A tank container or tanktainer is an intermodal container for the transport of liquids, gases and powders as bulk cargo. It is built to the ISO standards, making it suitable for different modes of transportation; as such, it is also called an ISO tank.[1] Both hazardous and non-hazardous products can be transported in tank containers.
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A tank container is a vessel of stainless steel surrounded by an insulation and protective layer of usually polyurethane and aluminum. The vessel is in the middle of a steel frame. The frame is made according to ISO standards and is 19. feet (6.05 meters) long, 7.874 feet (2.40 meters) wide and 7.874 feet (2.40 meters) or 8.374 feet (2.55 meters) high. The contents of the tank range from 17,500 to 26,000 liters (3,800 to 5,700 imp gal; 4,600 to 6,900 U.S. gal). There are both smaller and larger tank containers, which usually have a size different from the ISO standard sizes. For example, there are some 27,000 liters (5,900 imp gal; 7,100 U.S. gal) and above litre tank containers in the European swap body fleets in Europe but they are not used on international business only on intra European traffic. The trade organization ITCO estimates that as of January 1, , the global fleet of tank containers stands at 848,400 units.[2] Most of these tank containers are owned by operators and leasing companies.
ISO tank containers built to transport hazardous cargo have to meet a variety of regulations including but not limited to IMDG, ADR-RID- US DOT and other. There are a variety of UN Portable tank types, the most common of which is T11 as it is permitted to transport a thousand or more hazardous bulk chemicals.
There are hundreds of tank container operators worldwide; they can vary on the service they offer. The bigger operators typically offer a wide range of services, while smaller operators may only offer services in one region or with one type of tank.
The tank container concept was also employed in Europe by Bob Fossey, an engineer who worked for Williams Fairclough in London. They improved on the s framed American elliptical container tanks, oft noted carrying specified USA engine oils for the UK’s MoD aircraft built in Preston, Lancashire. In , Fairclough made a swap body tank for combined transport by truck and train, but not yet constructed according to ISO standards. In , commercial production began and one year later the first tank container to ISO dimensions was developed. The first mass-produced tank containers were purchased by Trafpak, a part of Pakhoed.
In , the ISOTANK was registered as a name by Andrews of Aintree Ltd., Liverpool. Their's were the first ISO container tanks in the world to get Lloyds Register and the UK DoT Hazardous Goods Department design approvals for international transport. They were essential and additional to UK approvals, much good advice was gained from several relevant, sound authorities in USA; Canada; Australia; R S Africa et al..
Built by Andrews of Aintree., Liverpool, and tested at Ellis Research facility. George Lambert, the ISOTANK’S designer, was also the company’s division head, thus responsible for sales or advising clients on the new product’s wide range of complex issues.
This first order to Andrews came from a major shipping line entering the bulk sensitive liquids by ISO means. It was reported as won by merit of the approved data and reputation. The initial order was for 20 off insulated and electrically heated units, 10 for hazardous substances, 10 for non- hazardous substances.
In the early s, the tank container evolved to its current form and the production was also well underway. In the early days, production took place in Europe. In and afterward, production is mainly in China and South Africa.
A tank container can be loaded and unloaded from the top and the bottom. On a standard tank container there is a manhole, at least one valve on the top, and there is a valve at the bottom. Loading and unloading is done by connecting hoses of the loading and unloading facility to the valves of the tank. The loading or unloading is often done using a pump. Depending on the installation and regulation of certain products, it is determined how the tank container should be loaded or unloaded.
Designed to store and transport LNG in its liquid condition, the 40 ft LNG ISO tank is an example of a standardized container. These tanks are essential to the world’s LNG supply chain since they are built using high-quality materials and are designed to resist the harsh conditions associated with LNG. The outer shell and inner shell geometries of the ISO tank are depicted in Figure 2. The selection of suitable materials and determination of the necessary thickness for the pressure vessel of the 40 ft LNG ISO tank are both covered in detail in this section. It starts by exploring important elements and standards defined in ASME Sections II and VIII [21,22], including material choice, allowed material stress, and the specific methods used to calculate pressure vessel thickness.
