Nozzle preheating before welding
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Nozzle preheating before welding shall comply with the provisions of the welding procedure specification, preheat width should not be less than groove on both sides of the 50 mm, using temperature crayons, infrared thermometer temperature measuring tools such as measurement, nozzle should be uniform heating, when the environment temperature below minus 5 degrees Celsius, using electrical heating to preheat.(2) pipe welding shall conform to the requirement of the welding procedure specification, after completion of root welding, heat welding shall be immediately, each bead appropriate continuous welding, control the temperature between; In welding operation, welding bead welding by personal introspection and mending, every patch length should not be less than 50 mm. Daily homework after the pipeline end pipe should be temporary plugging, and under the influence of water groove welding pipeline under waterproof measures should be taken. Joint should be marked, joint symbol including project name abbreviations, blocks, pile number, serial number written in marker pen from the joint (oil, gas flow downstream) 1 meters anticorrosive coating surface, and at the same time to make a good record of welding.(3) all weld with crack must be removal from the pipeline, the emergence of non crack defects, can be directly repair, in accordance with the repair welding procedure specification and welding seam at the same site doesn't allow more than two times of repair, root only allow repair time, otherwise the weld shall be removed.5. Weld inspection and acceptance(1) the weld appearance inspection qualified rear can for nondestructive testing1) weld forming uniform appearance, welding seam and heat affected zone on the surface can not have crack, incomplete fusion, porosity, slag inclusion, splash, arc crater defects, etc.1 P1142) weld surface should not be lower than the parent metal surface, the weld residual high shall, within the range of 0 to 3 mm should be smooth transition to the parent metal.3) the surface of the weld width on each side should be wider than groove surface 1 to 2 mm.4) the maximum size of the bit edge should comply with the rules.(2) the NDT should comply with the provisions of the country and the current standards to the oil industry, radiographic testing and ultrasonic testing of qualified level to level 2. Wear, pipeline weld across water, roads, railways, bend and straight pipe section of the weld and touch the death without the pressure of pipeline welding seam, ultrasonic testing and radiographic testing shall be 100%.For standard groove groove form for the mechanical processing, weld cannot free shrinkage of welded joint, commonly known as touch dead.(7) pipeline anticorrosion repairingAfter pipe nondestructive testing qualified, shall promptly carry out anti-corrosion repairing. Heat-shrinkable sleeve repairing is the commonly used method, deal with the tube preheated before repairing, preheating temperature of 60 to 80 degrees Celsius, usually, preheating temperature is reached quickly install the heat-shrinkable sleeve in place, heat shrinkable sleeve and nozzle side lap over 50 mm. The outer surface of the coating should level off, without leakage besmear, fold, flowing, bubble and pinhole defects such as; Coating should be able to effectively adhere to the metal surface; PE heat-shrinkable sleeve (tape), polyethylene cold wrap adhesive tape, and the two-component epoxy powder fluid of patching and patching hot melt stick repairing, patching material should be used according to its manufacturer, illustrates the requirements of the construction.(eight) pipe trench excavation1. The pipe trench slope should according to category, mechanical property and soil trench excavation depth, the depth of the trench within 5 meters the steepest slope gradient should be determined according to the requirements of specification. Depth of more than 5 m pipe trench slope should be according to the actual situation, adopt measures to slow, support or stepped excavation slope.2. The general location of trench excavation, will dig out the conditions of pile up to the opposite side of the welding construction, pile soil should be away from the river bank not less than 1 m.3. The blasting excavation trench should be completed before the cloth tube, blasting operations shall be borne by units in blasting quality.4. The center line of the pipeline, bottom elevation, groove width, variable slope point displacement deviation should be allowed to meet the requirements. Regarding the section of the pipe GouGou wall can not have already faltering stone, bottom should not have stones.。
