5.21

DEMOLITION, INSPECTION AND TESTS OFDISUSED LNG TANK IN BRUNEI

LA DEMOLITION, LINSPECTION ET LES ESSAIS SURUN RESERVOIR DE GNL A BRUNEI

Dick UittenbroekSenior Tank Specialist, Research & Technical Services

Andre BlaauwMaterial and Corrosion Engineer, Research & Technical Services

Shell International Oil Products B. V.

Hamdillah H. A. WahabExecutive Director cum Plant Manager

Brunei LNG Sendirian Berhad

Hitoshi Hirose, P.E.General Manager, Engineering Department

Shuichi HiraiSenior Researcher, Engineering Department

Machinery & Plant DivisionToyo Kanetsu K. K.

ABSTRACT

A 20-year-old LNG storage tank at BLNG, Brunei, was successfully demolished.Before, during and after demolition, BLNG and TKK jointly performed inspections on thetank, and various tests were carried out on materials in order to obtain information aboutthe tank integrity after its operational life time.

This paper presents information on how the tank was decommissioned, inspected anddemolished, and shows inspection and test results, i.e., visual inspection includingcorrosion checks, non-destructive examinations and physical and mechanical tests ofinsulation materials. The paper also presents the results and assessment of generalmechanical tests and fracture toughness tests of the 9% nickel steel and welds.

The decommissioning and demolition operation demonstrated an effective procedurefor future similar operations on aboveground LNG storage tanks. The inspection andtesting further demonstrated the design and construction integrity of the LNG storagetank, and provides confidence in the continued development of such facilities.

5.22

RESUME

Un reservoir stockage de GNL vieux de 20 ans a t dmont avec succs BLNG(Brunei). Avant, pendant et aprs la dmolition, BLNG et TKK ont men conjointementles inspections et differents essais ont t realiss sur les matriaux dans le but dobtenirdes informations sur lintgrit du reservoir aprs son temps dutilisation.

Cet article fournit les informations sur les moyens employs lors de la mise hors service,de linspection et de la dmolition. Il prsente ensuite, les rsultats des inspections et desessais incluant les essais de corrosion, les essais non-destructifs et les essais mecaniquessur les matriaux disolation puis les rsultats et valuations des essais mcaniquesgnraux et des essais de rsistance de l'acier a 9% de nickel et des soudures.Les oprations de mis hors service et de dmontage ont prouv lfficacit de la procduremise en uvre pour des interventions semblables sur des rservoirs hors-sol.Les inspections et essais ont en outre dmontr lintegrit de ltude et de la constructiondu rservoir et donnent toute confiance dans le dveloppement futur de telles installations.

5.23

DEMOLITION, INSPECTION AND TESTS OFDISUSED LNG TANK IN BRUNEI

1. INTRODUCTION

In 1972 three 65,000m3 LNG Storage Tanks were designed and constructed by ToyoKanetsu K.K. (TKK) for Brunei LNG Sendirian Berhad (BLNG). The basic designrequirements were specified by Shell International Petroleum Maartschappij BV [nowcalled Shell International Oil Products BV (SIOP)] as advisor of BLNG.

The tanks, which are of the single containment type with double steel walls, weredesigned and constructed according to the requirements of API Standard 620 Appendix Qand have been successfully operated for 20 years. During that time they have handledsome 5 million tons of LNG per year, all of which has been shipped to Japan.

During discussions on plant lifetime extension of the BLNG plant, the suitability of theLNG storage facilities for an additional long term service period was questioned. As aresult a joint BLNG-SIPM safety study was carried out. The following subjects wereincorporated: tankfarm layout, single containment tank concept, piping manifolds next tothe tanks and structural details of the tanks.

