuels are used during start-up, shutdown, or hot standby.

Tube and Tube Weld Corrosion and Tube Collapse

Dennis Martens, Brimstone 2011

Significant unscheduled outages and extended shutdowns have resulted from sulfur recovery unit (SRU) Claus Thermal Reactor Waste Heat Exchanger (WHE) tube and tube weld corrosion and from tube collapse. Sulfidation corrosion rates increase with metal temperature, and design operating temperatures in the Claus Thermal Reactor ranging from 2000° F (1090° C) to 2800° F (1540° C) are typical. In the last few decades, the use of oxygen enrichment and acid gas enrichment has resulted in more units being operated at the upper limit of this temperature range, resulting in increased likelihood of accelerated corrosion. This paper describes the conditions that can lead to corrosion or collapse of WHE tubes in a Claus SRU WHE.

Valve-Induced Piping Vibration

Mike Porter, Dennis Martens, Ramesh Harrylal, Charles Henley, PVP2011-57391, ASME 2011

During the startup process of a 600 MMSCFD Gas Processing Plant, the piping downstream of a gas expander bypass valve and supporting structure was observed to be shaking abnormally. The shaking was significant enough that plant personnel limited the valve flow rate to well under the design capacity to a level that limited the plant startup. The initial assumption was that the piping or the piping supports had been improperly designed. An investigation revealed no unusual looseness in the piping supports and no significant piping natural frequency at the observed vibration frequency.

Further investigation revealed that the root cause of the problem was a flow-generated pulsation in the discharge of the bypass valve that excited the piping and structural supports. Changing the valve flow path and the applied valve opening limits provided a temporary work-around that allowed the plant to operate at sufficient flow rates to complete the startup. Subsequent replacement of the valve with one using the same trim but with different gas flow path characteristics proved to be the ultimate solution to the problem.

Combining CFD Derived Information and Thermodynamic Analyses to Investiagte Waste Heat Boiler Characteristics

Sean McGuffie, Mike Porter, Dennis Martens, Michael Demskie, PVP2011-57625, ASME 2011

A series of computational fluid dynamics (CFD) and numerical analyses were performed to investigate operational characteristics in a sulfur recovery unit waste heat boiler (WHB). Similar analyses of WHBs have been reported by the authors. The initial focus for the current investigation was to determine the reason for metal loss on the inside of a WHB tube. This required extending the focus of the previous analyses that concerned a) the departure from nucleate boiling (DNB) leading to critical tube temperatures, and b) the fluxes and temperatures downstream from the inlet ferrule, to also investigate the high inside tube surface temperatures caused by shell-side tube outer diameter (OD) fouling. The results of the investigations were combined to provide future operational guidance for the boiler.

Using Computational Fluid Dynamics and Finite Element Analysis to Determine Bolt Stresses Due to Thermal Cyclic Loading

Phil Martinez, Sean McGuffie, Mike Porter, PVP2010-26035, ASME 2010

This paper details the procedures necessary to accurately determine the stress in bolts on a coke gasifier inlet flange using current state-of-the-art practices. Using accepted ASME Code practices (ASME[1]), the stress results are then used to justify the elimination of the spacers that were specified in the original design. Computational fluid dynamics (CFD) is employed to determine heat transfer coefficient distributions in the areas of interest. Finite element (FE) analysis is used to compute the transient assembly temperatures and related bolt stresses.

By evaluating the bolt stresses as specified in ASME Div. 1 [1], these analyses were used to determine that the spacers could safely be eliminated during operation.

Diaphragm Closure Analysis Using Nonlinear FEA and CFD, Sean McGuffie

Mike Porter, Dennis Martens, PVP2010-25833, ASME 2010

In the previous work PVP2006-93731 “Reinvestigation of Heat Exchanger Flange Leak” (Porter [1]), a series of finite element (FE) models were constructed of a heat exchanger flange. Current FE capabilities were used to further elucidate the reasons for the flange’s leakage in-service, reported in a 1994 paper (Porter[2]). The flange leakage was primarily caused by differential thermal expansion causing yield in the flange bolts and gasket scuffing. Correcting the leakage required the implementation of a weld ring gasket.

A similar service exchanger was later designed to eliminate the critical differential thermal expansions. This exchanger employed a diaphragm closure method to eliminate the possibility of gasket leakage. This design included an internal pass partition arrangement such that the end closure flanges were exposed to a single process fluid temperature. In the authors’ experience, typically the exchanger vendor provides proprietary calculations verifying the serviceability of the closure design. This prompted the question, “What analysis methodology would be required for an engineer to qualify or verify the design of a welded diaphragm closure configuration?”