Figure 2For this calculation, the selected material is SUS 304L alloy steel, which possesses an ASME Section II specification conversion known as SA 240 Gr 304L-S . SA 240 Gr 304L-S is based on ASME. It refers to a stainless-steel material that complies with the ASME SA 240 specification, specifically using grade 304L stainless steel (low-carbon variant) with the UNS designation of S. Within ASME Section II [21], the material properties are meticulously regulated and categorized based on distinct types of nominal material composition. By adhering to these stringent guidelines and rules established by ASME, the procedure ensures that the material selection and thickness calculation for the pressure vessel meet the required standards for safety and functionality in LNG transportation. These systematic methodologies are essential in guaranteeing the structural integrity and operational reliability of the LNG ISO tank, thereby minimizing potential risks and ensuring the secure transport of LNG cargo.
The minimum thickness calculation is provided in UG-27 of ASME VIII-1 [22]. The description of the input parameters is shown in Figure 2. The thickness required by the code is greater than the result by
(1) t = PR SE − 0 .6 P ,where P is the internal design pressure, R is the inner radius, S is the allowed stress for steel stainless (SUS 304L), and E is the butt joint efficiency. For further information, see Table UW-12 ASME [22]. Further, as demonstrated by Eqs (2) and (3), the computation of the toruspherical shell’s concave side for the cylinder’s two ends refers to paragraph UG-32
(2) t = P L M 2 SE + P ( M − 0.2 ) , (3) M = 0.25 3 + L R ,where r denotes the inside knuckle radius and L denotes the inside crown radius in mm. Figure 2 describes the geometry of the torispherical head.
Meanwhile, Section VIII UG-28 [22] paragraph has resorted to estimating the maximum allowed external pressure (MAEP) for the planned cylindrical shell. To utilize the following formula, the geometry D 0/t ≥ 10 must be verified in the first stage. Following verification, the external load graph reference of Figure G in ASME Section II, Part D Subpart 3 [21], is used to obtain A utilizing L/D 0 and D 0/t. After obtaining the A value, the B value in Figure HA-3, which is appropriate for the 304L material specification, is calculated using this value. Finally, the maximum is determined using the B value using Eq. (4). The process is comparable to determining the convex side of the cylindrical end’s maximum pressure based on UG-33. B is used in the following equation:
(4) p a = 4 B 3 D t , (5) p a = B R t .The calculation relates to paragraph UG-29 ASME Section VIII [22] to determine the ring stiffener’s compressive pressure on the pressure vessel. The techniques needed for this phase presume the original size and shape of the ring stiffener.
(6) B = 0.75 P D t + A s L s / 14 ,where A s is the ring stiffener’s anticipated cross-sectional area, L s is the space between stiffeners, and t is the predicted shell thickness from the previous step. After that, the B value is calculated using Eq. (6). Utilizing the resulting B value, find the A value that equals the calculated B value using the external pressure table in ASME Section II, Part D [21]
(7) I s ′ = D 0 2 L s t + A s L s A / 14 , (8) I = t w h w x 3 12 .The moment of inertia necessary for the stiffening ring alone is then calculated using Eq. (7). Next, depending on the initial assumptions made by Eq. (8), determine the actual moment of inertia of the ring stiffener. Additionally, the needed moment of inertia must be equal to or greater than the findings of the actual moment of inertia. The result of pressure vessel thickness according to ASME Section VIII [22] is stated in Table 1.
