JPH02107947A - External corrosion detector for buried metal pipeline - Google Patents

Abstract

PURPOSE:To enable detection (estimation) of an external corrosion of a metal pipeline simply by a method wherein a box body having a closed hollow part is buried at a position near the outer surface of a buried metal pipeline to introduce a pressure fluid into the hollow part of the box body and then, a change in pressure is monitored. CONSTITUTION:A box body 2 has closed hollow parts 3a-3c with wall thicknesses thereof of T1-T3 and formed to meet a requirement of Ts>T3>T2>T1 when a pipe thickness of a metal pipeline 1 is represented by Ts. A through hole 6 pierces each of the hollow parts, then, a pressure fluid introduction tube 7 is connected thereto as sealed while being opened at a manhole 8 at the other end of the tube 7. Then, a pressure fluid is introduced from the tube 7 leading to the hollow part 3a within the manhole 8 to apply a specified pressure to the hollow part 3a and a change in the pressure is checked with a manometer. When the pressure lowers, it is learned that a tiny hole is caused in the wall of the hollow part 3a. The same test is conducted for the hollow part 3b and then, that 3c. Thus, it is possible to presume that a corrosion of the same degree as that on the wall surface of the hollow part 3c occurs on the outer surface of the metal pipeline 1 with a confirmation that the pressure at the hollow part 3c can not be maintained.

Description

[Detailed Description of the Invention] This invention enables the degree of corrosion on the external surface of a buried metal conduit to be easily detected without excavating the buried portion and without destroying the conduit. This is related to a device that can do this.

Buried pipes such as water pipes and gas pipes are subject to high internal and external pressures, so these pipes are generally made of high strength steel pipes or ductile pipes whose outer surfaces are coated with paint or lining. A metal tube made of aluminum is used. However, in the case of such buried metal conduits, when used for a long period of time, the outer surface coating deteriorates over time, and as a result, the outer surface of the conduit corrodes due to the soil condition of the buried part or electrolytic corrosion, which leads to corrosion. As it progresses, the transport fluid may leak, or the pipe line may be destroyed due to lack of strength against internal and external pressure.

Therefore, in the maintenance and management of buried metal pipes as described above, it is an important task for managers (workers) to know when to replace them.

In other words, if the replacement time is delayed, leakage or destruction will occur, causing great impact and damage to local residents and customers who use the fluid transported in the pipeline, while if the replacement time is too early, there is still insufficient water available. Usable pipes will be discarded, resulting in a large economic loss.

To determine when to replace buried metal pipes, it is common to measure the remaining thickness of corroded pipes over time, and the conventional methods for measuring this pipe thickness are as follows: There are (1) a method for measuring pipe thickness by sampling, (2) a method for measuring pipe thickness by using an ultrasonic thickness meter.

Method (1) involves excavating the buried part of the metal conduit to expose the outer surface of the conduit, and after blocking fluid transport within the pipe (water cutoff, etc.) in the exposed part, a hole is made in the pipe using a drill, etc. A part of the tube piece is sampled, and the tube thickness is measured from the cross section of this sample.

Method (2) is similar to (1) in that the buried part of the metal pipe is excavated to expose the outer surface of the pipe, a part of the outer surface of the exposed part is polished, and then ultrasonic waves are applied to the polished part. A thickness gauge sensor is attached to measure the tube thickness using ultrasonic waves.

Problems to be Solved by the Invention By the way, in the two conventional pipe thickness measurement methods,
There are the following problems.

In the case of method (1), the buried portion of the metal pipe must be excavated to expose the outer surface of the pipe, which requires a great deal of labor and expense for excavation and backfilling. In addition, the impact on local residents, such as traffic disturbances, is significant.

(2) Since the transport fluid in the pipe must be shut off during the work, it causes great influence and damage to the users who use the fluid.

(2) It is necessary to repair the part where the sample was taken or replace the tube, which increases the cost.

In the case of method (2) ■, same as method (1) ■, if there is corrosion in a minute area such as pitting corrosion in the buried metal pipe, the ultrasonic thickness meter measures the pipe thickness accurately. Can not do it.

(2) It is necessary to polish a part of the outer surface of the pipe to be measured, so if the outer surface is severely corroded, the labor and cost will be enormous.

Therefore, the present invention solves the problems of the conventional methods and easily measures the degree of corrosion on the outer surface of metal pipes without excavating the buried part of the pipe or destroying the pipe as in the case of sample collection. The purpose is to provide a device that can detect

In order to achieve the above object, the present invention has a sealed hollow part near the outer surface of the buried metal conduit, and a separate casing made of the same material as the metal conduit. is buried with a part or the entire wall thickness thinner than that of the metal conduit, and one end of the pressure fluid introduction pipe for pressurizing the hollow part is connected in a sealed state to the sealed hollow part of this casing. At the same time, the other end of the introduction pipe is opened into a space such as a manhole or a side gutter.

