Failure Investigation of a Low Chrome Long-Seam Weld in a High-Temperature Refinery Piping System

1995 ◽  
Vol 117 (3) ◽  
pp. 227-237 ◽  
Author(s):  
G. M. Buchheim ◽  
D. A. Osage ◽  
R. G. Brown ◽  
J. D. Dobis
Keyword(s):  
Finite Element ◽  
High Temperature ◽  
Stress Analysis ◽  
Hoop Stress ◽  
Weld Seam ◽  
Creep Damage ◽  
Piping System ◽  
Testing Program ◽  
Metallurgical Investigation ◽  
Fabrication Tolerances

The results of an investigation of a long-seam welded low chrome pipe that failed in a high-temperature refinery piping system are presented in this paper. Based upon the results of a metallurgical investigation, which included a creep testing program and a detailed finite element stress analysis, the cause of the failure has been attributed to creep damage at the weld seam. The metallurgical investigation and creep testing program indicated that the 1-1/4 Cr-1/2 Mo pipe material was normalized and exhibited greater than average creep strength and creep ductility. The results of a piping stress analysis indicated that all pressure, weight, and thermal stresses were in compliance with the ASME B31.3 Piping Code (ASME, 1993a). Nonetheless, the pipe failed after only 100,000 h at a nominal hoop stress of 6 ksi (41.4 MPa) with an operating temperature range of 970°F (521°C) to 1000°F (538°C). Results from subsequent detailed finite element stress analyses of the failed pipe indicated that very high localized bending stresses were present in the pipe due to peaking at the long-seam weld. These stresses partially relax by creep, but after 100,000 h they were still approximately 38 percent higher than the nominal hoop stress. The creep strains resulting from stress relaxation and those associated with the long-term value of the sustained stresses cause severe creep damage at the weld seam. As a result of this damage, cracks initiated at the inside of the pipe and primarily grew through the HAZ/fusion line until an 18-in. through-wall crack developed. The pipe was produced to ASTM A691, Grade 1-1/4 Cr, Class 41 (ASTM, 1989), and the peaked geometry was found to satisfy the fabrication tolerances of this standard. The need for the development of an acceptable tolerance for peaking in addition to the outside diameter and out-of-roundness fabrication tolerances currently included in this standard is highlighted for long-seam welded pipe that is to operate in the creep range.

Life Prediction of the Tapered Pipe With High Temperature and High Pressure by Finite Element Methods

2007 ◽  
Author(s):  
Juntao Bao ◽  
Jianming Gong ◽  
Shantung Tu ◽  
Yuesheng Li ◽  
Yanfei Qiu
Keyword(s):  
Finite Element ◽  
High Pressure ◽  
High Temperature ◽  
Internal Pressure ◽  
Creep Damage ◽  
Piping System ◽  
Bending Moments ◽  
Finite Element Program ◽  
Element Program ◽  
Main Steam

Tapered pipe used in the main steam pipelines, which operated at high temperature and high pressure, including concentric tapered pipe and eccentric tapered pipe, they are sources of weakness in the piping system serviced in the power stations and the chemical plants, and creep is the significant reason that caused their failure. Creep damage analyses are carried out for these two kinds of tapered pipes by introducing user subroutine based on the modified Karchanov-Rabotnov constitutive equations into finite element program ABAQUS, then the effects of bending moments and internal pressure to the serviced life of the components are investigated by comparing four group of calculated results under different loads, the results indicated that eccentric tapered pipe is more inclinable to broken than concentric tapered pipe under the same conditions, so it is not recommended to use the eccentric tapered pipe in the piping system. The bending moments will accelerate the components’ failure, so it is necessary to take some advantages to reduce the bending moments near the tapered pipe, on the other hand, the life of the tapered pipe will decrease quickly with the internal pressure increasing, so the control of the operated pressure is important to ensure the serviced life of the pipelines.

