Spiral Welded Pipe Datang
4691/5000 Luóxuánhànguǎn: (Spiral Welded Pipe Datang)
Industrial TV internal inspection equipment: inspection of welding quality appearance.
Magnetic flaw detector: inspection of large diameter steel pipe near the table defects.
Ultrasonic continuous flaw detector: inspection of spiral steel pipe full length of the transverse and longitudinal defects.
Ultrasonic manual flaw detector: the inspection of large diametersteel pipe defects, welding weld inspection and water quality after theweld.
X-ray automatic flaw detection machine and industrial televisionimaging equipment: test the full quality of spiral steel pipe weldinternal quality, sensitivity of not less than 4%.
X-ray film equipment: the original weld and welds to test, the sensitivity of not less than 2%.
2200 tons of hydraulic press and computer automatic recording system:test the quality of each large diameter steel pipe pressure.
Inspectionof raw materials - leveling test - butt welding inspection - forminginspection - internal welding inspection - external welding inspection -pipe inspection - ultrasonic inspection - groove inspection -dimensions inspection - X-ray inspection - Hydraulic test - final inspection
To ensure product quality, we have developed a sound quality plan, on-site work procedures and testing, pilot program.
The project's anti-corrosion requirements and other domestic projects are significantly different, the main difference is:
Internal anti-corrosion materials are generally used in domesticcement mortar, the project uses non-toxic epoxy coating (thickness0.4mm).
External anti-corrosion coating EDM test voltage is generally domestic3000 volts, the maximum does not exceed 5000 volts, the project is 10kV.
Anti - corrosion spiral welded pipe
Anti - corrosion spiral welded pipe
In response to the above requirements, we focus on the following two aspects of the work:
Strict sand work procedures to ensure the quality of rust, and within 1hour to complete the paint inside and outside the primer, which is toensure the quality of anti-corrosion.
In the development of anti-corrosion process, we particularly requireglass fiber cloth first soaked epoxy epoxy asphalt coating,semi-mechanical rolling wrapped, and the glass cloth by the artificialroller flattened method to ensure that the outer coating uniform andfine.
Inside and outside the anti-corrosion pipe, on the open yard up to 4months test, the coating is not yellow pimple and other undesirablephenomena, external coating EDM test is still up to 10 kV requirements.
Spiral welded pipe and straight seam welded pipe technical characteristics to do a simple comparison:
Metallurgical properties of materials
The straight seam submerged arc welded pipe is made of steel plate, and the spiral welded pipe is produced by hot rolled coil. Hotstrip mill rolling process has a series of advantages, with theproduction of high quality pipeline steel metallurgical processcapacity. Forexample, a cooling system is provided on the output gantry toaccelerate cooling, which allows the use of low alloying components toachieve special strength grades and low temperature toughness, therebyimproving the solderability of the steel. But this system is basically no steel production plant. The alloy content (carbon equivalent) of the coil is often lower thanthat of a similar grade, which also improves the weldability of thespiral welded pipe.
Itis to be noted that since the rolling direction of the spiral weldedpipe is not in the direction of the vertical steel pipe (the clampingangle depends on the helix angle of the steel pipe) and the striprolling direction of the straight seam steel pipe is perpendicular tothe pipe axis direction, The crack resistance of welded pipe material is better than that of straight seam steel pipe.
Fromthe welding process, the spiral welded pipe and the straight seam steelpipe welding method is consistent, but the straight seam welded pipewill inevitably have a lot of T-shaped weld, so there is the probabilityof welding defects are greatly improved, and TIG welding at the weldingresidue Stress is large, the weld metal is often in a three-way stress state, increasing the possibility of cracking.
Moreover,according to the submerged arc welding process, each weld should havearc and arc at the arc, but each straight seam welded pipe in thewelding seam, can not achieve the conditions, which may be at the arc More welding defects.
Whenthe tube is subjected to internal pressure, two main stresses areusually generated in the pipe wall, ie radial stress δY and axial stressδX. The stress at the weld is δ = δY (l / 4sin2α + cos2α) 1/2, where α is the helix angle of the spiral welded pipe weld.
Thespiral angle of the spiral welded pipe is generally 50-75 degrees, sothe synthetic stress at the spiral weld is 60-85% of the main stress ofthe straight seam welded pipe. At the same working pressure, the same diameter of the spiral weldedpipe than the straight seam welded pipe wall thickness can be reduced.
