Boilers in coal-fired thermal power plants were often damaged by earthquakes such as the Great East Japan Earthquake in 2011. Since the coal-fired thermal power generation has been one of the main power generation methods after the Great East Japan Earthquake, mitigation of damage of boilers in thermal power plants by earthquakes is the very important subject in order to recover our daily life immediately after strong earthquakes. Meanwhile, a boiler in a coal-fired thermal power plant was damaged by Hokkaido Eastern Iburi Earthquake in 2018, and this damage was one of the causes of Hokkaido’s prefecture-wide blackout. According to a report by an electric power company, a damage occurred between a furnace and a cage of the boiler. In general, lengths, shapes, weights and so on of a furnace are different from a cage, so vibration characteristics and seismic response are different as well. Thus the connecting part between the furnace and the cage is a weak point in the boiler, and the damages often occurred there. Therefore this paper investigates seismic response of a boiler by a numerical analysis using a frame model from the viewpoint of the damage of the furnace and the cage. Various seismic waves were used as input waves in order to investigate the influence of the input wave. A result of a modal analysis was also provided in this paper.

In Hokkaido Eastern Iburi Earthquake in 2018, strong ground motion attacked a coal-fired thermal plant. A connecting part of a furnace and a cage of a boiler in the power plant and steam tubes in that part were damaged. Consequently the damage of the power plant induced a large impact to society. Suppressing relative displacement between the furnace and the cage might be effective to reduce this kind of the damage, because the furnace and the cage vibrate independently during earthquakes. Therefore this paper proposes application of dampers to the connecting part of the furnace and the cage of the boiler based on the results of the Part 9. The dampers are installed horizontally between the furnace and the cage and suppress relative displacement. The length and shape of the furnace are different from the cage, thus amount of the thermal expansion is also different. Therefore the damper has to allow the difference of the amount of the thermal expansion. In addition, the damper has to generate large damping force from the small vibration. Thus a viscous damper with high viscosity fluid is applied as a damper which satisfies above-mentioned requirements. A seismic response analysis using a frame model was conducted in order to verify the effect of the damper and to investigate the influence of the damping capacity of the damper. As a results, it was confirmed that the relative displacement between the furnace and the cage can be suppressed by applying the damper.

The proof test results of 1669 Spring-Operated Pressure Relief Valves (SOPRV), which were previously installed in active processes, were analyzed with respect to proof test ratio (R), time-in-service (TIS), set pressure (SP), working fluid (WF), material composition of the SOPRV and, if an SOPRV failed-to-open (FTO), the root cause of failure in the FTO failure mode if available. Many of these SOPRV had accumulated TIS in excess of the normal maximum of five years yet proof testing indicated that most would have functioned properly. This paper examines the results of the analysis and provides guidelines under which it is appropriate to consider extending TIS for individual SOPRV.

When cylindrical tanks installed in the ground, such as oil tanks and liquid storage tanks, receive strong seismic waves, including the long-period component, motion of the liquid surface inside the tank called sloshing may occur. If large-amplitude sloshing occurs and the waves collide with the tank roof, it may lead to accidents such as damage of the tank roof or outflow of internal liquid of the tank. Also, there is a possibility that the internal components in the tank may be damaged due to the fluid force generated by the flow of the sloshing. In order to evaluate the load acting on the tank roof, it is considered that the liquid surface shape and the liquid surface velocity are required as input parameters. In order to evaluate the load acting on the internal component in the tank, the flow velocity generated by sloshing is required as an input parameter. If the sloshing wave height is small, these values can be calculated based on the linear potential theory. However, when the sloshing wave height increases, the sloshing becomes nonlinear, and the difference between the nonlinear sloshing behavior and the linear sloshing behavior. Therefore, the method of evaluating nonlinear sloshing behavior is necessary to evaluate the design load of tank under the large sloshing wave height condition. In this paper, new methods of evaluating nonlinear sloshing behavior are proposed for the first-order sloshing mode of a cylindrical tank, which can evaluate the maximum nonlinear sloshing wave height, the nonlinear liquid surface shape, the liquid surface velocity, and the flow velocity. Proposed methods, which consist of simplified equations, are expected to be applied to a new sloshing load evaluation method in primary design. 1

