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    DISMANTLING OF ABOVEGROUND LNG STORAGE TANKS

    AND THEIR AGING RESEARCH

    Hiroshi Nishigami

    Maki Yamashita

    Shunsuke Ohnishi

    Nobuhiro Wadama

    Osaka Gas Co., Ltd

    Hiroto Yamaoka

    Tatsuo Tsuji, Yu Murakami

    IHI Corporation

    Takehiro Inoue

    Naoki Saito

    Motohiro Okushima

    Nippon Steel & Sumitomo Metal Co., Ltd

    KEYWORDS: aboveground LNG storage tank, aging research, dismantling method]

    ABSTRACT

    In 2011, Osaka Gas commenced the dismantlement of two aboveground LNG storage tanks with a storage

    capacity of 45,000 m3 each at the Senboku 1 terminal. The said LNG storage tanks had been in commercial

    operation for approximately 40 years, and were the first to be dismantled in Japan. Concurrent with the

    dismantlement of the said LNG storage tanks, Osaka Gas also began the research on the deterioration due to

    their aging. Aging evaluation of the said LNG storage tanks will contribute to the LNG industry by not only

    potentially increasing its lifetime, but by improving its functions and safety as well. In this paper, the method of

    dismantling and the research results with regard to the aging for the two types of LNG storage tanks,

    respectively made of 9% Nickel steel and Aluminum alloy are reported. The contents of the research will be of

    the following criteria: (1) Mechanical properties of 9%Ni steel and Aluminum alloy (2) Thickness of steel pipe

    piles (3) Deterioration of instrument devices (4) Deterioration of insulation materials. After dismantling of the

    said LNG storage tanks, Osaka Gas decided to construct a large scale LNG storage tank applying newly

    developed 7% Ni-TMCP steel for its inner tank. The storage capacity of the new LNG storage tank will be

    230,000m3, and is scheduled to be completed by November, 2015. The present state of the construction of the

    innovative LNG storage tank will be reported in this paper as well.

    1. INTRODUCTION

    In 1972, IHI Corporation (IHI) built three LNG storage tanks

    with capacities of 45,000m3in Osaka Gas Co., Ltd (Osaka Gas)

    Senboku I Terminal. Since then, the tanks, which were of the

    single containment type with double steel walls, had been

    successfully operated without any trouble for 40 years. However,

    the conventional LNG storage tanks were getting more

    inefficient in the use of receiving terminal because of its lower

    dike in comparison with the state-of-the-art full-containment

    LNG storage tanks. (Figure1)

    Figure 1. One of the demolished

    LNG storage tanks

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    To keep up with the increasing demand for LNG and for effective practical use, Osaka Gas started to demolish

    the two conventional LNG storage tanks in 2011, and now a large LNG storage tank of 230,000m3has been

    under construction since September 2012.

    Demolition of old LNG storage tanks was executed with paying sufficient attention to the safety in consideration

    of the influences on the other facilities in operation and neighboring companies. Then, Osaka Gas investigated

    the demolished LNG inner tanks material and its thermal insulation material jointly with IHI as the constructor

    and Nippon Steel & Sumitomo Metal Co., LTD (NSSMC) as the supplier of tanks steel products. Moreover, we

    examined the steel pipe piles and the instrumentation devices from Osaka Gass own point of view. This paper

    describes the study on dismantling method of LNG storage tanks, the results of the investigations, and also

    reports on the new material used for the LNG storage tank under construction.

    Investigation items:

    1) Base metal mechanical properties (chemical composition / macro-micro structure / tensile strength /

    Charpy absorbed energy / retained austenite)

    2) Weld metal mechanical properties (chemical composition / macro-micro structure / tensile strength /Charpy absorbed energy)

    3) Fracture toughness properties (CTOD test / duplex ESSO test / wide plate test)

    4) Corrosion of foundation piles (steel pipe piles)

    5) Deterioration of concrete

    6) Deterioration of instrumentation devices

    7) Deterioration of thermal insulation material

    2. DISMANTLING METHOD OF THE LNG STORAGE TANKS

    2.1 Specification of the tanks

    Table 2.1 and Figure 2.1 show the specifications of the two demolished tanks.

