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Int. J.MAr.Sci.Eng., 3(1), 33-42, Winter 2013 ISSN 2251-6743 © IAU
Nonlinear statics analysis of on offshore jaket platform in the case of explosion
1M. Tajari; 1*F. Azarsina; 2N. Ashrafi Khorasani
1Department of Marine Industries, Faculty of Marine Science and Technology, Science and Research Branch, Islamic Azad University, Tehran 1477893855, Iran
2Faculty of Mechanical and Aerospace Engineering, Science and Research Branch, Islamic Azad University, Tehran 1477893855, Iran
Received 5 November 2012; revised 18 December 2012; accepted 2 January 2013
ABSTRACT: Explosion and fire on an offshore rig can lead to its minor or complete damage and sinking which means the loss of life or environmental pollution. Hence the use of techniques such as blast wall is crucial to reduce the detrimental effects. These blast walls are designed for explosion wave of length between 0.1 to 1 of load mainly to protect the personnel and critical sections. In this research, the behavior of an offshore platform jacket under blast wave 0.2 and 0.7of load is studied with the blast wall thickness of 1, 5 and 10 mm. The analysis is performed in both plastic and elastic aspects in which we need to consider the nonlinear geometrical and material properties. Keywords: Blast, platforms, static analysis, cover analysis, blast walls
INTRODUCTION1 Marine structures such as platforms, jetties and sea floor pipelines may be exposed to load caused by accidental explosion malicious attacks, in addition to loads such as wind load, water flow, wave, tidal currents, earthquakes, dead and live loads. Because of the importance of these structures, their resistance to loads caused by blasts is an important factor in the safety of the entire structure and in some cases it seems important to study of effects of explosions on these structures (Schlyer and Campbell, 1996). Blast is a chemical reaction in explosive material that converts the explosives to gas with high pressure and temperature. This process is done with the utmost speed and a lot of heat. Temperature of gases produced is about 3000 degrees (API LRFD, 2002). Gas explosion depends on the following aspects (API LRFD, 2002):
• Type of fuel and its components • Size and Richness • Position and strength of the fire source • Degree of Compression in position of
structural element sizes and Equipment. In this regard, different theories and experiments have been conducted for explosion. In 1997, an explicit *Corresponding Author Email: [email protected] [email protected]
finite element method was performed to evaluate the effects of explosions on an offshore production platform. Due to the size and complexity of the platform, an explicit finite element analysis was not possible for the whole platform. So the blast site was modeled with the help of some boundary conditions. The results show that the inertial effects are low impact while studying the single wall panels, but are high impact while studying the support pillars. Fire is usually caused by oil pipelines that may disrupt the structural members. In the vicinity of the blast, the pressure is high and the blast winds can cause local damage. Generally, at least one blast wall is necessary in order to protect equipment and personnel from explosion where fuel is generated. The size and shape of this blast wall, changes considerably in different platforms (DNV-RP-D 101).
MATERIALS AND METHODS The general principles of a blast wall The offshore show a good resistance against the explosion due to having an open space frame structural system consisting of members of rolled sections. When it sounds necessary to make some part of the deck of the platform in the form of the closed container, due to the risk of gas explosions, the walls
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or side covers of these containers should have some panels that are damaged by the low pressures so as to minimize the effects of loads on the main elements of the structure. This stainless steel walls that consists of sheet profiles are widely used in offshore platforms, where there is the risk of explosion (Offshore Technology Report 046 1999, 2000). These paper sections should have good resistance to corrosion, good mechanical properties and energy absorption characteristics and also good ductility to make them ideal for the construction of a blast wall. In general, blast walls are designed for added pressure of between 0.1 and 0.5 of load to protect personnel and critical systems. Firewalls are designed for low blast pressures that are mostly located around the “well head” (Interim Guidance Notes, 1992). The stress - strain curve in the plastic range should have the most plastic resistance compared to other carbon steel sections. Also their good mechanical strength should be able to tolerate temperatures above 500 degrees. Generally the thickness of blast walls is between 2 to 6 mm. a view of these walls is provided with an amplifier, is shown in Fig. 1.
Evaluation methods for the this analysis The evaluation is such that two factors of the degree of a wall being exposed to and the liability of an occurrence with the help of a risk level matrix are chosen and consequently the pressure-time curve associated with the risk level is chosen by HSE engineer. Factors that influence the probability of occurrence include the type of equipment used, type of platforms products, the type of action that takes place on the platform, processes and manufacturing operations, deck type, location, and other factors stipulated in the regulation of the structure. When a structure exposes to a damaging incident, it might be totally or partially damaged or only some of its elements get out of stable state depending on the intensity of the incident (Mays and Smith, 1995). According to regulation of themes 51300, providing that there is sufficient control then the criteria to a structural element failure would be the deformation up to 12 degree of rotation and this value would be 2 degrees for beams and plates. The loading in blast analysis includes dead and live loads caused by explosion, and the environmental loads are not considered (Offshore Technology Report 047 1999, 2000).