The stress corrosion cracking of tube-to-tubesheet joints is one of the major faults causing heat exchanger failure. After the expansion process, the stresses are developed in a plastically deformed tube around the tube-to-tubesheet joint. These residual stressed joints, exposed to tube and shell side fluids, are the main crack initiation sites. Adequate contact pressure at the tube-to-tubesheet interface is required to produce a quality joint. Insufficient tube-to-tubesheet contact pressure leads to insufficient joint strength. Therefore, a study on the residual stress and contact pressure that have a great significance on the quality of the tube-to-tubesheet joint is highly demanded. In this research, a 2D axisymmetric numerical analysis is performed to study the effect of the presence of grooves in the tubesheet and the expansion pressure length on the distribution of contact pressure and stress during loading and unloading of 400 MPa expansion pressure. The results show that the maximum contact pressure is independent of the expansion pressure length. However, the presence of grooves significantly increased the maximum contact pressure. It is proven that the presence of grooves in the tubesheet is distinguishable from the maximum contact pressure and residual von mises equivalent stress. The tube pull-out strength increases with the expansion pressure and the number of grooves. In conclusion, the presence of the grooves affects the tube-to-tubesheet joints.

In the steam generator, anti-vibration bars are often provided to support the tube bundle. Due to the non-linearity of the support, the fluid-solid coupling simulation of large-scale tube bundles supported by the anti-vibration bars will bring great trouble. In order to solve this problem, this paper conducts experiments on the heat exchange tube based on the turbulent power spectrum to generate the excitation force. By changing the support form, the force of the lift and the direction of the drag and the ratio of the force, the excitation of the heat exchanger tube is researched. The results of the displacement response, the contact force and friction force distribution, and the contact angle distribution provide reference for the subsequent model simplification. Experiments show that the contact rate increases with the increase of the excitation force, and the contact force and the friction force increase with the increase of the excitation force. When the heat exchange tube contacts with the anti-vibration bars, the contact angle is mostly less than 45°, more than 50% of the contact angle is less than 45°. The work rate of the tube at the edge is greater than the work rate of the tube in the center.

A 3D parallel high-order spectral difference (SD) solver with curved local mesh refinement is developed in this research to simulate flow through stenoses of varied degrees (50%, 60%, 65%, 70% and 75%) of radius constriction at inlet Reynolds number of 500. This solver employs high-order curved mesh in the vicinity of arterial wall and the local mesh refinement technique reduces the overall computational cost by distributing more elements in critical regions. In simulation of flow through stenosis of 50% radius constriction, velocity profiles predicted from the SD solver agree well with previous DNS results and experimental data. Mesh independency study shows that numerical results from a conforming and a non-conforming mesh agree well with each other. When the constriction degree is larger than 50%, visualizations through iso-surfaces of Q-criterion show that vortex rings are ejected from the stenosis throat, advecting downstream before they hit the vessel walls and they finally break down and merge into a large bulk region of small-scale turbulence. The observation is consistent with the vorticity contour which is characterized by development of the Kelvin-Helmholtz instability when shear layers are formed, rolled up and advected downstream between the central jet and the recirculation region. When the constriction degree turns to 75%, the flow transitions rapidly downstream of stenosis throat and dramatic pressure drop is witnessed. This provides a fluid-dynamic explanation for clinical definition of critical stenosis (i.e. over 75% luminal radius narrowing). Furthermore, pressure drop across a stenosis is found to be proportional to square of ratio of non-stenosed area to minimum area at the stenosis throat with a linear correlation coefficient equal to 0.9998. Finally, this solver is proven to have excellent scalability on massively parallel computers when multi-level refinement of meshes is performed to capture small-scale structures in the turbulence region.