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    Table 2.1 Specification of the tanks

    1 Internal liquid LNG

    2 Capacity 45,000KL

    3 Type single containment type with double steel walls

    4

    Dimensions inner tank outer tank

    Diameter 44,600mm 46,400mm

    Height 28,820mm 31,850mm

    Roof radius 35,700mm 36,600mm

    5 Design temp. -162 ambient temp.

    6 Design pressure 0.12kg/cm2 50mmH2O

    7 Main material 9%Ni steel(Al alloy) carbon steel

    8 Insulation perlite & perlite concrete

    9 Thickness of insulation

    tank shell & roof; 900mm

    tank bottom ;1,100mm

    10 Foundation slabreinforced concrete

    diameter :44,600mm thickness ;800mm

    11 Dike

    reinforced concrete

    height :4,000mm(3,000mm from the ground)

    thickness ; 1,400mm

    12 Earthquake historyground surface acceleration;

    178gal

    13 Commercial operation Feb.1972.

    Note; ( ) shows Al alloy tank

    Figure 2.1 Configuration of the demolished LNG storage tank

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    2.2 Dismantling procedure

    The LNG tanks were demolished through the following procedure in Figure 2.2.

    Step 2 Perlite extraction from the annular space Step 4 Removal of the outer tank roof

    Step 6 Removal of the outer tank shell plate Step 7 Removal of the inner tank shell plate

    Figure 2.2. Dismantling procedure

    (1) Since the tank structure changes at every step during the tank dismantling, the dismantling steps should

    be observed by FEM analysis, ABAQUS. Figure2.3 shows some examples of the results by the analysis.

    (2) The tanks were dismantled by 150 tons cranes.

    (3) Perlite was removed by a new extraction machine.

    (4) Some samples for the study were taken before the tank dismantling.

    1. Setting of entering road into the dike

    2. Perlite extraction from the annular space

    3. Removal of the pipe, pipe frame etc.

    4. Removal of the outer tank roof

    5. Removal of the inner tank roof

    6. Removal of the outer tank shell plate

    7. Removal of the inner tank shell plate

    8. Removal of the outer tank bottom plate

    & bottom insulation

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    Figure 2.3. The examples ofthe strain diagram

    3. INSPECTION AND TEST RESULTS

    3.1 Visual inspection

    3.1.1 Inner tank

    K11 tank (9% Ni steel) and K31 tank (AL alloy) were found to be in good condition. No damages and buckling

    were detected due to the Hanshin Awaji Great Earthquake in 1995. There was no influence on the soundness

    of the tank. There was no damage to the instrumentation devices (level gauge, thermometer) installed in the

    tanks.

    3.1.2 Outer tank(a) Manhole for perlite filling

    Some corrosion was found at the blind flange of perlite manhole. The doubling plate and the root of the

    manhole were also corroded.

    (b) Outer tank roof plate and shell plate

    Some corrosion was seen at the welding seam. It is estimated that the repair painting had not been done

    enough.

    (c) Roof walkway

    Corrosion was seen just right under the protecting seal due to the deterioration of it. In addition, corrosion was

    found at checker plate of walkway.

    (d) Anchor bolt

    Some anchor bolts especially under the pipe rack were corroded. After removing a weather seal, the surface of

    several bolts were corroded and decreased its thickness.

    (e) Inner tank anchor strap

    As a result of the investigation, the conspicuous deterioration, damage, deformation and corrosion were not

    seen. The reason of these phenomena was that the annular space had been filled with nitrogen since the time

    of the construction.

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    3.2.1 Base Metal of Inner Tank

    Table 3.1 shows sampling parts and investigation items of each tank. Details are given as follows.

    Table 3.1. Sampling Parts and Tests (Base Metal)

    Tank Sampling Part

    Chemical

    Component

    Analysis

    Tensile TestCharpy

    Impact TestCTOD Test

    Duplex

    Esso

    Test

    K31

    (A5083)

    1st Course - - -

    13th Course - - -

    Annular Plate - - - -

    Bottom Plate - - - -

    K11

    (9%Ni-Steel)

    1st Course

    13th Course - -

    Annular Plate - - - -

    Bottom Plate - - - -

    (a) Chemical Compositions of Base Metal

    Chemical analyses were carried out on representative samples taken from the 1st and 13th shell courses andannular bottom plate of each tank. Table 3.2 shows the results of K31 tank (made by aluminum alloy), and

    Table 3.3 shows that of K11 tank (made by 9%Ni steel).

