Scholarly article on topic 'Contribution to Structural Integrity: Fatigue and Fracture Related Full Scale Experimental Investigations Carried Out at CSIR-SERC'

Contribution to Structural Integrity: Fatigue and Fracture Related Full Scale Experimental Investigations Carried Out at CSIR-SERC Academic research paper on "Materials engineering"

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{"Full scale component testing" / "fatigue crack growth" / "corrosion fatigue" / fracture / "internal pressure" / "sub-zero temperature" / "high temperature" / ratcheting}

Abstract of research paper on Materials engineering, author of scientific article — G. Raghava

Abstract CSIR - Structural Engineering Research Centre (CSIR-SERC), Chennai, has state-of-the-art facilities and expertise for carrying out R&D studies in the areas related to fatigue and fracture behaviour of structural components and materials. In the last 25 years, the laboratory has efficiently utilised the facilities and expertise available in serving various institutions and industries related to energy sector, automobile applications, railways, aerospace applications, construction industry etc. Fatigue and fracture studies have been carried out on steel tubular joints of offshore jacket platforms, carbon steel and stainless steel piping components used in power plants, automobile components (connecting rods, air springs, air suspension systems, industrial and automobile chains, stabiliser legs, hub brackets, sub-frames, rubber bushes, parallel link brackets etc.), tyre curing press, alumino-thermit and flash-butt welded rail joints used in Indian Railways, reinforcing bars (thermo-mechanically treated bars, corrosion resistant steel etc.), and many other components and materials. This paper describes some of the important investigations carried out in the Fatigue and Fracture Laboratory (FFL) of CSIR-SERC and presents some salient test results.

Academic research paper on topic "Contribution to Structural Integrity: Fatigue and Fracture Related Full Scale Experimental Investigations Carried Out at CSIR-SERC"

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Procedía Engineering 86 (2014) 139 - 149

Procedía Engineering

www.elsevier.com/locate/proeedia

1st International Conference on Structural Integrity, ICONS-2014

Contribution to Structural Integrity: Fatigue and Fracture Related Full Scale Experimental Investigations Carried Out at

CSIR-SERC

G. Raghava

Fatigue & Fracture Laboratory, CSIR - Structural Engineering Research Centre CSIR Campus, Chennai - 600 113, India E-mail ID: raghavag@serc.res.in

Abstract

CSIR - Structural Engineering Research Centre (CSIR-SERC), Chennai, has state-of-the-art facilities and expertise for carrying out R&D studies in the areas related to fatigue and fracture behaviour of structural components and materials. In the last 25 years, the laboratory has efficiently utilised the facilities and expertise available in serving various institutions and industries related to energy sector, automobile applications, railways, aerospace applications, construction industry etc. Fatigue and fracture studies have been carried out on steel tubular joints of offshore jacket platforms, carbon steel and stainless steel piping components used in power plants, automobile components (connecting rods, air springs, air suspension systems, industrial and automobile chains, stabiliser legs, hub brackets, sub-frames, rubber bushes, parallel link brackets etc.), tyre curing press, alumino-thermit and flashbutt welded rail joints used in Indian Railways, reinforcing bars (thermo-mechanically treated bars, corrosion resistant steel etc.), and many other components and materials. This paper describes some of the important investigations carried out in the Fatigue and Fracture Laboratory (FFL) of CSIR-SERC and presents some salient test results.

© 2014 The Authors. Published by ElsevierLtd.This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/3.0/).

Peer-review under responsibility of the Indira Gandhi Centre for Atomic Research

Keywords: Full scale component testing, fatigue crack growth, corrosion fatigue, fracture, internal pressure, sub-zero temperature, high temperature, ratcheting

1877-7058 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

Peer-review under responsibility of the Indira Gandhi Centre for Atomic Research doi: 10.1016/j.proeng.2014.11.022

