Cold Stretching of Cryogenic Pressure Vessels from Austenitic Stainless Steels

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Cold Stretching of

Cold Stretching of Cryogenic Pressure Vess

Cryogenic Pressure Vessels f

els from Austenitic Stainless Steels

rom Austenitic Stainless Steels

Jinyang Zheng

Jinyang Zheng11, Abin Guo, Abin Guo11, Cunjian Miao, Cunjian Miao11, Ping Xu*, Ping Xu*22, Jian Yang, Jian Yang11, Jianjun Ye, Jianjun Ye11, Li Ma, Li Ma11, Linlin Wu, Linlin Wu11,, Guoyi Yang

Guoyi Yang33 (1. Institute of Process Equipm

(1. Institute of Process Equipm ent, Zhejiang University, Hangzhou 310027, Pent, Zhejiang University, Hangzhou 310027, P. R. China;. R. China; 2. Institute of Applied Mech

2. Institute of Applied Mech anics, Zhejiang University, Hangzhou 310027, anics, Zhejiang University, Hangzhou 310027, PP. R. China;. R. China; 3. China Special Equipment Inspection and Research Institute,

3. China Special Equipment Inspection and Research Institute, Beijing 100013, Beijing 100013, PP. R. China). R. China)

*corresponding author, Phone: +86-571-879-53-393; Fax: +86-571-879-53-393; E-mail:*corresponding author, Phone: +86-571-879-53-393; Fax: +86-571-879-53-393; E-mail:pingxu@zju.edu.cnpingxu@zju.edu.cn ))

ABSTRACT:

ABSTRACT: Austenitic stainless steel (ASS) exhibitsAustenitic stainless steel (ASS) exhibits considerable work-hardening upon deformation while considerable work-hardening upon deformation while retaining the characteristics of the material. The high rate retaining the characteristics of the material. The high rate of austenite deformation hardening was utilized by cold of austenite deformation hardening was utilized by cold stretching (CS) of cryogenic pressure vessels. A few stretching (CS) of cryogenic pressure vessels. A few  percent

 percent deformation deformation will will give give the the vessel vessel a a considerableconsiderable and homogeneous yield strength improvement, and the and homogeneous yield strength improvement, and the wall thickness may be greatly reduced. The authors have wall thickness may be greatly reduced. The authors have conducted extensive experimental and numerical studies conducted extensive experimental and numerical studies on CS of cryogenic pressure vessels from ASS. A on CS of cryogenic pressure vessels from ASS. A summary of our work as well as a brief introduction of summary of our work as well as a brief introduction of the history, standards, safety, and advantages of CS are the history, standards, safety, and advantages of CS are given in this paper. What should be further investigated, given in this paper. What should be further investigated, such as fatigue properties of cold stretched ASS such as fatigue properties of cold stretched ASS especially under cryogenic temperature, design of cold especially under cryogenic temperature, design of cold stretched transportable cryogenic vessels based on life, stretched transportable cryogenic vessels based on life, are also presented.

are also presented.

KEYWORDS:

KEYWORDS: cold stretching, austenitic stainless steel,cold stretching, austenitic stainless steel, cryogenic pressure vessels, strengthening stress

cryogenic pressure vessels, strengthening stress

NOMENCLATURE NOMENCLATURE

R kk—— Design stressDesign stress

INTRODUCTION INTRODUCTION

With wide use of liquefied nitrogen, liquefied With wide use of liquefied nitrogen, liquefied oxygen, liquefied hydrogen, liquefied argon, and oxygen, liquefied hydrogen, liquefied argon, and liquefied natural gas (LNG), more and more cryogenic liquefied natural gas (LNG), more and more cryogenic  pressure

 pressure vessels vessels (CPV)(CPV) from Austenitic Stainless Steelfrom Austenitic Stainless Steel (ASS) are being used in recent years.

(ASS) are being used in recent years.

According to the Chinese pressure vessels standard According to the Chinese pressure vessels standard GB150

GB150[1][1], the allowable stress of ASS is dominated by, the allowable stress of ASS is dominated by  proof stress

 proof stress (also called yield (also called yield strength) because of strength) because of its lowits low ratio of yield strength to tensile strength and thus results ratio of yield strength to tensile strength and thus results in thicker wall thickness, which would cause a waste of in thicker wall thickness, which would cause a waste of materials and make the

materials and make the vessel heavier.vessel heavier.

