There are many reasons for pipeline leakage, which can be divided into three categories: corrosion perforation, fatigue cracking and external damage.
Although corrosion control measures can significantly reduce corrosion, it does not prevent corrosion. When the cathodic protection is insufficient, the pipeline corrosion process will be slow but will not stop due to cathodic protection; when the cathodic protection is shielded, the pipeline corrosion will not be inhibited at all. Insufficient cathodic protection means that the protection current provided by the cathodic protection system cannot meet the pipeline protection requirements; cathodic protection shielding means that the cathodic protection current is blocked in the flow and cannot reach the predetermined position. When a large area of damage, continuous leakage points or overall insulation performance decline on the coating, it is easy to cause insufficient cathodic protection.
If the oil and gas pipeline is operated under high pressure for a long time, the mechanical properties of the pipeline metal will gradually decay, and the micro-cracks existing in the pipeline weld itself and due to stress corrosion will expand. When the cracks develop to a certain extent, they will cause sudden pipeline rupture accident, leading to leakage. For gas pipelines, pipeline rupture may have catastrophic consequences.
External damage mainly includes natural disasters and human disasters. Floods, landslides, mudslides, and earthquakes can all damage pipelines; human disasters mainly refer to third-party damage, including unintentional damage caused by various construction projects such as road construction and excavation and deliberate damage caused by perpetrators such as drilling holes, stealing oil and gas.
http://www.xysteelpipe.com/info/Causes-of-oil-and-gas-pipeline-leakage-1654-1.htm
2020年4月19日星期日
2020年4月16日星期四
ERW, SSAW, LSAW welded steel tube
ERW steel pipe: high-frequency straight seam resistance welded pipe, using hot-rolled wide coil as the material, through pre-bending, continuous forming, welding, heat treatment, sizing, straightening, blocking and other processes, it has a shorter weld seam than the spiral, standard High precision, uniform wall thickness, good surface quality, and high-end benefits under pressure, but the defect is that only small and medium-diameter thin-walled pipes can be produced, and the welds are prone to gray spots, unfused, and groove-shaped corrosion defects. At present, the widely used fields are city gas, crude oil products and oil transportation, etc.
SSAW steel pipe: spiral submerged arc welded pipe, which has a forming angle (adjustable) with the center line of the forming pipe when the pipe is rolled, and is welded while forming, and its welding seam is formed into a spiral line, and the same standard can produce a variety of diameters Standard steel pipe, the material is used to planning larger, the weld can avoid the main stress, the stress is better, the defect is a few standards are poor, the length of the weld is longer than that of the straight pipe, the crack is easy to crack, the slag is included, the welding deviation, etc. Welding defects, welding stress is tensile stress. The general design rules and regulations of long-distance spiral submerged arc for oil and gas pipelines can only be used in category 3 and category 4 areas.
LSAW steel pipe: Straight seam submerged arc welded pipe, which is made of a single medium-thick plate by pressing (rolling) the steel plate in a mold or forming machine, using double-sided submerged arc welding and expanding the diameter to produce. Its product standard planning is wide, and the resistance, plasticity, uniformity and fineness of the weld are good. It has the advantages of large pipe diameter, pipe wall thickness, high pressure resistance, low temperature resistance and corrosion resistance. When creating high-strength, high-endurance, high-quality long-distance oil and gas pipelines, most of the steel pipes required are large-diameter thick-walled straight-seam submerged arcs. According to API standard rules, in large oil and gas transportation pipelines, when passing through Class 1 and Class 2 areas such as the seabed in high cold areas and densely populated urban areas, the straight-seam submerged arc is the only designated pipe type.
SSAW steel pipe: spiral submerged arc welded pipe, which has a forming angle (adjustable) with the center line of the forming pipe when the pipe is rolled, and is welded while forming, and its welding seam is formed into a spiral line, and the same standard can produce a variety of diameters Standard steel pipe, the material is used to planning larger, the weld can avoid the main stress, the stress is better, the defect is a few standards are poor, the length of the weld is longer than that of the straight pipe, the crack is easy to crack, the slag is included, the welding deviation, etc. Welding defects, welding stress is tensile stress. The general design rules and regulations of long-distance spiral submerged arc for oil and gas pipelines can only be used in category 3 and category 4 areas.