    Table 3.2. Chemical Composition (A5083 Base Metal)

    Sampling

    PartSi Fe Cu Mn Mg Zn Cr Ti B

    Shell Plate

    1st Course0.08 0.10 0.01 0.67 4.51

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    (b) Tensile Properties

    Tensile tests were carried out by using specimens: a full thickness specimen in accordance with JIS Z 2201

    No.1A. The tests were performed in both the L and C rolling directions at room temperature in accordance with

    JIS Z 2241.

    Table 3.4 shows the results of K31 tank, and Table3.5 shows that of K11 tank.

    Table 3.4. Results of Tensile Test (A5083-O Base Metal)

    Sampling PartRolling

    Direction

    0.2% Proof

    Stress [MPa]

    Tensile

    Stress [MPa]

    Elongation

    [%]

    Shell Plate

    1st Course

    L 136 297 23

    C 139 303 24

    Shell Plate

    13th Course

    L 153 304 20

    C 139 302 21

    Bottom PlateL 160 299 18

    C 139 303 22

    Requirement1)

    -125 (0.8

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    Figure 3.1. Results of Charpy Impact Test (9%Ni-Steel Base Metal)

    Test Temperature:-196

    (d) Other

    For the 1st shell courses of K11 tank, CTOD test and duplex Esso test were carried out and we make sure of

    the soundness of material used in the construction days. The details are omitted due to space limitation.

    3.2.2 Weld Joint of Inner Tank

    Table 3.6 shows sampling parts and investigation items of each tank. Details are given as follows. Table 3.7

    shows the welding procedure of each weld joint. Table 3.8 shows the pictures of macro structure of vertical

    weld joint of shell plate 1st course.

    Table 3.6. Sampling Parts and Tests (Weld Joint)

    Tank Sampling Part Weld Joint

    Chemical

    Component

    Analysis

    Tensile

    Test

    Charpy

    Impact TestCTOD Test

    Wide Plate

    Test

    Bending

    Fatigue

    Test

    K31

    (A5083)

    1st Course Vertical - - - -

    1st&2nd Course Horizontal - - - -

    13th Course Vertical - - - -

    Annular Plate Fillet - - - -

    K11

    (9%Ni-Steel)

    1st Course Vertical -

    1st&2nd Course Horizontal - -

    13th Course Vertical - - -

    Annular Plate Fillet - - - -

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    Table 3.7. Welding Procedure of Each Weld Joint

    Sampling PartK31 (Aluminum) K11 (9%Ni-Steel)

    Process Material Groove Process Material Groove

    Shell Plate 1st Course

    Vertical Weld JointLarge

    Current

    MIG

    JIS Z 3232

    A5183-WY

    (AWS 5.10

    ER5183)

    SMAW

    JIS Z 3224

    ENi 6133

    (AWS 5.11

    ENiCrFe-2)

    Shell Plate 1st&2nd

    Course

    Horizontal Weld Joint

    Shell Plate 13th Course

    Vertical Weld Joint

    MIG

    Shell Plate 1st Course

    & Annular Plate

    Fillet Weld Joint

    Bottom Plate

    One Side

    Lap Weld Joint

    Table 3.8. Macro Structure of Vertical Weld Joint of Shell Plate 1st Course

    K31

    Aluminum Tank

    K11

    9%Ni-Steel Tank

    (a) Chemical composition of weld metal

    Chemical analyses were carried out on representative samples taken from the different parts of weld metal.

    Table 3.9 shows the results of weld metal of K31 tank, and Table 3.10 shows that of K11 tank.

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    Table 3.9. Chemical Composition (K31 Aluminum Tank Weld Metal)

    Sampling Part Si Fe Cu Mn Mg Zn Cr Ti B

    Shell Plate 1st Course

    Vertical Weld Joint0.08 0.10 0.01 0.67 4.51

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    Table 3.12. Results of Tensile Test (K11 9%Ni-Steel Tank Weld Metal)

    Sampling Part

    Test after DismantlingConstruction

    Management Test

    Tensile

    Stress [MPa]

    Fracture

    Location

    Tensile

    Stress [MPa]

    Shell Plate 1st Course

    Vertical Welded Joint756 Weld Metal 761

    Shell Plate 1st&2nd Course

    Horizontal Weld Joint756 Base Metal 767

    Shell Plate 13th Course

    Vertical Welded Joint781 Base Metal 788

    Requirement1)

    655 (at 20 deg C) - -

    [K31]

    These results on tensile strength at room temperature satisfy the requirements1)

    , and fracture locations are not

    particular. It is apparent that soundness of tank was kept.

