Stress Analysis of a Cryogenic Corrugated Pipe

2011 ◽  
Author(s):  
Vikas Srivastava ◽  
Jaime Buitrago ◽  
Scott T. Slocum
Keyword(s):  
Finite Element ◽  
Stainless Steel ◽  
Strain Hardening ◽  
Stress Responses ◽  
Full Scale ◽  
Main Body ◽  
Transfer System ◽  
Cold Forming ◽  
Steel Pipes ◽  
Local Stresses

One method to develop offshore gas reserves is to use a floating LNG plant (FLNG) on site and export the LNG via tankers. This alternative requires the use of a reliable LNG transfer system between the FLNG and the tanker under offshore conditions. One such system involves a flexible cryogenic hose whose main body is a pipe-in-pipe hose made of two concentric corrugated 316L stainless steel pipes (C-pipe) with flanged terminations. Thermal insulation is achieved by maintaining vacuum between the inner and outer corrugated stainless steel pipes. In addition, the hose assembly contains two outer layers of helical armor wires to sustain the axial load. Given the complexity and novelty of the transfer system, a finite element study was performed on the inner C-pipe — the critical fluid containment layer. The effects of strain hardening of corrugations due to cold forming and temperature were modeled. Finite element (FE) analyses of the C-pipe under axial, bending, and internal pressure loading were carried out to evaluate global load-deformation and local stress responses. Comparisons of full-scale tests at room and cryogenic temperatures to simulation predictions including the novel material model showed good agreement. However, fatigue life predictions for the C-pipe that were based on local stresses and sheet metal fatigue S-N curves did not agree with the full-scale fatigue test results. The results indicated that the spatial variation in strain hardening due to corrugation forming and biaxial local stresses during pipe deformation could play important roles in the fatigue response of the C-pipe.

A Simple Design Equation for Preventing Buckling in Fabricated Torispherical Shells Under Internal Pressure

1986 ◽  
Vol 108 (4) ◽  
pp. 521-526 ◽  
Author(s):  
G. D. Galletly
Keyword(s):  
Stainless Steel ◽  
Carbon Steel ◽  
Austenitic Stainless Steel ◽  
Internal Pressure ◽  
Strain Hardening ◽  
Factor Of Safety ◽  
Full Scale ◽  
Simple Equation ◽  
Design Equation ◽  
Simple Design

A simple equation is proposed which will enable a designer to estimate the onset of buckling in internally pressurized steel torispherical end closures. The equation applies to both crown and segment ends and spun ones. Apart from a factor which accounts for strain hardening, the same equation applies to both carbon steel and austenitic stainless steel torispheres. The proposed equation for the allowable internal pressure was checked against all known experimental buckling results and a minimum factor of safety of 1.5 was found. The equation was also checked against a number of full-scale vessels, some of which had failed in service. Once again, the equation was found to be satisfactory.

Analysis of a Thermal Fatigue Test of a Stepped Pipe

2004 ◽  
Author(s):  
D. P. Jones ◽  
J. E. Holliday ◽  
T. R. Leax ◽  
J. L. Gordon
Keyword(s):  
Finite Element ◽  
Stainless Steel ◽  
Crack Initiation ◽  
Thermal Shock ◽  
Thermal Fatigue ◽  
Fatigue Curve ◽  
Low Oxygen ◽  
Steel Pipes ◽  
Elastic Plastic ◽  
Best Fit

Results from thermal-structural finite element analysis (FEA) were used to predict cycles to crack initiation in thermal fatigue tests of stainless steel pipes. The pipes were fatigued by alternately pumping hot and cold low oxygen water every four minutes through 304 stainless steel pipes. The rapid change in water temperature imparted a thermal shock to the inner wall of the pipe. The pipes were stepped to four different thicknesses to give four different values of thermal shock stress depending on thickness. The pipes were pressurized to 17.2 MPa (2500 psi) and the temperature cycled between 38°C (100°F) and 343°C (650°F) in three seconds. This was followed by holding at 343°C for 237 seconds and then quenching to 38°C in three seconds followed by another 237 second hold period. Thermal cycling continued until significant cracking was detected on the inside surface of the pipes. Measurements of fatigue striation spacing on the fracture surfaces allowed determination of cycles to the initiation of defects 0.254 mm (0.01 inch) deep. Alternating stresses and strains were calculated using both elastic and elastic-plastic finite element analyses (FEA). The analysis results were used with a best-fit fatigue curve to predict cycles-to-crack initiation for comparison to the experimental data. Using elastic analysis corrected for stresses beyond yield in accordance with the ASME B&VP Code and the best-fit fatigue curve adjusted for low oxygen water environments resulted in under-estimates of the observed cycles to crack initiation from the tests. Improved predictions of cycles to crack initiation are possible by using an elastic-plastic FEA method with a kinematic hardening model along with the best-fit fatigue curve.

