Repair - repair and mark protection technology

Technical requirements for repairing, repairing and cathodic protection

One, the main project quantity

1. Repair mouth, repair injury

• 2. Cathodic protection

Ii. Technical requirements for construction

1. Fill the mouth

Epoxy resin primer and radiation crosslinked polyethylene heat shrinkable sleeve (belt) three-layer structure is used for filling.

General process:

Construction preparation → pipe opening cleaning → pipe opening preheating → pipe opening rusting and dusting →PE layer preheating and pipe opening heating → temperature measurement and primer painting → heat shrinkable tape installation → heating heat shrinkable tape → inspection and acceptance → port filling identification → filling in construction inspection records

1.1 Pretreatment

(1) Welding joints should be cleaned. Burrs, welding slag, spatter, welding nodules and other burrs near the circumferentially welded joints should be cleaned. Dirt, oil and impurities (propane cleaner if necessary) at the filling should be cleaned.

(2) When sandblasting is used, the steel pipe should be preheated to 3 ℃ above the dew point of ambient air (about 30℃~50℃) before surface sandblasting and derusting. The derusting grade shall reach Sa 2.5, and the anti-rust effect of the steel pipe surface shall be visually compared with the corresponding photos or standard comparison plate. Dust should be removed from the surface after derusting. If there is dust pollution, use pure cotton towel to wipe qualified.

(3) The thermal shrinkage belt and the 3PE anticorrosive layer of the pipe body of 100 mm, the depth of the wool is 0.3~0.4mm, the width of the wool is not more than the length of the closing piece.

(4) The depth of the anchor grain is measured by the anchor grain instrument or the 0-shape tablet and kept for record. The depth of the anchor grain is kept between 50 and 90 mm.

The time interval between the surface pretreatment of steel pipe and the construction of the filling should be controlled within 2 hours, and the surface of steel pipe should be prevented from being affected with moisture and pollution during the period. Prior to primer, if rust or surface contamination occurs, surface pretreatment must be re-carried out.

1.2 Primer

(1) The epoxy resin base material A should be fully stirred, and then the curing agent B into the epoxy resin base material A, stirring about 3 to 5 minutes. Use for about 30 minutes at ambient temperature, as long as the primer remains liquid.

(2) Adjust the flame so that the end is yellow and the root is blue. Preheat the steel pipe at the seams to 60 ° C ~80 ° C (subject to the product instruction), and preheat the anticorrosion coating surface within the overlapped seams to 90 ° C ~100 ° C (measured by infrared thermometer) (subject to the product instruction). After heating, the point-contact thermometer or the point-contact thermometer should be used to measure the temperature compared with the calibrated infrared thermometer, and at least the temperature of four points evenly distributed in the circumferential direction on the surface of the patch site should be measured.

Infrared thermometer has the advantages of fast response time, non-contact, safe use, convenient and long service life, the use of low temperature section (≤300℃) infrared thermometer, the general accuracy can reach ±2℃ or higher, can meet the construction requirements. However, it should be noted that after sandblasting, the temperature measured by infrared thermometer on the surface of steel pipe will be low, so it is required to use contact thermometer to calibrate regularly.

(3) Use a special paint brush to evenly brush the primer on the surface of the steel pipe and the anticorrosive layer, the wet film thickness of the primer should not be less than 120 mm, and the anticorrosive layer is less than the width of the heat shrinkable tape overlapped by 20~30mm.

1.3 Installation of heat shrink belt

(1) When the primer is still wet, quickly place the heat shrink belt on the central part of the welding joint. First, the chamfered end is pasted on the pipe, and the position should be at 10 and 2.

(2) After the heat shrinkable tape is wound to the pipe, the gap between the bottom and the pipe shall be at least 25mm, and the lap length of the heat shrinkable tape itself shall be at least 50mm.

Note: As the thickness of the adhesive layer at the lap joint is doubled, in order to ensure that the bottom adhesive layer can melt, special heating and rolling should be done to the lap joint to prevent the occurrence of clamping.

(3) Heat the inner side of one end of the heat shrinkable tape and paste it to the other end of the heat shrinkable tape. Smooth with a gloved hand.

1.4 Installing fixing plates

Heat the inner side of the fixing sheet for 1 to 2 seconds. The axial center line of the fixed sheet is on the joint of the heat contraction belt, and the joint is placed flat and pressed by hand. Heat the retainer from end to end with a flame and compact with a press roller.

1.5 Heat shrinkable zone

(1) Heat the heat shrinkable zone evenly from the middle of the heat shrinkable zone along the circumference. Until the thermal bubble is smooth. (In the process of heating along the circumferential direction, if it is found that the fixed plate is separated from the thermal shrinkage belt, it shall be glued by hot tapping or pressing roller, and the flame must cover the closing plate during the heating process).

Note: In the process of heating and shrinkage, the heater head should not be too large, too large will make the substrate rapidly shrink, and the inner layer of hot melt adhesive has not yet melted on the surface of the tube, is not conducive to bonding, and can avoid burning, carbonization phenomenon.

(2) When the wind is strong, the flame should be turned against the wind and heated from the leeward side of the heat shrinkage zone.

