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CASES OF DIAGNOSES AND LIFE EXTENTION MEASURES OF LNG FACILITIES AT TOKYO GAS NEGISHI AND

SODEGAURA RECIEVING TERMINALS

EXEMPLES DE DIAGNOSTIC ET DE MESURES DE PROLOGEMENT DE LA DUREE DE VIE DES INSTALLATIONS

DE GNL AUX TERMINAUX D’ARRIVEE DE NEGISHI ET DE SODEGAURA DE TOKYO GAS

Akio Kobayashi LNG Facilities Engineering Sect., Negishi LNG Terminal

Tokyo Gas Co., Ltd. 34,Shin isogo-machi, Isogo-ku

Yokohama-shi, Kanagawa pref. Japan a-koba@tokyo-gas.co.jp

Hiroshi Hiraga LNG Facilities Engineering Sect., Sodegaura LNG Terminal

Tokyo Gas Co., Ltd. 1-1 Nakasode, Sodegaura-shi, Chiba pref. Japan

hhiraga@tokyo-gas.co.jp

ABSTRACT

Tokyo Gas Co., Ltd. began receiving shipments of what was Japan's first import of liquefied natural gas (LNG) in 1969, and therefore already has more than 30 years of experience in the operation and maintenance of LNG receiving terminals. Aged LNG-related facilities in these terminals are subject to the occurrence of various phenomena associated with deterioration, and such occurrences are anticipated to increase over the coming years. Meanwhile, there are needs for effective use of aged LNG facilities into the long term while maintaining their reliability, and also for reduction of their operating cost.

For that reason, in addition to exhaustive analysis and diagnosis of aged facilities, Tokyo Gas is developing technology and countermeasures for minimizing life cycle costs.

This paper presents a profile of the countermeasures being taken by Tokyo Gas for facility deterioration by aging, and describes cases of deterioration diagnosis and countermeasure deployment.

RESUME

Depuis la première importation du gaz naturel liquéfié (GNL) au Japon en 1969, cela fait plus de 30 ans que Tokyo Gas Co., Ltd. exploite et entretient des terminaux de réception de GNL. Les installations vieillissantes relatives au GNL dans ces terminaux sont sujettes à divers incidents associés à la détérioration, et de tels incidents

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augmenteront au cours des années à venir. Par ailleures, il y a une forte demande d’utiliser efficacement les installations de GNL vieillissantes pour une période prolongée tout en maintenant leur fiabilité et de réduire leur coût d’exploitation.

De ce fait, en plus des analyses et des diagnostics exhaustifs de vieilles installations, Tokyo Gas aborde actuellement le développement des technologies et des contre-mesures pour minimiser les coûts du cycle de vie.

Ce rapport présente un aperçu des mesures prises par Tokyo Gas contre la détérioration des installations due au vieillissement, et décrit des cas de diagnostic sur la détérioration et des mesures appliqués.

1. INTRODUCTION

Tokyo Gas owns the three LNG terminals shown in Table 1. Of these, deterioration caused by facility aging is proceeding at the Negishi and Sodegaura terminals, which were placed into operation in the 1960s and 1970s, respectively. As such, Tokyo Gas formulated policy for countermeasures specific to each type of facility and deterioration mode, and is proceeding with the work of diagnosis and implementation of countermeasures in accordance with it.

Table 1 Major LNG terminals of Tokyo Gas

Terminal Month and year of start-up

Comments

Negishi November 1969 The first LNG receiving terminal in Japan Sodegaura July 1973 The biggest LNG receiving terminal in Japan Ohgishima December 1998 The state-of-the-art LNG receiving terminal

2. PROFILE OF COUNTERMEASURES FOR DETERIORATION IN AGED LNG FACILITIES

2.1 Basic Perspectives

Tokyo Gas is promoting countermeasures in line with the perspectives noted below toward the goal of both maintaining the reliability and lengthening the service life of aged LNG facilities. - Assessment of aging phenomena with a view to lengthening the service life to at least

50 years even in the case of aged LNG facilities dating from the start of LNG import in Japan

- Assessment of not only facilities where age-related phenomena are already surfacing but also facilities where fatigue and other latent age-related phenomena are progressing.