Identifying the coupled system natural frequencies and dynamic behavior of systems in the presence of fluid-structure interaction is one of the most important issues in the engineering design of buildings, road vehicles and aircraft. This paper presents an efficient and flexible finite element procedure using fully vectorized codes for the free and forced vibration analysis of a rectangular plate in contact with fluid. The 4-node MITC plate finite element (MITC4) based on the Mindlin plate theory is used to simulate the plate, while the 8-node acoustic pressure element is used to simulate the fluid. The derived system of equations using structural displacements and fluid pressures yields a non-symmetric system of equations. Solving the generalized eigenvalue problem for the non-symmetric system is more computationally intensive compared to solving the generalized eigenvalue problem for symmetric systems. The modal expansion technique is used to reduce the model size. Then the reduced non-symmetric system is symmetrized by right eigenvectors. The Newmark method is used to solve the forced vibration problem of the coupled systems. The effect of the height of the fluid on the natural frequencies is discussed. The natural frequencies and transient responses are in good agreement with those obtained from the commercial finite element software. Moreover, the technique is proved to be effective to solve the coupled system.

Since 1982 the nuclear industry has employed weld overlay repairs to address intergranular stress corrosion cracking (IGSCC) in boiling water reactors (BWR) and primary water stress corrosion cracking (PWSCC) in pressurized water reactors (PWR). The American Society of Mechanical Engineers (ASME) has created several documents to provide rules and guidelines for weld overlay repair of nuclear components that have experienced stress corrosion cracking (SCC). These documents include ASME Code Case N-504-4 and ASME Section XI, Nonmandatory Appendix Q which specifically address weld overlay repair of stainless steel components. Recently, stainless steel components that have experienced thermal fatigue cracking at the inner diameter surfaces have been repaired with structural weld overlays (SWOL) using the methodology of Code Cases N-504-4 and N-740-2. The SWOL is a good choice for repair of thermal fatigue cracks in piping because it provides structural reinforcement to the affected location and places the inside diameter (ID) surface into compression preventing, or significantly reducing, further flaw growth. However, the rules of Case N-504-4 and N-740 were not specifically written to address thermal fatigue cracking as the primary cause and may not adequately address design, analysis and examination requirements when thermal fatigue is the active mechanism because it is very different in nature than SCC. For example, SCC is driven by a combination of environment, steady state operating stresses, residual stresses from welding and fabrication processes, and operating temperature, whereas thermal fatigue is driven by thermal stress cycles resulting from fluid thermal cycling or stratification. The source of the thermal events that result in cracking may not be as well understood or predictable as SCC degradation. In addition, weld overlays applied to address SCC are constructed of SCC resistant material but are not resistant to thermal fatigue. Therefore, ASME Section XI recognized that alternative rules were needed for repair of piping damaged by thermal fatigue. This paper provides a technical basis for weld overlay repair of components that have experienced thermal fatigue cracking. It addresses design, analysis and examination requirements considering the nature of thermal fatigue in nuclear piping systems. The Code Case was originally drafted based on the industry accepted rules of Case N-504-4 and Appendix Q but includes appropriate modifications needed to address thermal fatigue cracking. These modifications include removing restrictions such as the delta ferrite limit for PWRs that is only applicable to address SCC in BWR environments, and enhancements to the examination requirements to ensure that the repaired location is adequately monitored throughout the remaining service life of the plant. The purpose of this paper is to document the technical basis for Code Case N-894, which is currently still under development by ASME Section XI.