Table 1 Design parameter Value Unit Internal design pressure (P int) 1 MPa External design pressure (P ext) 0.8 MPa Inner Tank Inner shell thickness (t) 7.1 mm Inner head thickness (t) 11.22 mm Inside diameter (D) 2,218 mm Cylindrical length (L cyl) 11,018 mm Inside crown radius (L) 2,218 mm Knuckle corner radius (r) 221.8 mm Outer Tank Outer shell thickness (t) 3.95 mm Outer shell thickness (t) 6.28 mm Inside diameter (D) 2,438 mm Cylindrical length (L cyl) 11,018 mm Inside crown radius (L) 1,950.4 mm Knuckle corner radius (r) 243.8 mm Material: steel stainless (SUS 304L)FEA involves the utilization of scenarios outlined in ISO to perform calculations. To receive certification and approval, new or modified designs must undergo testing per ISO standards [23]. The loading scenario for the ISO tank structure is described in detail based on the ISO standard data provided in Table 2. According to the aforementioned standard, a 40 ft ISO tank is classified under class A, which entails a stacking load of 942 kN at each shoe/corner fitting location. For example, a 40 ft ISO tank container with a gross weight of approximately 32 tons is assumed, divided equally at each corner, resulting in a minimum load of 8 tons or 73 kN. Thus, ISO specifies exceptionally high strength requirements, estimated to accommodate up to three tiers (excluding the dynamic safety factor of 1.8). However, the intended transportation method for the ISO tanks is via mini-LNG carriers. These carriers have a capacity of 36 TEUs. The ISO tanks will be stacked in a maximum of two tiers during the voyage, as illustrated in Figure 3. A summary of the loading scenarios is given in Table 2.
Table 2 Load scenario Loading layouts Stacking strength Lifting strength Racking (transverse) Racking (longitudinal) Figure 3The stacking loading test assesses the weight capacity of a 40 ft container. This test is designed to determine whether any fully loaded container can withstand the whole weight stacked on top. Based on ISO standards, the container is subjected to vertical forces of about 942 kN (approximately 384 tons) applied to all four corner fittings simultaneously or at each pair of end fittings. The capacity of the LNG tank also contributes about 189.3 kN distributed load, equivalent to 19.3 tons of cargo. The load is precisely applied at the midpoint of the upper surface of the corner fitting. This test demonstrates the ISO tank’s structural ability to support stacked containers while considering sea conditions.
Moreover, the lifting test demonstrates a container’s capabilities to withstand being lifted vertically from an appropriate set of four corner fittings. This test is also intended to determine whether the floor’s loading capability is sufficient to withstand the acceleration forces experienced by laden containers when handled by cranes. The load on the container under test must be spread uniformly on the floor so that the combined weight of the container and test load equals 2R. The container must be hoisted at the four top corners so that no significant acceleration or deceleration forces occur. The R (gross weight) and T (tare weight) components are required for this test.
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Further, the racking test is conducted to verify the structural integrity of the container when subjected to racking loads during transportation via various intermodal routes such as ships and trains. The ISO procedure outlines two types of racking loads: transverse and longitudinal. In the transverse racking test, the container tank is assumed to be empty, and a load of 150 kN is applied. This test is intended to prove the ability of containers to withstand the transverse racking forces in the end frames resulting from ship movements. The container under test will be placed in unladen (tare) condition on four level pads, one under each bottom corner fitting. It shall be restrained against lateral and vertical movement using anchor devices acting through the bottom apertures of the bottom corner fittings. The concentrated load is applied simultaneously on the top corners, parallelly, or diagonally. The bottom area is securely fixed to prevent any vertical or lateral movement.
Further, the longitudinal racking test is designed to demonstrate the ability of containers to withstand longitudinal racking forces in side frames caused by ship movements. The container under test is to be placed unladen (tare) on four level pads, one beneath each bottom corner fitting, and fastened through the bottom apertures such that no vertical movement is permitted. Forces of 75 kN must be applied simultaneously to each top corner fitting at one end of the container parallel to both the side wall and the base plane.
This study aims to analyze the impact of different structural frame designs of the LNG ISO tank on its overall structural performance. Three specific scenarios will be examined: increasing the thickness of the frame, incorporating a support plate, and introducing saddle support. The initial design variant involves a gradual increase in frame thickness, check plate thickness, and saddle support thickness, ranging from 6 to 14 mm, as illustrated in Figure 8. A total of nine variations in frame thickness will be investigated. The loading conditions for each frame thickness model variant are outlined in Table 4.