- Use of the assessment results as the basis for revision of maintenance management plans for facilities and execution of countermeasures and management to lengthen the service life of aged facilities

- Performance of checks, diagnoses, and countermeasures for aging phenomena as necessary for carrying out the facility assessments and countermeasures, and development of technology for the lengthening of service life and reduction of the life cycle cost(LCC)

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2.2 Profile of Countermeasures

At the Negishi and Sodegaura terminals, deterioration phenomena have consequently surfaced in facilities in all phases, from receiving to vaporization and sendout. In addition, there is a wide-ranging assortment of materials including metals, non-metals, and concrete, and the mode of deterioration ranges from ordinary corrosion and abrasion to fatigue.

As such, Tokyo Gas examined deterioration phenomena of each type of facility and composition parts, and implemented to assessments and measures to these phenomena. And in implementation, various development of technology was performed and it was applied to actual Equipment. Table 2 shows Major Facilities and measures against deterioration.

Moreover, Tokyo Gas has adopted risk-based maintenance (RBM) that takes into account the effect of facility failure on operation, security, and environment based on the failure data we have accumulated thus far. And the plan and performance of maintenance was assessed quantitatively from a viewpoint of reservation of the reliability of facilities.

Table 2 Major Facilities and measures against deterioration

Facility Deterioration Measure, Disposal, etc. Salt damage of concrete structures

Inspection, Diagnosis, Repair, Coating

Deterioration of rubber fenders

Inspection, Diagnosis, Replacement

Berths

Corrosion of piles Inspection, Diagnosis : No problem Corrosion of each parts Inspection, Diagnosis, Repair Corrosion of piles Inspection, Diagnosis : No problem

Above ground LNG tanks

Deterioration of diaphragms of breathing tanks

Inspection, Diagnosis, Replacement

Fatigue of roofs Inspection, Diagnosis : No problem Fatigue of membranes Inspection, Diagnosis : No problem

In-ground LNG tanks

Corrosion of each parts Inspection, Diagnosis, Repair Salt damage of concrete structures

Investigation, Diagnosis, Repair, Coating Open-rack vaporizers

Corrosion Inspection, Diagnosis, Improvement of corrosion-proof

LNG cryogenic pumps

Deterioration of motors Inspection, Diagnosis : No problem

Sea water pumps Crevice corrosion Improvement of structures, Coating Performance fall Inspection, Diagnosis, Replacement Insulation of

LNG Pipelines Corrosion of plates Replacement with stainless steel sheets Cryogenic valves of LNG pipelines

Corrosion of carbon Steel parts

Replacement with stainless steel parts

Carbon steel pipes

Corrosion in support parts

Improvement of support structures

Electrical facilities

Functional fall of each equipment

Inspection, Diagnosis, Replacement, Improvement of environment of installation place(Air-conditioning)

Instrumentation equipment

Precision fall, corrosion Inspection, Diagnosis, Replacement

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Tokyo Gas is promoting the countermeasures for deterioration of aged LNG facilities shown above. The succeeding sections present cases of such countermeasures with a focus on technology development and application.

3. DEVELOPMENT AND APPLICATION OF TECHNOLOGY FOR CHECKING AND DIAGNOSIS OF AGED LNG FACILITIES

Tokyo Gas is developing technology for items that cannot be checked and diagnosed with the conventional technology, and is applying it for checking and diagnosis of actual facilities.

For the purpose of example, this section presents an account of the development and application of technology for checking and diagnosis of underground LNG tanks.