Introduce pressure fluid from the other end of the pressure fluid introduction pipe opened in the space into the sealed hollow part of the casing, apply a predetermined pressure to the hollow part, and check whether the pressure can be maintained. . If pressure cannot be maintained in a sealed hollow part, it is found that holes, cracks, etc. have occurred due to corrosion on the outer surface of the casing around the hollow part, and this indicates that metal pipes buried under almost the same conditions It is estimated that the outer surface is corroded to the same extent as the minimum wall thickness of the casing.

On the other hand, if the pressure can be maintained in the sealed hollow part, it can be seen that there is no corrosion on the outer surface of the metal conduit, or even if corrosion occurs, it is less than the minimum wall thickness of the casing, and Tonosho and It is assumed that metal conduits can still be used in consideration of internal and external pressures such as fluid pressure.

In Figures 1 to 3, 1 is a metal conduit consisting of a plurality of pipes buried underground, and 2 is a separate housing made of the same material as the conduit. It is buried near the outside surface.

The casing 2 has a plurality of sealed hollow parts 3a, 3b, and 3c, and the thickness of at least one wall (the front and rear walls in the drawing) is T.
1. T2. Both are formed thinner than the thickness of the tube forming T3 and the metal conduit 1. That is, if the thickness of the tube forming the metal conduit 1 is, for example, T5, then T5>T3>T
2>T-shaped. Although not shown, the outer surface of the casing 2 is coated with the same anti-corrosion coating as the metal conduit 1. As shown in Fig. 2, the casing 2 and the metal conduit 1 are connected by a conductor 5 and kept at the same potential level in order to equalize the conditions for electrochemical corrosion (galvanic corrosion) due to local battery action. There is.

Communication holes 6 communicating with each hollow part 3a, 3b, 3c of the housing 2
are formed through the bottom wall thereof, and one end of a pressure fluid introduction pipe 7 made of a hard resin or the like having corrosion resistance and pressure resistance is connected to these communication holes 6 in a sealed state by an appropriate sealing means. The other end of the introduction pipe 7 is opened into a manhole 8 .

Since the introduction pipe 7 is for introducing pressure fluid into the hollow parts 3a, 3b, and 3e to pressurize the hollow parts, its durability is the same as that of the casing 2 that forms the hollow part 3c with the largest wall thickness. It needs to be at least better than the wall. The other end of the introduction pipe 7 that opens into the manhole 8 is normally closed with a plug. In addition, when the other ends of a number of introduction pipes 7 are collected into one manhole 8 and opened as in the embodiment,
Since it is unknown which introduction pipe 7 is buried in which hollow part of the casing 2, in such a case, it is desirable to attach a necessary identification mark to the other end.

In order to detect the degree of corrosion on the outer surface of the metal conduit 1 in the above,
An operator opens the other end of the introduction pipe 7 in the manhole 8, and introduces pressure fluid into the hollow part 3a of the casing 2, which has the thinnest wall thickness than the pipe thickness T5 of the metal conduit, and into the hollow part. Apply the specified pressure.

Whether or not the pressure can be maintained is checked using, for example, a pressure gauge installed at the other end of the introduction pipe 7 inside the manhole 8.

If the pressure cannot be maintained in the hollow part 3a and the pressure in the hollow part falls below the predetermined pressure, the casing 2 around the hollow part 3a
It can be seen that micropores and cracks were generated on the outer surface of the steel due to corrosion. Since the hollow portion 3a is sealed, corrosion from the inner surface of the hollow portion 3a of the casing 2 is unlikely, and it is clear that the occurrence of the holes is due to corrosion on the outer surface of the casing 2.

If it is confirmed that the pressure in the hollow part 3a cannot be maintained, then pressurized fluid is introduced into the hollow part 3b from the introduction pipe 7 to check whether the pressure can be maintained. Then, when it is confirmed that the pressure cannot be maintained in the hollow part 3b as well.

Further, pressure fluid is introduced into the hollow portion 3c from the introduction pipe 7, and it is confirmed whether the pressure can be maintained.