1.6 The heat shrinkable zone is flattened

(1) When the thermal contraction belt is completely contracted, then the entire thermal contraction belt is heated for 5 ~ 8 minutes, so that the surface temperature is kept at 150~170℃ (according to the product instructions) for no less than 3 minutes, so that the hot melt adhesive is fully melted and overflowed from both sides, in order to achieve better bonding effect. During the heating process, press the heat shrinkable belt with your finger, and the dent should disappear automatically after leaving.

(2) When the surface of the heat shrinkable belt is still soft, roll while hot and squeeze out bubbles. Drive from the weld to both sides, especially pay attention to the weld and the corrosion layer of the pipe body. When bubbles are found, they can be reheated and driven out by rollers.

1.7 Marks for construction workers

Mark the name of the construction worker and the date of the repair in white writing.

1.8 Repair quality inspection

The appearance, leakage point and bonding force should be inspected for the quality of the patch, and the inspection should be carried out 24 h after the patch installation.

(1) The appearance of the filling mouth should be visually inspected one by one, and the surface of the thermal shrinkage belt should be flat, no wrinkle, no bubble, no hollow drum, no charring and other phenomena; The heat shrink zone should have adhesive overflow evenly in the circumference. The slippage at the lap position of the fixing plate and the heat shrinkable tape shall not be greater than 5mm;

(2) Spark leak detection: an electric spark leak detector shall be used for leak detection at each patch. The spark leakage detection voltage is 15kV, if there is a leakage point, should be re-filling and leakage detection, until qualified.

(3) Detection of bond strength:

The bonding force of the heat-shrinkable zone after filling should be tested according to the method specified in the appendix of this guide. The temperature of the tube body should be 10 ° C to 35 ° C. If the temperature is too low, the anticorrosion layer can be heated to the detection temperature before testing. At the filling point, the peeling strength of the steel pipe should not be less than 50 N/cm; For the lap of the heat shrinkable material and the original steel pipe polyethylene anticorrosive layer, the peel strength of polyethylene should not be less than 50 N/cm; For the three-layer structure, the primer on the peeling surface shall be completely attached to the surface of the steel pipe. At least one spot test should be made for every 100 filling holes. If unqualified, double spot test should be made. If there is still one unqualified after double spot test, all the repair openings of this section of pipeline should be repaired. After the peel strength test, the patch shall be cleaned and a new patch shall be made.

1.9 Quality control points during operation and construction

(1) The derusting grade shall reach Sa 2.5;

(2) Before applying primer, preheat the steel pipe at the filling part to 60℃~80℃ (subject to the product instruction), and preheat the surface of the anti-corrosion coating within the lap range of the filling part to 90 ℃~ 100℃ (measured by infrared thermometer);

(3) When the thermal contraction band is completely contracted, then the entire thermal contraction band is heated to keep the surface temperature at 150~170℃ (according to the product instructions) for no less than 3 minutes;

(4) mark the name of the construction worker and the date of the filling at the filling place;

(5) The quality of anti-corrosion repair shall be inspected, and the repair shall be cleaned after the peel strength test, and a new repair shall be made.

1.10 Construction equipment, instruments and tools

(1) Sandblasting derusting car;

(2) hygrometer (-20 ~ +60℃, 0 ~ 100%);

(3) far infrared thermometer, point contact thermometer;

(4) Electric spark leak detector, wet film thickness gauge, anticorrosive layer thickness gauge;

(5) roughness measuring instrument, anchor grain depth testing paper, dial meter, shovel;

(6) liquefied gas bottle and baking handle, press roller, wire brush.

2. patching

The repair operation of three layers of PE anticorrosive coating often adopts the repair piece, which is carried out according to the following steps:

2.1 Principle of repair

For damage less than or equal to 30mm, radiation cross-linked polyethylene patch should be used for repair, and the peel strength of pipe POLYETHYLENE patch should not be less than 50 N/cm.

For damage greater than 30mm, the patch shall be subsidized in accordance with 4.1.1, and then a thermal shrink strip shall be coated at least 50mm wider than either side of the patch.

2.2 Steps of repair

(1) Remove the soil and oil stains at the damage, and use a wire brush or similar tool to debrize the coating around the damage. The debrizing area should extend more than 50mm to the edge of the wound.

(2) Heat the cleaned surface with flame, and the heating temperature is measured with an infrared thermometer (about 40℃ ~ 60℃).

(3) For the corrosion coating defects without pinholes, the pipe body can be directly repaired with the patch without being exposed. For corrosion coating defects with pinholes, the tube body should be exposed, then filled with filler and repaired with a patch.

(4) The size of the patch shall be subject to the distance between the patch edge and the damage edge not less than 50mm.

(5) For the damage with a length greater than 300 mm, the edge of the damage shall be trimmed into a groove after cleaning, and then filled with glue, and a thermal shrinkage strip shall be coated on the repair. For damage with a length greater than 500mm, multiple shrink strips can be used to repair the damage.

(6) Heat the patch (belt), put on a heat-resistant glove and squeeze the patch to exhaust all the air, and the glue around the patch (belt) should overflow evenly.