    [K11]

    The same as K31 tank, all results satisfy the requirements1)

    , it is apparent that soundness of tank was kept.

    (c) Charpy Impact Properties

    Charpy impact tests were carried out on weld joints of K11 tank, machining the notch at center of weld metal,

    fusion line (FL: 50% weld metal + 50% heat affected zone), FL+1mm, FL+3mm, FL+5mm, using specimens in

    accordance with JIS Z 2202 and 3128. Notch is 2mm depth, V shape. The central axis of the specimen was the

    same as base metal. The tests were carried out at -196 deg C in accordance with JIS Z 2242.

    Figure 3.2 shows the results of Charpy impact tests. All plates conform to the requirements1)

    . Those

    results have indicated that the weld joints dont deteriorate with age.

    Figure 3.2. Results of Charpy Impact Test (K11 9%Ni-Steel Tank Welded Joint)

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    (d) Other

    For the vertical weld joint of 1st shell courses of K11 tank, CTOD test and wide plate test were carried out and

    we make sure of the soundness of welded joints. The details are omitted due to space limitation.

    3.3 Corrosion survey on corrosion of foundation piles

    3.3.1 Purpose and method

    Corrosion countermeasure for foundation piles is important for maintenance of LNG tank substructure. Osaka

    Gas adopts a corrosion allowance by adding 2mm margin to the specification of foundation piles in

    construction design as a corrosion countermeasure. Meanwhile, heads of piles are bonded in advance during

    construction so that a cathodic protection can be applied in preparation for significant corrosion progression in

    service. Moreover, the installation method of electrodes using a horizontal boring technique for cathodic

    protection has been developed, and the corrosion condition has been monitored in order to judge the necessity

    of cathodic protection.

    The corrosion condition has been judged according to the thickness measurement which is executed by

    remote field testing and actual pile investigation by excavating the upper portion of piles. Based on the

    evaluation in this way indicated that there was no necessity of corrosion countermeasure for the next 50 years

    at least. Because actual measurement data is still not enough, we conducted a survey on actual piles that

    pulled out on this occasion of tank demolition in order to make up for scant data of actual corrosion condition.

    Figure 3.3 shows the section view of the LNG tank. There were 496 foundation piles in total that driven with

    steel pipe piles; length 25m, outer diameter 406.4mm, thickness of upper pile 12.7mm and lower pile 9.5mm.

    As shown in Figure 3.4, the survey was conducted with 31 piles among all foundation ones of LNG storage

    tank. The thickness of pile was measured down to 6m below pile head, where the lateral bearing force is

    susceptible due to corrosion. In addition, 5 piles among them were measured over the entire length of pile.

    The measurement of thickness was carried out after removing extraneous matters such as corrosion products

    and residual material. Then the averages of pile thickness were calculated from measured thickness and

    weight for each 1m.

    Also note that the cathodic protection of impressed current method had been applied to the removed tank from

    one year after start-up.

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    Figure 3.3. Specification of tank foundation

    Figure 3.4. Framing plan of piles and the measured piles in corrosion survey

    3.3.2 Result

    Observing the appearance of piles, corrosion is found on the outside surface evenly, where local corrosion of

    particular part is not found, nor rust inside of the steel pipe. Therefore, the corrosion content is estimated from

    the outer wall of a pile by reducing the measured value from the initial thickness of a pile. Figure3.5 shows the

    corrosion content according to the depth. The corrosion content is about 0.6mm at a maximum, so it is kept

    within 2.0mm margin. Also, no specific difference is found in the corrosion conditions between each depth.

    The averaged corrosion rate is obtained as 0.014mm/year at a maximum. It also stays within the confines of

    normal corrosion rate that reported various research literatures. The evaluation criterion is estimated at up to

    0.073mm/year before this corrosion survey; the total corrosion rating was calculated from adding

    0.042mm/year as macro-cell corrosion rate of steel in concrete to 0.031mm/year as maximum natural

    corrosion rate. However, the corrosion rate obtained from this survey resulted in far below the conventional

    value we estimated.