3.1 Checking and Diagnosis of In-ground LNG Tanks

Tokyo Gas utilizes a total of 29 in-ground LNG tanks, the oldest of which was constructed some 30 years ago. Continued operation of terminals with a high level of dependability and low level of cost will require continued use of the installed tanks into the long term, determination of their degree of deterioration, and preparation of countermeasures as necessary. There has been no surfacing of deterioration on major structural elements of underground tanks, such as their roofs and membranes. However, damage due to fatigue or other causes would have a tremendous impact on operations and safety.

To check and diagnose these elements with the conventional technology, it is necessary to fill the tanks with air and overhaul them. This, in turn, entails a huge cost and shutdown of the tank for a long time, with a big impact on operations. Tokyo Gas consequently developed technology for checking and diagnosis without taking the tanks out of service, and is applying it to actual tanks.

3.2 Diagnosis Technology for Roofs

Thus far, it has been difficult to assess the degree of deterioration in parts such as fillet welds on the inner side of roofs while tanks are in service. Tokyo Gas established technical means of analysis and inspection for diagnosis of the deterioration at such parts, and applied it to actual tanks.

3.2.1 Profile of the Diagnosis

The diagnosis of roof deterioration was carried out by the following procedure. Figure 1 shows the overall diagnosis flow.

- Selection of the parts requiring diagnosis based on the results of analysis of the growth of fatigue cracks.

- Inspection of the actual tank

- Assessment (diagnosis of remaining service life)

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Figure 1 Roof diagnosis flow

3.2.2 Analysis to Determine the Growth of Fatigue Cracks

(1) Overall analysis of the roof

First, an axisymmetric model was used for the roof as a whole to obtain the parts with a high stress fluctuation by an FEM analysis(see Figure 2). The inputted loads were the internal pressure, dead load plus the load of attachments, framework displacement, and temperature load. The internal pressure and temperature were varied in such loads. The analysis confirmed that there was a big stress amplitude on the outer roof perimeter.

(2) In-depth analysis of the roof

Next, an FEM analysis was made of the detailed model of the outer roof perimeter (see Figure 3) to derive the detailed stress amplitude, and selected the locations that could possibly have cracks.

(3) Analysis of crack growth

For the locations identified as possibly having cracks in the in-depth analysis, an FEM stress analysis and crack analysis (for the K value) were carried out to assess crack growth. For locations where cracks were possibly growing, a calculation was made of the amount of growth assuming a service life of 50 years.

1) Load conditions

In light of the action of fluctuation in internal pressure and temperature during ordinary operation, analyses were made for two cases of load condition: design load and real (historical) operating load.

Decision on crack growth ΔK is greater than ΔKth

<Overall roof analysis>Plots for fluctuating load

<Fluctuating load>Internal puressure and

temperature

Selection of parts requiringinvestigation of crack growth

<In-depth localized analysis of partsrequiring investigation of crack growth >

Determination of the location andgrowth direction of cracks

Calculation of the stressexpansion coefficient (ΔK)

ΔKth: lower limit of crack growth

End:crack isnot growing

No

Analysis of crack growth(50 yeras)

Determination of the correlation betweencrack measurements and crack growth

<Selection of the inspectionequipment and method>

<Flow of analysis> <Flow of inspection>

<Establishment of the inspectionmethod>

the test of probes and detectionmethods

<Inspection of the acutualequipment>

Yes

<Flow of diagnosis>

<Diagnosis of the reimaining service life>Diagnosis based on the results of the analysisof crack measurements on actual equipment

Decision on remaining lifeT is more than 50 years

Yes

No

Confirmation of reliabilityfor 50 years

Study ofmeasures,etc.

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2) Analytical method

The stress expansion coefficient on the crack tip (∆K) was calculated using the model containing plots for the initial crack depth (a) chosen as deemed appropriate on the model for in-depth analysis of the roof(see Figure 3). The result was compared with the lower-limit stress expansion coefficient (∆Kth) to decide on the possibilities of crack growth.