Based on the results of the study, BLNG decided in 1990 to upgrade their LNGstorage facilities to ensure a reliable future supply of LNG. Accordingly a contract wasawarded for the design and construction of two new 65,000 m3 storage tanks andassociated facilities. The new tanks were of the full containment type with pre-stressedconcrete outer tanks in accordance with the requirements of API 620 Appendix Q, andEEMUA Publication 147. These new tanks also meet the essential requirements of BS7777 and have formed the basis for similar tanks built elsewhere. As leader of theconsortium, TKK was responsible for the mechanical, electrical and instrumentationworks, forming a partnership with a civil contractor and a local company. The Project wassplit into two phases; firstly the construction of the two new tanks including associatedfacilities, and secondly demolishing one existing tank and mothballing two existing tanks.

BLNG and TKK took this opportunity to jointly inspect the inner 9% nickel steel tank,the outer carbon steel tank, the insulation materials, and to research the durability of thematerials exposed to cryogenic, ambient or intermediate temperatures. This paperintroduces the results of the inspection and tests and presents an assessment of theintegrity of the tank.

Inspection and Tests Performed:

1) Visual inspection of outer tank steel including roof, shell and floor plates, anchorbolts, piping, nozzles, steel structures and accessories.

2) Visual inspection of suspended ceiling deck including deck plates and hangers.3) Visual inspection and non-destructive examinations of inner tank steel including

shell and floor plates, shell stiffeners and attachments.

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4) Thermal conductivity check, density check, sieve analysis and organic analysis ofexpanded loose perlite insulation material.

5) Thermal conductivity check of fiberglass blanket insulation material.6) Visual inspection and compressive strength test of perlite concrete block and

foamglass insulation materials.7) Chemical analysis of 9% nickel steel and welds.8) Mechanical tests of 9% nickel steel and welds including tension tests and Charpy

impact tests.9) Brittle fracture (crack initiation and arresting) resistance tests of 9% nickel steel

and weld metal including CTOD tests, Wells notched welded wide plate tests,NRL drop weight tests and Duplex ESSO tests.

2. DEMOLITION

2.1 Decommissioning

The two new tanks went into service mid October 1993. The tank to be demolished T-4103 was taken out of service 2 December 1993.

The decommissioning work started with pumping-out the liquid. This was done withboth the loading and circulation pump to a very low level (0.02m) due to the availability ofbottom outlets. Around 13 m3 liquid was left and was evaporated using hot gas.

5.25

This was routed to the tank via a bottom outlet. A warming-up rate of 13oC per daycould be obtained and on 17 December 1993 the average tank temperature reached-20oC. The tank was further warmed-up with hot nitrogen gas until the average tanktemperature reached +15oC.

During the whole heating-up period the bottom heaters were fully energized. Themaximum temperature difference between adjacent inner tank temperature sensors waskept within 30oC.

Purging the tank with nitrogen followed warm-up and was achieved in two steps.First, nitrogen was introduced into the bottom of the inner tank and was allowed to escapeto atmosphere at the top. In the second step, the annular space and tank dome space werepurged with nitrogen at the same time, again with the gases being released to atmosphere.

Before cutting the inner tank bottom, water was pumped into the annular space up tothe inner tank bottom level. Holes were drilled into the inner tank bottom so thathydrocarbon(s) could escape.

On 19 January 1994 (49 days after the tank was taken out of service) the tank wasdeclared hydrocarbon(s) free (oxygen content exceeding 20%, and hydrocarbon(s)content less than 1%).

2.2 Perlite Removal

The 4 outer tank 24 shell manways were opened to allow perlite to freely flow outfrom the annular space. During this initial stage, the tank was kept under a light nitrogenoverpressure. Later, during the removal of perlite by mechanical means, air ventilation wasused. Water spray systems were installed to suppress the perlite dust. At a later stage, toaccelerate the perlite removal, several additional holes were cold cut in the outer tankshell.

Perlite removal from the annular space was completed 15 February 1994. During thewhole periods gas tests were performed to ensure safe operation.

After removing the perlite from the annular space the suspended deck was inspected.No hydrocarbon(s) was detected in the polythene bags containing perlite. A hole wasmade in the roof plates and the perlite bags were handled manually, and dropped throughto the inner tank floor. The work was completed 19 March 1994.

