Research Papers: Design and Analysis

J. Pressure Vessel Technol. 2018;140(6):061201-061201-6. doi:10.1115/1.4041488.

In this paper, a novel visual experimental apparatus for simulating seafloor hydrothermal venting is proposed. The instrument consists mainly of an acrylic pressure vessel and a hydrothermal fluid syringe pump, which provided a 360 deg view of the simulated hydrothermal venting and plumes. Theoretical calculation and finite element analysis (FEA) were conducted to demonstrate the appropriateness of material selection and structural design for the acrylic pressure vessel. The experimental apparatus was tested at elevated temperature and pressure of up to 300 °C and 12 MPa. Hydrothermal venting experiments were successfully carried out with this apparatus, and clear images of hydrothermal plumes were obtained.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2018;140(6):061202-061202-11. doi:10.1115/1.4041489.

Hydraulic accumulators are vessels charged with inert gas used to store pressurized fluid to actuate specific functions. In particular, they are widely used as controls for remote system such as in deep water drilling. In this application, they assume a fundamental importance because they are responsible of the actuation of the blowout preventer valves (BOP), which have to be intrinsically safe and reliable. A direct method (DM) for the design of the subsea rapid discharge accumulators is presented and compared with the API 16D Method C, which is the primary international standard concerning the accumulators sizing. The design must ensure that the entire functional volume required (FVRtot) by all the functions will be delivered at or above the minimum operating pressure (MOPi). The DM presented is based on a fully mathematical model of the charging and discharging phases, which evaluates the pressure inside the accumulators during all the actuations. The actuator design includes physical representation of the processes, the influence of the operating conditions, and the effect of thermal uncertainties. A specific “failure plane” has been demonstrated, in a sequence of three actuations, where failure at specific condition of subsea and surface temperatures may occur.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2018;140(6):061203-061203-18. doi:10.1115/1.4041340.

The design and fabrication of shop-welded and prefabricated relatively small tanks, when compared to field-welded tanks, used in the upstream segment of the oil and gas industry is governed by the American Petroleum Institute specification 12F (API 12F). This study explores the changing designs of API 12F tanks to include a new rectangular cleanout design with reinforcement as shell extension internally of cleanout frame and a stepped shell design. This study also investigated the introduction of two additional tank sizes in addition to existing eleven tank sizes in the current 12th edition of API 12F. The adequacy of the new design changes and proposed tank designs were verified by elastic stress analysis with nonlinear geometry, elastic–plastic stress analysis with nonlinear geometry, and elastic buckling analysis to verify their ability to operate at a design internal pressure of 16 oz/in2 (6.9 kPa) and maximum pressure during emergency venting of 24 oz/in2 (10.3 kPa). A vacuum pressure of 1.5 oz/in2 (0.43 kPa) was also investigated using the elastic buckling analysis. The stress levels and uplift of the tanks are reported in this report to provide insights into the behavior of proposed API 12F tanks exposed to higher internal pressure and vacuum pressure.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2018;140(6):061204-061204-14. doi:10.1115/1.4041264.

In this paper, modified transfer entropy theory is combined with a surrogate data algorithm to produce a new method in order to identify nonlinearity in the vibration data of a damaged cylindrical shell. The proposed identification method can eliminate the necessity of acquiring baseline statistics by comparing the transfer entropy of original vibration data and that of surrogate data. Moreover, a new index ξ is established to reflect the degree of nonlinearity by quantifying the discreteness of the entropy of each group of surrogate data. Vibration tests are conducted and experimental data are analyzed to confirm the effectiveness of this method. Then, a semi-analytical method based on a Galerkin method and the classic shell theory is used to precisely predict the linear and nonlinear vibration response of a cylindrical shell under different damage circumstances. The corresponding results show that the proposed method can not only identify the structural damage but also be further applied to the evaluation of such damage for cylindrical shells. In addition, the influence of different load pressures and degrees of damage on the effectiveness of the identification method is analyzed and discussed. As verified, the proposed methodology can be potentially used for structural damage identification and evaluation in areas such as civil engineering, mechanical engineering, and ocean engineering.