For locations where cracks were judged to be possibly growing, an FEM analysis

was carried out to change the crack depth (a) and obtain the ∆-K-a relationship. Then, data for the speed of crack growth in materials were used to calculate the amount of growth over 50 years of service.

Where: C,n= constant

A step calculation was made on the basis of the load conditions using these da/dN-∆K (Paris law) and ∆K-a relationships.

3) Results of analysis

Figure 4 presents the results of analysis in an actual case. It shows curves for crack growth on the welding line of the roof perimeter, with plots for each case of load condition.

屋根板

胴板

溶接部

溶接部

コンプレッシ

ョン リング（Ｃ／

Ｒ）

Roof panels

Shell plate Weld

Weld

Weld

Compression ring

Figure 2 Overall roof analysis model

Figure 3 Sample in-depth analysis model for outer roof perimeter

Shell plate

C / R

( ) nKCdNda .ƥ=

Figure ４ Crack growth curve (results of analysis)

Design load

Real operatingload

Plate thickness

1

1Internal crack depth : a

Am

ount

of c

rack

gro

wth

for 5

0ye

ars :

△a

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3.2.3 Establishment of the Inspection Method and Inspection of Actual Equipment

(1) Establishment of the inspection method

The inspection of crack measurements at the parts selected through the analysis described above was made by ultrasonic detection.

We prepared a test piece with a quasi-flaw at the roof perimeter and performed the test. Based on the test results, we selected an optimal combination of a detection probe and a detection method for each type of part, and performed the inspection on actual equipment.

(2) Inspection of actual equipment

Because the inspection ranges over a wide scope, we performed a rough detection to screen flaw locations. This was followed by a precise detection to take the flaw measurements for locations that exceeded the detection level in the rough detection. The flaw measurements were obtained by automatic image processing of the measured data. Figure 5 shows the actual equipment inspection with the automatic detection unit.

3.2.4 Diagnosis of Remaining Service Life

The remaining service life was assessed from the crack measurements judged to be problems based on the analysis and the crack measurements detected on the actual equipment. The assessment revealed that there was no possibility of damage to the roof due to fatigue even in continued operation for the next 50 years in the same manner as at present.

3.3 Development of a Submersible Observation Unit for In-ground LNG Tanks and Application to Actual Equipment

For the purpose of checking the membranes inside tanks without overhauling them, Tokyo Gas developed a unit for internal observation that can even be submerged in LNG. A check of the interior of aged tanks confirmed the absence of problems.

Figure 5 Inspection of actual equipment

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3.3.1 Features of the Submersible Observation Unit

The features of the submersible observation unit developed by Tokyo Gas are noted below. The unit is compact, light-weight, and easy to handle. For these reasons, it can be used to check the interior of tanks in a short time in the event of earthquakes or other emergencies.

- Ability for use even in LNG

- Compact size enabling insertion into tanks from nozzles of at least the 6B size

- Compact size and light weight enabling observation solely with human force

- Ability to perform internal checking within about one week, inclusive of the preparations and restart-up

3.3.2 Results of Membrane Observation

Since 2000, the newly developed units have been used to check membranes, one after the other, with consideration of the number of years after construction and type of membrane model. The newly developed units confirmed that there was no abnormal deformation or other such problems in membranes. Figure 6 and 7 show the pictures when checking membranes.

4. DEVELOPMENT AND APPLICATION OF TECHNOLOGY FOR

AGE-RELATED DETERIORATION

Tokyo Gas is developing technology of countermeasures against deterioration phenomena of the sort that would cost too much, and is applying this technology to actual equipment.

For the purpose of example, this section describes the application of technology to counter deterioration of concrete and the development of maintenance technology for LNG-use cryogenic valves.

4.1 Technology to Counter Deterioration of Concrete

4.1.1 Conventional Technology and Problems

Concrete structures that are in contact with sea water and spray, such as berths for LNG tankers and frames for open rack vaporizers (ORV), are subject to corrosion by salt.