2.3 Tank Demolition

2.3.1 Demolition Procedure. Demolition of the tank started only after removal of allperlite.

The inner tank was opened by cold cutting a 4m x 4m hole in both the outer and innertanks. Gas freeing the areas where possible hydrocarbon gases are trapped underneath theinner tank floor is considered one of the most critical activities for subsequent hot workoperations. To achieve this, water was filled in the annular space to the level of the inner

5.26

tank floor thereby pushing trapped hydrocarbon gases out through drilled holes in the tankfloor.

Openings, which were provided with access ramps, enabled the entry of a crane andother demolition equipment at a later time.

After packing the floor of the inner tank with sand, the suspended ceiling deck androof were cut away and allowed to fall to the inner tank floor. During this period, allopenings to the inner tank were closed to prevent inadvertent entry of personnel.

The outer and inner tank shells were then cut away ring by ring, with one ring of theouter tank being removed for approximately half of the circumference before starting onthe corresponding inner tank ring. This was inspected until all shell courses had beenremoved.

The inner tank floor plate were cut and removed to expose the insulation which wasthen removed by mechanical shovels. Finally the outer tank floor plates were cut andremoved. The concrete foundations were broken up and the site was levelled and graded.

3. INSPECTION AND TEST RESULTS

3.1 Visual Inspection

As a result of the visual inspection the following observation were made:

- Outer tank: the general condition of the shell and roof plates was found to bemainly in good condition. Although the tank shell plates were stained in many areas,no breakdown of the paint system was detected during inspection. Some corrosionwas detected on the roof plates in the areas where the fire deluge system stands hadbeen located;

- holding down bolts: heavy corrosion took place on the holding down bolts of thesteel outer tank. Maximum loss of diameter thickness was 14.8mm of the original32.5mm bolt diameter.

- all roof nozzle flange joints were in badly corroded condition;

- remaining: the electrical and instrumentation supports were heavily corroded as wellas the fire deluge system spray nozzles;

- suspended deck: visual inspection was carried out on deck hangers, deck plates,deck stiffeners and some welds. No indications were detected that required furtherinvestigation;

- inner tank: the inner tank bottom was found to be clean with only a small looserust/scale type deposit around the annular plates. The usual highs and lows of platesdue to welding deformation was evident and were uniform across the completefloor surface. Visual inspection was carried out on all bottom welds. Noabnormalities were detected;

- outer tank bottom: after demolition of the outer tank bottom, corrosion wasdetected at the underside edge of the annular plate (pitting up 3.0 mm, nominal

5.27

plate thickness 9.0mm) and on the underside of the product drain trays (pitting upto 4.0mm, nominal plate thickness 9.00mm).

Also the heating conduits, located in a sand layer under the outer tank bottom wereheavily corroded. Some were in poor condition.

3.2 Non-destructive Inspection

The following non-destructive testing was carried out on the inner tank:

- Around 10% of the bottom welds and 100% of the circumferential weld to the innertank annular bottom plate were inspected with dye penetrant. The welds were firstcleaned with power buffing to a bright weld finish. No indications of defects weredetected that required further investigation.

- Dye penetrant inspection was also carried out on the inner tank shell welds. Aminimum of 10m of weld per course was inspected, with both sides being inspected.In general, welds were in good condition. Some very small surface indications weredetected but none that required further investigation.

- Two butts and a minimum of 10m of fillet weld per the inner tank shell stiffener(total 10 stiffeners) were inspected by dye penetrant. Three crack-like indicationswere detected in the fillet welds.

- Radiography was carried out on a total of 34 vertical welds of the inner tank shellplate. No abnormal indications or other areas of interest were noted.

3.3 Insulation Materials

The following insulation materials were inspected:

3.3.1 Perlite Powder. Perlite samples were taken from the annular space at threedifferent height locations. The samples were tested and showed the following properties:

Table 3.1 Thermal Conductivity of Perlite Powder

Sample Location Test Temperature oC Thermal ConductivityW/mK

Top -1.7 0.0400Middle -1.4 0.0399Bottom -1.0 0.0388

3.3.2 Fibreglass. All fibreglass blankets were inspected and appeared to be in goodcondition. In all areas where blankets had to be removed, the fixing/holding pins were allstill firmly attached to the shell plate.