Commentary by Dr. Valentin Fuster

Research Papers: Materials and Fabrication

J. Pressure Vessel Technol. 2018;140(6):061401-061401-7. doi:10.1115/1.4041433.

Pipe inspection is generally executed with ultrasonic pulse echo testing where a small range of pipe wall under an ultrasonic transducer can be evaluated in one measurement. Costly and laborious point-by-point testing is required if a whole range of a pipe should be inspected. The author has investigated fast defect imaging for a plate-like structure using a scanning laser source (SLS) technique as an efficient defect inspection technique. Although the imaging technique is feasible in noncontact remote measurements, only a plate cross section under the laser irradiation surface can be evaluated. This study describes detection of wall thinning on the back of a pipe using resonance of guided wave propagating in a pipe circumference by noncontact remote measurements with the SLS technique. The narrowband elastic waves are generated in a pipe by modulating laser pulses with fiber laser equipment. When the modulation frequency is in harmony with the resonance frequency of a circumferential guided wave, the distribution of the frequency spectrum peak obtained with the SLS technique becomes identical to the resonance pattern of the circumferentially guided wave mode. The distributions are distorted for a pipe with wall thinning on the back indicating that this technique has a potential for detection of defects on the back of a pipe.

Topics: Resonance , Pipes , Lasers , Waves
Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2018;140(6):061402-061402-10. doi:10.1115/1.4041339.

Autofrettage is a means of generating compressive residual stresses at the inner side of a thick-walled cylinder or hollow disk by causing nonhomogeneous plastic deformation of the material at the inner side. The presence of residual compressive stresses at the inner region of the cylinder/disk enhance the pressure withstanding capacity, fatigue life and the resistance to stress corrosion cracking of the component. Despite the hydraulic and swage autofrettage are the widely practiced processes in industries, there are certain disadvantages associated with these processes. In view of this, in the recent years, researchers have proposed new methods of achieving autofrettage. Rotational autofrettage is such a recently proposed autofrettage method for achieving the beneficial compressive residual stresses in the cylinders. In the present work, the rotational autofrettage is studied for a thick-walled hollow circular disk. A theoretical analysis of the residual stresses produced in the disk after unloading are obtained assuming plane stress condition, Tresca yield criterion and its associated flow rule. The analysis takes into account the effect of strain hardening during plastic deformation. Further, the effect of residual stresses in the typical SS304 and aluminum disk is studied by subjecting them into three different types of loads viz., internal pressure, radial temperature difference, and rotational speed individually. A three-dimensional (3D) finite element method (FEM) validation of the theoretical stresses during rotational autofrettage of a disk is also presented.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2018;140(6):061403-061403-7. doi:10.1115/1.4041057.

This paper proposes simplified methods to evaluate fatigue damage in a component subjected to cyclic thermal loads to visualize damage distribution by using typical computer-aided engineering systems. The objective is to perform the evaluations on a standard desktop PC within a reasonably short computation time. Three simplified methods for defining elastic stress ranges are proposed in place of the method in the ASME Subsection NH procedures. A thermal fatigue test that was previously performed using a type-304 stainless steel (304SS) cylinder is simulated to validate the proposed methods. Heat transfer and elastic analyses are conducted. Simultaneously with the analyses, fatigue usage factors are calculated using user subroutines formulated in this study, including the three simplified methods and the ASME NH-based method. The calculated values of the fatigue usage factor are visualized using a graphical user interface (GUI) incorporated into a commercial finite-element analysis (FEA) code. The fatigue usage factor distribution obtained using the simplified methods could be calculated without requiring large amounts of memory and long computation time. In addition, the distribution of the fatigue usage factor was consistent with the distribution of cracks observed in the test.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2018;140(6):061404-061404-5. doi:10.1115/1.4041435.

If a single subsurface flaw is detected that is close to a component's free surface, a flaw-to-surface proximity rule is used to determine whether the flaw should be treated as a subsurface flaw, or transformed to a surface flaw. The transformation from subsurface to surface flaw is adopted as flaw-to-surface proximity rules in all fitness-for-service (FFS) codes. These proximity rules are applicable when the component's free surface is without a stress concentration. On the other hand, subsurface flaws have been found under notches, such as roots of bolts, toes in welded joints, or geometrical discontinuities of components. The stress intensity factors of the subsurface flaws are affected by the stress concentrations caused by the notches. The stress intensity factor of the subsurface flaw increases with increasing stress concentration factor of the notch and decreasing ligament distance between tip of the subsurface flaws and the notch, for a given notch width. Such subsurface flaws are transformed to surface flaws at a distance from the notch tip for conservative evaluations. This paper shows the interactions of stress intensity factors of subsurface flaws under stress concentration fields. Based on the interaction, a flaw-to-surface proximity criterion is proposed for a circular flaw under the stress concentration field induced by a notch.