The authors have used a thorough methodology for the analysis of a diaphragm closure. This was used for verification of the design suitability for design temperature gradients and related thermal expansion. To conduct the analysis, the authors performed a series of computational fluid dynamics (CFD) and non-linear FE analyses on a representative diaphragm closure geometry (under specific service conditions) to determine the closure’s capability to withstand the design load cases. This paper serves to demonstrate how such analyses can be used to qualify a diaphragm closure’s suitability for a specific service.

It should be noted that this paper does not represent a complete analysis of a diaphragm closure. Code (ASME [3]) specifies all procedures that shall be employed. The procedures under investigation were applied to the two cases analyzed. Complete engineering of the closure may require the analysis of additional cases.

Experimental and CFD Evaluation of a Bubble Column Reactor

Sean McGuffie, Mike Porter, Dennis Martens, PVP2010-25823, ASME 2010

During the scale-up design of a slurry bubble column reactor from a pilot demonstration facility to a production reactor, the design team used computational fluid dynamics (CFD) as a tool to quantify design variables, such as gas holdup, liquid velocities, and structural pressures within the reactor. At the time of the analysis, all available physics models for modeling the multi-phase flow had significant limitations that would require tuning of the CFD input parameters to ensure confidence in the results. The authors initially conducted a literature search to find data that could be used to calibrate the model. While a wide variety of literature is available, none provided the exact data required for model calibration. For this reason, the authors constructed a test column and performed experiments to derive data for tuning the CFD models. Statistical analysis of the experimental data provided distributions on the input parameters of interest. CFD studies were then used to tune the CFD input parameters to match the experimental data. A correlation was developed, tested and verified. This correlation was then used to provide confidence in the results of the design analysis performed on the scaled-up reactor.

A Means of Avoiding Sulfur Recovery Reaction Furnace Fired Tube Boiler Failures

Mike Porter, Dennis Martens, Sean McGuffie, John Wheeler, PVP2009-78073, ASME 2009

One of the common causes of premature tube failure in fired tube boilers is overheating of the tubes caused by steam blanketing, technically described as film boiling. Current literature contains a significant amount of information on this problem, but not much in the way of definitive guidance for avoiding the problem. General “rules of thumb” are available for identifying the heat flux limit required to avoid the problem as in Martens et al [1]. Unfortunately, values presented by different sources are often in disagreement.

This paper will look at a sulfur recovery unit (SRU) Claus waste heat boiler application, and through the use of Computational Fluid Dynamics (CFD), develop a means of predicting the conditions that lead to steam blanketing and resultant tube failure. Local heat flux conditions at gas side discontinuities (such as the tube inlet ceramic ferrule terminations), associated local water-side steam entrainment, and steam generation with coupled velocity effects are discussed.

Vaporization of LNG using Fired Heaters with Waste Heat Recovery

Dennis Martens and Marty Rosetta, PVP 2008 – 61648 ASME Pressure Vessel and Piping Conference Proceedings July 27 31, 2008

Liquefied Natural Gas (LNG) is an important component in meeting the future energy needs of the United States and other industrialized countries. The ability to locate (produce), process, liquefy, transport, and re-gasify stranded natural gas is vital to maintaining a stable long-term natural gas supply necessary for sustained economic growth [1]. Two key components in this supply chain are the vaporization of the LNG at the import terminal and the peak shaver trains that liquefy pipe line natural gas, store it, and then vaporize the liquid to feed the gas to the pipe line when additional flow is required.

This paper outlines a novel approach incorporating a traditional fired heater with waste heat recovery to vaporize LNG at an import terminal or peak shaver train while maintaining a high thermal efficiency. A comparison is made between the new technology and more conventional methods, with emphasis on emissions. Some of the advantages and disadvantages associated with the design and implementation of these systems are explored in this presentation.

As a fundamental canon of ethics, engineers are obligated to address the most efficient and responsible use of resources. The environmental impact of supplying the necessary natural gas energy to industry and consumers is significant. This paper addresses these aspects as considered during the development of the alternative LNG vaporization technology.

CFD Analysis and Optimization of an Inlet Manifold for a Large TGU Reactor

Mike Porter, Sean McGuffie, PVP2008-61621, ASME 2008

This paper discusses the use of Computational Fluid Dynamics (CFD) to study the flow characteristics of inlet manifolds into a large TGU reactor. The design parameters for the operation of the reactor required a very minimal system pressure drop outside of the pressure drop across the reactor bed. For this reason, several alternative designs were considered for the inlet manifolds and distribution into the reactor. Detailed CFD models were constructed of each proposed variant and analyzed to determine their pressure drop and distribution characteristics. The results of these analyses were then used to choose the best candidate for optimization as well as to provide guidance in system changes that would improve pressure drop and flow distribution characteristics. A discussion of how the results’ guidance was used in optimizing the flow path will be provided. The paper will conclude with a brief overview of other considerations in the complete analysis of the reactor system.