1. A Facility for Fatigue and Fracture Studies

In structures and components involving repeated load applications, fatigue and fracture investigations on structural components and standard test specimens for material characterisation are extremely important for validating engineering designs. In spite of the analytical tools and computational facilities available, fatigue and fracture testing provides the only reliable tool available for solving complex problems. CSIR - Structural Engineering Research Centre (SERC), Chennai, has excellent and state-of-the-art facilities for conducting fatigue and fracture studies. The facilities available in the Fatigue & Fracture Laboratory (FFL) of the Centre include a heavy duty test floor of plan dimensions of 36.36 m x 10.5 m, together with two vertical reaction walls of 10.5 m wide and 7 m high. The laboratory is equipped with servo-controlled fatigue testing systems with actuators of capacities ±50 kN, ±100 kN, ±500 kN (two nos.), ±1000 kN (two nos.), and ±2000 kN. In addition, the laboratory is also having fatigue rated Universal Testing Machines (UTMs) of ±250 kN and ±500 kN capacity. The laboratory has the necessary facilities and expertise to carry out flaw detection and sizing by ultrasonic and potential difference techniques. In the last 25 years, the laboratory has efficiently utilised the facilities and expertise available in serving various institutions and industries related to energy sector, automobile applications, railways, aerospace applications, construction industry etc. Fatigue and fracture studies have been carried out on steel tubular joints of offshore jacket platforms, carbon steel and stainless steel piping components used in power plants, automobile components (connecting rods, air springs, air suspension systems, Role Over Protective Structures - ROPS, industrial and automobile chains, stabiliser legs, hub brackets, sub-frames, rubber bushes, parallel link brackets etc.), tyre curing press, alumino-thermit and flash-butt welded rail joints used in Indian Railways, reinforcing bars (thermo-mechanically treated bars, corrosion resistant steel etc.), and many other components and materials [1].

Some selected experimental investigations carried out in the laboratory have been explained in the following pages. These include: (1) air and corrosion fatigue investigations on steel tubular joints of offshore jacket platforms, with and without internal ring stiffeners; (2) fractures studies on large diameter pipes having through wall cracks and subjected to internal pressure - the tests require specialized sealing arrangements; (3) fracture studies on 135 mm thick steel cruciform specimens at sub-zero temperature of -70° C to simulate the brittle behaviour after exposure to certain operational conditions; (4) fracture studies on carbon steel pipes at high temperature of +300° C -the pipes were heated at the notch location alone using special heating elements and insulation provisions; (5) ratcheting studies on stainless steel straight pipes and elbows under combined internal pressure and in-plane bending moment; (6) cyclic fracture studies on welded straight pipes; (7) Fatigue Crack Growth (FCG) studies on straight pipes and elbows; and (8) fatigue life evaluation of welded rail joints.

2. Fatigue and Corrosion Fatigue Studies on Steel Tubular Joints of Offshore Jacket Structures

Fatigue studies have been carried out in air and synthetic sea water environments on unstiffened and stiffened steel tubular T and Y joints. The stiffened joints consisted of three internal rings in the chord, one at the centre and the other two at the branch face locations. Typically, the joint dimensions: diameter, thickness, and length of chord member = 320 mm, 12 mm, and 1800 mm respectively; diameter, thickness, and length of brace member = 220 mm, 8 mm, and 600 mm respectively. Only in the case of a few joints, there were marginal variations in the dimensions. The joints were approximately quarter scale models of a typical tubular joint of a jacket platform in the Bombay High region. Some joints tested in sea water environment were cathodically protected against corrosion by providing aluminium alloy based sacrificial anodes. Thus, tubular joint fatigue test results for three different environmental conditions are available: joints in air, joints freely corroding in sea water, and joints immersed in sea water but provided with adequate cathodic protection. All the air fatigue tests were conducted at 2 Hz frequency and the corrosion fatigue tests were conducted at 0.2 Hz frequency [2, 3].

Corrosion fatigue test set-up of a tubular T-joint specimen is shown in Fig.1. Close-up view of a tubular T joint specimen enclosed in a corrosion chamber is shown in Fig.2. Instrumentation wires and field cables for crack depth measurement and sacrificial anode fitted to the chord member for cathodic protection are also seen in the figure. Figure 3 shows a close-up view of a corrosion chamber enclosing a tubular T joint specimen under corrosion fatigue test. Because of the cathodic protection provided, the joint has not undergone any corrosion. Based on the fatigue test results, a penalty factor of two under corrosion fatigue was considered appropriate for both unstiffened

and stiffened steel tubular joints. Development of multiple cracks was observed under corrosion fatigue conditions resulting in accelerated crack growth and consequent reduction in fatigue life. It was also observed that adequate cathodic protection would help in regaining the in-air fatigue life of the joints.

