Monday, July 15 | 4:15 PM – 6:00 PM
Centralizer subs are run in conjunction with the casing strings to ensure that the casing is centralized while it is installed downhole. Centralizer subs are fabricated of stronger material than the casing strings and designed such that it can sustain a higher collapse pressure than the attached tubing string. A typical centralizer sub is a tube with some complex geometrical features, so the collapse pressure of a centralizer sub can only be estimated by conducting a finite element analysis or subjecting it to a collapse pressure test. Both the options are time consuming and expensive. In this work, a machine learning based regression model is used to derive a parametric equation for calculating the collapse pressure of a centralizer sub. The data needed to train and test the regression model is obtained from finite element analysis (FEA). As a first step, a number of FE models are built by varying the parameters related to the geometric features of the centralizer sub. The collapse pressure of each model is calculated from FEA to generate a data set. A few regression models are trained on a part of this data set (training data). These regression models are tested on the remaining data (test data).
Tuesday, July 16 | 8:15 AM – 10:00 AM
From a series of recent tests performed on damaged materials involving hydrogen induced cracking (HIC), it was discovered that HIC damage may have an anisotropic response when loaded to a tensile overload. This appears to be an avenue to remove potential over-conservatism present in the current API 579 – 1/ASME FFS – 1 standard. Additionally, tensile testing in a hydrogen environment was used to quantify the effects of hydrogen on the strength of HIC damaged ligaments. In order to develop a more accurate estimation of the damage and assessment techniques, several non-destructive techniques (NDT) were used. This paper outlines the aforementioned work performed and potential implementation of the testing results onto the HIC damage parameter (DH) for fitness for service assessments involving HIC damage.
Tuesday, July 16 | 8:15 AM – 10:00 AM
High Temperature Hydrogen Attack Life Assessment
Key elements of high temperature hydrogen attack (HTHA) assessment methodologies for equipment and piping operating in hot hydrogen service are presented. Two assessment methodologies have been developed: (1) a Screening Assessment and (2) an Advanced Assessment, both of which predict the development of HTHA damage with time. The HTHA assessment methodologies utilize fitness-for-service (FFS) frameworks and are in good agreement with reported HTHA incidents in API 941RP and API 941TR for carbon steel and C-0.5Mo materials. The Screening Assessment provides an improved decision basis by classifying and ranking equipment operating in hot hydrogen service, which are tied to recommended action and levels of concern. The Advanced Assessment models through-wall damage progression. Additionally, the use of inspection findings as a means of risk mitigation and guidance on inspection interval decisions are also discussed. Select case studies are used to illustrate the advantages of the proposed methods. The developed methodologies provide an improved link between HTHA damage assessment and progression, inspection and detection limits, damage tolerance, and operation severity.
Reduced Toughness Fittings and Potential Effect on Low Temperature FFS
It has been reported in industry that recently manufactured piping and pressure vessel components may have reduced toughness where the component fails the Code -20F impact exemption. This presentation will review the industry reported findings and outline a potential analysis path forward to address fitness for service (FFS) concerns for potentially at-risk components that are currently in service. Representative analysis results for various configurations will be presented along with highlighting the need for further industry work to develop a methodology to identify the systems with the highest risk for brittle fracture if these reduced toughness components are within the system.
Tuesday, July 16 | 10:15 AM – 12:00 PM
This paper describes the work performed to study the shell mode vibration of a large cross-section flue gas duct. The work involved the collection of field vibration data, as well as predictive computational models associated with finite element analysis (FEA) and computational fluid dynamics (CFD). The goal of this work was to use predictive models to ascertain whether a proposed design change would reduce the vibration levels of the duct under similar operating conditions. As a first step, high frequency shell mode vibration data was collected with a portable laser vibrometer at a number of locations all around the duct. The vibration of the duct was flow induced. The forcing function for the shell mode vibration was estimated from a CFD model using typical operating conditions for the duct. The CFD model provided pressure frequency spectrum estimates over a certain frequency range, which served as the input to the finite element (FE) model for the random response analysis. A random response analysis was conducted using the FE model and the output was compared with the field data. After the model calibration, both the CFD and FE models were revised to reflect the proposed design changes. The vibration of the modified system was estimated using the revised FE model using the input pressure spectra input obtained from the revised CFD model. The results were used to determine whether the proposed design changes would indeed reduce the vibration levels of the duct. This case study serves as an example of using predictive computational models (FEA and CFD), calibrated with vibration response data from field measurements, to represent the real world situation as closely as possible within specified budget and schedule constraints. Such calibrated models can be useful for forecasting the effectiveness of various proposed design changes.
Tuesday, July 16 | 4:15 PM – 6:00 PM
Brittle fracture assessments (BFAs) of pressure vessels based on API 579-1/ASME FFS-1, Section 3 procedures are frequently easier and more straightforward to implement in comparison to the BFAs on piping systems. Specifically, the development of the MSOT curves. This is due to the complexities involved in the piping systems due to the branch piping interactions, end conditions of piping systems such as nozzle flexibilities at the pressure vessel connections, temperature changes in the length of piping especially when the piping is significantly long as seen in flare header piping systems. MSOT curves that are alternatively used for MAT curves provide a better picture to the plant personnel in understanding the safe operating envelope. Development of MSOT curves is an iterative process and therefore involves significant number of piping stress analyses during their development. In this paper, an approach to develop the MSOT curves is discussed with two case studies that are of relevance to olefin plants.
Wednesday, July 17 | 10:15 AM – 12:00 PM
In this paper, an analytical method to estimate the deformation strains that can quantify the severity of bulges as it applies to coke drums is presented. The proposed method is based on classical shell theory and API 579-1/ASME FFS-1 (2016) procedures involving triaxiality limits. In this first part of the work, only the theoretical development is presented along with the comparison of the results from this theoretical approach with two case studies that emulate the bulging due to different loading scenarios. The developed approach is then applied to a deformed coke drum. In the next part of this paper, the application of this approach on selected in-service coke drums that are equipped with strain gages will be presented. The authors would like to emphasize the well-known fact that the coke drum is a complex pressure vessel for which any single simplified assessment technique may not be sufficient to quantify the life or fitness-for-service (FFS) of a coke drum due to the complexities associated with the various parameters that affect the mechanical integrity of the coke drum. This paper is an attempt to advance the assessment techniques that are currently utilized in the industry.
Thursday, July 18 | 2:15 PM – 4:15 PM
Elbow fittings are manufactured using quenching and tempering heat treatment processes. Such fittings can occasionally exhibit localized regions with lower yield strength than the design target, potentially due to non-uniform heat treatment. This paper presents an analytical methodology to examine the influence of these localized lower yield zones on the load capacity of the affected pipe fitting. In parallel, full-scale testing has been performed to quantify the actual response of the elbows under a combination of different loading conditions. The experimental data is used to validate the analytical approach. Details of the analytical method include a two-fold criterion: a global failure based on elastic–plastic stress analysis and a local failure based on the tri-axial strain limit per ASME Boiler and Pressure Vessel Code Section VIII, Division 2. This paper presents the details of the finite element model development, assessment procedure, validation and parametric analysis of the size and location of the low yield zones in the elbow fittings. The fittings are analyzed for three possible operating scenarios: internal pressure, internal pressure with opening moment and internal pressure with closing moment. To characterize the influence of the low yield zone on the strength of the pipe, a parameter termed as “effective yield strength” is introduced. This approach is further demonstrated and found suitable for predicting burst pressures of components with lower yield zones of various diameters and thicknesses. This assessment method can be further extended to assess other pipeline components that exhibit similar behavior.