Figure 8 Table 4 Frame thickness (mm) Load scenario (kN) Stacking Lifting Racking (transverse) Racking (longitudinal) F 1.8R − T 942 + ((1.8 Rg)/4) Rg/2 2R − T F F 6 942 434 1,080 153 496 150 75 7 942 437 1,081 155 499 150 75 8 942 439 1,083 156 502 150 75 9 942 442 1,084 158 505 150 75 10 942 444 1,085 159 508 150 75 11 942 447 1,087 161 511 150 75 12 942 449 1,088 162 514 150 75 13 942 452 1,090 164 517 150 75 14 942 454 1,091 165 520 150 75The comparison of the total weight of a 40 ft LNG ISO tank, considering the variation of frame thickness, is presented in Figure 9. Such containers are ISO containers if their maximum gross weight (R) does not exceed 36 tons based on ISO 668: Series 1 freight container classification, dimensions, and ratings [28]. It is important to note that all models in this comparison have the same cargo payload of approximately 19.3 tons. The results indicate that increasing the frame thickness leads to a corresponding increase in the gross weight (R) within a range of 0.99–8.03%. While this weight increase may seem marginal, it is an important factor to consider in designing and operating LNG ISO tanks. The total weight of the tank affects various aspects, such as transportation costs, load capacity, and overall structural integrity.
Figure 9Various model variations are considered when investigating the effects of support plates on ISO tank containers. The effect of adding support plates, with the number of plates ranging from 8 to 32, on the structural performance will be assessed. Figure 10 illustrates the six different model variations that are developed for the model with a frame thickness of 10 mm. These variations are created to evaluate how adding support plates influences structural behaviour. To assess the effect of the support plates, loading conditions are defined for each model variant, as outlined in Table 5. It is observed that the magnitude of the applied load increased with the addition of more support plates. The increase in loading magnitude can be attributed to the corresponding increase in the container’s tare weight and gross weight, which accompanies the addition of support plates.
Figure 10 Table 5 Total of support plate Load scenario (kN) Stacking Lifting Racking (transverse) Racking (longitudinal) F 1.8R − T 942 + ((1.8 Rg)/4) Rg/2 2R − T F F 8 942 444.2 .4 159.3 508.0 150 75 12 942 444.9 .8 159.8 508.8 150 75 16 942 445.7 .2 160.2 509.8 150 75 20 942 446.5 .7 160.7 510.8 150 75 26 942 447.7 .3 161.5 512.3 150 75 32 942 448.5 .8 162.0 513.3 150 75The calculation of the overall weight of a 40 ft LNG ISO tank, considering the addition of support plates, is illustrated in Figure 11. It is noteworthy to emphasize that all the models included in this comparison possess an equivalent cargo payload of approximately 19.3 tons. The findings reveal that adding support plates results in a marginal increment in the gross weight (R), ranging from 0.27 to 1.66%. It is evident that the weight increase resulting from the addition of support plates is negligible compared to the increasing frame thickness.
Figure 11The saddle support system is designed to cradle and stabilize the tank, especially during transportation or storage. The saddle support is a crucial component of this frame and is located underneath the tank at specific support points. The saddle support structure is designed to distribute the weight of the tank and its contents evenly across its base. The saddle support system is connected to the tank frame or chassis, ensuring a secure and stable attachment. In the third variation, the LNG ISO tank model is varied between 1 and 4 saddle supports at the model with a frame thickness of 10 mm, as depicted in Figure 12. To assess the effects of the saddle supports, loading conditions are defined for each model variant, as outlined in Table 6. It is observed that the magnitude of the applied load increased with the addition of saddle supports. Figure 13 shows the comparison of weight components due to saddle support variations. It can be found that adding more saddle support can increase the gross weight (R) by about 1.4–4.4%.