Discussion of Issues Related to Surge in LNG Pipelines at Offloading Terminals

Sean McGuffie, PVP2008-61620, ASME 2008

Due to requirements of LNG unloading terminals, the pipelines used to transport the liquid operate near the vapor pressure of the LNG. If the operational pressure in the pipeline falls below the vapor pressure, pockets of gas will develop; when these pockets collapse, very high pressure pulses can be transmitted through the pipeline, an event known as surge or waterhammer. This paper discusses transients that occur during normal and upset plant operation and how these transients can induce surge in the pipeline. The paper concludes with an overview of the methods used to evaluate whether surge will occur and the peak pressure associated with surge events, with an overview of cases that are typical candidates for analysis.

Investigation of a Shell and Tube Exchanger in Process Gas Heating Service

Mike Porter, Martens, D.H., PVP2008-61635, ASME 2008

The design requirements for a large shell and tube vertical heat exchanger (to be used in a sulfur recovery tail gas treatment unit) included startup, shutdown, and upset conditions that would subject the exchanger to significant temperature changes. The exchanger was designed to the requirement of the ASME Boiler and Pressure Vessel Section VIII Division 1 [1]. A detailed analysis of the thermal profiles and related stresses was performed to confirm the use of a flexible tube sheet design. The heat exchanger uses high pressure superheated steam on the shell side to heat a low pressure process gas on the tube side. The heat exchanger was sized and thermally rated, using commercially available analysis software. The proposed design was analyzed by Finite Element methods that included both thermal and stress analysis. These evaluations confirmed that a flexible tube sheet design was satisfactory when using specific dimensions.

Investigation, Analysis and Mitigation of Combustion Driven Vibration in a Sulfur Recovery Burner Assembly

Mike Porter, Martens, D.H. and Fenton, H.C., PVP2008-61644, ASME 2008

During initial operation, one of three identical Claus furnace burners of a large Sulfur Recovery Complex was observed to develop a vibration at certain operational conditions that affected the reliability of some of the instruments attached to the burner front. The resonance was not sufficient to lead to mechanical damage of the burner or the instruments, but led to spurious operational trips and corresponding plant shutdowns. The observed vibration, first considered to be a result of mechanical resonance within the burner assembly, was found to be the direct result of acoustic excitation of a burner pressure head by the natural acoustical frequencies present in the attached furnace during the combustion process. The investigation included gathering field operational conditions, field vibration measurements, and analytical computations using finite element methods. This paper reports the investigation process, results obtained, and the modifications that were determined necessary to sufficiently reduce the vibration of the instruments.

Interpreting Surge Analysis Results

Mike Porter, Sean McGuffie, PVP2007-26676, ASME 2007

This paper details methods for interpreting maximum surge pressures in LNG pipelines due to valve closures and other transient events. The standard methodology for determining the onset of surge events and the pressure transients involved uses explicit integration, but that method of analysis produces inherent “noise” in the solution results due to the integration method. This paper discusses methods of filtering data obtained through explicit integration and demonstrates which filters provide the best results for these analyses. Filtered and unfiltered results are presented for an actual LNG unloading facility subjected to a number of transient events, with discussion provided on determining the maximum peak pressures, their duration, and the frequency content of secondary pressure waves.

Investigation of a Shell and Tube Exchanger in Liquefied Natural Gas Vaporization Service

Mike Porter, Doug Miller, Martens, D.H. and Sean McGuffie, PVP2007-26592, ASME 2007

Liquefied natural gas (LNG) is commonly converted from liquid to vapor for gas distribution. One of the methods for vaporizing LNG is to use a shell and tube heat exchanger. Water is used on the shell side to provide the heat source and LNG is then vaporized through the tube side passages of the exchanger. In many of these applications, the LNG is at a high pressure on the tube side while the water is at a lower pressure than the LNG on the shell side. The industry consensus document API 521[1] “Guide to Pressure Relieving and Depressuring Systems,” Fourth Edition, paragraph 3.18 “Heat Transfer Equipment Failure” states that a complete tube rupture is to be considered for the possible overpressure of the equipment. The typical shell and tube exchanger application described above has rupture discs on the shell body to protect the shell from being over-pressured due to a tube rupture scenario. The possible freezing of the water in the shell due to mixing with cryogenic LNG is a concern. The issue to consider is whether freezing will occur before the rupture discs can safely relieve a possible over-pressure condition of the shell. A numerical analysis of the condition was performed using Computational Fluid Dynamics (CFD) software. The exchanger service, the analysis procedure, and the conclusions are detailed in this paper.