ASS exhibits considerable work-hardening upon ASS exhibits considerable work-hardening upon deformation while retaining the characteristics of the deformation while retaining the characteristics of the material. A few percent deformation will give the vessel a material. A few percent deformation will give the vessel a considerable and homogeneous yield strength considerable and homogeneous yield strength improvement, and the wall thickness can be greatly improvement, and the wall thickness can be greatly reduced. Plastic deformation of 10% is possible with reduced. Plastic deformation of 10% is possible with steels having an elongation at fracture of at least 35% in steels having an elongation at fracture of at least 35% in the heat treated condition.

the heat treated condition.

Proceedings of the ASME 2011 Pressure Vessels & Piping Division Conference Proceedings of the ASME 2011 Pressure Vessels & Piping Division Conference PVP2011 PVP2011 July 17-21, 2011, Baltimore, Maryland, USA July 17-21, 2011, Baltimore, Maryland, USA

PVP2011-57331

PVP2011-57331

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The high rate of austenitic strain hardening can be utilized by cold stretching (CS) of cryogenic pressure vessels from ASS[2]. In practice the strengthening is  performed by pressurizing the finished vessel to a  pressure known to produce the required stress which in turn gives the required amount of plastic deformation to withstand the pressure load.

The authors have conducted extensive experimental and numerical studies on CS of cryogenic pressure vessels from ASS. A summary of our work as well as a  brief introduction of the history, standards, safety, and advantages of CS are given in this paper. What should be further investigated, such as fatigue properties of cold stretched ASS especially under cryogenic temperature, design of cold stretched transportable cryogenic vessels  based on life, are also presented.

STANDARDS AND ADVANTAGES OF CS

CS technology has been involved in several standards such as AS 1210 Supplement 2[3], EN 13458-2 Appendix C [4], EN 13530-2 Appendix C [5], ISO 20421-1:2006[6], ISO 21009-1:2008[7], and ASME Code Case 2596[8].

The Avesta Sheffield company in Sweden began to investigate CS in 1956. Three years later, the first vessel was manufactured by using CS in 1959. Later in the year of 1969, the Avesta Sheffield company obtained a patent in the United States (US 3456831A [9]). In 1975, CS was  brought into Swedish pressure vessel standardization, i.e.,

Cold-Stretching Directions 1991  [10]. In Australia, AS 1210-Supplyment2-1999 was promulgated for vessels using CS in 1999. In 2002, the CS technology were added into EN 13458-2 Appendix C and EN 13530-2 Appendix C, respectively. Later on, Code Case 2596, ASME Boiler and Pressure Vessel Code, Section VIII, Division1, for cold stretching of static ASS pressure vessels was issued in 2008. Furthermore, ISO 20421-1:2006 and ISO 21009-1:2008, which are equivalent to the relative EU standards, were issued. Chinese standard for CS is being developed.

The main advantages of cold stretched ASS CPV can  be summarized up as follows.

(1) Saving materials

The allowable stress of ASS can be approximately improved by 83%~130% and the weight of CPV can be normally reduced by 20%~50% by using CS[11]. Table 1 shows the allowable stress of ASS in different standards.

Several thousand cryogenic pressure vessels including static vacuum-insulated vessels and transportable vacuum-insulated vessels have been constructed by using CS technology in P.R.China. In  practice, weight was reduced by 30%~50% in comparison with conventional vessels. A lot of material has been saved, which makes the products more competitive in the market.

Table 1 Allowable stress of ASS in different standards

Materials

GB150 EN13458-2 Appendix C ASME BPVC VIII-I Code Case 2596 Allowable stress /MPa Allowable stress1)/MPa Rate of increase /% Allowable stress /MPa Rate of increase /% S304082) 137 273 99.3 270 97.1 S30403 120 267 122.5 247 105.8 S30453 137 313 128.5 -- --S32168 137 267 94.9 --

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--S34778 137 267 94.9 -- --S30458 160 313 95.6 293 83.1 S31658 160 -- -- 293 83.1 S31608 137 -- -- 270 97.1 S31603 120 -- -- 247 105.8 S31653 137 -- -- 270 97.1

1)It is calculated by/n s,n s=1.5; 2) The material name references to GB 24511-2009

[12] .

(2) Energy conservation and emission reduction

Due to the reduction of wall thickness, energy consumption can be reduced in the welding and forming. According to the statistical report of the International Aluminum Association  [13], about 60% fuel is used to carry the weight of automobile itself. It also indicates that fuel can be reduced by 10% to 15% if the weight of automobiles cuts by 10%. For transportable ASS CPV, it means that less fuel is consumed and less carbon dioxide exhaust during operation by using CS.