Figure 12 Table 6 Total of saddle support Load scenario (kN) Stacking Lifting Racking (transverse) Racking (longitudinal) F 1.8R − T 942 + ((1.8Rg)/4) Rg/2 2R − T F F 1 942 437.0 .3 154.8 498.9 150 75 2 942 440.7 .8 159.8 503.5 150 75 3 942 444.2 .2 160.2 509.8 150 75 4 942 447.9 .5 161.6 512.6 150 75 Figure 13The structural evaluation of an LNG ISO tank is critical to guaranteeing its safe and dependable operation. Understanding the relationship between frame thickness and stress levels is critical for designing and constructing LNG ISO tanks capable of withstanding harsh transportation and storage conditions. Manufacturers can balance structural strength and weight issues by optimizing frame thickness, assuring the tank’s safe functioning while avoiding unnecessary material. This study focused on how increasing frame thickness affected the structural strength of the ISO tank structure. The results, shown in Figure 14, indicated an intriguing relationship between frame thickness and stress levels. The stress value reduced dramatically as frame thickness increased, particularly in structural frames. This study implies that stronger frames improve structural integrity and load-bearing capacities. The stress reduction is caused by the greater stiffness and stability of the frame, which effectively distributes the applied loads more uniformly over the tank structure.
Figure 14Among the various structural parts, the structural frame experienced the highest stress levels among all the loading scenarios because it is primarily responsible for bearing the weight of the tank and supporting its contents. The higher stress values in the structural frame highlight its critical role in maintaining the tank’s overall integrity and safety during transportation and storage. In contrast, the pressure vessel experienced the lowest stress levels. This observation can be attributed to the design and engineering considerations prioritizing the vessel’s strength and resistance to internal pressure. The pressure vessel is designed to withstand the high internal loads generated by the LNG cargo, ensuring its containment without compromising the tank’s structural integrity. Additionally, it is worth mentioning that the stress levels in the ISO corner casting, which provides connection points for the tank during transportation, fall within an acceptable range, as it is not highlighted as the component with the highest or lowest stress levels.
Compared with all loading scenarios, it can be found that stacking and longitudinal racking tests are critical load scenarios. The stacking load for the LNG ISO tank appears to be excessive. It is mostly due to the fact that under operational conditions, ISO tanks are considered differently from regular solid goods containers and, in this case, are only stacked up to a maximum of two tiers. Moreover, the largest stress reduction at the structural frame is discovered due to the longitudinal racking test in the 13.9–54.3% range compared to all examined loading scenarios in Figure 14. The longitudinal racking test results show that the ISO corner has the largest stress reduction, ranging from 9.9%. In contrast, the pressure vessel generally suffers stress increases due to stacking, lifting, and racking load. The stress increase, ranging from 9.7 to 65.4%, is subject to the largest trend due to longitudinal racking load.
Figure 15 compares all models’ safety factors in different structural locations. It is a measure that quantifies the level of safety margin or reserve strength within a structure, indicating how much it can safely handle loads beyond its design limits. In the LNG ISO tank context, the safety factor considers various factors such as material properties, design specifications, load conditions, and anticipated operational scenarios. It this case, safety factor is calculated by the ratio between occurred stress with the permissible stress of each material. The analysis demonstrates that the longitudinal racking and stacking strength tests result in a higher safety factor value for the structural frame and ISO corner casting than other load scenarios. The results of the longitudinal racking simulation are carried out using a load with a frontway direction of 75 kN at two concentration points on the top of the fitting corner.
Figure 15Conversely, the lifting and stacking load contribute to a higher safety factor value for the pressure vessel. Notably, structural frames featuring frame thicknesses ranging from 6 to 9 mm exhibit significantly high safety factors above 1 due to stacking and longitudinal racking tests indicating the occurred stress is higher than the yield strength of the material. It indicates that the structure possesses a substantial safety margin and is engineered to withstand loads well beyond its projected maximum capacity. The safety factor value reflects the structural robustness and substantial reserve strength of the system, installing confidence in its ability to endure applied loads and external loads without failure or compromising its integrity. In addition, the results of all load scenarios in pressure vessels and ISO corner casting are still within the safety limits in accordance with ISO regulations. In general, it is evident that an increase in frame thickness leads to a noticeable decrease in the safety factor value, particularly in the structural frame and ISO corner casting. Conversely, adding frame thickness tends to increase the safety factor for the pressure vessel.