Seismic Analysis of a Pressure Vessel

Mike Porter, Martens D.H., and Sean McGuffie, PVP2006-93732, ASME 2006

The seismic analysis of Section VIII Div 1 industrial pressure vessels has typically been accomplished using rather simplified “equivalent static force” procedures. In general, these procedures have proven to be safe and effective. However, this method assumes that deformation may occur but that containment will be maintained. A similar assumption of deformation is contained in the modification factor used in building codes. If the vessel is expected to function after some design earthquake event, such methods are not adequate for design. This paper addresses a more detailed procedure of seismic analysis involving a finite element analysis of the vessel that incorporates the interaction of the piping and the vessel. This methodology provides a better understanding of the localized stresses, such as at vessel nozzles with pipe attached, and may be used to analyze a vessel for a design that could be subjected to a specific earthquake response spectrum with minimal deformation and probable return to operation status.

Reinvestigation of Heat Exchanger Flange Leak

Mike Porter, Martens, D.H., PVP2006-93731, ASME 2006

In a paper presented in 1994 [1], the authors examined a heat exchanger flange to ascertain the cause for a leak. This examination was conducted using Finite Element (FE) analysis procedures. At that time, it was not practical to accurately model the interaction between the flanges and gaskets as a function of time and the resultant temperature. In the ensuing time period, the available FE technology has improved dramatically. Faster computers and new parallel solver technology allow modeling of the flange components that was not practical 10 years ago. In this paper, the authors will re-examine the exchanger system using current technology and discuss the improved insight that this new technology provides to the problem solution.

Analysis of Pressure Vessel Sloshing

Sean McGuffie, PVP2006-93632, ASME 2006

ASME BPVC Section VIII Division 1 Paragraph UG- 22 (f) requires consideration of the loadings from seismic conditions. For a vessel containing a fluid, the loading due to sloshing must be considered. ASCE Standard 7-02 (Section states that a damping value of 0.5% can be used to account for the fluid sloshing. This can lead to an overly conservative design by over-estimating the loads on the tank structure. A time-history analysis was performed on a horizontally mounted pressure vessel experiencing 3-axis time history loads in order to determine if this method is more accurate in determining the loads. The analysis employed a 3- dimensional computational fluid dynamics (CFD) model, using transient time-history techniques. The reactions at the mounting locations were compared to the reactions computed using closed form solutions, demonstrating good correlation. The results show that CFD is an excellent tool for investigating seismic sloshing loads in vessels.

Computational Fluid Dynamics Investigation of a High Temperature Waste heat Exchanger Tube Sheet Assembly

Mike Porter, Dennis Martens, Thomas Duffy, and Sean McGuffie, PVP2005-71143, ASME 2005

Many modern Sulfur Recovery Unit (SRU) process waste heat recovery exchangers operate in high temperature environments. These exchangers are associated with the thermal reactor system where the tubesheet/tube/ferrule assemblies are exposed to gases at temperatures approaching 3000 °F. Because sulfur compounds are present in the process gas, the carbon steel tubesheet and tubes in the assembly will be deteriorated by sulfidation as the operating metal temperature rises above 600 °F. Ferrule systems are used to protect the carbon steel from exposure to excessive temperatures. The temperature distribution in the steel tubesheet/tube/ferrule system is affected by process gas flow and heat transfer through the assembly. Rather than depend upon “assumed” heat transfer coefficients and fluid flow distribution, a Computational Fluid Dynamics (CFD) investigation was conducted to study the flow fields and heat transfer in the tubesheet assembly. It was found that the configuration of the ferrule installation has a large influence on the temperature distribution in the steel materials and therefore, the possible sulfidation of the carbon steel parts.

Comparison of Limit Load, Linear, and Nonlinear FE Analyses of Stresses in a Large Nozzle-to-Shell Diameter Ratio Application

Mike Porter, Dennis Martens, and Steve Massey, PVP Vol. 477, (Design and Analysis of Pressure Vessels, Heat Exchangers and Piping Components), ASME 2004

This analyses address a nominal 62-inch diameter nozzle in a nominal 124-inch diameter shell with a reinforcement pad. The nozzle is in a channel of a heat exchanger. This results in stiffening of the shell (adjacent to the nozzle) by the tube sheet and the channel head. The results of a WRC 297 analysis, a linear elastic analysis, a limit load analysis, and a plastic analysis are compared. The finite element analyses were accomplished utilizing commercial software and typical modeling techniques. As there is significant variance in the results derived with the different methodologies, the authors discuss the comparison of the results.

The Use of FEM in the Revamping of Existing Systems

Mike Porter, Dennis Martens, PVP Vol. 459, (Design and Analysis Methods and Fitness for Service Evaluations for Pressure Vessels and Components), ASME 2003

Often the revamping of existing sulfur recovery systems requires replacing some of the equipment. At the same time, economic considerations can dictate re-using as much of the existing system as is possible and practical. This paper examines the process used to connect a new thermal reactor to an existing waste heat exchanger. Included are some of the design considerations necessary to ensure a safe and reliable final arrangement. The complexity of the configuration – including the stresses developed in the existing equipment and the interconnection – required the use of Finite Element (FE) to assess the final design.