LSAW steel pipe: Straight seam submerged arc welded pipe, which is made of a single medium-thick plate by pressing (rolling) the steel plate in a mold or forming machine, using double-sided submerged arc welding and expanding the diameter to produce. Its product standard planning is wide, and the resistance, plasticity, uniformity and fineness of the weld are good. It has the advantages of large pipe diameter, pipe wall thickness, high pressure resistance, low temperature resistance and corrosion resistance. When creating high-strength, high-endurance, high-quality long-distance oil and gas pipelines, most of the steel pipes required are large-diameter thick-walled straight-seam submerged arcs. According to API standard rules, in large oil and gas transportation pipelines, when passing through Class 1 and Class 2 areas such as the seabed in high cold areas and densely populated urban areas, the straight-seam submerged arc is the only designated pipe type.
Disadvantages of Hot Rolled 20 # Straight Seam Steel Pipe
Disadvantages of hot rolled 20 # straight seam steel pipe:
1. Residual stress caused by uneven cooling. Residual stress is the stress of internal self-phase balance without external force. Hot-rolled steel sections of various cross sections have this type of residual stress. The larger the section size of general steel section, the greater the residual stress. Although the residual stress is self-balanced, it still has a certain influence on the performance of the steel member under the action of external forces. Such as deformation, stability, fatigue resistance, etc. may have adverse effects.
2. After welding, the non-metallic inclusions in the straight seam steel pipe are pressed into thin slices, and the delamination phenomenon occurs. The delamination greatly deteriorates the performance of the 20 # straight seam steel tube in the thickness direction, and there may be interlayer tearing when the weld shrinks. The local strain induced by shrinkage of the weld often reaches several times the yield point strain, which is much larger than the strain caused by the load.
Submerged arc welding straight seam steel pipe advantages: it can destroy the casting structure of the steel ingot, refine the grain of the steel, and eliminate the defects of the microstructure, so that the steel structure is compact and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the 20 # straight seam steel tube is no longer an isotropic body to a certain extent; bubbles, cracks and looseness formed during casting can also be affected by high temperature and pressure Welding.
1. Residual stress caused by uneven cooling. Residual stress is the stress of internal self-phase balance without external force. Hot-rolled steel sections of various cross sections have this type of residual stress. The larger the section size of general steel section, the greater the residual stress. Although the residual stress is self-balanced, it still has a certain influence on the performance of the steel member under the action of external forces. Such as deformation, stability, fatigue resistance, etc. may have adverse effects.
2. After welding, the non-metallic inclusions in the straight seam steel pipe are pressed into thin slices, and the delamination phenomenon occurs. The delamination greatly deteriorates the performance of the 20 # straight seam steel tube in the thickness direction, and there may be interlayer tearing when the weld shrinks. The local strain induced by shrinkage of the weld often reaches several times the yield point strain, which is much larger than the strain caused by the load.
Submerged arc welding straight seam steel pipe advantages: it can destroy the casting structure of the steel ingot, refine the grain of the steel, and eliminate the defects of the microstructure, so that the steel structure is compact and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the 20 # straight seam steel tube is no longer an isotropic body to a certain extent; bubbles, cracks and looseness formed during casting can also be affected by high temperature and pressure Welding.
The role of oil casing and oil drill pipe
The casing pipe is used to strengthen the well wall, and the inner and outer diameters are much larger than the drill rod; the drill rod is used to connect the drill collar and the drill bit, and the length is sufficient to support the drill bit in the downhole operation. Regardless of function or size, they are all different.
The essence of the casing pipe is:
1. During the drilling process, as the depth of the well increases, the required mud density will increase, and the upper bottom layer may be leaked. The role of the casing is to prevent the upper layer from being leaked when drilling the lower layer.
2. The last oil pipe and tail pipe is the oil passage. The purpose is to stabilize the formation and prevent collapse. If the formation is hard, the well can be completed with open holes.
Open-hole completion can only be applied to a single oil or gas layer with hard and dense rock formations, no water-containing interlayers, and no easy-to-collapse interlayers or some oil and gas layers with the same properties and similar pressures.
http://www.xysteelpipe.com/info/The-role-of-oil-casing-and-oil-drill-pipe-1653-1.htm
The essence of the casing pipe is:
1. During the drilling process, as the depth of the well increases, the required mud density will increase, and the upper bottom layer may be leaked. The role of the casing is to prevent the upper layer from being leaked when drilling the lower layer.
2. The last oil pipe and tail pipe is the oil passage. The purpose is to stabilize the formation and prevent collapse. If the formation is hard, the well can be completed with open holes.
Open-hole completion can only be applied to a single oil or gas layer with hard and dense rock formations, no water-containing interlayers, and no easy-to-collapse interlayers or some oil and gas layers with the same properties and similar pressures.
http://www.xysteelpipe.com/info/The-role-of-oil-casing-and-oil-drill-pipe-1653-1.htm
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