Mixing flow causes fluid temperature fluctuations near the pipe walls and may result in fatigue crack initiation. The authors have previously reported the loading sequence effect on thermal fatigue in a mixing tee. The fatigue damage around the hot spot, which was heated by the hot jet flow from the branch pipe, obtained by Miner’s rule was less than 1.0. Since the strain around the hot spot had waveforms with periodic overload, the loading sequence with periodic overload caused reduction of the fatigue life around the hot spot. In this study, the effect of a single overload on the fatigue crack growth rate was investigated in order to clarify the reduction of the fatigue life at the mixing tee due to strain with periodic overload. In addition, the prediction method of the fatigue life for the variable thermal strain at the mixing tee was discussed. It was shown the crack growth rate increased after an overload for both cases of tensile and compressive overloads. The effective strain amplitude increased after the application of a single overload. The fatigue life curve was modified by considering the increment of the effective strain range. The fatigue damage recalculated using the modified fatigue life curve was larger than 1.0 except in a few cases. The fatigue life could be assessed conservatively for variable strain at the mixing tee using the developed fatigue curve and Miner’s rule.

This paper presents a concept design methodology to establish robust designs against thermal fatigue of 2″ and 3″ thermal tee branch sizes on 14″ pipework, which are subjected to relatively hot and cold fluid turbulent mixing, for use in Pressurised Water Reactor Plant. Thermal tees can be subjected to extremely demanding thermal fatigue conditions, e.g. high temperature fluctuations causing high stress ranges where hot and cold fluid mix at the tee position from different branches of the system, these conditions ultimately limiting design life. Prior to conducting a full design justification to the ASME Section III code [1], which for these components Rolls-Royce has justified by a section NB3200 approach using finite element analysis and computational fluid dynamics, analysis/iteration time can be saved, and the likelihood of a robust design being found increased, by understanding the effect and significance of geometric features of the tees. Fundamentally, establishing which features have a greater influence on the thermal fatigue performance of the tee and setting maximum and minimum values for these features. This paper presents an approach that can be used in the concept design phase to understand the influence of variables such as: branch throat internal diameter, run versus branch reinforcement, inclusion of integral orifices and branch fluid flow rate, and also of how they interact with each other in relation to providing a code compliant design. The approach is also used to size such features so that they are away from ‘cliff edges’ in performance, i.e. away from values that are likely to produce high stress levels and reduce design life. The paper covers: the variables chosen to be investigated, the methodology including the associated stress models to understand the effect of variable change and positioning in the ‘design landscape’, and identifies which geometric features should be maximised or minimised in size to maximise thermal fatigue life.

In the valve industry, there is combined demand from the end-users for fugitive emissions reduction and energy efficiency improvement through the reduction of stem/packing friction forces. These two different goals will involve opposite trends on the load to be applied on the packing i.e. high load for good tightness and low load for low friction. Thus, the ability to define optimal ranges of packing tightening is important. Nevertheless, no standardized method for packing calculation nor packing full characterization (mechanical, friction, sealing performance vs. packing load,..) exists in Europe, as for bolted flange joints and associated gasket with EN1591-1 [1] and EN13555 [2]. In collaboration with ESA (European Sealing Association, www.europeansealing.com ) and FSA (Fluid Sealing Association, www.fluidsealing.com ), the Fluid Equipment Committee of CETIM has developed a tool for the optimization of packing. A set of tests enables to get the packing characteristics needed for the calculation. These tests can also be used for the comparison of packing materials and/or installation procedures performances in defined test conditions. This paper details the proposed calculation method and describes the associated test rigs and procedures. First test results and a calculation example are also given to show how the method works.