Thermo-Well Vibration Investigation and Analysis

Mike Porter, Dennis Martens, PVP Vol 446, ASME 2002

The current industry design practice for addressing vortex shedding-induced vibration in thermowells is to use the ASME Power Test Code 19.3, Part 3 (PTC) [1], which essentially requires the vortex shedding frequency to be less than the first natural frequency of the thermowell by a reasonable design margin. The PTC also provides guidance for establishing the vortex shedding frequency and the natural frequency of the thermowell. In a 1996 paper presented at the ASME Pressure Vessel and Piping Conference, Blevins, et al [2] published test results for the natural frequencies and damping coefficients of several standard design thermowells. Also presented were the classic formulations for the calculation of the Von Karman vortex shedding and the thermowell natural frequency. The Blevins data indicated that for certain types of thermowells, there was a discrepancy between the measured thermowell natural frequency and the frequency calculated using the PTC method. In this paper, the authors will review the basic calculations related to vortex shedding and thermowell natural frequency. This paper will also present Finite Element (FE) analyses of several thermowells from the Blevins paper and discuss the results of the FE analysis with respect to that paper’s test results. Discrepancies between the natural frequency calculated by the PTC methodology and the thermowell natural frequency test data presented by Blevins, and the results of the FE analyses will be discussed. The authors also introduce a design technique using fatigue analysis to assess the likelihood of thermowell failure. Use of the FE-derived natural frequency information and the fatigue analysis techniques will improve the safety of thermowell applications and may extend the service velocity in which a specific thermowell can be used.

Comparison of Limit Load, Linear and Nonlinear FE Analysis of a Typical Vessel Nozzle

Mike Porter, Wolf Rienhardt, and Dennis Martens, PVP Vol. 430, (Pressure Vessel and Piping Design and Analysis), ASME 2001

A limit load analysis of a vessel nozzle with pressure and external force loading was conducted. The limit load was defined by increasing the pressure and the nozzle external loads proportionally until collapse occurred. The evaluation of the limit load analysis was conducted in accordance with ASME BPVC Section VIII Division 2 [1]. The limit load analysis provides insight into the collapse load and failure mode. The results of the limit load analysis and a plastic analysis are compared to the results obtained by linear and nonlinear shell and plate element analyses of the same nozzle. The authors discuss the comparison of the results, as there is some variance between the different methodologies.

Investigation and Repair of a Heat Exchanger Tubesheet-to-Channel Flange

Mike Porter, Dennis Martens, Steven Massey, Donald Skaggs, and Brian Hiatt, PVP2001-VOL430, ASME 2001

During its fabrication hydrotest, the flanged joint between the tubesheet and the channel of a shell and tube heat exchanger leaked. The design of the joint was confirmed as complying with the ASME Boiler and Pressure Vessel Code Section VIII Division 1[1] stress requirements and rigidity index recommendations. The joint was investigated using finite element analysis (FE). The results indicated that the flange was rotating significantly during bolt up and under pressure. The flanged joint design was judged to be unacceptable and the design was converted to a welded configuration. This paper reports the results of the FE analysis and the ASME BPVC Section VIII Division 1 flange design calculations. The results of commonly used mechanical and code design software are also discussed. These results are compared and recommendations for the design of similar flanges are presented.

Comparison of Linear and Nonlinear FE Analysis of a Typical Vessel Nozzle

Mike Porter, and Dennis Martens, PVP-Vol. 399, ASME 2000

In an earlier paper by Porter & Martens, 1996 (1), the authors demonstrated that five different FEA software codes produced comparable results in the analysis of a typical thin wall nozzle-to-shell junction where the indicated stresses remained below the material yield point. Where the indicated stresses were above yield, considerable divergence was noted. In order to explore the stress redistribution patterns that may have caused the divergences, this paper presents a nonlinear (elastic-plastic, material nonlinear only) analysis of the same nozzle. The results are compared with the results from the previous linear analysis. The results are discussed with respect to an evaluation procedure for Shell/Plate element Finite Element investigations presented in a paper by Porter, et al, 1999 (2).

Flanged Joint Analysis Using Parametrically Controlled Finite Element Approach

Dennis Martens, Charlie Hsieh, and Steve Massey, PVP-Vol. 399, (Design and Analysis of Pressure Vessels and Piping – 2000), ASME, 2000

The results of Finite Element Analysis (FEA) analysis of an ANSI 24 inch ANSI Class 150 flanged joint is presented. The use of 3-D FEA allows the engineer to more accurately evaluate a flange assembly subjected to internal pressure, external forces, and moments for flange stresses, gasket contact stresses, and address leak tightness. In a critical process piping system, the integrity of flanged joints is of great importance to the safety of operating facilities. To facilitate the finite element analysis of a flanged joint, a parametric-driven program was developed to aid the engineer in investigating flanged joints within the time and expense parameters associated with the normal design process in the refinery and chemical industry. The ability to predict the leak tightness of a flanged joint is discussed by the authors. The authors present recommendations for assuring that the flanged joint will be suitable for the intended service.