(3) Increasing the ratio of weight to volume

The ratio of weight to volume is an important index of energy efficiency for transportable pressure vessels. Volume of ASS CPV can be increased by 2% to 10% due to plastic deformation during CS. The ratio of weight to volume is reduced approximately by 50% caused by increase in volume and decrease in weight.

SAFETY ANALYSIS OF COLD STRETCHED ASS CPV

MECHANICAL PROPERITES

Based on extensive experimental and numerical studies on material specimens and prototype vessels, a large amount of data from tensile test, bending test and impact test, have been obtained. Meanwhile, strain hardening rate, deformation-induced α’-martensite [14],

flow stress and mechanical properties of ASS with various degrees of CS are studied [15, 16].

Owing to high ductility and excellent properties at

cryogenic temperature, ASS after CS still has favorable mechanical properties. It is found that, for welded test  plate of ASS with no less than 40% elongation after fracture, the elongation at ambient temperature is still more than 25%, and the Charpy V-notch impact energy at -196℃ can still satisfy the requirement of 31J if plastic deformation is within 9%.

DESIGN STRESS

The design stress is the maximum allowable stress at CS pressure, which is used to determine allowable stress. Proof stress of ASS can be increased by CS. The larger the plastic deformation takes place, the higher is the proof stress. However, excessively high proof stress may lessen safety margins. So how to determine the design stress (also called strengthening stress) is a key factor for the application of the CS.

There are two methods for determining the design stress.

(1) The design stress is proof stress plus 200MPa, which is used in EN13458-2, EN 13530 -2.

(2) Considering the increment of proof stress by CS, dissipated strain energy, the strain energy function-based method was developed to determine the design stress [17], which is strongly related to the nonlinearity of stress-strain curve of the material.

SAFETY MARGINS

In order to understand the safety margins of ASS CPV constructed by using CS, burst tests were

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conducted[18]. Six such vessels were pressurized to burst at room temperature. Then the ratio of the collapse  pressure to the design pressure, which is shown in Table 2,

is used as safety margins.

It shows that the safety margins of cold stretched vessels under room temperature are between 2.09 and 2.49. But it should be remembered that the collapse

 pressure was measured under room temperature. The actual tensile strength of ASS at -196℃ is at least twice that at room temperature[19]. So the actual strength margins will reach to 4.18-4.98, which indicates the safety of cold stretched ASS CPV can be guaranteed.

Table 2 Safety margins of pressure vessels under different codes

 No. material Thickness /mm Diameter /mm Plastic collapse  pressure/MPa GB150 EN13530-2 Appendix C Design pressure /MPa Strength margins Design pressure /MPa Strength margins 1 1.4301 6.5 500 16.2 3.52 4.60 7.01 2.31 2 6.5 500 14.8 3.52 4.20 7.01 2.11 3 12.6 500 28 6.74 4.15 13.42 2.09 4 12.8 500 29 6.84 4.24 13.63 2.13 5 6.1 600 11.1 2.79 3.98 4.5 2.49 6 11.3 600 19.3 5.16 3.74 8.2 2.37

So far, thousands of cold stretched ASS CPV have  been manufactured according to the CS standards such as AS 1210 Supplement 2, EN 13458-2, EN 13530-2 and ASME Code Case 2596 and there have no related accidents reported. It has been demonstrated that the security of the CS CPV can be guaranteed as long as they are under normal use.

NONLINEAR SIMULATION

In contrast with static CPV with small volume, transportable CPV, and static CPV with large volume always have some structural attachments such as openings, stiffening rings, anti-wave boards, subplates, etc, which would cause local structural discontinuity, and thus stress concentration under pressure. It is crucial to ensure that plastic deformation in those areas be within 9%.

 Nonlinear finite element analysis model has been developed by considering material nonlinearity, geometrical nonlinearity, and contact nonlinearity, which

is verified by test results [17].

PRESSURE CONTROL SYSTEM FOR CS

It is shown that pressurizing rate and CS pressure have significant effects on plastic deformation during CS[20]. In order to accurately control pressurizing rate and CS pressure, a unique pressure control system for CS has  been developed by the authors. It consists of four sub-system, i.e., multi-task control subsystem, on-line automatic parameters (including pressure, circumference, etc.) measuring subsystem, automatic water filling subsystem, and automatic de-loading system. The system has the following functions:

(1) Cold stretch several ASS CPV in parallel. (2) Automatically measure the change in circumference and volume.

(3) Automatically fill water, pressurize, and de-pressurize.