Figure 16 comprehensively depicts the stress contour response at various structural locations resulting from the longitudinal racking test. Notably, the joint connecting the vertical frame and top support plate exhibits the most significant stress concentration within the entire structural frame. This location consistently experiences the highest stress levels across all loading scenarios, as illustrated in Figure 17. Consequently, it is advisable to reinforce the vertical and horizontal frames by incorporating supplementary supporting plates, as recommended by Muttaqie et al. [15]. Furthermore, the inner head demonstrates localized stress due to the longitudinal racking test because there is no supporting stiffener between the inner and outer head.
Figure 16 Figure 17Figure 18 compares displacement values for different frame thicknesses under various loading scenarios. Generally, it can be observed that an increase in frame thickness results in a decrease in displacement values for all loading scenarios. The results indicate that increasing the frame thickness leads to a notable reduction in displacement, particularly in the structural frame and ISO corner casting. The highest displacement reduction in the structural frame can be found in the longitudinal racking test in the range of 23.3–76.6%. The highest displacement reduction in the ISO corner casting can be found in the same loading scenario with the 23.9–77.7% range. Notably, the longitudinal racking test emerges as a critical loading scenario, producing the highest displacement response among all the scenarios examined. This finding suggests that the ISO tank structure is particularly vulnerable to longitudinal forces, emphasizing the need for robust reinforcement measures to counteract these forces effectively. In contrast, the lifting strength scenario exhibits the lowest displacement response.
Figure 18The analysis of displacement contours holds paramount importance as it visually represents the magnitude and distribution of displacements across the ISO tank structure. This information identifies regions susceptible to excessive displacement or deformation, posing a risk of structural failure or compromising the overall safety of the tank. Figure 19 compares displacement contours from critical longitudinal racking tests conducted on various structural components. It is evident that the greatest displacement occurs in the structural section situated at the midpoint of the top longitudinal frame. Additionally, the inner head exhibits the highest displacement within the inner tank due to its lack of support from stiffeners. Furthermore, Figure 20 compares displacement contours resulting from different loading scenarios. The highest displacement attributable to stacking and lifting tests is observed in the upper corner of the frame. In contrast, the top portion of the structural frame displays the highest displacement overall.
Figure 19 Figure 20The effect of the addition of support plates on structural strength is investigated. Support plates are strategically placed at critical locations within the structural frame, such as the corners or areas prone to higher stress concentrations. These components are suggested to play a crucial role in providing additional reinforcement and stability to the overall structure. Figure 21 compares maximum stress levels for different total support plate configurations under various loading scenarios. The findings indicate that adding support plates does not significantly influence the structural strength of LNG ISO tank containers. However, the presence of support plates effectively enhances the structural integrity of the framework by mitigating longitudinal racking, as depicted by the decrease in obtained stress. Adding support plates due to longitudinal racking can decrease the stress to 20.4% in the structural frame and 19.7% in the pressure vessel. In contrast, ISO corner casting experiences a stress increase of up to 23.2% due to longitudinal racking.
Figure 21Moreover, the structural frame experiences a slight reduction in stress when subjected to stacking, lifting, and transverse racking loads. Conversely, the addition of support plates can increase the safety factor in the pressure vessel and ISO corner casting, particularly during lifting and stacking strength tests, as seen in Figure 22. The load distribution becomes more balanced throughout the structural frame by incorporating support plates. This balanced load distribution helps minimize localized stress concentrations and ensures the container can withstand operational loads.
