Q V)CT/F2 ")U" 0Q66460 Method of Forming FRP Lining Background of invention Field of invention 5 This invention relates to an underground tank and, in particular, to a method of undertaking, in an existing underground oil reservoir steel tank, an activity of using an FRP (Fiber Reinforced Plastic) composite for forming an FRP lining. 10 Description of prior art Underground tanks are employed today for many gas stations and the like and used for storing oil products. Any underground tank, however, can develop corrosion and/or pitting 15 corrosion, which may leads to an oil leakage problem especially when it is used for many years. It is very difficult, however, to inspect from outside or from ground level visually such a tank for determining if the tank is deteriorated by such corrosion and/or pitting corrosion once it is buried in the 20 ground. Because of this constraint, pressurizing and depressurizing tests have been relied on for inspecting underground tanks and associated piping so as to determine if any oil leakage is taking place. The test is conducted so as 25 to determine a status concerned with corrosion, pitting corrosion, oil-leakage and so on, for example, by pressurizing or depressurizing the tank after closing valves at the oil inlet and suction pipes and all other openings such as vent pipes. According to the above-mentioned prior art system, an 30 examination device has to be designed for each underground tank to be inspected and a prior art examination device thus prepared is large in size. -Workability of such device is not good either. On the other hand, improvement has been made in the technology of opening a hole on an underground tank, and a method 35 has been proposed for opening a hole on an existing underground tank and modifying the hole into a manhole which enables a person to enter into the tank. Nothing is known however about procedures or execution schedules of activity undertaken in the tank. To be more specific, nothing is known about carrying out, in an underground tank, any work of using an FRP (Fiber Reinforced Plastic) composite for forming a lining. The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. Throughout the description and claims of this specification, the word "comprise" and variations of the word, such as "comprising" and "comprises", is not intended to exclude other additives, components, integers or steps. Summary of Invention The present invention has been made so as to overcome above-described problems and is related to undertaking, in an underground tank, an activity of handling an FRP composite in one hand and to a person entering the tank through an open hole for carrying out inspection and/or repair work of the tank in the other. According to the present invention there is provided a method of undertaking, in an existing underground oil reservoir steel tank, an activity of forming an FRP lining, the method comprising: an inspection process for conducting an inspection of the inside space of the underground tank for detecting flammable gases and determining concentrations of gases contained in the inside space; a process for introducing water into the underground tank, sprinkling oil-absorber material of V I V Vt. 4 A d -2a an organic composition 6ve the water s as to have the oil absorber material col ct floating oil like components, and discharging the water t a rainage after thus removing from the water the oil-like comp pe s and treatin the water further by an oil-water separation lumn; a tank opening process for forming an opening on It e underground tank; a tank washing process for washing the n de of the und rground tank on which the opening has been o d, sprinklin oil-absorber of an organic composition ov r ludge, pouri g a water-based 6% emulsifier solution o op of the oll-absorber material, minimizing the amount volatile gas mission, and finally discharging entire washi g mixture contained in the underground tank in one go; a priming process for applying a primer on the inside surface of the un rground tank; and a lining process for forming a lining of an RP composite on the inside surface of the underground tank. 1. The invention also rovides a method of undertaking, in an existing underground oil reservoir steel tank, an activity of forming an FRP lining, the method comprising: an inspection process for conducting a inspection of the inside space of the underground tank for det cting flammable gases and determining concentrations of gases Q ntained in the inside space; a process for introducing water int the underground tank, sprinkling oil absorber material of an o ganic composition over the water so as to have the oil-absorbe material collect floating oil-like components, and dischargi g the water to a drainage after thus removing from the water t oil-like components and treating the water further by an oil-w ter separation column;- a tank opening process for forming an o ning on the underground tank; a tank washing process for washi g the inside of the underground tank on which the opening has en formed, sprinkling oil-absorber of an organic composition o r sludge, pouring a water-based 6% emulsifier solution on op of the oil-absorber material, -2b minimizing