3.3.3 Foamglass. An area of approximately 6m x 6m was cut in the inner tank floorand the steel plates removed before tank demolition commenced.

Inspection showed that none of the upper layer auto-claved concrete blocks weredamaged or broken. A very high percentage of the foamglass blocks located under the

5.28

auto-clave blocks were broken in vertical plane. The average block was broken in three tofive pieces. However, despite being broken, there was very little evidence of crumbling orbreakdown of the blocks. Five Samples of foamglass blocks (200mm x 200mm x 120mm)have been tested. The results are summarised below.

Table 3.2 Compressive Strength of Foamglass Blocks

Foamglass HLB 135 Lot Average IndividualSpecification 0.93 MPa 0.64 MPaTested 1.21 MPa 0.99MPa

3.3.4 Perlite Concrete. The perlite concrete blocks were visually inspected. Noabnormalities were detected. At two locations 3 core samples (diam. 145mm) were drilled.The compressive strength of the samples were determined. The test results were shown inTable 3.3

Table 3.3 Compressive Strength of Perlite Concrete Blocks

Perlite ConcreteBlocks Individual (N/mm2)

Tested (CylinderSample)

1.72 1.82 1.80 1.52 2.04 1.44

Cube Strength(Coverted)

1.80 1.90 1.85 1.55 2.1 1.5

Specified: 1.2 0.2 N/mm2

4. TESTS OF 9% NICKEL INNER TANK STEEL AND WELDS

4.1 General

In order to obtain the information on the tank integrity after an operating life of 20years. mechanical properties of the base metal and welds sampled from the 1st (Bottom)and 14th (Top) inner tank shell courses were investigated by performing the testssummarised in Table 4.1.

The test programme for the material was selected to address the following areas ofinterest:

1) The basic chemical and mechanical properties.

2) Fracture toughness tests were performed to assess anti-crack initiation, and crackarrestability characteristics considering that the material had been manufactured for20 years ago.

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Table 4.1 Summary of Test Item

Fundamental test Fracture toughness test

Base plateChemical analysisMacro & MicrostructureTensile testCharpy impact test

CTOD testDuplex ESSO testNRL drop weight test

Welded jointChemical analysisMacro & MicrostructureTensile testCharpy impact test

CTOD testNRL drop weight testWells notched and welded wideplate test

This paper focuses mainly on the notch toughness and the fracture toughness for basemetals and welds.

4.2 Basic Test Results

4.2.1 Chemical Compositions of Base Metal. Chemical analyses for the base metalwere carried out on representative samples taken from the 1st and 14th shell courses andannular bottom plate.

Table 4.2 shows the results on each base metal. These results of the base metalconform to the requirements of ASTM A553 Type I

Table 4.2 Chemical Composition

Sampling Part PlateThickness

(mm)C Si Mn P S Cu Ni Cr Mo Nb V T-AI

Shell Plate1st Course

19 0.09 0.29 0.6 0.003 0.002 0.03 9.17 0.12 0.02 0.004 0.001 0.043

Shell Plate14th Course

8 0.06 0.29 0.6 0.002 0.002 0.03 9.35 0.05 0.01 0.003 0 0.046

Annular Plate 9 0.08 0.25 0.56 0.002 0.003 0.02 9.15 0.06 0.01 0.002 0 0.042

4.2.2 Tensile Properties. Tensile tests on the base metal were carried out using oneof two types of specimens: a full thickness specimen in accordance with JIS Z 2201 No.5,and a 6mm diameter specimen in accordance with JIS Z 3111 No. A2. The full thicknessused for testing the 14th shell course, was taken from the mid-thickness of the plate,whilst the 6mm diameter specimen was taken from the plane 6mm below the surface of the1st courses shell plate. Each tensile test was performed in both the L-T and T-Ldirections. The 6mm diameter specimens were tested at both room temperature and at -196oC whereas the full thickness specimen was tested at room temperature only.