    From pile head to 6m below

    Whole length

    (Measurement range)

    Steel pipe pile

    Length: 25.0m

    Outer diameter: 406.4mm

    Thickness: (Upper part) 12.7mm

    (Lower part) 9.5mm

    Number: 496

    Diameter of base slab: 48.0m

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    The effective range of cathodic protection related to the arrangement of foundation piles could not be

    ascertained because there was no specific difference found between the outer and the center piles due to the

    too small corrosion content.

    3.4 Deterioration survey for concrete

    3.4.1 Purpose and scope

    Diagnostic evaluation for concrete structure used for 40 years was undertaken based on chloride ion content,

    carbonation depth and compressive strength of concrete used for the base slab and dike of LNG storage tank.

    Measure points are selected at the marked point in Figure 3.6; 5 points on underside of base slab, 4 points on

    side surface of base slab, each 4points on outer and inner side of dike.

    Figure 3.6. Measure points for concrete deterioration survey

    Depth(m)

    Corrosion allowance

    Corrosion content (mm)

    Figure 3.5. Corrosion content

    Underside of base slab

    Side surface of base slab Outer and inner side of dike

    *Only from K031LNGtank on east side.

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    3.4.2 Result

    (a) Chloride ion content

    Chloride ion content as measured at each 20cm depth for 7 measuring points at t underside of base slab and

    for 5 measuring points at each side surface of foundation slab and dike. Figure 3.7 shows the chloride ion

    content. The covering depth of base slab and dike is 85~105mm, and the chloride ion content at the reinforcing

    steels was lower than 2.5kg/m3that specified as criteria of corrosion durability. Also, it shows that almost no

    chloride ion content made inroad into the underside of base slab.

    (b) Carbonation depth

    Figure 3.8 shows the measurement result of carbonation depth. Almost no carbonation progress is found at

    base slab. Even the carbonation found at side surface of base slab and dike wall are 25mm at a maximum, it

    shows that the carbonation depth does not reach to the reinforcing steels.

    Carbonation depth

    (mm)

    Underside

    of base slab

    Side surface

    of base slabDike

    Figure 3.8. Carbonation depth

    Minimum covering depth

    Chloride ion content

    (kg/m3

    )

    Depth from concrete surface (cm)

    Underside of base slab

    Side surface of base slab

    Dike

    Figure 3.7. Chloride ion content

    Criteria of corrosion durability

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    (c) Compressive strength

    Figure 3.9 shows the measurement result of compressive strength. The survey of compressive strength shows

    that all the specimens satisfy the design compressive strength of 24.0N/mm2.

    3.5 Deterioration of Instrumentation Devices

    The following are the report of deterioration investigation of instrumentation devices. The devices below are

    selected as objectives for investigation among the instrumentation devices mounted on the tank.

    Thermometer for Roll-over detection Guide wire for Float Type Level Meter

    These devices have not renewed since the construction of the tanks, and they have been in service without

    any failure. However, major renovation work including hot-up and opening of LNG tank would be necessary if

    these devices had failure and needed to be repaired. Also, operation of the entire LNG terminal might be

    interrupted. Therefore, it is important to investigate the deterioration of these devices for better approach to

    future construction and maintenance of LNG tanks.

    3.5.1 Thermometer for Roll-over

    (a) Outline of Thermometer for Roll-overHere is the detail of Thermometer for Roll-over.

    This thermometer has a very important role in monitoring LNG stratification that is considered as a warning

    symptom of roll-over phenomenon.

    As shown in Figure 3.10, 15 thermometers are arranged at intervals of 2m from the top of LNG tank.

    According to the indicated values of the thermometers, supervised computer system (hereafter SCS) judges

    the occurrence of LNG stratification. When SCS detects stratification, it sends an alert signal to the center

    control room (hereafter CCR) and requires the operator to take measures, such as sending out, transfer or

    circulation.

    Compressive strength

    (N/mm2)

    Underside

    of base slab

    Side surface

    of base slabDike

    Figure 3.9. Compressive strength

    Design compressive strength

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    Figure 3.11. Insulation

    resistance test

    Figure 3.10. Arranged thermometers

    (b) Objective for Investigation

    30 thermometers for roll-over taken from the two removed LNG tanks are used for investigation.