Commentary by Dr. Valentin Fuster

Research Papers: Operations, Applications and Components

J. Pressure Vessel Technol. 2018;140(6):061601-061601-7. doi:10.1115/1.4041688.

A resin slurry venting analysis was conducted to address safety issues associated with over-pressurization of ion exchange columns used in the plutonium uranium redox extraction (PUREX) process at the U. S. Department of Energy's Savannah River Site (SRS). If flow to these columns is inadvertently interrupted, an exothermic runaway reaction could occur between the ion exchange resin and the nitric acid used in the feed stream. This reaction generates significant quantities of noncondensable gases. To prevent the column from rupturing due to pressurization by these gases, rupture disks are installed on the column vent lines. The venting analysis models accelerating rate calorimeter (ARC) tests and data from tests that were performed in a vented test vessel with a rupture disk. The tests showed that the pressure inside the test vessel continued to increase after the rupture disk opened, though at a slower rate than prior to the rupture. The increase in the vessel pressure is modeled as a transient phenomenon associated with expansion of the resin slurry/gas mixture upon rupture of the disk. It is postulated that the maximum pressure at the end of this expansion is limited by energy minimization to approximately 1.5 times the rupture disk burst pressure. The magnitude of this pressure increase is consistent with the measured pressure transients. The results of this analysis demonstrate the need to allow for a margin between the design pressure and the rupture disk burst pressure in similar applications.

Commentary by Dr. Valentin Fuster

Research Papers: Pipeline Systems

J. Pressure Vessel Technol. 2018;140(6):061701-061701-11. doi:10.1115/1.4041792.

Oil and gas pipelines are subjected to various types of deterioration and damage over long service years. These damaged pipes often experience loss of strength and structural integrity. Repair mechanisms have been developed in restoring the loading capacity of damaged pipelines, and composite repair systems have become popular over the past few years. The mechanical properties of the putty/grout are critical to their potential application as infill materials in structural repair. In this paper, the compression, tensile, and flexural behavior of four epoxy grouts was investigated through laboratory tests. The stiffness of the grouts for compression, tensile, and flexural was found to be 6 GPa to 18 GPa, 4 GPa to 15 GPa, and 4 GPa to 12 GPa, respectively. The ultimate strength for all grouts was found from 62 MPa to 87 MPa, 18 MPa to 38 MPa, and 34 MPa to 62 MPa under compression, tensile, and flexural tests, respectively. The behavior of all the tested grouts is discussed. A finite element (FE) model simulating a composite-repaired pipe was developed and compared with past studies. The FE results show a good correlation with experimental test with margin of error less than 10%. By replacing the infill properties in FE model to mimic the used of different infill material for the repair, it was found that about 4–8% increment in burst pressure can be achieved. This signifies that the role of infill material is not only limited to transferring the load, but it also has the potential to increase overall performance of composite-repaired pipe.

Commentary by Dr. Valentin Fuster
J. Pressure Vessel Technol. 2018;140(6):061702-061702-6. doi:10.1115/1.4041689.

The economical and efficient transportation of hydrogen gas is necessary for it to become a widespread source of energy. One way to improve the economics is to lower the cost of building hydrogen gas pipelines. The recent modification to the ASME B31.12 Code for Hydrogen Piping and Pipelines begins to lower the cost of building pipelines for hydrogen service by allowing the use of high-strength steel that will provide the same margin of safety with thinner pipe walls. Less steel directly impacts the cost of materials and welding. A means of improving efficiency would be to increase the hydrogen gas pressure to augment the volume of products transmitted through the pipeline. The recent B31.12 code modification characterized dozens of fatigue crack growth test results conducted in hydrogen gas pressurized up to 21 MPa with an upper boundary of fatigue crack growth rate (FCGR), defined as a function where all measured FCGRs fall below this boundary. In this study, different pipe geometries, strengths, and pressures with established design protocols were evaluated to determine if the code would require further modifications should linepipes be designed for higher hydrogen gas pressures, up to 34 MPa. It was shown through a numerical exercise that the code could be minimally modified and safety margins would be adequate for those pressures for steels up to and including API-5 L Grade X70.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Pressure Vessel Technol. 2018;140(6):064501-064501-6. doi:10.1115/1.4041434.

A numerical simulation method is adopted to analyze the effects of three types of defect geometries ((1) a single defect on the inner surface, (2) a single defect on the outer surface, and (3) double coaxial defects on the inner surface and the outer surface.) on the residual strength of corroded X60 steel pipelines and equivalent stress and plastic strain distribution of the local defect area. The results show that the defect geometry exerts obvious effects on stress–strain distribution. The earliest plastic deformation occurs at the edge of the inner surface defect (type 1), but it occurs on the central part of both the outer surface defect (type 2) and the double defects (type 3). The appearance of defects greatly weakens the stability of the pipeline. For equivalent sum total corrosion defect depth, a single defect is more harmful to the pipeline than double defects.

Topics: Stress , Corrosion , Pipelines
Commentary by Dr. Valentin Fuster

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