A Computational Study of the Creep Response of High-Temperature Low Chrome Piping With Peaked Longitudinal Weld Seams

2016 ◽  
Author(s):  
Phillip E. Prueter ◽  
Jonathan D. Dobis ◽  
Mark S. Geisenhoff ◽  
Michael S. Cayard
Keyword(s):  
High Temperature ◽  
Weld Seam ◽  
Creep Damage ◽  
Weld Deposit ◽  
Simulation Techniques ◽  
Piping Systems ◽  
Longitudinal Weld Seam ◽  
Fabrication Tolerances ◽  
Weld Seams ◽  
Metal Weld

There have been a number of failures of high-temperature, low chrome piping in the power generation and petrochemical industries, some with catastrophic consequences. Several of these failures have been attributed to peaking of longitudinal weld seams. Generally, local weld peaking occurs during pipe manufacturing due to angular misalignment of the rolled plate at the weld seam location (the pipe locally deviates from a true circular cross-section). Furthermore, for many fusion-welded piping fabrication standards, no specific tolerance for longitudinal weld seam peaking exists; that is, some of the high-temperature pipes that have failed in-service met the required original fabrication tolerances. Additionally, depending on original heat treatment, creep damage progression is known to be accelerated by the mismatch in creep properties of the base metal, weld deposit, and heat affected zone (HAZ). This mismatch results in stress intensification and triaxial tension that accelerates the rate of cavity growth near the weldment (typically in or adjacent to the HAZ). Local weld seam peaking can induce significant local bending stresses in the pressure boundary. For piping components that operate in the creep regime, the presence of local peaking can lead to an increased propensity for creep crack initiation/propagation and eventual rupture of the pressure boundary. An overview of some of the well-known historical low chrome piping failures is provided in this paper and a literature review on existing creep analysis methodologies that have been applied to high-temperature piping systems is offered. Detailed finite element analysis (FEA) is employed in this study and coupled with advanced, non-linear creep simulation techniques to investigate the elevated temperature response of piping with peaked longitudinal weld seams. The objective of this study is to use analytical methods to estimate the remaining life of select low chrome piping geometries and to assess the sensitivity in results to variations in key parameters such as operating temperature, magnitude of longitudinal weld seam peaking, and the effect of pipe heat treatment resulting in a creep property mismatch between the base metal, weld deposit, and HAZ. Additionally, commentary on different creep damage failure criteria is rendered. Specifically, the effect of implementing a damage parameter that adjusts the elastic modulus of the material as a function of creep damage accumulation is examined. The creep simulations utilize the Materials Properties Council (MPC) Omega creep methodology and compare the creep damage progression for multiple postulated cross-sections of 30 and 36-inch diameter 1 1/4 Cr - 1/2 Mo pipes with and without local weld seam peaking. Simulation techniques such as the ones discussed herein are not only valuable in estimating remaining life of inservice piping, but detailed analysis can be leveraged to establish recommended local weld seam peaking fabrication tolerances, appropriate inspection practices, and reasonable non-destructive examination (NDE) intervals for in-service high-temperature low chrome piping systems.

Creep Life Simulation and Assessment of High Temperature Piping Systems and Components

2012 ◽  
Author(s):  
Brian Rose ◽  
James Widrig
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
High Temperature ◽  
Creep Behavior ◽  
Material Behavior ◽  
Piping System ◽  
Remaining Life ◽  
Creep Life ◽  
Element Analysis ◽  
Piping Systems

High temperature piping systems and associated components, elbows and bellows in particular, are vulnerable to damage from creep. The creep behavior of the system is simulated using finite element analysis (FEA). Material behavior and damage is characterized using the MPC Omega law, which captures creep embrittlement. Elbow elements provide rapid yet accurate modeling of pinching of piping, which consumes a major portion of the creep life. The simulation is used to estimate the remaining life of the piping system, evaluate the adequacy of existing bellows and spring can supports and explore remediation options.

On-Line Health Monitoring Research on T-Joint of Main Steam Piping

2013 ◽  
Vol 330 ◽  
pp. 549-552 ◽  
Author(s):  
J.H. Jia ◽  
H.C. Zhang ◽  
X.Y. Hu ◽  
L.P. Cai ◽  
S.T. Tu
Keyword(s):  
High Temperature ◽  
Power Plant ◽  
Residual Life ◽  
Thermal Power ◽  
Creep Damage ◽  
Piping System ◽  
Main Challenge ◽  
On Line ◽  
Main Steam ◽  
Creep Monitoring