    The specifications of the thermometer are described below:

    Model : Metal-sheathed resistance thermometer sensor

    Sheath material : SUS316

    Sheath outer diameter : 4.8mm

    Sheath length : 13m~41m (at intervals of 2m)

    Classification : 0.5

    Detection element : Platinum resistor

    (Standard resistance value : Pt100at 0 (JPt100))

    Conductor : 3-wire type

    (c) Investigation Contents / Method

    It has already reported that there are some thermometers indicating the

    signs of insulation degradation before the LNG tanks removal. If the

    insulation degradation occurred, the ability of measuring temperature

    deteriorated. Furthermore, if the insulation completely damaged,

    temperature measurement became impossible subsequently. Prior to the

    investigation, we implemented insulation resistance test (applied voltage:

    100CV) for all thermometers just before removing them to identify the

    thermometers having the insulation degradation. Then we cut off the

    sheath off from the head of the thermometer having insulation degradation

    and implemented insulation resistance test (Figure 3.11) again to investigate

    the region where insulation degradation occurred.

    (d) Result of Investigation

    Table 3.13 shows the result of the insulation resistance test. There were 5 thermometers that had lower

    insulation resistance value than 20M at the time of measurement before removing. However these

    thermometers had more than 20Mof insulation resistance in the second test after cutting the sheath for 1m

    off from the head. Therefore, it can be said that insulation degradation of the thermometers occurred within1m from the head.

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    Table 3.13. The result of insulation resistance test and region of insulation degradation

    Thermometer No.Insulation resistance

    [M]

    Region of insulation

    degradation [m]

    (distance from the head)

    No.1 LNG tank

    1 1 13 6 1

    5 2 1

    12 11 1

    No.3LNG tank 1 0.1 1

    (e) Conclusion

    The insulation degradation was found on 5 thermometers among all 30 objective thermometers. However,

    they did not have severe degradation to the extent of influencing the measuring ability of thermometers. The

    degradation occurred within 1m from the thermometers head according to the investigation of region. It is

    assumed that the cause of insulation degradation was the influent water from the terminal area covered with

    epoxide resin. The epoxide resin used for insulating the terminal area had deteriorated.

    The insulation degradation was solved by cutting off the deteriorated region in upper 1m. We conclude that

    the thermometer should be installed with extra length to deal with insulation degradation.

    3.5.2 Guide wire for Float type level meter

    (a) Outline of Float type level meter

    Here is the detail of Float type level meter.

    Figure 3.12 shows the float type level meter removed from the tank on this occasion. It is used to measure the

    liquid level according to the length of the tape that goes up and down depending on the float on the liquid

    surface. The float moves along the guide wires. Therefore, friction arises between the float and the guide

    wires every time when the float moves. In this investigation, the deterioration condition of guide wires were

    inspected for taking into account the risk of broken guide wires.

    Figure 3.12. Float type level meter

    (b) Objective for investigation

    There were 2 floating type level meter mounted on each removed LNG tank. One of the guide wires on eachLNG tank was selected as objectives. Specification of the guide wire is described below.

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    Applied standard : JIS G 3550

    Material : SUS304

    Product name : Independent strand core rope

    Constructive number : 719

    Length : approx. 37.5m

    Diameter of wire : 10mm

    Diameter of strand : 0.67mm

    (c) Investigation Contents / Method

    We supposed that the worn volumes were different depending on the positions of a guide wire in

    consideration of normal liquid level; too high and too low level were less frequent. Therefore, the samples for

    investigation were picked up for each 1000mm from three positions, upper, middle and lower part. Table 3.14

    shows the details of samples. Then we made a comparison of deterioration degree of these guide wires.

    Table 3.14. Details of samples

    Distance from the bottom of

    tank [m]

    Total times of

    round-trip [time]*

    Sample 1 (upper) 33 0

    Sample 2 (middle) 17 1,000

    Sample 3 (lower) 6 200

    * Total times of round-trip after the installation are estimated from liquid level change for a year in 2010.

    1) Observation of appearance / gauging of diameter

    We inspected the worn volume of sampled wires and their strands by visual and a digital microscope.

    Also, we gauged the diameters of each sample to compare the values to the standard criterion of JIS

    and among the samples obtained from each position.