(4) Production procedure record contains at least the following information: pressurizing sequence,

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changes in circumference and volume, strain rate calculated from circumference measurements.

(5) Data management.

CONCLUDING COMMENTS

Although CS technology has been successfully used all over the world, the following future investigations should be conducted.

(1) There is no fatigue design curve for cold stretched ASS. The effect of plastic deformation achieved by CS on fatigue properties of ASS should be studied  both at room temperature and -196℃.

(2) Stress due to dynamic load on the road may cause fatigue of cold stretched transportable cryogenic vessels. Method for calculating such stress, which is the basis for fatigue prediction, should be developed  by considering the effect of structure-fluid

interaction.

ACKNOWLEDGEMENTS

This research is supported by National High Technology Research and Development Program of China (863 Program) (Number: 2009AA044801).

REFERENCES

[1] GB150-1998, Steel Pressure Vessel[S]. (in Chinese) [2] J.S. Peterkin. Cold Stretched Austenitic Stainless

Steel Pressure Vessels[C]. Symposium on Stress Analysis for Mechanical Design 1981: Preprints of Papers 1981.96-98.

[3] AS1210Supp2-1999, Pressure Vessels Cold-stretched Austenitic Stainless Steel Vessels [S]. [4] EN 13458-2:2002, Cryogenic Vessels-Static Vacuum Insulated Vessels-Part 2: Design, Fabrication, Inspection and Testing[S].

[5] EN 13530-2:2002, Cryogenic Vessels-Large Transportable Vacuum Insulated Vessels-Part2: Design, Fabrication, Inspection and Testing[S]. [6] ISO 20421-1:2006. Cryogenic vessels-Large

transportable vacuum-insulated vessels-Part 1:

Design, fabrication, inspection and testing[S].

[7] ISO 21009-1:2008. Cryogenic vessels-Static vacuum-insulated vessels-Part 1: Design, fabrication, inspection and tests[S].

[8] ASME BPVC VIII-I Code Case 2596: 2008, [S]. [9] Cold-Stretching Directions 1991. Swedish Pressure

Vessel Standardization[S].

[10] Johan Ingvar, Johansson. Austenitic Stainless Steel Pressure Vessels [P]. US 3456831 A, 1969.

[11] ZHENG Jinyang, MIAO Cunjian, SHOU Binan. Light-weight: A Trend in the Development of Pressure Vessels [J]. Pressure Vessels Technology, 2009, 26(9):42-48.

[12] GB 24511-2009, Stainless Steel Plate, Sheet and Strips for Pressure Equipment[S]. (in Chinese) [13] CAI Qigang. The Application and Trends of

Aluminium Alloy for Automobile Body [J]. Guangxi Journal of Light Industry, 2009, 25(1):28-29.

[14] Cunjian Miao, Yaxian Li, Jinyang Zheng. Effect of Strain Rate on the Deformation-Induced Martensitic Transformation and Mechanical Behavior of Austenitic Stainless Steels for Cold Stretched Pressure Vessels[C]. Washington: 2010 ASME Pressure Vessels and Piping Conference.

[15] ZHOU Gaobin. Strain Hardening of Cryogenic Vessels form Austenitic Stainless Steels [D]. Hangzhou, P.R.China, Dissertation Submitted to Zhejiang University for Master Degree of Engineering. 2007.

[16] LI Yaxian. Study on the Material and Forming Process of Strain Strengthening Austenitic Stainless Steel Cryogenic Vessel [D]. Hangzhou, P.R.China, Dissertation Submitted to Zhejiang University for Master Degree of Engineering, 2009.

[17] Li Ma, Jinyang Zheng, Cunjian Miao, etc. Nonlinear Analysis of Pressure Strengthening For Austenitic Stainless Steel Pressure Vessels[C]. Chicago: 2008 ASME Pressure Vessels and Piping Conference. [18] Li Ma, Jinyang Zheng, Cunjian Miao, etc. analysis

of strength margins for austenitic stainless steel  pressure vessels[C]. Chicago: 2008 ASME Pressure

Vessels and Piping Conference.

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Analysis For Austenitic Stainless Steel Pressure Vessels [J]. Pressure Vessels Technology, 2008, 25(1):1-5, 23.

[20] ZHENG Jinyang, GUO Abin, MIAO Cunjian, MA Li, WU Linlin. Cold Stretching Technique for Austenitic Stainless Steel Cryogenic Pressure Vessels [J]. Pressure Vessels Technology, 2010, 27(8): 28-32, 56.

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