The value of load caused by the explosion is taken from the Norooz Soroosh Shell Company. The value of this load cause by the explosion is maximum dynamic pressure of 0.7 which is conservatively intended for the uniform static pressure. In API regulation there would be some reviews and cap binding analysis needed for the following cases:
• Personnel addition • Equipment addition (an increase of pipelines,
wells, etc.) • increase of the load on the structure • Insufficient height of the deck (if the deck
height of the platform has been insufficient enough to meet the burden of the wave board then it should be evaluated for the new conditions.)
• Damage observance [1] When considering a platform that is not damaged, it would mean that its deck had sufficient height, and significant changes to the design criteria and regulations is not acceptable and does not require evaluation. But in case of major damages and significant changes to the design criteria then it would be required to perform the following analysis (Pueksap, 2010).
• Design level analysis • Ultimate strength analysis
Based on the API regulation theory, the ultimate strength analysis should be performed for the explosion analysis which is done using the COLLAPSE module of SACS software (Golafshani et al., 2011). Thus, a static analysis and a fracture analysis with nonlinear geometric and properties of the structures was performed. Platform model specifications The deck of the platform has 4 working levels including the lower deck, mid deck, main deck and the helicopter deck which are located on levels of 6,16,11,21 respectively. The jacket alignments are -60.6 of mud level, -44، -28، -12 ، 5.2 ، 4.1 of spark plug level and 4.5 of work point level. The distance of lines on the mud level is 32.11 by 33.5 and the distance of lines on the workflow level is 16 by 29. Fig. 3 shows a view of the first-level deck layout which shows the blast wall. Fig. 4 shows the blast have been modeled in sacs. These profiles shown in Fig. 1 in which a statics analysis is performed.
I
Fig. 3: the location of blast walls in the first
Int. J. MAr.Sci.Eng., 3(1), 33-42, Winter, 2013
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Fig. 1: A view of the profile of a blast wall.
Fig. 2: 3D view of the platform
3: the location of blast walls in the first-level of the deck
Nonlinear statics analysis of on offshore jaket platform
RESULTS AND DISCUSSIONThe results of the explosion Fig. 5 shows the total displacement of the first level of the deck under static analysis while the blast wall is not considered. Fig. 6 shows the horizontal displacement of the blast wave with the added pressure of 0.2 of load and the Fig. 7 shows the horizontal displacement
Fig. 5: Horizontal displacement in static analysis without explosion wave and the blast wall
linear statics analysis of on offshore jaket platform
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N
ement of the first analysis while the
splacement of the sure of 0.2 of load ontal displacement
of the blast wave with the added pressure of 0.7 of load that are reviewed.Fig. 8 shows the horizontal displacement of the wall with the thickness of 5 mm with an added pressure of 0.2 of load. In horizontal displacement of the blast wall with the thickness of 1, 5 and 10 mm with the added pressure of 0.7 of load is analyzed.
Fig. 4: the total location of blast wall
lacement in static analysis without explosion wave and the blast wall
e added pressure of 0.7
tal displacement of the f 5 mm with an added
n Figs. 9, 10 and 11 the f the blast wall with the 0 mm with the added analyzed.
blast wall
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Fig.6: Horizontal displacement in static analysis with explosion wave and the added pressure of 0.2 of load
Fig. 7: Horizontal displacement in static analysis with the explosion wave and the added pressure of 0.7 of load.
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t in static analysis with explosion wave and the added pressure of 0.2 of load
n static analysis with the explosion wave and the added pressure of 0.7 of load.
ure of 0.2 of load
ssure of 0.7 of load.
Fig. 8: Horizontal displacement in static analysis with blast wall of thickness of 5 mm and the added pressure of 0.2 of load
Fig.9: Horizontal displacement in static analysis with blast wall of thickness of 1 mm and the added pressure of 0.7 of load.
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c analysis with blast wall of thickness of 5 mm and the added pressure of 0.2 of load
c analysis with blast wall of thickness of 1 mm and the added pressure of 0.7 of load.
ed pressure of 0.2 of load.
d pressure of 0.7 of load.