    2) Tensile test

    We implemented tensile test of sample wires if these wires satisfy the breaking force specified in JIS G

    3550; for tensile test, both edges of wires were bonded by white metal.

    We picked up 1 strand of each 6 strand excluding the core as objectives for tensile test of wire, and

    implemented tensile test if these wires satisfied the breaking force specified in JIS G 4314 under the

    condition; length of specimen between grips100mm, tension rate 50mm/min.

    (d) Result of inspection

    1) Observation of appearance / gauging of diameter

    Figure 3.13 shows the pictures of wires appearance and their diameters. There was no thinner wire

    than 10mm (the criterion specified in JIS G 3550) and no difference was found among each position.

    Red rust was found on some wires however it could be wiped off easily (it is supposed that this red rust

    adhered at the removing work).

    Figure 3.14 shows the pictures of strands appearance and their diameters observed by a digital

    microscope. There were small wears found at the parts marked with red arrows. However these wears

    were not serious and the wires had enough diameters over the 0.67mm of regulation size. It can besaid that there was no wear on the wires.

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    Figure 3.13. Wires diameters Figure 3.14. Strands diameters

    2) Tensile test

    Table 3.15 shows the result of tensile test for wires. All wires at each position satisfy the level of

    standard breaking force 61.8kN for 10mm wire. Also, no difference was found among each position.

    Therefore, it can be said that there was no deterioration of wires.

    Table 3.16 shows the result of tensile test for strands. Some strands of No.3 LNG tank exceeded over

    the maximum level of standard breaking force 1850~2100MPa for 0.67mm wire. However, no strands

    exceeded the minimum level and no difference was found among each position. Therefore, it can be

    said that there was no deterioration of strands.

    Table 3.15. The result of tensile test for wires

    Standard breaking

    force of wire [kN]

    Breaking force of wire [kN]

    No.1 LNG tank No.3 LNG tank

    Upper

    61.8

    64.0 68.2

    Middle 64.8 71.4

    Lower 66.8 72.2

    Table 3.16. The result of tensile test for strands

    Breaking force of strand [MPa]Standard breaking

    force of strand [MPa]No.1 LNG tank No.3 LNG tank

    Upper Middle Lower Upper Middle Lower

    1 2037 2036 2009 2102 2179 2169

    1850~2100

    2 2030 1996 2044 2089 2185 2094

    3 2100 1962 2052 2089 2127 2149

    4 1996 2000 2016 2169 2146 21635 2038 1978 2036 2137 2194 2135

    6 2056 1989 1990 2143 2165 2114

    Average 2043 1994 2025 2121 2166 2137

    (e) Conclusion

    We investigated the deterioration condition of guide wires for Float type level meter that had been installed in

    two LNG tanks. The guide wires have no specific wear and satisfy the standard specifications for both

    diameter and breaking force. We conclude that the guide wires for Float type level meter have enough

    properties that allow continuous use for 40 years.

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    3.6 Thermal insulation material

    The following thermal insulation materials (i.e. perlite, Mesalite (Mitsui Expanded Shell Light-Weight

    Aggregate) concrete, perlite concrete block and cylindrical perlite concrete) were investigated (Figure.3.15).

    Figure 3.15. Structural drawing of thermal insulation

    3.6.1 Perlite

    Perlite was sampled from the top, the middle, and the bottom of annular space, and also from inside of the

    cylindrical concrete.

    (a) Thermal conductivity

    Thermal conductivities were measured under the temperature condition of 3 steps(-20~30, 5~35, 20~50

    ). We calculated these values by using the regression equation and obtained the thermal conductivities at

    the zero Celsius degree. Thermal conductivities of each sample of perlite satisfy the specifications at the time

    of the construction.

    Table 3.17. Thermal conductivity of perlite

    Sample LocationThermal conductivity(T.C.)

    W/mK)(at 0Ratio

    *1

    Top of annular space 0.0433 0.98

    Middle of annular space 0.0429 0.97

    Bottom of annular space 0.0391 0.88

    In cylindrical perlite concrete 0.0399 0.90

    specification 0.0442 1.00

    note;*1:The ratio of the measured values to the specification value

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    3.6.2 Mesalite concrete

    (a) Compressive strength

    The test was carried out in accordance with JIS A1108 (this standard follows ISO 1920-4). The test results are

    shown in Table 3.18. Compressive strength of the samples satisfies the specification value at the time of the

    construction. The specific gravity was almost the same as the value at the time of the construction.