3. Fracture Studies on Carbon Steel Pipes with Internal Pressure

Fracture studies have been carried out on carbon steel pipes having circumferential through-wall notch under monotonic bending with internal pressure. One category of pipes was of 219 mm OD and 18.5 mm thickness; the crack angle was 152.8°. The test was conducted under four point bending, under load control, using ±1000 kN servo-hydraulic actuator. The inner and outer spans were 990 mm and 3480 mm respectively. The through-wall notch of the pipe was sealed with a sealing arrangement. A sealing arrangement consisting of 2 mm thick stainless steel sheet as backing material at notch location, silicon rubber sheet, and two component 'Fevitite' super strength epoxy adhesive was used to withstand internal pressure and bending. The pipe was pressurised to 10 MPa and the pressure was maintained for the entire duration of the test. During the fracture test, maximum load, load-line displacement, crack mouth opening displacement, deflection of the pipe at four locations and surface crack growth were continuously monitored. Fracture test was also conducted on a carbon steel pipe of 610 mm OD having circumferential through-wall notch under monotonic bending with internal pressure. The crack angle was 151° and the pipe thickness was 57.5 mm. The test was conducted under four point bending, under load control, using a hydraulic jack of 5000 kN capacity. Figure 4 shows fracture test on a 610 mm OD carbon steel pipe with internal pressure. Deflected shape of the pipe is shown in Fig.5. Figure 6 gives a close-up view of the pipe at the notch

Fig. 1 (left) Corrosion fatigue test on a tubular T joint; Fig. 2 (right) Close-up view of corrosion fatigue test set-up

Fig. 3 Close-up view of corrosion chamber and joint location

location after fracture test. Figure 7 gives the load-deflection curve of a fracture test on 219 mm OD carbon steel pipe with circumferential through-wall notch [4].

Fig. 4 (left) A view of fracture test on a 610 mm OD carbon steel pipe with internal pressure; Fig. 5 (right) A view of the deflected shape of the pipe

Fig. 6 (left) A close-up view of 610 mm OD carbon steel pipe at the notch location after fracture test; Fig. 7 (right) Load-deflection curve: fracture test on 219 mm OD carbon steel pipe with circumferential through-wall notch

4. Fracture Studies on Cruciform Specimens at Sub-Zero Temperature

Ductile and highly tough material is used in reactor pressure vessels. However, the material would lose the ductility and toughness due to irradiation over the years. Such a scenario of low ductility and low toughness can be simulated in the laboratory by exposing the material to low temperature. Fracture studies have been carried out on cruciform specimens at sub-zero temperature. The specimens typically had a notch length of 430 mm, width 3 mm and depth 18 mm; thickness of the specimen was 135 mm. The specimens were instrumented with Crack Mouth Opening Displacement (CMOD) gauges along the notch and rectangular rosette strain gauges. A low temperature chamber was fixed at the centre of the cruciform specimen. Liquid nitrogen was used to bring down the temperature to -70°C at the core of the specimen and it was maintained throughout the test. The test was conducted using a 5000 kN capacity hydraulic jack and under load control. During the tests, maximum load, load-line displacement, crack mouth opening displacements and strains at critical locations were continuously monitored. Initial crack profile, profile after fatigue pre-cracking and final crack profile after fracture test were determined both by ultrasonic and Alternating Current Potential Difference (ACPD) techniques. Figure 8 gives a close-up view of the cruciform specimen showing the instrumentation for strain and crack depth measurements. Figure 9 gives a close-up view of fracture test on the cruciform specimen at sub-zero temperature; the low temperature chamber is seen at the centre