In flanged connections, all gaskets have some level of fluid leakage, depending on gasket type and other factors. Using published Room Temperature Tightness (ROTT) test data and draft PVRC (Pressure Vessel Research Council) equations, a simple model to calculate the predicted tightness / leak rates of various gasket materials has been previously documented. The model assumes a set of draft empirical equations previously published by ASME / PVRC but with an incorporated stress loss factor. Tightness at flange assembly as well as following unloading can be estimated with the model. The EN 13555 test standard includes measuring the test gas leak rates for a series of gasket stresses but at a single operating pressure for each test. Correlation of EN 13555 data with PVRC model predicted leak rates over a range of manufactured gasket materials is demonstrated. The leak rate data for specific gasket materials have been found to compare favorably with the leak rates at assembly as determined in using the PVRC model. The application and corresponding limitations of certain EN 13555 gasket parameters are discussed. The end user may wish to consider the use of the PVRC empirical approach to estimate predicted long-term leak rates of competing gasket materials as a key factor in the gasket selection process.

A typical Fluid Catalytic Cracking Unit (FCCU) generates high temperature flue gas in the process of regenerating the catalyst. This flue gas is diverted to a stack after removal of catalyst fines and excess heat using a Waste Heat Recovery Unit (WHRU) or CO boiler. This flue gas line is a large diameter (1.2 m /2 m) piping and is a combination of Hot Wall (bare SS304H piping with external insulation) upstream of Orifice Chamber and Cold Wall (Carbon steel piping with internal refractory lining) for the downstream side. In a major revamp project, large portion of flue gas line was replaced with some dimensional and design changes. A crack was noticed at the SS304H side of hot wall to cold wall transition joint downstream of Orifice Chamber after approximately 2 years in operation. The line operates around 700 °C and 0.15 Bar(g) at the location of the crack. The initial crack was measured to be approximately 250 mm to 300 mm and grew to a full circumference crack in a short time resulting in minor flue gas leaking with catalyst fines. This paper discusses the details on how the issue was addressed on site and a temporary repair (i.e. welding of a box on high temperature piping) was carried out online safely, while the unit remained in operation. Further, the paper presents the root cause assessment and design modifications implemented for hot wall to cold wall transition joint during a scheduled turnaround.

Compact and thermally efficient, Printed Circuit Heat Exchangers (PCHEs) are favored for use in next generation nuclear power plants. Containing thousands of small working fluid channels distributed in a solid 316H or 800H block, PCHEs can handle high pressures and operating temperatures required by generation IV nuclear plants. Advanced nuclear reactors will require the certification of a nuclear service PCHE design by construction codes, such as BPVC Sec-3. Compliance with this standard requires Creep fatigue and ratcheting analyses be performed for expected loading service transients. Realizing this analysis in PCHEs requires a simplified and flexible modeling approach that can be run over dozens of transients for multiple heat exchanger geometries. The Rich Environment Heatex-changer Transient (REHT) model is being developed to provide a full PCHE model needed to properly resolve Sec-3 loading conditions without the complexity inherent in resolving all facets of the PCHE geometry. This work introduces the thermohydraulic model that is the core of the REHT model. An example problem modeling an experimental scaled PCHE is presented. The ability of the REHT model to simulate fluid flow through a directional varying microchannel core of two heat exchanging streams is demonstrated. The REHT model resolves PCHE thermohydraulics using simple model definitions and minimum computational overhead, making it an ideal design tool.

This paper describes the use of Carbon Fiber Reinforced Polymer (CFRP) for the repair of leaking Fiber Reinforced Polymer (FRP) pipe. The existing piping system, which is used for slurry transport, consisted of straight pipe, reducers, and elbows connected by bell and spigot joints. The piping system was evaluated for pressure, deadweight, and fluid thrust loads in accordance with B31.1 Power Piping Code and ASME BPVC Section III, Code Case N-155. The pipe leaks and joint repairs were in accordance with ASME PCC-2 and ASME BPVC, Section III, Code Case N-155. The CFRP repair was done with Aegion TYFO ® Fibrwrap ® carbon fiber reinforced fiber wrap (TYFO SCH-41-2X) saturated with epoxy. The repair uses the unidirectional carbon fiber installed in layers 90° to each layer. The circumferential layers are used for hoop pressure stress while the axial layers restrain axial pressure, deadweight, and fluid thrust loadings on the pipe.

