JP2005307329A - Corrosion prevention method for weld zone of piping - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform corrosion prevention operation of excellent quality free from air voids caused by the entanglement of the air, regarding the method for subjecting the weld zone of piping welded in a sheath pipe buried underground to corrosion prevention with a heat-shrinkable tube where the size of the sheath pipe is reduced, so as to attain the reduction of construction expenses, by automating corrosion prevention construction or the like including welding, so as to correspond to the reduction of the space occupied by the sheath pipe, and further by performing the corrosion prevention operation with a heat-shrinkable tube under the reduced pressure even after the welding. <P>SOLUTION: Regarding the corrosion prevention method for the weld zone of piping in a sheath pipe, at the time when piping is welded in a sheath pipe, and the weld zone is subjected to corrosion prevention with a pipe-shaped heat-shrinkable tube, a vertical halving type cylindrical vacuum heating furnace made of duralumin or aluminum by far-infrared rays is, in the sheath pipe, moved sideways to the weld zone with wheels by hands, and heating is performed under the reduced pressure of ≤600 mmHg, and the degree of vacuum, heating temperature, heating starting time, a warning device, the flashing of a signalling lamp or the like are automatically controlled by a control panel, and the heat-shrinkable tube is thermally shrunk. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

Detailed Description of the Invention

Industrial application fields

The present invention relates to a method for preventing corrosion of a welded portion of a pipe welded in a sheath pipe buried underground with a heat-shrinkable tube.

Problems to be solved by the prior art and the invention

When burying gas pipes and other pipes on roads, it is common to use the open-cut method with low construction costs, but in the case of high-traffic roads or roads that are likely to be underground, The shield method and the propulsion method are often applied in consideration of the increase in construction costs due to the prolonged period and the influence on the surrounding residents.

Due to the remarkable progress in technology in recent years, when pipes are installed in long extension pipes where long-distance construction is common for shield construction methods and propulsion construction methods, it is necessary to perform welding construction and anti-corrosion construction for the pipe connection parts in the sheath pipe. Currently.

In that case, reduction of the construction cost is the utmost command, and the construction dimensions are such that the sheath tube diameter is reduced to the maximum and no useless space is created. For this reason, welding and other anti-corrosion work are being automated to reduce space as much as possible. In other words, when using a heat-shrinkable tube when performing anticorrosion work, we provide a method for performing anticorrosion by field assembly in a vacuum system using far-infrared heating as a method that does not use a direct heating method that requires a relatively large space. Is.

Means and action for solving the problem

The present invention solves the above problems, and when a pipe is welded in a sheath tube and a welded portion is protected by a pipe-shaped heat-shrinkable tube, a cylindrical vacuum heating furnace using far-infrared rays made of duralumin or aluminum, which is divided into upper and lower parts. The wheel is moved laterally to the welded part manually by the wheel, heated under a reduced pressure of 600 mmHg or less, and the control panel automatically controls the degree of pressure reduction, heating temperature, heating start time, alarm device, flashing signal lights, etc. A method for preventing corrosion of a pipe welded portion in a sheath pipe, wherein the heat shrinkable tube is thermally shrunk.

Examples of the heat-shrinkable tube used in the present invention include Furukawa Electric's Rapco tube for automatic heating or Nitto Denko's Neocover # 1150. All of these have a heat-shrinkable polyethylene surface layer on the front surface and an adhesive layer on the back surface. A release paper is attached to the adhesive layer. The release paper is peeled off before heating the heat shrinkable tube. The heat-shrinkable tube is softened and shrunk when heated, and closely adheres with the adhesive layer previously provided on the back surface of the welded portion of the pipe to form an anticorrosion layer.

When the heat-shrinkable tube is heated and shrunk, when the temperature before heating is lower than 20 ° C., it is preferable to heat in advance according to the following criteria before heating. That is, the heating time is preferably 40 minutes when the temperature is 20 ° C. or higher, 45 minutes when the temperature is 5 to 20 ° C., 50 minutes when the temperature is 0 to 5 ° C., and 55 minutes when the temperature is 0 ° C. or lower. This temperature management is controlled by the temperature control of the control panel, and the vacuum pump is automatically switched on by switching on the temperature control panel. On the other hand, the reduced pressure heating furnace and the pipe in the sheath tube are kept at a reduced pressure by vacuum packing.

The far-infrared heater is programmed to automatically switch on when the vacuum pump pressure reaches the set vacuum level. When the heater is turned off after heating for a predetermined time, the heating end lamp is turned on. Thereafter, the vacuum heating furnace is removed, and the entire shrink tube is inspected for pinholes with an inspection voltage of 12,000 V as a holiday detector.

As an example, a case where a gas pipe having a diameter of 750 mmφ is extended by automatic welding in a sheath pipe diameter of 2400 mmφ buried in the ground by a shield method will be described. The gas pipe is anti-corrosion-lined throughout the gas pipe at the factory, except for the welds where the gas pipe is welded at a fixed scale. When welding a gas pipe on site, a heat-shrinkable tube that can cover the welded part is separated from the welded part and put on the gas pipe. Heating for about 40 minutes at a temperature of 300 ° C. or higher is preferable in a vacuum furnace having a split type (cylindrical heating furnace having an outer dimension of about 850 mmφ and a length of about 820 mm). In this way, the heat-shrinkable tube is brought into close contact with the weld location. This series of operations is automatically controlled based on data previously input to the control panel. When the anticorrosion processing of the welding point is completed, the heating furnace is opened and moved to the next welding point manually. The control panel is connected to a power heater cable, a vacuum hose, a control cable, a thermocouple for displaying temperature, and the like.

The invention's effect

As described above, the present invention is intended to reduce the construction cost by reducing the diameter of the sheath tube, but intends to counter the reduction of the space occupied by the sheath tube by automating corrosion prevention work including welding. It is. And even after welding, by performing the anticorrosion work using a heat-shrinkable tube under reduced pressure, it has an effect that an excellent quality anticorrosion work can be performed without air voids by trapping air.

Claims (1)

  When pipes are welded in a sheath tube and the welded part is anticorrosive with a pipe-shaped heat-shrinkable tube, a cylindrical vacuum heating furnace with a far-infrared type made of duralumin or aluminum far infrared is used to manually weld the inside of the sheath tube with wheels. It is laterally moved and heated under a reduced pressure of 600 mmHg or less, and the control panel automatically controls the degree of pressure reduction, heating temperature, heating start time, alarm device, flashing of signal lights, etc. A method for preventing corrosion of a pipe weld in a sheath pipe.