On Using Finite Element analysis for Pressure Vessel Design

Mike Porter, Dennis Martens, and Pedro Marcal, PVP-Vol. 388, ASME 1999

This paper presents a practical review of the use of PC-based Finite Element software in the analysis of typical pressure vessel components. The authors discuss element type selection criteria and features. Some of the different element formulations are discussed. Modeling parameters and convergence procedures are examined. Practical evaluation tolerances are discussed.


A Suggested Evaluation Procedure for Shell/Plate Element Finite Element Nozzle Models

Mike Porter, Dennis Martens, and S. M. Cauldwell, PVP-Vol. 388, ASME 1999

A procedure for evaluating the results of a finite element analysis employing shell/plate elements is proposed based on several previous papers by the authors and a review of other related works. This procedure relates the stress levels produced by the finite element software to the provisions of ASME Section VIII, Division 2.


Design of Flanged Joints Subjected to Pressure and External Loads

Dennis Martens, Charlie Hsieh, and Steve Massey, 388, (Fracture, Design Analysis of Pressure Vessels, Heat Exchangers, Piping Components, and Fitness for Service), ASME, 1999

The integrity of flanged joints is of great importance to the safety of operating facilities. This paper presents an analysis of a typical ANSI weld neck gasketed flanged joint. The analysis utilizes ASME Sect. VIII design rules plus design considerations from the ASME course “Design of Bolted Flange Joints” plus finite element methods to analyze flange design stresses and deflections. Comparisons of ASME Code vs. Finite Element Analysis (FEA) flange stresses as well as gasket contact stress distribution are presented in this study.


Results of FEA Analysis at Nozzle/Shell Junctions Subjected to External Loads

Dennis Martens, Steve Massey, Charlie Hsieh, and Willem Van Riet, PVP-Vol. 388, (Fracture, Design Analysis of Pressure Vessels, Heat Exchangers, Piping Components, and Fitness for Service), ASME, 1999

This paper presents the results of several nozzle and shell dimensional configuration analyses utilizing finite elements (FE). The authors utilized typical shell and nozzle dimensions with typically allowed external nozzle loading. These FE results are compared to WRC 107 results to determine if the FE results may be used to establish the critical variables necessary to construct a standard allowable piping load basis.


Sulfur Recovery Units

Dennis Martens, Joe Livesay, Mark Tonjes, NACE 1998

This paper reviews the fundamental corrosion issues encountered in sulfur recovery units. The information presented addresses the most common process applications, materials of construction, and corrosion mechanisms. The units considered are: Cold Bed Absorption (CBA), tail gas treating, and incineration. These units remove sulfur compounds from the acid gas process streams before they are vented to the atmosphere.

Measurement and Analysis of the Wind Induced Vibration of a Tall Stack

Mike Porter, Bob Blevins, and Dennis Martens, PVP-Vol. 377, n1, (Computational Technologies for Fluid/Thermal/Structural/Chemical Systems with Industrial Applications), ASME 1998

Field observers reported that two 260-ft (80 m) high stacks of a sulfur recovery plant exhibited significant vibration levels when wind velocities were between 35 and 45 ft/sec (10 and 13 m/sec). A static and dynamic Finite Element (FE) analysis of the stack was conducted to determine the natural frequency and stress in the stack. A flow-induced vibration analysis indicated that the vibration would occur at the coincidence of the vortex shedding frequency with the predicted natural frequency (0.5 to 0.7 Hz ) of the stack. Field measurements were conducted to quantify the natural frequency and damping of the stack by exciting the stacks with an attached cable and then measuring the rate and frequency of the free decay. These measurements confirmed the natural frequency predicted by the FE analysis. The measured damping factor of between 0.015 and 0.009 corresponds to a predicted response amplitude near the observed 0.5-ft (0.2 m) vibration amplitude. Analysis of the stresses in the stack and a field inspection showed that this level of vibration is not damaging to the stack or refractory lining.


Investigation of Flanges Subjected to Operating Conditions of Pressure, Temperature and Bending Moments

Dennis Martens, Charlie Hsieh, and Steve Massey, PVP-Vol. 368, (Analysis and Design of Composite, Process, and Power Piping and Vessels), ASME, 1998

The integrity of flanged joints is of great importance to the safety of operating facilities. This paper presents stress investigations of standard ANSI weld neck flanged joints utilizing spiral-wound and composite type gaskets. The joints are analyzed for the effects of pressure, temperature, and bending moments from the attached piping. The finite element investigation included the effect of varying gasket contact stress on the joint.

