Abstract : With the development of China's energy industry and the adjustment of energy structure, the construction of pipeline engineering has developed rapidly. As the key technology for long-distance oil and gas pipeline construction, welding technology is directly related to engineering quality, construction efficiency, construction cost, and safety, reliability and economic benefits during pipeline operation. According to the characteristics of welding construction of long-distance oil and gas pipeline engineering, this paper systematically introduces the construction technology, selection principle and current status of pipeline welding, including welding materials, welding equipment, welding methods and welding processes.
Key words : oil and gas pipeline; pipeline steel; automatic welding;
0 Preface
Long-distance pipelines are the main way of long-distance oil and gas transportation. With the development of China's energy industry and the adjustment of energy structure, the construction of pipeline engineering has developed rapidly. By the end of 2003, the cumulative length of oil and gas pipelines was 45,865 Km, ranking sixth in the world; among them, the crude oil pipeline was 15,915 Km, the natural gas pipeline was 21,299 Km, the refined oil pipeline was 6525 Km, and the submarine pipeline was 2,126 Km. Domestic large-scale pipeline projects such as “West-East Gas Transmissionâ€, “Suining Linkageâ€, “Shaanxi-Beijing Second Line†and “Western Pipeline†have been completed or put into operation, and the “China-Kazakhstan Pipeline†of the multinational pipeline is about to be completed, with Russia and Pipeline construction in neighboring countries, Central Asia and other countries has been under intense planning. According to the national plan, by 2020, China's oil and gas pipelines will basically form a well-distributed, networked, mutually coordinated, safe and reliable oil and gas pipeline network covering major areas of the country to meet social and economic development and people's living needs.
The ring welding part in pipeline construction is the frequent location of failure accidents. Pipe welding technology is the key technology that must be ensured during construction. It is not only directly related to the welding quality, construction efficiency and cost of the project, but also the safety and reliability during the operation of the pipeline. Economic benefits also have an important impact.
Therefore, it is an inevitable requirement for modern high-quality and efficient construction to carry out research on welding technology of pipeline engineering and improve the level of welding technology.
1. Pipeline steel weldability
In order to increase the pipeline transportation volume, reduce the engineering cost, and meet the increasingly demanding conditions of use, large-diameter, high-pressure, thin-walled high-strength and toughness pipeline steel is the development trend. The domestic high-strength X70 pipeline steel is fully used in the “West-East Gas Transmission†project, and the X80 is currently only successfully tested on the Suining pipeline. Germany, Canada and other European and American countries have built many X80 pipelines on land and in the sea; Canada Trans Canada Pipeline Company completed the 1km φ1219mm×14.3mm X100 steel pipe test section in 2002, and Exxon Mobil Company built X120 steel pipe in Canada in 2004. The 1.6km test section. ã€1】
High-strength and toughness pipeline steel belongs to low-alloy high-strength steel, low-carbon or ultra-low-carbon microalloyed controlled-rolled steel. It adopts advanced technologies such as refining technology, microalloyed steel technology, controlled rolling and controlled cooling technology, and deformation heat treatment, which makes the carbon content of the pipe. Very low, high cleanliness, fine grain, high toughness and good weldability, especially in the heat affected zone, the cold crack sensitivity is greatly reduced, the coarse grain zone toughness is greatly improved, and further suitable for high efficiency, Large line energy welding process.
However, new problems have arisen, such as the low carbon equivalent high strength of the base metal, which causes the cold crack to transfer from the weld heat affected zone to the weld metal, the local brittle zone problem in the multilayer welded joint, and the like. Therefore, for low-alloy high-strength steel, attention should be paid to the problem of cold cracking of weld metal. For large-line energy welding, it is necessary to evaluate the microstructure and toughness of the heat affected zone of the welding, paying particular attention to the problem of local brittleness of the multilayer welding. For the newly developed ultra-fine grain steel, a high energy density, low heat input welding process is used to prevent excessive growth of the grain in the heat affected zone of the weld.