Fig. 8 A close up view of instrumentation for a cruciform specimen; Fig. 9 A close-up view of fracture test on a

cruciform specimen at sub-zero temperature

5. Fracture Studies on Carbon Steel Pipes at Elevated Temperature

In order to study the effect of high temperature on the fracture behaviour of piping components used in power plant structures, fracture tests were conducted on carbon steel pipes of 219 mm OD and 406 mm OD having circumferential part-through notches, under monotonic bending and at an elevated temperature of 300°C. The initial notch angles were 34° and 37.8° and the pipe thicknesses were 18.8 mm and 26.9 mm respectively. The tests were conducted under four point bending, under load control, using servo hydraulic actuator of ±1000 kN capacity. Prior to the fracture tests, both the specimens were fatigue pre-cracked till the crack depth at the centre of the notch reached 2.5 mm. Subsequently, fracture tests were conducted on the pipes at 300°C. For heating the pipe at the notch location, the notch portion of the pipe was wrapped with heating elements covered with ceramic cloth. Above this, insulation material was provided to prevent heat loss. Temperature regulators were used for setting the required temperature and maintaining the same throughout the test. The temperature was measured at regular intervals with a non contact type laser based temperature measuring instrument. In addition, thermocouples were also used to measure the temperature. Maximum load, load-line displacement, rotation at the supports, and crack mouth opening displacement were monitored throughout the test. Figures 10-13 show fracture test on a 406 mm OD carbon steel pipe at elevated temperature, the temperature indicator, close-up view of the pipe with heating element covered by insulation material, and a view of the deflected shape of the pipe after fracture test [6].

Fig. 10 (left) Fracture test on a 406 mm OD carbon steel pipe at elevated temperature; Fig. 11 (right) Temperature indicator

Fig. 12 (left) Close-up view of 406 mm OD carbon steel pipe with heating element covered by insulation material;

Fig. 13 (right) Deflected shape of the pipe after fracture test

6. Cyclic Fracture Studies on Welded Straight Pipes

Piping components, forming part of primary heat transport system of Nuclear Power Plants (NPP), experience dynamic-cyclic loads during an earthquake event. The fully reversible cyclic loading reduces the fracture resistance and hence the load carrying capacity of cracked components considerably. For realistic assessment of applicability of Leak Before Break (LBB) justification, even though studies under dynamic-cyclic loads are required, quasi-static cyclic load studies can also be carried out, since the effects of cyclic history are more pronounced in the latter. Experimental investigations were carried out on 170 mm and 324 mm Outer Diameter (OD) Shielded Metal Arc (SMA) and Narrow Gap (NG) welded stainless steel straight pipes, with initial notch in the weld, under quasi-cyclic loading. The pipe specimens were made of TP 304LN stainless steel conforming to ASTM A 312/A 312 M - 09 standard [7]. The yield strength and ultimate tensile strength were 345 MPa and 521 MPa respectively. The percentage elongation was 65 and the Young's modulus was 195 GPa.

Totally 16 specimens were tested under static and cyclic loading under four point bending [8, 9, 10]. All the pipes had circumferential through-wall notch in the weld. The length of the pipes varied from 1995 mm to 5090 mm. The average thickness of the pipes varied from 14.5 mm to 26.1 mm. The initial notch length was approximately 90 mm in the case of 170 mm OD specimens and 170 mm in the case of 324 mm OD specimens. The corresponding notch angle in both the cases was approximately 60°. Prior to the fracture experiments, all the specimens were fatigue pre-cracked under four point bending. The fracture studies were carried out under load-control, displacement-control and combination of the two. The maximum and minimum load values in the load-controlled fracture tests were decided as a percentage of the static load carrying capacity of similar specimen. The specimens were tested till failure, i.e., either the crack grew in an unstable manner or reached a stage where the specimen could not carry any further load. Figure 14 shows a typical test set-up.

7. Fatigue Crack Growth (FCG) Studies on Straight Pipes and Elbows

NPP piping components may contain pre-existing flaws, which would grow under service conditions, leading to failure of the component or structure. The service environment may be air or water environment; the service condition or type of loading include cyclic loads due to thermal transients and seismic events, bending or torsion load or a combination of the two, vibration loading etc. In this background, fatigue crack initiation and growth rate studies were carried out on full-scale piping components, 14 straight pipes and four elbows made of TP 304LN stainless steel, containing pre-existing flaws, subjected to different exposure and loading conditions [11]. The material details have already been given in the previous section.

