Case Histories of the Resolution of Bolted Joint Leakage in the Oil and Gas Industry

Over the course of the past 20 years, methods have been developed for assessing the probability and root cause of bolted joint leakage based on sound engineering assessment techniques. Those methods were incorporated, in part, into ASME PCC-1-2010 Appendix O [7] and provide the only published standard method for establishing bolted joint assembly bolt load. As detailed in previous papers, the method can also be used for troubleshooting joint leakage. This paper addresses a series of actual joint leakage cases, outlines the analysis performed to determine root cause of failure and the actions taken to successfully eliminate future incidents of failure (lessons learned).

Numerical Simulation of Cavitating Flow in a Globe Valve: Comparison of OpenFoam and CFX

The efficiency of control valves operating with liquids is highly conditioned by the occurrence of cavitation when they undergo large pressure drops. For severe service control valves, the subsequent modification of their performance can be crucial for the safety of an installation. In this work, two CFD codes, OpenFoam [1] and Ansys-CFX, are used to characterize the flow in a globe valve, with the objective to compare their capabilities in solving cavitating flows in complex 3D geometries. In both codes, an Homogeneous Equilibrium approach is adopted, and phase change is modeled with a similar cavitation model. It is found that both solvers predict correctly the location of vapor cavities, but tend to underestimate their extension. The flow rate is correctly calculated, but in strong cavitating regimes, it is affected by the underprediction of vapor cavities. The force acting on the stem is found to be more sensitive to the computation parameters.

Elastic Allowable Stress Basis for Elevated Temperature Design in the Creep Regime

ASME Section VIII, Division II, Boiler and Pressure Vessel Code does not have any design by analysis procedures for designing pressure vessel components in the creep regime. This publication presents a methodology for evaluating and categorizing elastic stresses calculated from finite element stress analysis when designing in the creep regime. The proposed methodology is compared with multi axial creep results for various pressure vessel components and found to be in reasonable agreement.

FFS Assessment of Pressurized Equipment Utilizing a Thickness Mapping Tool

For pressure vessels, loss of thickness detected during scheduled maintenance utilizing UT scans can be assessed based on Level 1 or 2 analyses as per API 579 guidelines. However, Level 1 and 2 analyses can point to excessively conservative assessments. Level – 3 assessments utilizing the finite element method can be performed for a more accurate estimate of the load carrying capacity of the corroded structure. However, for a high fidelity structural response prediction using the finite element method, the characteristics of the model must be accurately represented. Although the three nonlinearities, namely, the geometric, material, and contact nonlinearities can be adequately included in a finite element analysis, procedures to accurately include the thickness measurements are not readily available. In this paper, a tool to map thicknesses obtained from UT scans onto a shell based finite element models, to perform Level – 3 analyses is discussed. The tool works in conjunction with Abaqus/CAE and is illustrated for two different structures following the elastic-plastic analysis procedure outlined in the API 579 document. The tool is intended only as a means to reduce the modeling time associated with mapping thicknesses. The results of the analyses and insights gained are presented.

A Simple Approach for Including Weld Residual Stresses in the Calculation of Pipe Circumferential Through-Wall Crack Opening Displacements

Current methodologies for predicting the crack opening displacement (COD) of circumferentially through-wall cracked pipe do not include the effect of weld residual stresses (WRS). Even the most advanced COD prediction methodology only includes the effect of applied axial force, bending moment, and crack face pressure. For some years, it has been known that weld residual stresses do alter the COD, but there has been no convenient way to include them in a COD prediction without doing case-specific finite element analyses. This paper documents a generalized solution for including WRS effects on COD. The model uses a closed-form analytic solution to approximate the crack face rotations that the WRS would induce which, subsequently, can be added to the typical axial force-bending-crack face pressure COD solution. The methodology is described and the basic equations for the solution are presented. Following this, application to cases to evaluate the efficacy of the approach are presented which show a mixture of results ranging from amazingly good to “of questionable value” with respect to the FEA results.

PWR Effect on Crack Initiation Under Equi-Biaxial Loading Development of the Experiment

Fatigue lifetime assessment is essential in the design of structures. Under-estimated lifetime predictions may generate overly conservative usage factor values and hence result in unnecessary in-service inspections. In the framework of upgrading the fatigue design rules (RCC-M, RCC-MRx), the uniaxial reference fatigue curve was altered by taking into account effects like: Multiaxiality, Mean stress or strain, Surface roughness (polished or ground), Scale effect, Loading History... In addition to this effect, Environmentally Assisted Fatigue is also receiving nowadays an increased level of attention. To formally integrate these effects, some international codes have already proposed and suggested a modification of the austenitic stainless steels fatigue curve combined with a calculation of an environmental penalty factor, namely Fen, which has to be multiplied by the usual fatigue usage factor. The aim of this paper is to present a new device “FABIME2E” developed in the LISN in collaboration with EDF and AREVA. These new tests allow quantifying accurately the effect of PWR environment on semi-structure specimen. This new device combines the structural effect like equibiaxiality and mean strain and the environmental penalty effect with the use of PWR environment during the fatigue tests.