All of the results on 0.2% proof stress, tensile strength and elongation at roomtemperature satisfied the requirements of ASTM A553 Type I. The tensile properties at -196C as to be slightly lower in elongation and reduction of area than at room temperature,in spite of increasing of strength due to changing test temperature from room temperature

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to -196C. Tensile test for the welds of vertical joints of c and 14th shell courses were alsocarried out in accordance with API 620 Appendix Q. The results of the welded joint andall-weld-metal at room temperature were well over the requirements of API 620 AppendixQ at the construction time specified a minimum tensile strength of 95,000psi (655MPa)and a minimum yield strength of 52,500psi (362MPa). Moreover, the tensile properties at-196C were also very good as to show a good ductility and higher strength than roomtemperature.

4.2.3 Charpy Impact Properties. Charpy impact test for the base metal of the 1st

shell course were conducted on total 18 plates also for the welds of 1st shell course andboth the base metal and welds of the 14th shell course and annular plate, the tests wereconducted on the representative plates of the lowest value in Charpy absorbed energy ofthe mill test reports at the construction time. The test specimens of base metal were takenfrom the both L-T and T-L directions. The central axis of the specimen of 19mm inthickness were in the plane of 5.5mm under the surface, and 8 or 9mm in the mid-thickness. The test was carried out at -164C and -196C.

(a) Base metal of 1st shell course

Fig. 4.1 Histogram of Charpy absorbed energy on the 1st shell course

The test results at -196C are shown in the histogram of Figure 4.1. All plates conformto the requirement of Type V material, improved 9% Ni steel in BS7777 Part 2 as well asAPI 620 Appendix Q. Besides, this histogram shows remarkable tendency that the absorbedenergy of the 9% Ni steel plates about 20 years ago were effected by the final rollingdirection. In short, the plates have large anisotropy between L and C direction. Inscattering, T-L direction at -164C was the smallest, L-T at -164C, T-L at -196C, L-T at -196C were following, respectively. And there was no brittle part in the fractured surfaces of

Fig. 1 Histgram of Charpy absorbed energy on the 1st shell course.

21

4

11

14

10

32

7

2

5 5

7

5

8

13

7

2

0

2

4

6

8

10

12

14

16

18

20

70-80

80-90

90-100

100-110

110-120

120-130

130-140

140-150

150-160

160-170

170-180

180-190

190-200

200-210

Charpy absorbed energy ( J )

F r e q u e n c y

N

L C

L: N =54 MIN =115 MAX =210 AV. =169.4 STD =20.8C: N =54 MIN =80 MAX =152 AV. =120.2 STD =21.3

Test temperature: -196C

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all tests at -164C, but a little percentage of brittle fracture appears in almost test results at -196C.

(b) Base metal of the 14th shell course and annularThese results showed basically same tendency in absorbed energy value and brittle

fracture rate between each test temperature as 1st shell course.

(c) WeldsCharpy impact tests were carried out on welds of 1st and 14th shell courses,

machining the notch at weld metal, fusion line( FL: 50%weld metal + 50% heat affectedzone ), FL+1 mm, FL+3mm. These test results conformed to the requirement of API 620Appendix Q. Moreover, welded metal also conformed to the requirements of BS7777.Figure 4.2 shows the relation between the absorbed energy and notch location for 1st shellcourse. It is observed that the lowest value is weld metal, the second is fusion line and asthe location is further from the fusion line, the value become higher. This tendency isnormally observed in the general welds of 9% Ni steel.

4.3 Fracture Toughness Test Results

4.3.1 CTOD Tests. CTOD tests were carried out in accordance with BS5762-1979on the base metals and welds selected from the 1st and 14th shell courses. The testdirection of the base metal was both L-T and T-L but the welds were L-T only. Threetests were conducted for each test condition at -164C and -196C. The base metal andwelds of 1st shell course showed good properties no less than 0.26mm at -164C. Theproperties at -196C showed minimum CTOD value of 0.05mm and appeared some pop-inat FL+1mm and 3mm.

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Fig. 4.3 CTOD test results of 19mm thickness welded joint.