Fig. 14 Cyclic fracture studies on a straight pipe Fig. 16 Close-up view of FCG studies on a

straight pipe under combined torsion and bending

Approximate specimen and notch dimensions were: OD and thickness of the pipes 169 mm and 14.75 mm respectively; OD and thickness of the elbows 168 mm and 15.75 mm; notch length and depth in pipes 36 mm and 3.4 mm; and notch length and depth in elbows 13.25 mm and 3.5 mm respectively. Three specimens were NG welded with notch in the weld; the remaining 11 specimens were unwelded with notch in the base metal. All the specimens were tested under load-control except one elbow which was tested under displacement-control. One pipe was studied under block loading and one under variable loading. Normal fatigue loading was preceded by vibration loading of 10,00,000 cycles in two pipes. Nine straight pipes were tested under four point bending in air environment; three under four point bending in water environment; and two under combined torsion and bending in air environment. All the four elbows were studied under closing moment in air environment. Figures 15 and 16 show close-up views of FCG studies on straight pipes in water environment and under combined torsion and bending, respectively.

8. Ratcheting Studies on Straight Pipes and Elbows Under Combined Internal Pressure and in-Plane Bending Moment

'Ratcheting' is a phenomenon which leads to reduction in fatigue life of a structural component by loss of ductility due to cycle by cycle accumulation of plastic strain. Ratcheting can occur in a structure subjected to a combination of steady/sustained and cyclic loads such that the material response is in the inelastic region. NPP piping components, which are under high pressure, are subjected to large amplitude reverse cyclic loading during earthquake events and the stresses are likely to exceed the elastic limit of the piping material. In this situation, there is a strong possibility of plastic strain accumulation by ratcheting. Accurate prediction of such ratcheting response in piping components is very important to avoid catastrophic failures.

Fig. 17 Close-up view of ratcheting studies Fig. 18 Close-up view of ratcheting studies on

on a straight pipe an elbow

Ratcheting experiments were carried out on four straight pipes and four elbows of 168 mm OD [12]. All the pipe and elbow specimens were made of TP 304LN stainless steel, the material details of which have already been given. The straight pipes were of 2800 mm length. The average initial thickness varied from 14.3 mm to 15.3 mm. The thickness was reduced to 12.0 mm in the gauge length portion of 200 mm at the centre of the pipe by machining. The length of straight portions of the elbows was 500 mm, the radius of the bent portion was 225 mm and the total length of the elbows was 1342 mm. The average thickness of the elbows varied from 14.7 mm to 15.1 mm. The pipe specimens were subjected to completely reversed four point bending load. The inner and outer spans were 900 mm and 2000 mm respectively. In the case of elbow specimens, cyclic bending load under in-plane opening and closing moments was applied under pin-pin support conditions. All the eight tests were carried out under displacement control by subjecting the specimens to different levels of load-line displacement. The specimens were filled with water and pressurized; the pressure was maintained by using an automated high pressure hydraulic pump. Figures 17 and 18 show the close-up views of experimental set-up for pipe and elbow specimens respectively. Occurrence of through-thickness crack in the specimens was indicated by a sharp water jet. The specimens underwent significant ballooning, ovalisation and consequent thinning of the cross-section during ratcheting.

9. Fatigue Life Assessment of Welded Rail Joints

Long welded rails are used extensively in railway tracks in India for increasing the speed of the rolling stock and better travel comfort. Fatigue fracture of rails is a possible occurrence in railway tracks because of the fluctuating stresses due to the varying traffic conditions and low fracture toughness of rail steels. Most rails are made from plain carbon steel to keep their cost low. Due to heat affected zone adjacent to the weld, fatigue becomes critical in welded joints. Fatigue life evaluation of a number of welded rail joints from various companies have been carried out as per the standards of the Research Designs and Standards Organisation (RDSO), Lucknow. The rail joints have to withstand two million cycles of constant amplitude sinusoidal cyclic loading. The test samples have an overall length of 2 m. They are supported over a span of 1.5 m and the load is applied at two points at a distance of 75 mm from the centre. Three samples have to be tested and all the three have to pass the specified number of cycles. Till date, test results of fatigue life evaluation of nearly 160 rail joints are available. Figure 19 shows fatigue test on a flash-butt welded rail joint; a close-up view of the joint is shown in Fig.20.