Micro-Porous Coatings and Enhanced CHF for Downward Facing Boiling During Passive Emergency Reactor Cooling

During a Reaction Initiated Accident (RIA) or Loss of Coolant Accident (LOCA), passive external-cooling of the reactor lower head is a viable approach for the in-vessel retention of Corium; while this concept can certainly be applied to new constructions, it may also be viable for operational systems with existing cavities below the reactor. However, a boiling crisis will inevitably develop on the reactor lower head owing to the occurrence of Critical Heat Flux or CHF that could reduce the decay heat removal capability as the vapor phase impedes continuous boiling. Fortunately, this effect can be minimized for both new and existing reactors through the use of a Cold-Spray delivered, micro-porous coating that facilitates the formation of vapor micro-jets from the reactor surface. The micro-porous coatings were created by first spraying a binary mixture with the sacrificial material then removed via etching. Subsequent quenching experiments on uncoated and coated hemispherical surfaces showed that local CHF values for the coated vessel were consistently higher relative to the bare surface. Moreover, it was observed for both coated and uncoated surfaces that the local rate of boiling and local CHF limit varied appreciably along the outer surface. Nevertheless, the results of this intriguing study clearly show that the use of Cold Spray coatings could enhance the local CHF limit for downward facing boiling by more than 88%. Moreover, the Cold-Spray process is amenable to coating the lower heads of operating reactors.

Guidelines for MACA: The Optimization of Corrosion Allowance

Excess capacity in the design of a pressure vessel can be recognized in a maximum allowable working pressure (MAWP). This pressure value is the result of the calculations for minimum thickness, in the new condition, being rounded up to the next nominal plate thickness and then working the formulae to establish limiting pressure based on the actual thickness used. Another variable which may be optimized is the design temperature. Raising the design temperature tends to result in a reduced allowable stress. Once a plate thickness has been determined, the necessary allowable stress can be back calculated. From this allowable stress, an optimized design temperature can be determined. Excess capacity can also be recognized in the form of increased corrosion allowance or MACA, the Maximum Allowable Corrosion Allowance. This is particularly helpful in the maintenance and inspection realms where life extension or unexpected thinning can force an unplanned shutdown of the unit, a fitness for service evaluation, or repair once the specified corrosion allowance is exhausted. This paper presents a set of guidelines or rules for establishing a MACA based optimization for the design of new pressure vessels.

Failure of Thin-Walled Pipes With D/T up to 140 and Conclusions for the Design Codes

The influence of imperfections on the instability bending moment of thin-walled straight pipes with D/t-ratios (D - outside diameter, t - wall thickness) up to 140 is determined using nonlinear Finite Element (FE) analyses. The analyses show that the type and size of the imperfection, the D/t ratio and the material properties have significant influences on the instability moment. The nominal bending stress of pipes (yield stress 500 MPa) with D/t > 70 and an ovality of 0.5% is smaller than the yield stress at the instability point. That means, the failure occurs by buckling in the elastic range of the nominal bending stress. In static analyses the moment decreases abruptly after reaching the instability moment. In the dynamic analyses the pipe jumps abruptly to the state with smaller moment. The obtained results are applied to calculate the B2 index for pipes with D/t ≤ 140. The B2 indices for thin-walled straight pipes with D/t > 40 are considerably higher than 1.0. In general, there is a good agreement between the calculated B2 values and the values of the ASME Code. A correction factor for higher temperatures is not necessary. The allowable moments calculated with the B2 index and the stress intensification factor i are compared. The bending moments from disabled thermal expansion and anchor movements have the same effect on the failure due to (plastic) buckling as the primary moments and must be taken into account.

Evaluation of Constraint Effect due to Crack Location and Bottom Head Shape

The aim of this paper is to evaluate the constraint effect due to the crack location and bottom head shape. To do so, two types of bottom head shape such as a semi-spherical bottom head and semi-elliptical bottom head were considered. In addition, five types of axial crack and two types of circumferential crack, classified by location, were adopted to conduct FE analyses. As a result, the bottom head shape does not affect the stress intensity factor of the circumferential flaw. Moreover, the crack location is not a sensitive parameter of the stress intensity factor for an axial crack located at the semi-spherical bottom head. In contrast, the crack location should be considered when the stress intensity factor of an axial crack located at the semi-elliptical bottom head is calculated. In addition, a heatup curve and cooldown curve were derived from the FE analysis results. As a result, the constraint effect owing to a crack location, except for the transition area, is not shown in the case of a semi-spherical bottom head. In the case of a semi-elliptical bottom head, the difference between each crack location is shown. These results will be helpful to enhance the understanding of the constraint effect and P-T limit curve.