Fig. 4.4 Specimen geometry and location of measurement.

7

7

2

10

Clip gauge position

Test weld

63

63

63

63

Notch

800

G.L .500mm

Gauge length for elongation

Gauge length for elongation

G.L .500mm

1000600

1000

R100R100

Thermo coupleposition( every 63mm)

210 38

2

2

Notchconfiguration0.1R

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Configuration ( mm ) Test Fracture Fracture stress Notch opening ( mm ) 2) Crack

SpecimenThickness Width Notch Angular temperature load ( MPa ) CG disp. 1) Kc pass length distortion ( 0 C ) (kN) Gross Net Vg CTOD (M pa m

1/ 2)

t 2W 2a w/ 1000 s g s n Ave. d cWPA- 1 19.8 800 38.0 13.7 - 163 12082 762.8 800.8 Upper 2.75 1.94 1.60 187 HAZ to

1.12 Weld Metal

Lower 2.68 1.84 1.84

1.00

WPA- 2 19.9 800 38.0 13.4 - 163 12160 763.8 801.9 Upper 3.13 2.09 1.73 187 HAZ to

1.04 Weld Metal

Lower 2.61 1.77 1.46

0.92

WPB- 1 8.3 800 38.0 8.2 - 163 4943 744.4 781.6 Upper 2.16 1.94 1.55 184 HAZ to

1.76 Weld Metal

Lower 2.16 1.96 1.57

1.72

WPB- 2 8.6 800 38.0 8.2 - 163 5315 772.5 811.1 Upper 2.16 1.82 1.53 189 HAZ to

1.48 Weld Metal

Lower 1.96 1.68 1.41

1.40

Table 4.3 Results of Wells notched and welded wide plate test.

(Remarks) 1) From BSC model2) Kc = sg x (pa) x [sec(pa/2W)]

These pop-ins were judged as significant ones in accordance with BS7448. Besides,the base metals and welds of the 14th shell course showed also good properties and theminimum CTOD value was 0.145mm at -164C. But the minimum CTOD value at -196Cwas 0.05mm and two significant pop-ins were observed at FL+1mm and 3mm. Figure 4.3shows the relation between the critical CTOD value and the notch location in the results of1st shell course.

This indicates a tendency that the lower the critical CTOD appears as the notchlocation is closer to the base metal. It is remarkable in the results at -196C. And thistendency was also same in the results of 14th shell course. It is concluded that thematerials including the welds fabricated 20 years ago have enough properties against thebrittle fracture initiation at LNG temperature of -164C.

4.3.2 NRL Drop Weight Tests. NRL drop weight tests were performed on the basemetal and the heat affected zone of welded joint of 1st shell course. The tests wereconducted at -196C using P-3 type specimen in accordance with ASTM E206-91 andrepeated by three specimens on each conditions. All tests showed no-break performanceand ensured that Nil Ductility Transition ( NDT) temperature were below -196C.

4.3.3 Wells notched and wide plate test. The main object of this test is to evaluatenot only the characteristics on brittle fracture initiation of welded joints but also thepropagation phenomena of them, such as the crack path, pop-in size, its direction, re-initiation toughness etc. In other words, the object is to evaluate the overall performanceof weldments against brittle fracture.

The test specimens were prepared from the selected vertical joints of the 1st and 14th

shell courses. These specimens had a centered though thickness notch along to weldedjoint as shown in Figure 4, and the notch was machined at the heat affected zone. The testwere carried out using a 2,000 ton horizontal tensile test rig and a automatic temperaturecontrol system keeping the temperature at -163C with spraying liquefied nitrogen gas.Notch opening displacements, overall elongation and test temperature were measured at

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the points shown in Figure 4.4. The notch opening displacements were measured on bothsurfaces using clip gauges. And the charts of load to clip gauge displacement and load toelongation were recorded by X-Y plotter. These test results are shown in Table 4.3. Thegross fracture stresses for WPA-1,WPA-2, WPB-1 and WPB-2 are so high as to show762.8, 763.8, 744.4 and 775.5MPa respectively. Furthermore, their notch openingdisplacements are 1.56, 1.60, 1.56 and 1.47mm in average value. And no pop-in appearedin all test specimens. The crack initiated at the notch deviated into the weld metal andshowed a very ductile fracture. This demonstrated that the welds had excellent fracturetoughness properties to withstand fracture initiation.