Cryogenic Structural Performance of Corrugated Pipe

2010 ◽  
Author(s):  
Jaime Buitrago ◽  
Scott T. Slocum ◽  
Stephen J. Hudak ◽  
Randy Long
Keyword(s):  
Fatigue Tests ◽  
Full Scale ◽  
Experimental Methodology ◽  
Structural Performance ◽  
Experimental Program ◽  
Main Body ◽  
Transfer System ◽  
Cryogenic Temperatures ◽  
Limit States ◽  
Static Tests

One alternative to developing offshore gas reserves is to use a floating LNG plant (FLNG) on site and export the LNG using tankers. This alternative requires the use of a reliable LNG transfer system between the FLNG and the tanker under offshore conditions. One such system involves a cryogenic hose, whose main body is a vacuum insulated, pipe-in-pipe hose made of corrugated stainless steel pipe (c-pipe) and flanged terminations. Given the novelty of the transfer system, ExxonMobil conducted an experimental program to understand the structural performance of the basic c-pipe under static and cyclic loading at room and cryogenic temperatures. This paper discusses overall qualification issues and presents the experimental methodology and results of structural performance tests of the full-scale c-pipe at both ambient and cryogenic temperatures. Fourteen full-scale, c-pipe static tests are reported, including tension, compression, bending, torsion, and internal pressure. In addition, 11 axial and three pressure fatigue tests are presented. One key result is that, overall, cryogenic temperature improves structural performance for the limit states tested, indicating that future qualification at room temperature would be sufficient. Moreover, the fatigue performance at both ambient and cryogenic temperatures surpassed the design curve reported in the literature for c-pipe.

The Influence of the UOE Forming Process on Material Properties and Collapse of Deepwater Linepipe

2009 ◽  
Author(s):  
Chris Timms ◽  
Luciano Mantovano ◽  
Hugo A. Ernst ◽  
Rita Toscano ◽  
Duane DeGeer ◽  
...  
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Manufacturing Process ◽  
Thermal Ageing ◽  
Full Scale ◽  
Sensitivity Analyses ◽  
Thickness Variation ◽  
Forming Process ◽  
Cold Forming ◽  
Pipe Manufacturing

It has been demonstrated in previous work that, for deepwater applications, the cold forming process involved in UOE pipe manufacturing significantly reduces pipe collapse strength. To improve the understanding of these effects, Tenaris has embarked on a program to model the stages of the UOE manufacturing process using finite element methods. Previous phases of this work formulated the basis for model development and described the 2D approach taken to model the various stages of manufacture. More recent developments included some modeling enhancements, sensitivity analyses, and comparison of predictions to the results of full-scale collapse testing performed at C-FER. This work has shown correlations between manufacturing parameters and collapse pressure predictions. The results of the latest phase of the research program are presented in this paper. This work consists of full-scale collapse testing and extensive coupon testing on samples collected from various stages of the UOE pipe manufacturing process including plate, UO, UOE, and thermally-aged UOE. Four UOE pipe samples manufactured with varying forming parameters were provided by Tenaris for this test program along with associated plate and UO samples. Full-scale collapse and buckle propagation tests were conducted on a sample from each of the four UOE pipes including one that was thermally aged. Additional coupon-scale work included measurement of the through-thickness variation of material properties and a thermal ageing study aimed at better understanding UOE pipe strength recovery. The results of these tests will provide the basis for further refinement of the finite element model as the program proceeds into the next phase.