The main challenge of long-time creep monitoring on site is a reliable sensor. In this paper, a sensing device is developed specifically for high temperature creep monitoring. And it is applied to on-line monitor the strain of material on T-joint of main steam piping. Its reliability is verified theoretically using the finite element method and experimentally by high temperature on site test. The creep damage of the T joint is evaluated basing on the creep rate sensed by the sensing device. And the residual life is predicted for the piping system using the Monkman-Grant equation. This system is useful for safety assessment procedures in thermal power plant, nuclear power plant and petrochemical industries.

scholarly journals Modeling of Thermal and Mechanical Behavior of ZrB2-SiC Ceramics after High Temperature Oxidation

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Jun Wei ◽  
Lokeswarappa R. Dharani ◽  
K. Chandrashekhara ◽  
Gregory E. Hilmas ◽  
William G. Fahrenholtz
Keyword(s):  
Heat Transfer ◽  
Finite Element ◽  
Thermal Stress ◽  
High Temperature ◽  
Mechanical Behavior ◽  
Stress Analysis ◽  
Heat Transfer Analysis ◽  
Temperature Oxidation ◽  
Thermal Stress Analysis ◽  
Sic Ceramics

The effects of oxidation on heat transfer and mechanical behavior of ZrB2-SiC ceramics at high temperature are modeled using a micromechanics based finite element model. The model recognizes that when exposed to high temperature in air ZrB2-SiC oxidizes into ZrO2, SiO2, and SiC-depleted ZrB2 layer. A steady-state heat transfer analysis was conducted at first and that is followed by a thermal stress analysis. A “global-local modeling” technique is used combining finite element with infinite element for thermal stress analysis. A theoretical formulation is developed for calculating the thermal conductivity of liquid phase SiO2. All other temperature dependent thermal and mechanical properties were obtained from published literature. Thermal stress concentrations occur near the pore due to the geometric discontinuity and material properties mismatch between the ceramic matrix and the new products. The predicted results indicate the development of thermal stresses in the SiO2 and ZrO2 layers and high residual stresses in the SiC-depleted ZrB2 layer.

Enhanced Creep Life Evaluations for Grade 91 Circumferential Weldments

2017 ◽  
Author(s):  
Marvin J. Cohn
Keyword(s):  
Applied Stress ◽  
Hoop Stress ◽  
Axial Stress ◽  
Creep Damage ◽  
Creep Rupture ◽  
Piping System ◽  
Remaining Life ◽  
Creep Life ◽  
Rupture Properties ◽  
Applied Stresses

The basic power piping creep life calculations consider the important variables of time, temperature and stress for the creep rupture properties of the unique material. Some engineering evaluations of remaining life estimate the applied stress as the design stress obtained from a conventional piping stress analysis. Other remaining life evaluations may assume that a conservative estimate of the applied stress is no greater than the hoop stress due to pressure. The creep rupture properties of the unique material are usually obtained from the base material creep rupture properties. The typical methodologies to estimate remaining life do not consider the actual applied stress due to malfunctioning supports, multiaxial stress effects, axial and through-wall creep redistribution, time-dependent material-specific weldment creep rupture properties, residual welding stresses, and actual operating temperatures and pressures. It has been determined that the initiation and propagation of Grade 91 creep damage is a function of stress to about the power of 9 at higher applied stresses. There have been many examples of malfunctioning piping supports creating unintended high stresses. When the axial stress is nearly as high as the hoop stress, the applicable corresponding uniaxial stress for creep rupture life is increased about 30%. Multiaxial stress effects in circumferential weldments (e.g., when the axial stress is nearly as high as the hoop stress) can reduce the weldment creep life to less than 1/6th of the predicted life assuming a uniaxial stress or hoop stress due to pressure only. Since 2012, the ASME B31.1 Code has required that significant piping displacement variations from the expected design displacements shall be considered to assess the piping system’s integrity [1]. This paper discusses a strategy for an enhanced creep life evaluation of power piping circumferential weldments. Piping stresses can vary by a factor greater than 2.0. Consequently, the range of circumferential weldment creep rupture lives for a single piping system may vary by a factor as high as 40. Although there is uncertainty in the operating times at temperatures and pressures, all of the weldments within the piping system have the same time, temperatures, and pressures, so the corresponding uncertainties for these three attributes are normalized within the same piping system. Since the applied stresses are the most important weld-to-weld variable within a piping system, it is necessary to have an accurate evaluation of the applied stresses to properly rank the creep rupture lives of the circumferential weldments. This methodology has been successfully used to select the lead-the-fleet creep damage in circumferential weldments over the past 15 years.