Finite Element Investigation of a CBA Reactor for the Effects of Thermal Cycling

Dennis Martens and Charlie Hsieh, PVP-Vol. 368, (Analysis and Design of Composite, Process, and Power Piping and Vessels), ASME, 1998

The Cold Bed Adsorption sulfur recovery process utilizes carbon steel reactor vessels that are subjected to thermal cycles. This paper presents the results of finite element investigation of the cyclic temperature profiles and operating stresses for the reactor vessels. The authors utilized a thermal model to establish temperature profiles resulting from the hot and cold processing conditions. These temperature results were placed in a stress investigation model. This model was utilized to investigate thermal, pressure and dead loading induced stresses. The stress results are compared to the 1995 (with addenda to 1996) ASME Section VIII Division 2 fatigue stress allowables utilizing the procedures included in the 1995 (with addenda to 1996) ASME Section VIII Division 2.


Stress Evaluation of a Typical Vessel Nozzle Using PVRC 3D Stress Criteria: Guidelines for Application

Mike Porter and Dennis Martens, PVP-Vol. 368, (Analysis and Design of Composite, Process, and Power Piping and Vessels), ASME 1998

The stress linearization methodology recommended in the PVRC 3D Stress Criteria: Guidelines for Application (Hechmer and Hollinger, 1997) is used to evaluate the stresses in a three-dimensional brick element model of a typical refining or chemical plant thin-walled nozzle. The results of the evaluation are compared with a 1996 analysis of the same nozzle using plate elements. The applicability of the Guidelines to routine nozzle analysis is discussed and a comparison is made to a previous evaluation proposal (Porter and Martens, 1996).


Investigation of Heat Exchanger Stayed Knuckle Tubesheet Stresses

Dennis Martens, Charlie Hsieh, and Mike Walker, PVP-Vol. 359, (Fitness for Adverse Environments in Petroleum and Power Equipment), ASME, 1997

This paper presents stress investigations of several stayed tubesheets utilizing knuckle designs using finite element analysis. The combination of pressure, differential tube and shell expansion, and tubesheet temperature gradient results in high localized stresses in the tubesheet knuckle area and tubes near the tube sheet. The necessary thermal boundary information required to support the stress investigation is addressed in the this paper.

The paper references previous work presented by Dennis Martens, Charles Hsieh and Christopher K. Brzon titled “Analysis of Tube Sheet Stress in a Sulfur Recovery Unit”, published in ASME PVP-Vol. 336, 1996.

A Comparison of Finite Element Codes and Recommended Investigation Methodology

Mike Porter, Dennis Martens, and Charles Hsieh, PVP-Vol. 359, (Fitness for Adverse Environments in Petroleum and Power Equipment), ASME 1997

Significantly different results attained from the use of three Finite Element codes used in the analysis of a large complex model are discussed. Building on previous work by the authors regarding the comparison of stress results from several commercial FE codes used on a simple model, this paper recommends steps for an investigation methodology to aid in ascertaining results which are most representative, useful, and correct.

Analysis of Tubesheet Stresses in a Sulfur Recovery Unit

Dennis Martens, Charlie Hsieh, and Christopher Brzon, PVP-Vol. 336, (Structural Integrity, NDE, Risk and Material Performance for Petroleum, Process and Power), ASME 1996

The effects of thermal gradients and pressure are analyzed for a Sulfur Recovery Unit (SRU) firetube-type waste heat recovery exchanger. Increased operating temperatures due to the advent of oxygen enriched sulfur recovery technology raised concerns regarding highly stressed areas of the tubesheet. Stayed tubesheet designs are typically used in these SRU applications. Finite Element (FE) was used due to the complexity of the geometry involved. A thermal FE model of the tubesheet, tubes, and tube ferrules was used to establish the temperature profile. The thermal model incorporated the overall gas and steam side heat transfer coefficients including temperature boundary conditions. The developed thermal profile was used as the basis for a FE stress analysis model.


Practical Vessel System Force/Moment Analysis Using Finite Element Techniques

Mike Porter, Dennis Martens, and Don Skaggs, PVP-Vol. 336, (Structural Integrity, NDE, Risk and Material Performance for Petroleum, Process and Power), ASME 1996

In the design of a sulfur recovery plant incorporating three closely coupled pressure vessels, differential thermal growth of the vessels was perceived as a potential stress problem for the vessel connections. Due to the size of the vessels, the anchor point locations, the foundation stiffness, and the type of connections, the results obtained from a typical piping flexibility analysis were deemed to be of questionable accuracy. Design questions were answered using Finite Element techniques that, due to advances in the software, were both timely and cost-effective for use in the design process. The process employed and the results obtained are presented as an example of the tools currently available to the design engineer.