Fig. 19 Fatigue test on a welded rail joint; Fig. 20 A close-up view of welded rail joint during fatigue test

10. Conclusions

Some selected large scale experimental investigations on structural components, in the area of fatigue and fracture, carried out at FFL, CSIR-SERC, Chennai, India, have been presented in this paper: long term fatigue and corrosion fatigue studies on steel tubular joints of offshore jacket structures, fracture studies on piping components with through-wall notch under internal pressure and bending, fracture studies on cruciform specimens at sub-zero temperature, fracture studies on carbon steel pipes at elevated temperature, ratcheting studies on stainless steel straight pipes and elbows, cyclic fracture studies on welded straight pipes, FCG studies on straight pipes and elbows, and fatigue life assessment of welded rail joints. The examples presented exemplify the capability and expertise available with CSIR-SERC for undertaking experimental studies related to fatigue and fracture behaviour of structural components.

Conducting experiments for specialized applications requires attention to minute details. When very high loads in excess of 1000 kN are involved, the energy stored in the specimen is enormous and special attention needs to be taken for avoiding accidents. With present day advanced instrumentation and online data acquisition facilities, the reliability of experimental studies has significantly improved. It is well known that fatigue strength exhibits large scatter, and hence the number of specimens required and the costs involved are also quite high. Hence, extensive instrumentation is required to be done in all the fatigue and fracture investigations that are conducted in the laboratory, so that the time and cost involved are optimised.

Some important observations of the investigations presented in this paper are given below:

• Based on the results of fatigue tests on steel tubular joints in air and seawater environments, a penalty factor of two under corrosion fatigue is considered appropriate for both unstiffened and stiffened steel tubular joints. Development of multiple cracks was observed under corrosion fatigue conditions resulting in accelerated crack growth and consequent reduction in fatigue life. It was also observed that adequate cathodic protection would help in regaining the in-air fatigue life of the joints.

• During the period 1997 to 2012, around 200 piping components (straight pipes and elbows) of OD 6" (152 mm) and 12" (305 mm), both carbon steel and stainless steel, have been studied at FFL, CSIR-SERC for fatigue and fracture behaviour. These include studies at elevated temperature, studies under internal pressure, compliance studies, ratcheting studies etc. These investigations have contributed valuable inputs to creating a large database with regard to LBB justification in damage tolerant design and assuring structural integrity.

• Based on the results of load-controlled cyclic fracture experiments on piping components, material specific plots between cyclic load amplitude, as a percentage of maximum load carrying capacity of a specimen under monotonic fracture, and number of cycles to failure were obtained. The results indicate that the piping components subjected to quasi-cyclic loading may fail in very less number of cycles even when the load amplitude is sufficiently below the monotonic fracture/collapse load.

• Vibration loading prior to cyclic loading results in increased fatigue crack growth. The applied load range being the same, combined torsion and bending has resulted in 31% reduction in fatigue life in comparison to that of pure bending.

• During ratcheting studies, the pipe specimens failed by occurrence of through-thickness crack accompanied by either simultaneous ballooning or simultaneous ballooning and bursting. The ballooning was found to be varying from 13.4% to 19.0% with respect to the original diameter. The percentage reduction in thickness varied from 8.0% to 16.3%. All the elbows failed by occurrence of axial through-thickness crack accompanied by simultaneous ballooning. The ballooning was found to be varying from 3.8% to 5.8% and the reduction in thickness was 12% to 15%.

• Till date, fatigue life evaluation of nearly 160 rail joints have been carried out. This is an important contribution towards ensuring safety of Indian rail tracks against fatigue failure.

11. Acknowledgement

The contents of this paper are based on the various experimental investigations that were carried out at the Fatigue & Fracture Laboratory of CSIR - Structural Engineering Research Centre, Chennai. The contribution to the growth, maintenance and activities of the laboratory by the scientists and technical staff of the laboratory is gratefully acknowledged. Some works reported in this paper were carried out for externally funded research projects; the author thanks the sponsors of these projects. The author thanks Dr Nagesh R. Iyer, Director, CSIR-SERC and Dr K. Ravisankar, Advisor (Management) for the encouragement and support provided by them to the R&D activities of the laboratory. This paper is published with the kind permission of the Director, CSIR-SERC, Chennai.