Figure 6 Corner of the in-tank membrane

Figure 7 Expansion of the bottom membrane

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Beginning in the 1980s, Tokyo Gas focused on such corrosion and started to implement separate countermeasures for older and newer structures.

For older concrete structures (i.e., those installed in the 1970s), Tokyo Gas started to apply surface coatings to isolate them from the environment. However, before they were coated, the concrete structures had been affected by the inner diffusion of chloride ions within the sea water that had penetrated the concrete. The penetration caused the corrosion and expansion of reinforcing bars, and it was possible that this affected the strength of the concrete.

Figure 8 shows a case of actual damage from salt, Figure 9 the incidence of such damage, and Figure 10, salt penetration and diffusion.

For newer facilities (i.e., those installed since the 1980s), it was decided to take the measure of making the cover of concrete from the surface to the main reinforcing bars thicker. This produced a comparatively high durability, but cases of corrosion of the main reinforcing bars have been surfacing in recent years.

In response, we investigated the degree of deterioration for different cover thicknesses and actively adopted new technology with consideration of factors including the remaining service life of the structures, workability, and cost. In addition, countermeasures that take account of LCC were carried out.

Figure 9 Incidence of salt damage

Stratiform scaling Corrosion of reinforcing bars due to chlorides

Surface coating

Figure 10 Salt penetration and diffusionDepth from the surface

Initial period

After several years

発錆限界Rusting limit

Location ofreinforcing bars

Salt

conc

entra

tion After surface

coating

Figure 8 Salt damage to concrete

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4.1. 2 Technology to Counter Deterioration on LNG Tanker Berths

(1) Deterioration of berths

Berths for LNG tankers are subject to damage from salt because they are built on the sea. The berth at the Sodegaura Terminal is particularly exposed to such damage because they jut about 400 meters into Tokyo Bay.

In addition, insulating sea water is sprayed on the tanker-side panels directly below the connection flanges on the pipe between the tanker and berth. This is to avoid damage to the tanker in the event of LNG leakage from the flange. The herths are sprayed with sea water each time an LNG shipment is received (see Figure 11). Coupled with the aforementioned siting conditions, this makes for an extremely harsh environment as far as corrosion is concerned.

Berths that have been in service since the start of terminal operations are therefore experiencing the outbreak of reinforcing bar corrosion and expansion due to a rise in the chloride ion concentration, and cracks on the concrete surface.

Berths built in the 1960s and 1970s were equipped with an isolating surface coating once they had been in use for ten or so years. However, since chloride ions has already permeated concrete and deterioration of surface coating has been expanded, there is a possibility that the strength of concrete may fall owing to the corrosion and expansion of reinforcing bars in service over the long term.

(2) Application of new technology

Countermeasures for deterioration on berths faced the problems noted below. The application of new technology made it possible to lengthen the service life of facilities and lower their LCC.

- The chloride ions that had penetrated the concrete before repair spread inside it even after surface coating and caused corrosion of reinforcing bars.

- Work on berths entails a cost that is higher than work on other facilities because of the lower pace of operations due to the adverse siting conditions and the inability to work while tankers are docked.

1) Study of the penetration of chloride ions and scope of removal

To prevent the expand of deterioration in service over the long term (the next 25 years), concrete which had been penetrated by chloride ions was removed, and new concrete which had not contained chloride ions restored. The scope of removal and

Figure 11 LNG tanker Sprayed with sea water

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restoration was determined upon analysis to predict the spread of ions over the next 25 years. This analysis was executed by the following procedure.

- We made an in-depth survey of the extent of chloride ion diffusion in the concrete on the actual facility.

- The survey results (concentration distribution) and depth remaining after removal and restoration of the concrete were used to determine the chloride ion concentration at the location (depth) of the reinforcing bars 25 years later.

- We made analyses at varying depths of concrete removal and restoration to determine the depth at which the chloride ion concentration at the reinforcing bar location (depth) would definitely be lowered, and applied this as the scope of concrete removal and restoration.