    Table 3.18. Compressive strength of Mesalite concrete

    specification (N/cm2) Test result (N/cm

    2) Ratio

    *1

    1470 1955 1.33

    note;*1: The ratio of the measured values to the specification value

    (b) Thermal conductivity

    The test was carried out in accordance with ISO 8301(Heat Flow meter apparatus Method). Thermal

    conductivity was calculated at zero Celsius degree by the equation regression as same as perlite. The test

    result value shown in Table 3.19 was less for approximately 67% than the construction specification and was agood value.

    Table 3.19. Thermal conductivity of Mesalite concrete

    Specification (W/mK) Test result (W/mK) Ratio*1

    0.93 0.309 0.33

    note;*1: The ratio of the measured values to the specification value

    The properties of Mesalite concrete have not been changed since the days of construction.

    3.6.3 Perlite concrete

    (a) Thermal conductivity

    The test was carried out in accordance with ISO 8301(Heat Flow meter apparatus Method).The test result

    value shown in Table3.20 was less for approximately 14% than construction specification and was a good

    value.

    Table 3.20. Thermal conductivity of perlite concrete

    Specification (W/mK) Test result (W/mK) Ratio*1

    0.1163 0.10028 0.86

    note;*1: The ratio of the measured values to the specification value

    3.6.4 Cylindrical perlite concrete

    (a) Thermal conductivity

    The test was carried out in accordance with ISO 8301(Heat Flow meter apparatus Method). The test result

    value shown in Table 3.21 was less for approximately 7% than construction specification and was a good

    value.

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    Table 3.21. Thermal conductivity of Cylindrical perlite concrete

    Specification (W/mK) Test result (W/mK) Ratio*1

    0.1163 0.10782 0.93

    note;*1: The ratio of the measured values to the specification value

    4. PRESENT SITUATION OF THE TANKS UNDER CONSTRUCTION

    The inner tank material for above ground LNG storage tanks has mostly been made of 9% Ni steel plate over

    the 50 years as it has excellent mechanical properties under -160deg.C. During this period, the LNG storage

    tanks made of 9%Ni steel plate have safety operated. It is known that 9%Ni steel has excellent cryogenic

    fracture toughness due to the retained austenite and refinement microstructure obtained by nickel content and

    heat treatment process.

    NSSMC, Toyo Kanetsu K.K (TKK) and Osaka Gas jointly developed 7%Ni-TMCP steel having the comparable

    performance to 9%Ni steel. Newly developed 7%Ni-TMCP is achieved 2% reduction of nickel content from the

    conventional 9%Ni steel by adopting Thermo Mechanical Control Process (TMCP). Various basic performance

    tests and fracture toughness tests in development process showed that the base metal and welded joints

    satisfy the regulatory and technical requirements for LNG storage tanks. In 2010, Japanese Ministry of

    Economy, Trade and Industry (METI) approved the use of 7%Ni-TMCP steel for newly-built tank of Osaka Gas.

    The development of 7%Ni-TMCP steel realizes the reduction of rare metal nickel to be used. Therefore, not

    only the cost of inner tanks material but also the cost of nickel in rising market can be saved.

    From September 2012, Osaka Gas started the construction of 230,000m3full-containment tank in Senboku I

    Terminal. Installation of steel pipe piles had been done at the time of October 2012 and the base slab is now

    under construction (Figure4). The construction of the tank will be completed by November 2015.

    Figure 4. The picture of present situation at construction area

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    5. CONCLUSION

    Osaka Gas demolished the two LNG storage tanks that had actually been used for about 40 years. On this

    occasion, we assured the secure dismantling method and verified that the mechanical properties (including

    chemical composition, tensile strength and Charpy absorbed energy) of 9%Ni steel and Al alloy used as inner

    tanks material satisfied sufficient levels. Thermal insulation material, steel pipe piles and instrumentation

    devices have no significant deterioration. These investigations proved the high integrity of the LNG storagetanks.

    The results of these investigations obtained from the demolished LNG storage tanks that had been used for

    about 40 years provide invaluable actual data and it contributes to the progress of LNG storage tank market in

    the future.

    REFERENCE

    1) Recommended Practice for LNG Aboveground Storage; Japan Gas Association 2012