A High Temperature Primary Load Design Method Based on Elastic Perfectly-Plastic and Simplified Inelastic Analysis

2020 ◽  
Author(s):  
M. C. Messner ◽  
R. I. Jetter ◽  
T.-L. Sham
Keyword(s):  
Finite Element ◽  
High Temperature ◽  
Creep Damage ◽  
Elastic Analysis ◽  
Allowable Stress ◽  
Perfectly Plastic ◽  
Inelastic Analysis ◽  
Stress Classification ◽  
Elastic Perfectly Plastic ◽  
Primary Load

Abstract The current primary load design provisions of Section III, Division 5 of the ASME Boiler and Pressure Vessel Code, covering high temperature nuclear components, represent an allowable stress methodology using elastic analysis and stress classification procedures to approximate stress redistribution caused by creep and plasticity. This process is difficult to implement and automate in modern finite element frameworks. This paper describes an alternate primary load design approach that uses elastic perfectly-plastic analysis in conjunction with the reference stress concept to eliminate stress classification while retaining a link to the existing Section III, Division 5 allowable stresses. This global, structural allowable stress check is supplemented with a local check to guard against the initiation of creep damage at local stress discontinuities like headers, nozzles, and other stress concentrations. This check is based on a simple elastic-creep analysis with creep damage calculated with the time-fraction approach, using the current ASME minimum-stress-to-rupture values already provided in the current Code. Both the global and local checks are easily implemented in modern finite element analysis software and greatly simplify Section III, Division 5 primary load design when compared to the current design-by-elastic-analysis method. Several examples demonstrate the utility of the new approach and its potential to reduce over-conservatism.

scholarly journals Thermal Stress Analysis of Process Piping System Installed on LNG Vessel Subject to Hull Design Loads

2020 ◽  
Vol 8 (11) ◽  
pp. 926
Author(s):  
Se-Yun Hwang ◽  
Min-Seok Kim ◽  
Jang-Hyun Lee
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Analysis ◽  
Evaluation Model ◽  
Element Model ◽  
Piping System ◽  
Wave Load ◽  
Element Analysis ◽  
Expansion Joints ◽  
Load Conditions

In this paper, the procedure for the strength evaluation of the piping system installed on liquefied natural gas (LNG) carriers is discussed. A procedure that accounts for the ship’s wave load and hull motion acceleration (as well as the deformation due to the thermal expansion and contraction experienced by the hull during seafaring operations) is presented. The load due to the temperature and self-weight of the piping installed on the deck is also considered. Various operating and load conditions of the LNG piping system are analyzed. Stress analysis is performed by combining various conditions of sustained, occasional, and expansion loads. Stress is assessed using finite element analysis based on beam elements that represent the behavior of the piping. The attributes of the piping system components (such as valves, expansion joints, and supports) are represented in the finite element model while CAESAR-II, a commercial software is used for finite element analysis. Component modeling, load assignment, and load combinations are presented to evaluate pipe stresses under various load conditions. An evaluation model is selected for the piping arrangement of LNG and the evaluated stress is compared with the allowable stress defined by the American Society of Mechanical Engineers (ASME).

Degradation Characteristics of Combined Rotor for Turbine Considering Stress Relaxation of Rod

2013 ◽  
Vol 387 ◽  
pp. 168-173
Author(s):  
Yong Lei Su ◽  
Ai Lun Wang ◽  
Xue Peng Li
Keyword(s):  
Finite Element ◽  
High Temperature ◽  
Stress Relaxation ◽  
Stress Analysis ◽  
Dynamic Characteristic ◽  
Natural Frequency ◽  
Contact Stiffness ◽  
Frequency Drift ◽  
Microscopic Model ◽  
Calculating Method

Considering stress relaxation of rod under high temperature, pretightening force of rod changing with time was obtained. A finite element contact model with interface was analyzed and contact stiffness under different loads was concluded. Combining contact stiffness of the microscopic model with the stress analysis result of turbine interface, a calculating method for dynamic characteristic of combined rotor considering contact stiffness was presented, effect of rod relaxation on dynamic characteristic of combined rotor was obtained. The results showed that pretightening force of rod was decreasing due to stress relaxation, degradation of combined rotor that natural frequency drift caused by the stress relaxation of rod.

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