2) Application of the FRP form method

The fiber-reinforced plastic (FRP) form method was applied to curtail the construction cost and lengthen the service life of coating. This method is characterized by the following features.

- Instead of surface coating material, FRP is used as a fill-up form for pouring concrete, and this eliminates the need for the work of removing the form.

- The method offers higher levels of reliability and durability than ordinary coating for sealing out salt, etc.

Figure 12 presents a diagram of the FRP form method, and figure 13, a picture of the facility after completion of the work.

4.1.3 Technology to Counter Deterioration on ORV Frames

(3) Deterioration of ORV frames

On ORVs, the concrete frame mounted with vaporizer panels is subject to damage from salt from the sea water sprayed on the vaporizing panels in ORV operation and the splash from this sea water spray. It was confirmed that the repeated wetting and drying of the concrete as the facility is put into and out of operation resulted in the levels of chloride ion concentration that were extremely high as compared to those in the aforementioned berths.

bar

Figure 12 Conceptual diagram of the FRP form method

Anchor Reinforcing

Filling

FRP form

Figure 13 Facility after execution of the FRP form method

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Even if given a surface coating, the frames constructed in the 1970s suffered a crack on the concrete and coating about five years later due to the action of the chloride ions accumulated within the concrete. Moreover, chloride ions began to penetrate from the cracked spots.

(1) Assessment in application of new technology

The following problems are associated with countermeasures for ORV frames.

- The damage from salt is extensive, and the proof stress of the concrete frame is lowered due to corrosion of the reinforcing bars.

- Mere removal and restoration of the concrete close to the surface as in the case of the berths would be insufficient to prevent recurrence, and the scope of removal and restoration would have to be larger and its cost also would become high.

- Cracking recurs relatively soon after surface coating, and accelerates the infiltration of chloride ions.

In response to these problems, technical assessments were made on the prospect of applying the carbon fiber sheet gluing method, which has a record of use in connection with reinforcement to prevent damage from earthquakes. The method was expected to yield the following performance effects.

- Recovery of proof stress that had been lowered by the extensive damage from salt - Prevention of cracking due to infiltration of the concrete by salt - Sure sealing out of chloride ions and other causes of corrosion

The test shown in Table 3 was conducted for assessment of application. The weatherproof testing was premised on long-term service for the next 30 years and consisted of a test by accelerated exposure based on the Japanese Industrial Standards (JIS).

As the test results confirmed that the performance was adequate, the method was applied to actual facilities. Figure 14 shows the results of a crack restraint test, and Figure 15, a diagram of the method actually applied.

Table 3 Outline of the test for application

of the carbon fiber sheet gluing method

Test items Test description Test of axial force maintenance performance

Affixing of the sheet to a concrete test piece with a slit in the axial direction (in consideration of the frame pillars), and confirmation of improved compression strength

Crack restraint test of carbon fiber sheet

Use of expansion materials to induce cracks in a concrete test piece, and confirmation of the crack-restraining effect of the sheet

Weatherproof test of carbon fiber sheet

Accelerated exposure test for confirmation of the influence of ultraviolet rays, chloride ions, and moisture on the long-term adhesion capabilities of the sheet

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ORVs constructed in the 1970s and other periods were divided into three groups (based on the year of construction) in light of the results of the survey of deterioration due to salt damage and LCC. Different methods are applied for each, as shown in Table 4.

Table 4 Countermeasures for salt damage to ORV concrete

Year of construction

1973-1979 1983 1985-1989

Reinforcing bar covering

50mm 70mm 100mm

Reinforcing bar corrosion

High Low None

Countermeasure method

Carbon fiber sheet method

Cross-section repairing plus

surface coating

Surface coating

4.2 Development of Maintenance Technology for LNG Cryogenic Valves

4.2.1 Deterioration Status

The LNG cryogenic valves installed before the 1970s had stainless steel parts that were in contact with LNG, but the valve stem seal parts and operating parts were made of carbon steel, and are consequently being corroded (see Figure 16).