References

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2. Raghava G, Gandhi P, Ramachandra Murthy D S, and Madhava Rao A G, "Fatigue studies on steel tubular joints in air and seawater environments", in Recent Advances in Solid Mechanics, Proceedings of the Conference on Engineering Applications of Solid Mechanics 1995 (CEASM '95), Indian Institute of Technology, Madras, December 7 & 8, 1995, published by Allied Publishers Limited, Madras (1995), pp.131138.

3. Raghava G, Madhava Rao A G, and Santhakumar A R, "Strength of steel tubular joints under corrosion fatigue", Proceedings of the International Conference in Ocean Engineering, Indian Institute of Technology, Madras, December 17-20, 1996, published by Allied Publishers Limited, Madras (1996), pp.33-40.

4. Gandhi P, Vishnuvardhan S, Saravanan M, Pukazhendhi DM, and Raghava G, "Fracture test on 610 mm OD carbon steel pipe having circumferential through-wall notch with internal pressure", Report No. 2 on Sponsored Project SSP 6341, March 2008, CSIR - Structural Engineering Research Centre, Chennai.

5. Saravanan M, Pukazhendhi DM, Gandhi P, Vishnuvardhan S, Raghava G, Chattopadhyay J, Sahu M K, and Dutta B K, "Fracture behaviour of cruciform specimens under uni-axial bending at room temperature and

subzero temperature', Proceedings of The Sixth Structural Engineering Convention, Chennai, December 18-20, 2008, Vol. II, pp. 1001-1010.

6. Saravanan M, Gandhi P, Vishnuvardhan S, Pukazhendhi DM, Raghava G, Sahu M K, Chattopadhyay J, Dutta B K, and Vaze K K, "Fracture studies on carbon steel piping components at elevated temperature", Proceedings of the 21st International Conference on Structural Mechanics in Reactor Technology (SMiRT 21), New Delhi, November 6-11, 2011 (in CD).

7. ASTM A312/A312M - 09, "Standard specification for seamless, welded and heavily cold worked austenitic stainless steel pipes", ASTM International, 2009.

8. Raghava G, Gandhi P, and Vaze, K K, "Cyclic fracture, FCG and ratcheting studies on Type 304LN stainless steel straight pipes and elbows", Procedia Engineering, Vol. 55, 2013, pp. 693-698.

9. Vishnuvardhan S, Gandhi P, Saravanan M, Pukazhendhi DM, Raghava G, Sumit Goyal, Suneel K Gupta, and Vivek Bhasin, "Quasi-cyclic fracture studies on TP 304LN stainless steel straight pipes", Proceedings of the 5th International Conference on Theoretical, Applied, Computational and Experimental Mechanics, Kharagpur, India, December 27-29, 2010.

10. Vishnuvardhan S, Gandhi P, Raghava G, Saravanan M, Pukazhendhi DM, Sumit Goyal, Sunil Satpute, Suneel K Gupta, Vivek Bhasin, and Vaze K K, 'Quasi-Cyclic Fracture Studies on Narrow Gap Welded Stainless Steel Straight Pipes', Proceedings of the 21st International Conference on Structural Mechanics in Reactor Technology (SMiRT 21), New Delhi, India, November 6-11, 2011 (in CD).

11. Pukazhendhi DM, Vishnuvardhan S, Saravanan M, Gandhi P, and Raghava G, "Fatigue and fracture studies on 168 mm OD stainless steel straight pipes with circumferential outer surface crack on base metal", Report Nos. 4 & 5 on Sponsored Project SSP 6041, March 2008 & November 2008, CSIR - Structural Engineering Research Centre, Chennai.

12. Vishnuvardhan S, Raghava G, Gandhi P, Saravanan M, Sumit Goyal, Punit Arora, Suneel K Gupta, and Vivek Bhasin, "Ratcheting failure of pressurised straight Pipes and elbows under reversed bending", International Journal of Pressure Vessels and Piping, Vols. 105-106, May-June 2013, pp. 79-89.