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Fig. 10: Horizontal displacement in static analysis with blast wall of thickness of 5 mm, and the added pressure of 0.7 of lo
Fig. 11: Horizontal displacement in static analysis with blast wall of the thickness of 10 mm and the added pressure of 0.7 of
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ic analysis with blast wall of thickness of 5 mm, and the added pressure of 0.7 of lo
tic analysis with blast wall of the thickness of 10 mm and the added pressure of 0.7 of load.
ded pressure of 0.7 of load.
e added pressure of 0.7 of
Nonlinear statics analysis of on offshore jaket platform
Analysis of cap binding First the failure of the first level of the deck under the presence and absence of blast wall has been studied. The damage to structures is 100 percent for the red color and 75 percent for the pink, 50 percent for the yellow color and 25 percent for the pand no damage for the green color. The final displacement for the failure analysis is 200 cm.
Fig.12: The failure analysis due to the load of the explosion without the blast wall and with the added pressure of 0.7 of lo
Fig. 13: The failure analysis due to the load of the explosion with the blast wall and with the added pressure of 0.7 of load
linear statics analysis of on offshore jaket platform
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of the deck under st wall has been
ercent for the red 50 percent for the he pale blue color color. The final
s is 200 cm.
The plasticity in members of the outer space of this wall occurred and moved to the side members under the failure analysis with nonlinear geometristructural properties. This is clearly seen in Fig. 12.blast wall is designed and considered the plasticity occurs inside the wall space which indicates that the blast wall has prevented from damage to the other parts. This is clearly seen in Fig. 13
oad of the explosion without the blast wall and with the added pressure of 0.7 of lo
e load of the explosion with the blast wall and with the added pressure of 0.7 of load
the outer space of this he side members under nlinear geometric and
But in the case that the onsidered the plasticity which indicates that the m damage to the other g. 13.
ed pressure of 0.7 of load.
d pressure of 0.7 of load.
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CONCLUSION In this research the horizontal displacement of the first level of the deck due to explosion has been studied which shows that the more the added pressure is the more the horizontal displacement. The horizontal displacement of the added pressure of 0.7 of load has been increased compared to its usual value which is maximum of 40 cm. Hence use of blast walls to reduce explosion effects was studied. wall blasts of three different thicknesses of 1, 5, 10 mm are used in our study in which regarding the cost effectiveness of the cases, the use of the blast wall with the thickness of 5 mm are suggested according to the results obtained from SACS. The cap binding analysis shows that under the cap binding analysis with nonlinear geometric and structural properties in the case that the blast wall is not considered the plasticity of the members has occurred in the outer space of the wall and then moved to the side members. But in the case that the blast wall is considered the plasticity occurs inside the wall space which shows that the blast wall has prevented from damage to the other parts. REFERENCES
API LRFD, (2002). Recommended practice for planning, designing and constructing fixed offshore platforms – Load and resistance factor design (API RP2A-LRFD).Supplement 1, American Petroleum Institute.
DNV-RP-D 101. Structural Analysis of Piping Systems.
Golafshani, A. A.; Bagheri, V.; Ebrahimian, H.; Holmas, T., (2011). Incremental wave analysis and its application to performance-based assessment of jacket platforms, Journal of Constructional Steel Research.
Interim Guidance Notes For The Design And Protection Of Topside Structures Against Explosion And Fire, SCI-P-112, The Steel Construction Institute, UK, 1992.
Mays, G.; Smith, P., (1995). Blast Effects on Buildings.
Offshore Technology Report 046 1999, (2000). Explosion Loading on Topsides Equipment: Part ١–Treatment of Explosion Loads, Response Analysis and design, HSE.
Offshore Technology Report 047 1999, (2000). Explosion Loading on Topsides Equipment: Part 2 – Determination of Explosion Loading on Offshore Equipment using FLACS, HSE.
Pueksap, P., (2010). Sensitivity study for RSR fixed offshore steel type platform .master thesis,
Asian institute of technology school of engineering and technology.
Recommended practice for design and hazards analysis for offshore production facilities, second edition, may 2001.
Schlyer, G.; Campbell, D., (1996). Development of Simplified Analytical Methods for Predicting the Response of Offshore Structures to Blast and Fire Loading. Marine Structures, 9, 949-970.
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How to cite this article: (Harvard style) Tajari, M.; Azarsina, F.; Ashrafi Khorasani, N., (2013). Nonlinear statics analysis of case of explosion. Int. J. Mar.Sci. Eng., 3(1), 33-41.
TEFLL, IAUNTB, 1(4), 3 -21, Fall 2009
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