Carrying Capacity of Strain-Hardening Austenitic Stainless Steel Pressure Vessels Under Hydrostatic Pressure

2011 ◽  
Author(s):  
Yang-chun Deng ◽  
Gang Chen
Keyword(s):  
Finite Element ◽  
Stainless Steel ◽  
Hydrostatic Pressure ◽  
Austenitic Stainless Steel ◽  
Strain Hardening ◽  
Carrying Capacity ◽  
Plastic Instability ◽  
Pressure Vessels ◽  
Load Carrying Capacity ◽  
Load Carrying

To reduce the waste of austenitic stainless steels due to their low yield strengths, the strain hardening technology is used to significantly improve their yield strength, in order to increase the elastic load carrying capacity of austenitic stainless steel pressure vessels. The basic principle of strain-hardening for austenitic stainless steel pressure vessels and two common models of strain hardening, including Avesta Model for ambient temperature and Ardeform Model for cryogenic temperature, were briefly introduced. However, it was fully established by experiments, the lack of a necessary theoretical foundation and the safety concern affect its widespread use. In this study, we investigated the load carrying capacity of strain-hardening austenitic stainless steel pressure vessels under hydrostatic pressure, based on the elastic-plastic theory. To understand the effects of strain hardening on material behavior, the plastic instability loads of a round tensile bar specimen were also derived under two different loading paths and validated by experiments. The results of theoretical, experimental and finite element analyses illustrated, considering the effect of material strain hardening and structural deformation, at ambient temperature, the static load carrying capacity of pressure vessels does not relate to the loading paths. To calculate the plastic instability pressures, a method was proposed so that the original dimension and original material parameters prior to strain hardening can be used either by the theoretical formula or finite element analysis. The safety margin of austenitic stainless steel pressure vessels under various strain hardening degrees was quantitatively analyzed by experiments and finite element method. A 5% strain as the restrictive condition of strain hardening design for austenitic stainless steel pressure vessels was suggested.

First and Second Order Elastoplastic Analyses of Thin-Walled Metal Members using Generalized Beam Theory

2018 ◽  
Author(s):  
Miguel Abambres
Keyword(s):  
Finite Element ◽  
Stainless Steel ◽  
Cross Section ◽  
Beam Theory ◽  
Second Order ◽  
Flow Rule ◽  
Non Linear ◽  
Thin Walled ◽  
Shell Finite Element ◽  
Generalized Beam Theory

Original Generalized Beam Theory (GBT) formulations for elastoplastic first and second order (postbuckling) analyses of thin-walled members are proposed, based on the J2 theory with associated flow rule, and valid for (i) arbitrary residual stress and geometric imperfection distributions, (ii) non-linear isotropic materials (e.g., carbon/stainless steel), and (iii) arbitrary deformation patterns (e.g., global, local, distortional, shear). The cross-section analysis is based on the formulation by Silva (2013), but adopts five types of nodal degrees of freedom (d.o.f.) – one of them (warping rotation) is an innovation of present work and allows the use of cubic polynomials (instead of linear functions) to approximate the warping profiles in each sub-plate. The formulations are validated by presenting various illustrative examples involving beams and columns characterized by several cross-section types (open, closed, (un) branched), materials (bi-linear or non-linear – e.g., stainless steel) and boundary conditions. The GBT results (equilibrium paths, stress/displacement distributions and collapse mechanisms) are validated by comparison with those obtained from shell finite element analyses. It is observed that the results are globally very similar with only 9% and 21% (1st and 2nd order) of the d.o.f. numbers required by the shell finite element models. Moreover, the GBT unique modal nature is highlighted by means of modal participation diagrams and amplitude functions, as well as analyses based on different deformation mode sets, providing an in-depth insight on the member behavioural mechanics in both elastic and inelastic regimes.

ALLEGHENY LUDLUM TYPE 305

Alloy Digest ◽  
2002 ◽  
Vol 51 (1) ◽  
Keyword(s):  
Stainless Steel ◽  
Corrosion Resistance ◽  
High Temperature ◽  
Physical Properties ◽  
Work Hardening ◽  
Deep Drawing ◽  
Heat Treating ◽  
Cold Forming ◽  
Temperature Performance ◽  
Low Rate

Abstract Allegheny Ludlum Type 305 (S30500) stainless steel is used for applications requiring a low rate of work hardening during severe cold-forming operations such as deep drawing. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on high temperature performance and corrosion resistance as well as heat treating and joining. Filing Code: SS-840. Producer or source: Allegheny Ludlum Corporation.

ARMCO 18-9LW

Alloy Digest ◽  
1962 ◽  
Vol 11 (11) ◽  
Keyword(s):  
Stainless Steel ◽  
Corrosion Resistance ◽  
Physical Properties ◽  
Surface Treatment ◽  
Tensile Properties ◽  
Work Hardening ◽  
Heat Treating ◽  
Cold Forming

Abstract Armco 18-9LW is a low-work-hardening stainless steel developed for severe cold heading, swaging and other cold forming applications. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, joining, and surface treatment. Filing Code: SS-138. Producer or source: Armco Inc., Eastern Steel Division.

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