4.3.4 Duplex ESSO test. The object of this test is to evaluate the crack arrestabilityof the materials against a running brittle crack after it ran at most 300mm in length underthe conditions similar to actual storage tanks. The shape of the test specimen is shown inFigure 4.5. The test specimen consists of two parts. The one part of 150mm in length forcrack starter and crack propagation, and the other part of 350mm in length for the test.The former is made of embrittled 9% Ni steel that is treated by annealing after heated to800C for an hour to initiate and propagate easily a brittle crack.

Both parts are welded with 3.5% Ni type welding materials. At the top of theembrittled plate, a notch of 29mm in length is machined where a wedge is driven by highpressure nitrogen gas to initiate a brittle crack in the test plate. While applying of thespecified load to the test plate at the temperature, the notch is struck by the wedge. Testresults are judged as No-Go(Arrest) or Go(Propagate) depending on whether thecrack is arrested in the test plate just after it hits or not.

The tests were conducted on the selected base metal of 1st and 14th shell courses. Atest specimen was installed into 2,000tonf horizontal tensile test rig and cooled down to -164C by controlling to use liquefied nitrogen gas. The test temperature at 6 points asshown in Figure 4.6 was measured by C-C thermocouples. Furthermore, as for the testplate of 19mm in thickness( 1st shell course ), the crack propagation speeds of 6 partswere measured as shown in Figure 4.6. Two test specimens were tested for each baseplates. The base metals showed excellent crack arrestability to indicate No-Go withsmall penetration under the applied stress 323 or 361N/mm2 for two specimens of 19mmin thickness and one under the applied stress of 323N/mm2 for 8mm in thickness. As foranother test specimen of 8mm in thickness, the results was considered to be No- Test,because the crack initiated in the embrittled plate before attaining to the specified load.Figure 4.7 shows the one sample of the fracture appearance for the specimen of 19mm inthickness. Besides, crack propagation speeds were measured successfully. It showed atrend that the propagation speed attain the maximum speed at the parts of #5-6 to be 932and 777m/sec before penetrating to the test plate, and they reduced at the parts of #6-7 tobe 595 and 442m/sec at just penetrating to the test plate. It was proven that actual baseplates had excellent crack arrestability.

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Plate thickness 19mm Location of test Base metal

Mark EAB-1 Test temperature -164 C

Stress 361 N/mm2 Test result No Go

Fig. 4.7 Fracture appearance of duplex ESSO test specimen.

30

60

60

60

60

60

Embrittled

Test plate

plate plate

Position of thermocouples

1030

25

25

20

20

35

# 1

# 2

# 3

# 4

# 5

# 6

# 7

Position of crack speed detector guage

Fig. 4.6 Position of thermocouple and crack speed detector gauge

Weld

Weld

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5. CONCLUSION

BLNG had been operating the three LNG storage tanks for 20 years. Only normalexternal inspection and maintenance was carried out. No internal inspection we required.The tanks had been designed and constructed in accordance with the conventional designcode (API620 Appendix Q) and construction practice applicable in those days. The 9%nickel steel and its welds used had been qualified only by charpy impact testing atCryogenic temperature of -196oC in terms of brittle fracture toughness. They wereactually qualified for the requirements of the BS7777, Part 2, issued in 1994. Theinspection and test results showed that the steel inner and outer tanks, inlcuding insulationmaterials, are in good condition although corroded details need improvements. BLNG isactually planning to reuse one of the mothballed tanks with modifications.

This series of works for decommissioning, demolition, inspection and tests contributedto LNG storage industry bringing knowledge of design and material technology of tanksused for 20 years, demonstrating of fitness of the above main components of aboveground LNG storage tanks as per either the old of current design code, etc.

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