Figure 22Figure 23 presents a comprehensive illustration of the stress contour response at various structural locations resulting from the longitudinal racking test at the model with 32 total support plates. Notably, the joint connecting the vertical frame and top support plate exhibits the most significant stress concentration within the entire structural frame. This location consistently experiences the highest stress levels in stacking, lifting, and transverse racking tests, illustrated in Figure 24. In addition, the highest stress in the frame due to longitudinal racking is experienced in the check plate. Furthermore, the inner head demonstrates localized stress due to the longitudinal racking test because there is no supporting stiffener between the inner and outer head.
Figure 23 Figure 24Figure 25 presents a comparative analysis of displacement values for different total support plate configurations under various loading scenarios. Notably, the longitudinal racking test emerges as a critical loading scenario, exhibiting the highest displacement response in the structural frame compared to other scenarios. It is evident that an increase in the number of support plates generally corresponds to a decrease in displacement values. The results clearly indicate that adding the support plate configuration significantly reduces displacement, particularly in the transverse and longitudinal racking tests. It can be found that the highest displacement reduction due to transverse racking load can be found in the structural frame between 7.5 and 27.8%. In addition, the highest displacement reduction due to longitudinal racking can be found in the structural frame in the range of 7.2–23.9%. Further, this reduction in displacement is consistently observed in the ISO corner casting and pressure vessel across all evaluated loads. However, it should be noted that adding support plates can result in increased displacement in structural frames during stacking and lifting loads. It is projected to increase displacement in the structural frame by about 12.5–32.4% in stacking load and about 16.3–35.4% in lifting load. This displacement shift occurs due to the redistribution of stresses, causing the highest displacement to transition from the top corner area to the middle of the top structural frame.
Figure 25Figure 26 compares displacement contours from critical longitudinal racking tests conducted on three structural components. The greatest displacement occurs in the structural frame situated at the midpoint of the top longitudinal frame. Additionally, the bottom of the inner tank exhibits the highest displacement. Furthermore, Figure 27 compares displacement contours resulting from different loading scenarios in the model with 32 total support plates. Adding a support plate in the structural frame due to stacking and lifting loads causes the highest displacement shifting from the upper corner area to the middle point of the structural frame.
Figure 26 Figure 27In the third variation, the effect of saddle support on the structural strength is investigated. Figure 28 compares the maximum stress of various total saddle supports under different loading scenarios. The results show that adding saddle support does not significantly affect the structural strength of LNG ISO tank containers. The stress reduction displayed in Figure 28 illustrates how the implementation of saddle support substantially improves the structural integrity due to longitudinal racking load tests. It is discovered that the structural frame experiences a stress reduction of between 4.9 and 5.4% as a result of the installation of saddle support, the pressure vessel experiences a stress decrease between 13.9 and 31.8%, and the ISO corner casting experiences a stress reduction between 4.6 and 5.5%. The addition of saddle support significantly affects the pressure vessel stress because the saddle support structure is designed to distribute the weight of the pressure vessel tank. Moreover, when stacked loads are applied, the stress in structural frame stress slightly decreases, notably in ISO corner casting. In contrast, the model has no stress reduction due to lifting and transverse racking tests. Moreover, the highest stress in the structural frame in all evaluated loading tests is experienced in the check plate, as seen in Figure 29.
Figure 28 Figure 29A comparison of displacement values for various saddle support systems under various loading conditions is shown in Figure 30. Notably, the longitudinal racking test exhibits the largest structural frame displacement response compared to other loading scenarios, making it a crucial loading scenario. It is evident that a decrease in displacement values often follows an increase in the number of saddle supports. The findings show that adding the saddle support causes a significant decrease in displacement, particularly in the longitudinal racking test. The pressure vessel exhibits the greatest displacement decrease caused by longitudinal racking load, with values between 53 and 71%. Furthermore, the displacement reduction carried on by longitudinal racking is 4.9–55 and 7.7–10.7%, respectively, in the structural frame and ISO corner casting. It is important to note that the installation of saddle supports may cause a slight increase in displacement in structural frames, pressure vessels, and ISO corner castings subject to stacking and lifting loading scenarios (Figure 31).
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Figure 30 Figure 31