When it is confirmed that the pressure cannot be maintained in the hollow part 3c, the wall thickness T3 of the hollow part 3c is thinner than that of the metal conduit 1, but is usually formed to a thickness very close to this, and Since the casing 2 is buried under almost the same conditions as the metal conduit 1, it can be seen that micro holes and cracks have occurred on the outer surface of the casing 2 around the hollow part 3c due to corrosion. It is presumed that the same degree of corrosion has occurred on the outer surface of the metal conduit 1, that is, corrosion to the extent that it reaches most of the thickness of the metal conduit. Of course, if the pressure cannot be maintained up to the hollow part 3a or 3b, but can be maintained in the hollow part 3c, it can be assumed that the corrosion has reached the wall thickness of the hollow part 3a or 3b, which cannot be maintained. Metal conduit 1
This means that it is possible to know the degree of corrosion, that is, the degree of progress of corrosion. Therefore, it can be seen that the metal conduit 1 still has a considerable thickness if it can be maintained in the hollow part 3c as described above, and it is presumed that it can be used for the time being. Furthermore, by periodically checking whether the pressure is maintained, it is possible to know the rate of progress of corrosion, and it is also possible to estimate the usage limit of the metal conduit 1.

In the above embodiment, an example of the casing 2 having a plurality of hollow parts 3a, 3b, and 3c was shown, but in order to simplify the manufacturing of the casing, a casing having a single hollow part is manufactured and a plurality of casings are made. If the purpose is to know only the limit value, a housing with a single hollow part may be buried to simplify detection.
You may bury just one. Furthermore, in order to improve detection accuracy, a plurality of casings having equal wall thickness may be buried adjacently. Furthermore, although the manhole 8 has been mentioned as the space where the other end of the introduction pipe 7 opens, it goes without saying that it may also be a side gutter or the like.

Further, in the above embodiment, the hollow portions 3a, 3b, 3c and the casing 2 have a rectangular shape, and the hollow portions are formed integrally, but this is only an example, and similar effects can be achieved. As long as it can be obtained, other shapes and structures such as those shown in FIGS. 4 and 5 may be used regardless of the shape and structure.

In the embodiment shown in FIG. 4, the casing 2' is made into a hollow cylindrical shape, and the hollow part 3 in the circumferential direction has a wall thickness of T 4 > Ta > T 2 > T1 due to the cross-shaped partition 10 provided integrally.
'a, 3'b, 3'c, 3'd are formed (
T4 < T5). Although not shown, the housing 2'
As in the previous embodiment, the communication hole as described above is formed and the pressure fluid introduction pipe is connected thereto.

In the embodiment shown in FIG. 5, the casing 2# is made of a casing body 11 and a lid 12 made of the same material as the metal conduit 1, respectively. The housing body 11 has a wall (bottom wall) thickness of T 3 > T 2 >
Hollow parts 3"a, 3"b, 3"C of the upper end opening of T1 are formed (T□<T,). Hollow parts 3"a, 3"b
, 3"c, the lid body 12 covers the upper end opening of the sealing material 1.
3 interposed therebetween, and is fixedly tightened with bolts and nuts 15.

If the housing body 11 and the lid body 12 are made of a weldable metal material, the lid body 12 may be directly welded to the housing body 11 instead of the bolts and nuts 15. and,
In this example, the communication hole as described above is formed in the lid body 12,
A pressure fluid introduction pipe is connected.

Since this invention has the above-described structure, it has the following effects.

(2) The degree of corrosion on the outer surface of a metal conduit can be easily detected without excavating the buried portion of the metal conduit and without destroying the conduit.

(2) Moreover, the labor and cost required for the work are less than those of conventional methods, and the workability and economy are extremely good.

■It has almost no impact on local residents, and since there is no need to cut off the transport fluid (water outage, etc.), there is no inconvenience to customers who use the transport fluid.

(2) It can be carried out not only for newly installed underground pipelines but also for existing underground pipelines. Moreover, detection at any location near the outer surface of the buried pipeline is possible.

[Brief explanation of drawings]

FIG. 1 is a front view showing one embodiment of the present invention, FIG. 2 is an enlarged side sectional view taken along the line ■-■ in FIG. 1, and FIG. Enlarged front cross-sectional view, (B) is (A)
II[B-I[[Enlarged cross-sectional view along line B, Nos. 4 and 5
Each figure is an enlarged side sectional view showing another embodiment of the housing. 1... Metal conduit 2... Housing 3a, 3b,
3c... Sealed hollow part 5... Conductive wire 6... Communication hole 7... Pressure fluid introduction pipe 8... Manhole patent applicant Kurimoto Iron Works Co., Ltd.

Claims (1)

[Claims] 1. A separate casing, which has a sealed hollow part near the outer surface of the buried metal conduit and is made of the same material as the metal conduit, and whose wall thickness is partially or entirely similar to that of the metal conduit. One end of the pressure fluid introduction pipe for pressurizing the hollow part is connected in a sealed state to the sealed hollow part of this casing, and the other end of the introduction pipe is connected to a space such as a manhole or side gutter. A device for detecting the degree of corrosion on the external surface of a buried metal conduit, characterized in that it has an opening.