The pressure surge in pipes due to change in operating conditions exerts an axial load on elbows proportional to the change in momentum of fluid and unbalanced pressure forces. The response of piping structure to such load needs the full time history analysis in three dimensional spaces which is cumbersome process due to high computing memory requirements and long simulation time. In present work it has been shown that using Rayleigh energy balance for each elbow-load configuration, the system can be reduced to equivalent 1D spring mass system and the response can be estimated by solving 1D equation of motion. Then it has been recommended to simulate the response of each elbow which gives good approximation of dynamic amplification of displacement also called as Dynamic Load Factor (DLF). These dynamic load factors for each elbow can be used for the interaction of forces using static equivalent response in 3D space. This approach is pseudo static equivalent analysis where the load amplifications factors DLF are estimated from the dynamic force profile and system response in one-dimensional space. An algorithm is developed for the above explained process. Most of the engineers are using the DLF = 2 for the load estimation due to absence of method to estimate the dynamic load factor. The approach was proposed by Goodling in 1989 and still widely followed in the industry. The present paper discusses uncertainty and inaccuracy involved in performing approximate analysis and shows the significance and need of performing full force time history analysis. The proposed method shows very good agreement with the time consuming 3D full force time history results. There are also limitations for the proposed method. As the spring mass system is simulated with dimensional reduction to single frequency domain, the pipe supports and guides should be properly placed before applying the present approach. It has been shown that with proper support configuration, this simplified approach yields very good approximation of surge load on pipes with reduced time.

Since 1982 the nuclear industry has employed weld overlay repairs to address intergranular stress corrosion cracking (IGSCC) in boiling water reactors (BWR) and primary water stress corrosion cracking (PWSCC) in pressurized water reactors (PWR). The American Society of Mechanical Engineers (ASME) has created several documents to provide rules and guidelines for weld overlay repair of nuclear components that have experienced stress corrosion cracking (SCC). These documents include ASME Code Case N-504-4 and ASME Section XI, Nonmandatory Appendix Q which specifically address weld overlay repair of stainless steel components. Recently, stainless steel components that have experienced thermal fatigue cracking at the inner diameter surfaces have been repaired with weld overlays using the methodology of Case N-504-4 and Appendix Q. This repair technique is appropriate to address thermal fatigue cracking because it provides structural reinforcement to the affected location and places the inside diameter (ID) surface into compression preventing, or significantly reducing, further flaw growth. However, the rules of Case N-504-4 and Appendix Q were not specifically written to address thermal fatigue cracking as the primary cause and may not adequately address design, analysis and examination requirements when thermal fatigue is the active mechanism because it is very different in nature than SCC. For example, SCC is driven by a combination of steady state operating stresses, residual stresses from welding and fabrication processes, and temperature, whereas thermal fatigue is driven by thermal stress cycles resulting from fluid thermal cycling or stratification. The source of the thermal events that result in cracking may not be as well understood or predicable as SCC degradation. Therefore, alternative rules are needed for repair of piping damaged by thermal fatigue. This paper provides a technical basis for weld overlay repair of components that have experienced thermal fatigue cracking. It addresses design, analysis and examination requirements considering the nature of thermal fatigue in nuclear piping systems. The basis begins with the industry accepted rules of Case N-504-4 and Appendix Q and discusses the appropriate modifications needed to address thermal fatigue cracking. These modifications include removing restrictions such as the delta ferrite limit that is only applicable to address SCC, and enhancements to the examination requirements to ensure that the repaired location is adequately monitored throughout the remaining service life of the plant. The purpose of this paper is to outline the basis for a new ASME Code Case that will contain the appropriate rules for weld overlay repair of Class 1, 2 and 3 stainless steel piping degraded by thermal fatigue cracking. The new Case is currently in draft form and the requirements and specific details are still evolving. Thus, it is envisioned that this technical basis will be revised to include updates and revisions to the Case.