(7) The repair is rolled and bubbles are extruded so that the repair piece is closely combined with the anticorrosive layer of the pipe body.

2.3 Repair quality inspection

The appearance, leakage and bonding should be inspected for repair quality, and the inspection should be carried out 24 hours after repair installation.

(1) The appearance after repair should be checked one by one, the surface should be flat, no wrinkle, no bubble, no charred carbonization and other phenomena; Patch patch around the adhesive should be uniform overflow of unqualified should be re-fill.

(2) Spark leak detection: an electric spark leak detector shall be used for leak detection at each repair place. The spark leakage detection voltage is 15kV, and the leakage point should be repaired and detected again until qualified.

(3) Peel strength:

The bonding strength after repair shall be tested according to the method specified in the appendix. The peeling strength at room temperature (10℃~35℃) shall not be less than 35 N/cm, and spot check shall be conducted at one place per 100 repair sites. If unqualified, double spot check shall be conducted; If there is still one unqualified after double spot check, all the repair damage of this section of pipeline should be repaired.

3. Cathodic protection

3.1 Sacrificial anode installation

(1) The quality of the sacrificial anode must be checked before it is used. First polish the steel core, and then weld it with the cable lead. Then the cable and the steel core are lapped and bundled tightly. The joint is insulated and sealed with heat shrink tube, and further insulated and sealed with epoxy resin, and necessary protective measures are taken to prevent the fracture of the connection during construction.

(2) The anode is buried in the general distance from the outer wall of the pipe 3-5 meters, the minimum should not be less than 0.5 meters. The spacing between groups of anodes should be 2-3 meters. The buried depth of the anode is generally equivalent to the depth of the pipeline, and the top of the anode is not less than 1 m away from the ground, and should be buried below the freezing line. In the dry zone where the groundwater level is less than 3 m, the anode should be appropriately buried.

(3) When the anode is arranged, there should be no metal structure between the anode and the pipe.

(4) the anode bag should be poured with enough water before the anode pit, so that it is fully soaked.

(5) The buried depth of the anode connection cable should not be less than 0.7 meters, and the surrounding pad is 50-100mm thick fine sand.

(6) The cable and the anode steel core should be connected by welding. The length of the bilateral weld shall not be less than 50mm. Before the cable and pipeline are welded, the welding spot of the pipeline should be treated to expose the metal surface.

(7) anode buried after backfill, every backfill 200-300mm should line tamping once, until fill, restore the landform.

(8) The welding position of cable and pipeline should not be within the range of 200mm on the elbow or on both sides of the pipeline weld. If thermite welding is used, the amount of thermite flux used for welding should not exceed 15g. When the section of the welding cable is greater than 16mm², the cable core can be divided into several strands, each less than 16mm², and welded separately.

3.2 Test pile installation

(1) Generally, the test pile should be located on the roadside and in the green belt, so as to occupy less land and affect traffic as far as possible. The installation position should be located 1.5 meters from the center line of the pipeline to the left of the medium flow direction.

(2) The installation method is: first welding a cable on the pipeline, after welding must be re-used with the original anticorrosive layer fusion material for anticorrosive insulation treatment, and then the other end of the cable into the test pile potential measurement connecting column. In order to facilitate measurement and avoid the defects of buried reference electrode such as poor maintenance and potential instability, it is suggested to use portable saturated copper sulfate reference electrode during measurement.

(3) The test pile is made of glass fiber reinforced plastic, and its anticorrosion layer is suitable for the local environment, with certain moisture resistance and corrosion resistance. When the test pile is buried, C15 concrete is cast and fixed. The test pile door lock should be coated with anti-embroidery paste. The upper part of the test door is welded with a rain shield to prevent the test door from being corroded by rain. The nameplate of the test pile shall indicate the name, number, mileage and type of the project.

(4) The connection of the test pile lead should be carried out after the pipeline down the ditch and before the earthwork backfill. After the lead is welded, the soft soil should be used to backfill, and the lead should be prevented from being broken or broken.

3.3 Insulation Installation

(1) The protective pipe and the branch line without the use of sacrificed anode protection shall be equipped with an insulation connector, which shall be equipped with a built-in anti-breakdown surge or external grounding battery.

(2) In the pipeline of cathodic protection, flange and threaded connection elbow, tee, valve and other non-welded pipe accessories are used. In order to ensure the electrical continuity, the pipes at both ends of the accessories are directly connected with the bonding cable.

3.4 Thermite welding

The test pile and the anode cable are connected with the steel pipe by thermic welding technology. Solder joints shall be re-treated with anti-corrosion insulation, and anti-corrosion materials shall be of the same grade as the original covering. For matters not covered herein, please follow the Technical Specification for Cathodic Protection of Buried Steel Pipelines (GB/T21448 -- 2008).

3.5 Others

(1) All buried sacrificial anodes must have a quality guarantee provided by the manufacturer, and each batch of products should be accompanied by a quality guarantee.

(2) Thermite welding mold, flux, ignition and other construction tools by the construction team.

(3) All cables shall be buried in the ground, and buried cables shall be laid in accordance with national Standard Atlas of General Electric Installations 94D164.