the amount of volatile gas emission, and finally discharging entire washing mixture contained in the underground tank in one go; a priming process for applying a primer on the inside surface of the underground tank; and a -spreading process for spreading an FRP composite on the inside surface of the underground tank. Brief Description of the Drawings -3 Fig.1 is a drawing for describing structure of the lining formed in a tank in a manner according to an embodiment of the present invention. Fig.2 is a drawing for indicating the appearance of the 5 underground tank 1 and its peripheral area at a stage just after a series of the subject processes has been completed. Fig.3 is a drawing of a cross-section of the underground tank 1 for specifically indicating processes expedited in the tank for forming a lining. 10 Fig.4 is a drawing of a cross-section of the underground tank 1 for specifically indicating processes expedited in the tank for forming a lining. Description of Preferred Embodiment 15 We will describe in the following about an embodiment of the present invention by making reference to attached drawings. Fig.1 is a drawing for describing structure of the lining formed in a tank in a manner according to an embodiment of the present invention. In this drawing, the part indicated by item 20 number 1 is an underground tank of a kind installed underneath the ground of a gas station and the like. According to this drawing, the underground tank 1 is provided with an oil inlet pipe 2 used for receiving oil (gasoline), a suction pipe 3 used for sucking out oil (gasoline) from the underground tank 1, a 25 ventilation pipe 4 for venting the underground tank 1 and a measuring unit (not shown in this drawing) for measuring amount of dispensed oil (gasoline). This underground tank 1 is installed under the ground at a depth falling with a specified depth range and is covered by a slab of concrete 5. The oil inlet 30 pipe 2 is equipped with a valve 6 and the suction pipe 3 is equipped with a valve 7, and these valves 6 and 7 are kept in the closed position when undertaking activities of repairing or fixing the underground tank 1. We will now describe about processes of a set by which 35 an FRP lining is formed, wherein all these processes except for the tank opening process are carried out within the underground -4 tank 1 of the above-described construction. Conducted, in the first place, is the inspection of the inside space of the underground tank 1 for detecting flammable gases. This process is one in which concentrations of gasses 5 contained in the inside space are determined with a measuring tool, which is not shown in the drawing, and at the same time it is investigated whether any oil is leaking into the tank. If any of these gas concentrations and oil-leakage situation is determined abnormal, relevant action must be initiated 10 immediately for removing such an abnormality and establishing a safe working environment within the underground tank. Once the inside space of the underground tank is judged safe on the basis of the results of the foregoing process, discharge of oil (gasoline) contained in the underground tank 15 may be commenced. This process comprises steps of isolating such pipes as the oil inlet pipe 2 and suction pipe 3, dismantling of an oil inlet measuring unit, inserting a suction hose and sucking out all the oil (gasoline) contained in the tank by means of a pump such as a pneumatic drive pump or a pressure-resistant 20 explosion-proof pump. Then the underground tank 1 is filled with water and oil absorber material is sprinkled over the surface of this water. Here the introduction of water into the underground tank 1 is accomplished by using, for example, the oil inlet pipe 2 but 25 it only begins only after completing the foregoing process of oil-discharge. The volume of water introduced here is about 50% of the tank volume so that the water reaches its 50% level. After filling this much of water, the surface of this water is sprinkled with the oil absorber material of an organic 30 composition so as to have this absorber material collects floating residual oil. The water from which oil-like components has been thus collected away is released to a drain via an oil-water separator column, which is not shown in the drawing. Performed next is a water-pressure test of the 35 underground tank, oil inlet pipe 2 and suction pipe 3, which is for determining presence or absence of oil leakage. This test -5 is performed only after the above-mentioned floating oil removing process has been completed. This water-pressure test is performed by fully filling the underground tank with water and pressurizing it to 0.7 Kg/m. 5 This test is followed by a tank-and-pipe disengaging process for disengaging all the peripheral pipes from the underground tank. Coming next are marking and temporally-wall placing processes. The marking is made for specifying the position, 10 shape, size of the opening to be produced on the underground tank. Here the location of the opening needs to be selected by carefully reviewing a relevant structure plan of the underground tank and the placement of the fire-protection walls is done only after the marking of the opening has been completed. 