During the solid fluidization exploitation of shallow non-diagenetic NGHs (Natural Gas Hydrates) in the deep-water, hydrates together with mineral sand, natural gas, seawater and drilling fluids flow in the production pipeline. Natural gas released from hydrates during the process of solid fluidization will reform hydrates under the suitable conditions. Therefore, research on the formation and dissociation of methane hydrates in the presence of fine-grain sands is of great significance for ensuring the flow assurance of solid fluidization exploitation of shallow non-diagenetic NGHs in the deep-water field. In this paper, a high-pressure autoclave was used to carry out the experiments of hydrate formation and dissociation under different initial pressures and particle sizes of the fine-grain sand, for investigating into the hydrate induction time, formation amount, rate and dissociation affected by the presence of the fine-grain sand. Results indicated that hydrate formation kinetics in the presence of fine-grain sand was supposed to be also affected by mass/heat transfer, thermodynamics and kinetics. The fine-grain sand would be dispersed in the water phase under the effect of buoyancy, gravity and shearing force. Besides, the fine-grain sand at the gas-water interface would hinder the mass transfer of the methane gas into the water, inhibiting the nucleation of the hydrates, which was more obviously at the lower pressure. When the driving force for hydrate formation was larger, hydrate formation amount increased with the decrease of the particle size of the fine-grain sand. However, hydrate formation amount decreased with the decrease of the particle size of the fine-grain sand when the driving force for hydrate formation was lower. The average growth rate in the presence of fine-grain sand with 2.9 μm was larger than that of 9.9 μm. However, hydrates grew rapidly and subsequently tended to grow at a lower rate in the presence of fine-grain sand with 2.9 μm at 8.0 MPa initial pressure, which was assumed to be affected by the unconverted water wrapped inside the hydrate shell. The changing trends of gas emission during the dissociation process between the sand-containing system and the pure water system were nearly the same. The amount of gas emission reached a peak value within 15 minutes and then tended to stabilize. The difference in the amount of gas emission mainly depended on the formation amount before hydrate dissociation. Hydrates grew rapidly once methane hydrates nucleated in the presence of the fine-grain sand at the lower pressure, which would increase the plugging risk during the process of the solid fluidization exploitation. Further study of the fine-grain sand on flow assurance during hydrate dissociation process should be done in the future. The results of this paper provided an important theoretical basis and technical support for reducing the risk in the process of the solid fluidization exploitation of shallow non-diagenetic NGHs in the deep-water field.

An important step in a pipeline-construction project is confirming that the piping and facilities are adequate for the expected operating pressures. This confirmation is done via a static strength test using a test fluid. All fluids have mass and internal energy. Fluids under pressure have significantly elevated internal energy. All fluids are compressible to some greater or lesser extent, and the fluid added to raise the pressure of the fluid in the bulk volume adds significant energy. The raw mass of a fluid must be considered when evaluating terrain elements and support elements (i.e., pipe stands and pipe racks). The selection process for a test fluid should always endeavor to minimize the total risk of the entire process. There is guidance in the primary pipeline design/construction codes (e.g., ASME B31 series) for many of the important considerations for managing the risk associated with the tests required to perform this confirmation of fitness for purpose. This code-guidance has historically not shown a clear preference for the selection of one particular test-medium over another. Some jurisdictions have written regulations that step away from ASME guidance and do show a clear preference for hydrostatic testing over pneumatic testing. This preference manifests itself in several ways, but the primary representation is the requirement in statutes and regulations that a pneumatic test have an “exclusion zone” around the test to reduce the risk of injury during the test. These documents tend to not have an exclusion-zone requirement for hydrostatic tests. This paper is undertakes to demonstrate the relative risks of liquid vs. gaseous test media and presents a background of why pneumatic tests have been singled out by regulators as higher risk and shows why this regulatory preference can result in actually increasing risk rather than decreasing it.