Nozzle Stiffness and Stress Computation Using a Parametrically Controlled Finite Element Modeling Approach

Mike Porter, Dennis Martens, and Charles Hsieh, PVP-Vol. 336, (Structural Integrity, NDE, Risk and Material Performance for Petroleum, Process and Power), ASME 1996

A method is presented which allows the vessel engineer to more accurately evaluate the flexibility and stresses in vessel nozzles within the time and expense parameters associated with the normal design process. In a critical process piping system design, the vessel design engineer first calculates nozzle stiffnesses for inclusion of the nozzle spring constants in the piping system analysis. The loads generated from piping analysis are then fed back to the vessel engineer for stress calculation. In an earlier paper “Improving the Accuracy of Piping Programs When Analyzing Closely Coupled Equipment,” the wide divergence in nozzle stiffnesses and stresses computed by the available formula approaches was illustrated. Additionally, it was shown that it is desirable to use the Finite Element approach to better assess both the stiffnesses and the stresses in vessel nozzles. To facilitate FE nozzle modeling, a parametric-driven program was developed to aid the vessel engineer in using the FE program COSMOS/M.


A Comparison of the Stress Results from Several Commercial Finite Element Codes with ASME Section VIII, Division 2 Requirements

Mike Porter and Dennis Martens, PVP-Vol. 336, (Structural Integrity, NDE, Risk and Material Performance for Petroleum, Process and Power), ASME 1996

The interpretation of 3-D stresses computed using Finite Element (FE) techniques has been the focus of an ongoing PVRC study “3D Stress Criteria: Guidelines for Application” (Hechmer and Hollinger, 1995). This paper proposes an FE stress evaluation procedure for plate element models in the spirit of that recommended in the PVRC guideline. A sample model is analyzed, using five commercially available FE codes. The results are compared to illustrate the variability in the FE codes. Additionally, the practical difficulties in implementing the PVRC recommended procedure in the various FE codes is discussed.

Vortex-Induced Vibration and Damping of Thermowells

Dennis Martens, Robert Blevins, and Bruce Tilden, PVP-Vol. 328, Flow Induced Vibration, ASME, 1996 with Robert Blevins and Bruce Tilden, (published in the Journal of Fluids and Structures (1998) 12, 427-444 Article No. fl970150)

Thermowells are installed in process piping to protect fluid temperature measuring instruments from the fluid flow. The thermowells are subject to vortex-induced vibrations by the process fluid. The resonant response is limited by damping. Measurements of thermowell vibration damping were made and used to establish criteria for acceptable design under vortex-induced vibration. Comparison is made with the damping of steel stacks and heat exchanger tubes.

Improving the Accuracy of Piping Programs When Analyzing Closely Coupled Equipment

Mike Porter, Dennis Martens, and A. C. Korba, PVP-Vol. 315, (Fitness for Service and Decisions for Petroleum and Chemical Equipment), ASME 1995

Standard piping analysis programs, used to determine the deflections and stresses in piping systems, are often employed under conditions that are not within the scope of assumptions in the formulation of the programs. Such a case is the analysis of closely interconnected heat exchangers, pressure vessels and other such equipment. The major problem when using a piping analysis program is that the nozzle connections are modeled infinitely rigid rather than as an element with a finite flexibility. The results generated by such misapplication of the programs is usually (but not always) very conservative. This paper will demonstrate a hybrid method which employs conventional piping analysis software, WRC-107, WRC-297 and Finite Element (FE) software to attempt to obtain a better estimate of the deflections, forces, moments, and stresses. The results of the hybrid analysis are then compared to a complete FE analysis and a standard piping analysis of a sulfur recovery system. The indicated nozzle flexibilities and stresses varied considerably depending upon the analysis methodology used.

Investigation and Repair of Heat Exchanger Flange Leak

Mike Porter and Dennis Martens, (Developments in Pressure Vessel and Piping), ASME 1994, (“Outstanding Technical Paper” for the 1994 ASME Piping and Pressure Vessel Conference)

During original operations, a leak developed in the bolted tube sheet joints of a stacked pair of type 321 stainless steel TEMA type BEU exchangers in 8.27×106 N/m2 (1200psi) 371 °C (700°F) Hydrogen and Oil service (see Figure 1). After unsuccessful attempts to repair the leak an evaluation of the flanged joint design was undertaken. Finite Element analysis of the tube sheet joint provided the basis for understanding the complex temperature profile, displacements, and stresses in the joint. The exchanger was successfully repaired using a weld ring gasket closure with the addition of disc spring washers to the bolting (see Figure 2). Observation of the flanged joint during startup and operation confirmed the Finite Element Analysis results.