2. Welding materials
The choice of welding materials is an important aspect to consider for long-distance pipeline welding. It includes welding rods, welding wire, flux and shielding gas in a broad sense. In the narrow sense, it refers to welding rods and welding wires. ã€2】
2.1 Welding rod
Welding rods for long-distance pipeline welding currently use all-position down-welding electrodes and conventional low-hydrogen welding rods. The implementation standards are GB/T 5117-1995, GB/T 5118-1995, AWS A5.1-91 and AWS A5. .5-96 and so on. The all-position down welding electrode is divided into two categories: one is high cellulose type (based on the low content of pipeline steel C, S, P, can be considered), the welding rod has good welding performance and less slag. Moreover, the blowing force is large, the slag and molten iron are prevented from being smashed, and the penetration capability and the faster deposition speed are large, and the single-sided welding double-sided forming effect is good in various positions, and is suitable for root welding and heat. Welding, representative of BOHLER FOX CEL (AWS A5.1-91 E6010) and BOHLER FOX CEL 85 (AWS A5.5-96 E8010-P1) electrodes produced by Austrian Böhler, FLEETWELD 5P+ produced by Lincoln, USA AWS A5.1-91 E6010) and SHIELD ARC 70+ (AWS A5.5-96 E8010-G) welding rod, SRE425G (AWS A5.1-91 E6010), SRE505 (AWS A5) developed by CSIC 725 .5-96 E7010—G) and SRE555 (AWS A5.5-96 E8010—G) welding rods, etc. The other type is iron powder low-hydrogen type down-welding electrode, which has fast solidification speed, good fluidity and wettability of molten iron, is not easy to squat during full-position welding, has good toughness of weld metal after welding, and has good crack resistance. Down-welding of each layer, representative of BOHLER FOX BVD 85 (AWS A5.5-96 E8018-G) electrode produced by Austria Bole Company, LINCOLN LH D80 (AWS A5.5-96 E8018) produced by Lincoln Company of USA -G) Welding rod. For the traditional low-hydrogen welding rod, due to its general position to root welding, the process performance is general, the arc ignition is difficult, the arc stability is poor, the splash is large, the back surface is poorly formed, and the air hole is easy to be used. Among the repair and rework solder-filled cap welding, CHE507GX (GB/T 5118-1995 E5015) and CHE557GX (GB/T 5118-1995 E5515) are produced by Sichuan Atlantic Company. The specifications of the above-mentioned commonly used high-cellulose electrode are generally Φ3.2mm, Φ4.0mm, the specification of the iron powder low-hydrogen type electrode is generally Φ4.0mm, and the specification of the ordinary low-hydrogen type electrode is generally Φ3.2mm.
Generally speaking, σ0.5(0.2)≤415MPa oil transmission and water pipeline main line welding can choose high-fiber type electrode for welding of each layer; gas pipeline or σ0.5>415Mpa oil pipeline main line welding can adopt high cellulose Type welding electrode root welding, heat welding + low hydrogen type down welding electrode filling, cover surface composite process.
2.2 welding wire
The long-distance pipeline is divided into two types: solid wire and flux cored wire.
(1) Solid wire
There are two main types of solid wire: one for submerged arc welding and the other for melting active gas shielded welding. Solid welding wire for submerged arc welding is carried out according to GB/T 5293-1999, with low manganese welding wire, such as H08A (such as CHW-SG welding wire produced by Sichuan Atlantic Company) with high manganese type smelting flux for low carbon steel and strength grade. Low pipeline steel welding; medium manganese welding wire, such as H08MnA, H10MnSi, combined with high manganese high silicon low fluorine type smelting flux is mainly used for pipeline steel welding, and can be used with low manganese flux for low carbon steel welding; high manganese welding wire, For example, H08Mn2Si and H08Mn2SiA are used for pipeline steel welding; Mn-Mo welding wire, such as H08MnMoA, HO8MnMoTiB, combined with low-manganese silicon in fluorine-type smelting flux, fluorine-alkaline sintered flux or silicon-calcium sintered flux, mainly used for high strength grade Pipeline steel welding. The wire diameter is generally in the range of 1.6 to 6.4 mm.
The solid welding wire for reactive gas shielded welding has the following standards: GB/T 14947-1994, GB/T 8110-1995, AWS 5.18-93 and AWS 5.28-96. The most commonly used welding wire is H08Mn2SiA (equivalent to GB/T 8110). ER49-1), it has good welding process performance and is suitable for welding pipeline steel with σs≤500MPa. When the steel grade with higher welding strength grade, the welding wire containing Mo should be selected, for example, domestic H10MnSiMo welding wire and JM-58 welding wire, BOHLER SG3-P welding wire produced by Jintai Company which performs American standard AWS 5.18 ER70S-G and Perform Jintai JM-68 welding wire of American standard AWS A5.28 ER80S-G. The specifications of common welding wires are φ0.9mm, φ1.0mm, φ1.2mm, and the like.
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