炭素繊維シート主筋方向２層帯筋方向１層

炭素繊維シート主筋方向２層帯筋方向１層

プライマ－プライマ－

Figure 14 Diagram of the carbon fiber sheet gluing method

Primer

Carbon fiber sheet

Without reinforcement with the carbon fiber sheet

With reinforcement with the carbon fiber sheet

(no break on the sheet)

Figure 15 Results of the crack restraint test

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This created apprehensions about the risk of breakage and LNG leakage due to the corrosion and thinning of the carbon steel components as the duration of use lengthened.

4.2.2 Policy for Countermeasures

As a measure for LNG cryogenic valves affected by corrosion, Tokyo Gas made plans to replace the components made of carbon steel with others made of stainless steel. Countermeasures are being promoted in accordance with the following guidelines, which were formulated with consideration of requisite cost and influence on operations.

- The cryogenic valves on the LNG discharge line on the pipeway are to be replaced by shutting down the LNG line and refilling it with inert gas.

- For the No. 1 valves on the LNG tank, whose replacement would require even the tank to be refilled with inert gas, as well as for the recieving and boil-off gas (BOG) lines, which would be difficult to shut down because of the influence on operations, we develop and apply technology for replacement of corroded components and other valve maintenance without purging the lines.

4.2.3 Development of Maintenance Technology for LNG Cryogenic Valves

Below Live Lines

Tokyo Gas has developed several types of method and equipment in correspondence with the type of maintenance in respects such as valve type, scope of replacement, and fit of the seat surface. This technology is being used to maintain valves without purging the line. This section describes some of the major such equipment developed by Tokyo Gas.

(1) Valve Maintenance Device 1

Figure 17 shows the first such device to be developed. Its application made it possible to replace the valve yoke and ground support without purging the line of LNG, by application of external force to the valve seat while keeping the valve closed.

(2) Valve Maintenance Device 2

The device 1 in Figure 17 did not enable replacement of the ground packing and bonnet gasket, or maintenance of the seat surface fit. The device developed in response is shown in Figure 18. It still requires purging of the liquid in the line, but can be used in a BOG atmosphere and at low temperatures. It enables safe removal of the top part of the valve bonnet, which it seals. It also enables grinding of the seat

handle(Cabon Steel)

Yoke(Cabon Steel)

Ground Support（Cabon Steel）

Ground Support Bolt（Cabon Steel）

Heat Discharge Plate（Cabon Steel）

Valve Bonnet（ＳＵＳ）

Figure 16 Valve structure

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surface on the valve box below the bonnet by means of a special jig. This makes it possible to restore the valve seal performance, which declines as the number of years in service rises.

The development of these devices made it possible to implement countermeasures for the No. 1 valves on LNG tanks as well as receiving and BOG lines, for which it had been difficult to execute countermeasures even if deterioration had surfaced.

4.3 Development of LNG Tank Valve Replacement Technology

Tokyo Gas is developing technology for replacement of main valve units and displacement level gauges on aged tanks without purging them. The device developed for replacement of main valve units is now undergoing testing, and prospects for its application to actual tanks are basically good.

5. CONCLUSION

Tokyo Gas intends to continue with the execution of these countermeasures for facility aging and development of related technology in keeping with its goal of making the cost of terminal operation even lower while maintaining levels of reliability.

By way of conclusion, the authors would like to express their gratitude to all concerned parties inside and outside Tokyo Gas for their valuable support and advice in the development of technology and implementation of countermeasures.

REFERENCES CITED

[1] Guidelines and commentary on fatigue design for steel structures, Japanese Society of Steel Construction (JSSC)

[2] The American Petroleum Institute, API581 First Edition (2000)

Figure 17 Replacement of carbon steel components

(Device 1)

Figure 18 Replacement of components above the bonnet

(Device 2)