15 These processes are followed by an excavation process for breaking the concrete slab 5 and digging the earth underneath. The drawing shown in Fig.1 indicates by reference number 5'the part dug out in this way of the concrete slab 5. This excavation process is progressed, first by cutting along the marking line 20 placed on the concrete slab 5 with a concrete cutter machine and then by crushing this part 5' of the slab 5 with a concrete breaker machine and digging the earth 8 until the underground tank is exposed. Next is a process of removing corrosion-protective 25 coating. In particular, only the part corresponding to the subject opening of the underground tank 1 coating is removed in this process. Next is a process for cutting the underground tank 1. A pneumatic-drive cutter machine is used for cutting the tank and 30 opening a hole to the tank. On completing this cutting process, a sealing water bath is removed. The drawing shown in Fig.2 indicates the structure of the underground tank 1 and its peripheral area as it is just after all the above-mentioned processes have been completed. Incidentally, the item indicated 35 by reference number 9 in this drawing is the cut-out opening. This cutting process is followed by a tank cleaning -6 process. This tank cleaning process starts from a step of pumping out water left in the underground tank 1 with a pneumatic drive pump or a pressure-resistant and explosion-proof pump and discharging it to a drain via a oil-water separation column. 5 Sludge remaining still in the underground tank 1 is sprinkled with oil-absorber material of an organic composition and further with a water-base solution containing 6% emulsifier for cleaning the tank so as the amount of volatile gas released later in the tank becomes minimal. The oil-absorber material is then 10 taken out from the underground tank 1 together with the dirt containing cleaning solution for disposal. When the tank cleaning process is completed as described above, an underground tank inspection process may be commenced. In this inspection, the entire surfaces of the inside structure 15 of the underground tank 1 is first inspected visually by exposing the real wall-forming substrate with a sand-blaster or buff-polishing tool such as a metal-wire brash. This inspection process is followed by another inspection process, which comprises reviewing locations and numbers of all 20 of the visually detectable corrosion developing points, scars, tool marks on the entire surfaces of the inside structure of the underground tank 1. The inspection process of this time includes, in particular: a pitting corrosion measuring step for measuring depth and determining location of every point found 25 associated with the pitting corrosion; a counting step for counting numbers of these pitting corrosion points; a wall thickness measuring step for determining wall thicknesses of all the structural parts inside the underground tank such as shells, mirror plates and so on with an ultrasonic thickness 30 gauge; and a liquid penetrant analysis step for analyzing such areas on the entire structure inside the tank as those associated with weld lines, nozzle-neck welds or damages, such as cracks, having been identified by the visual inspection. The liquid penetrant test is followed by a repairing and 35 fixing process. When it is found necessary to repair or fix the underground tank as result of the inspections or analyses -7 performed with respect to it, it is required to produce a restoration schedule best suited to the case of concern, which may only be a concession of such factors as the spare parts selection, repairing method, maintenance strategy, work period, 5 etc. In other words, it is required to decide which technologies or jobs are required for the case of concern among joint plate welding, weld cladding, corrosion protective coating, etc. and carry out so decided kind of repair and fixation work accordingly. 10 The process coming next is an FRP-lining formation process for undertaking, in a tank, an activity of using an FRP composite for forming an FRP lining. The lining formation process involves operation carried out in the tank and comprise a sand-blast step, a priming step, a prepreg layer placing step 15 for placing a pre-specified number layers of FRP prepreg sheets, and a curing step for curing the prepreg layers by UV-light radiation. Fig.3 and Fig.4 are drawings of cross sections of the underground tank 1 provided for illustrating the manner of 20 forming a lining in the tank. The underground tank 1, shown here, is a unit that has been fabricated originally from steel plates and has been given a due restoration job according to the above-described processes. Prepreg-sheets of an FRP composite are placed so as to cover the inside wall surfaces of the 25 underground tank 1. The FRP (Fiber Reinforced Plastic) composite here is one made of plastic-based, metal-based or rubber-based composite containing reinforcing fiber material of a high mechanical strength, of which examples are fiber-grass and carbon fiber material. 30 We will now explain in more detail on the manner of placing and adhering FRP prepreg sheets. Prepreg sheets 11 are placed and adhered to the inside walls of the underground tank 1 one after another starting from a pre-specified position on the walls after the substrate surface, i.e. the surface of these 35 inside walls has been covered with a primer coating in the aforementioned manner. In particular, the PRP prepreg sheets -8 11 are adhered to one after another in the counter clockwise direction from a pre-specified start position 10a to a pre-specified end position 10b, which are 2400 apart as indicated in the Fig.3 drawing, i.e., a cross section view of 5 the underground tank 1. The FRP prepreg sheets 11 employed for this process are of a type pre-spread with an adhesive and, therefore they can be placed on and adhered to the wall surface by removing them from associated plastic sheets (release paper sheets). It is 10 important to avoid trapping air between the inside wall 10 of the underground tank 1 and the FRP prepreg sheet 11 when placing the prepreg sheets 11 to the wall. This job of placing and adhering FRP prepreg sheets 11 must be progressed in the longitudinal direction starting from one end moving toward the 15 other end of the underground tank 1, and for covering the middle-and-low height 2400 wide region of the underground tank 1 in the first place. The process of placing and adhering FRP prepreg sheets 11 to the upper region of inside wall of the underground tank 20 1 is started after completing the job of covering the middle-and-low height region of the underground tank 1. The drawing shown in Fig.4 describes a placing and adhering process of a part for covering the top region of the underground reservoir tank 1. 25 As described in this drawing, the FRP prepreg sheets 11 are adhered this time to the region other than the middle-and-low height region that lies between the start position 10a and the end position 10b. Namely, the FRP prepreg sheets 11 are placed and adhered to one after another from the 30 start position of this time 10b toward the end position of this time 10a in the same counter clockwise direction so as to cover the top 1200 wide region of the inside walls of the underground tank 1. By progressing the placing and adhering process as 35 described in the foregoing, the entire surface of the inside walls of the underground tank 1 are covered by the FRP prepreg -9 sheets 11. These FRP prepreg sheets 11 are then cured by exposing them to UV light. When all these processes have been completed, a process for installing a manhole and an inspection hole is started. 5 Following the installation of these, the underground tank 1 is subjected to an air tightness test, which requires all the associated openings being closed completely. On confirming the absence of any leakage, the underground tank 1 is buried back and brought back to operation. 10 As described in the above, it becomes possible to repair and fix defects such as those associated with corrosion, pitting corrosion, an oil-leakage problem, which are arising on the walls of an underground tank in a truly reliable manner according to the embodiment of the present invention described 15 here, wherein said embodiment method comprises allowing a person entering into the underground tank 1 via the opening 9 produced on the underground tank 1 for undertaking activities of forming an FRP lining of a structure shown in Fig.3 and Fig.4 and of completing so required kind of restoration of the 20 underground tank 1. The underground tank 1 will never be free from age-related deterioration but once it is repaired and fixed in a manner specifying use of an FRP composite material the age-related deterioration becomes slower and hence it becomes possible to 25 use the underground tank 1 for longer years. In the above explanation of an embodiment of the present invention, the FRP sheets are first placed and adhered to the middle-and-low height 2400 region. But this may not be the 2400 region, and in correspondence to this change, the top region 30 covered by the FRP sheets may be change to include all the remaining top region. In the above explanation FRP sheets are used for forming a lining but it is possible to replace this liner forming procedure with an FRP layer forming process in which FRP 35 composite material is spread with a brush or the like to the inside walls of the tank, or an FRP layer forming process in -10 which FRP composite material is spray-applied to the inside walls of the tank. The step of spreading an FRP composite on the inside walls of the tank with a brush or the like is, for example, an activity 5 undertaken by a person who manually spreads the composite to the inside walls of the tank with a roller brush or a standard shape brush. The step of spray-applying an FRP composite on the inside walls of the tank is, for example, an activity undertaken by a person who holds a high pressure spray-gun connected from 10 a compressor spray-applying a flowable FRP composite on the inside walls of the tank. It is possible to employ either the brushing or spraying approach described above for forming an FRP layer on the inside walls of the underground tank 1 for completing the repairing 15 and fixing job of an underground tank 1 in a reliable manner.