According to the above characteristics we can see:
A? Spiral welded pipe blasting, due to the weld under normal stressand synthetic stress is relatively small, the burst is generally notoriginated in the spiral weld, its safety than the long seam weldedpipe.
B. When the spiral weld near the existence of parallel with thedefects, because the spiral weld force is small, so the risk ofexpansion than the straight seam large.
C.Since the radial stress is the maximum stress present on the pipe, theweld is subjected to the maximum load in the direction of verticalstress. That is, the maximum load of the straight seam is taken, the load ofthe circumferential weld is the smallest, and the spiral seam is betweenthe two.
Static pressure burst strength
Theresults show that the yield and burst pressure of the spiral weldedpipe and the straight seam welded pipe are in good agreement with thetheoretical value. But whether it is yield pressure or burst pressure, spiral welded pipe are lower than the straight seam welded pipe. Theblasting test also showed that the annular deformation rate of thespiral welded pipe burst was significantly larger than that of thestraight seam welded pipe. It is confirmed that the plastic deformation capacity of the spiralwelded pipe is better than that of the straight seam welded pipe, andthe burst is generally confined to a pitch, which is caused by thestrong effect of the spiral weld on the expansion of the gap.
Toughness and fatigue strength
Pipeline development trend is large caliber, high strength. Withthe increase in the diameter of steel pipe, the use of steel grade toimprove the toughness of the fracture produced a greater trend of steadyexpansion. According to the US research institutions of the test shows thatspiral welded pipe and straight seam welded pipe although the samelevel, but the spiral welded pipe has a high impact toughness.
Inthe actual operation process, the steel pipe is subjected to the effectof random alternating load due to the change of the transmission line. Understanding the low cycle fatigue strength of steel pipe is of great significance to judge the service life of pipeline.
According to the determination results, the fatigue strength of thespiral welded pipe is the same as that of the seamless pipe and theresistance pipe. The test data are distributed in the same area as theseamless pipe and the resistance pipe, and higher than the ordinarysubmerged arc welded pipe.
Spot weldability is mainly determined by the material and port size tolerances of the pipe.
Taking into account the requirements of steel pipe installation andconstruction, steel pipe production and continuity of the geometry ofthe consistency of the shape is particularly important.
Theproduction of spiral welded pipes is a continuous process that isbasically stable under the same operating conditions: the straight seamwelded pipe production process is segmented, including the entire plate /indenter / pre-roll / spot welding / welding / finishing / groupequivalence Multi-channel process. This is an important feature of spiral welded pipe production that isdifferent from the production of straight seam welded pipe.
Stable production conditions are very easy to control the quality of welding and geometric dimensions. As the spiral welded pipe tube structured, evenly distributed weld,relative to the straight seam welded pipe, spiral steel pipe has a verygood oval and the vertical face, to ensure that the field of steel pipewelding group on the group when the accuracy.
On the flow characteristics of the conveying medium
Thepressure drop in the pipeline is proportional to the length of thepipe, the fluid viscosity coefficient, the fluid velocity, and the fluidresistance coefficient, which is inversely proportional to the innerdiameter of the tube. Thefluid resistance coefficient is related to both the Reynolds number andthe roughness of the inner wall surface of the tube. It is determined that the effect of the roughness of the inner wallsurface of the tube is ten times greater than the effect of thelocalized area (such as a spiral weld or an elongated weld, even aninner annular weld).
Production and management
Spiral welded steel pipe production capacity to reflect the advantages of high quality and efficiency. Theproduction capacity of a spiral welded pipe unit is equivalent to 5-8sets of straight seam welded pipe equipment, how to make multipleproduction lines can achieve the same production standards, that is,according to a unified production process and quality assurance systemto meet the welding quality Requirements with the pipeline manufacturing level will be a heavy job.
Increased production ratio of project management and quality supervision. Thedifferences in operating skills, quality awareness, distribution pointsand control procedures of multiple straight seam pipe units andcorresponding welding equipment will bring many difficulties inproduction management, planned progress, inspection and acceptance,delivery coordination and so on. , Easily lead to management and coordination on the hectic andmanufacturers and the quality of construction units prevarication.
In accordance with the spiral pipe production standards, spiral weldedsteel pipe of the main inspection / control items include:
Dimensions: steel pipe diameter, wall thickness, oval, bending, tube vertical,
Length Appearance quality: weld height, wrong side, steel pipe surface, stratification, inclusion, weld defect judgment
Welded joint tensile test
Acid etching test
Non - destructive testing
The straight seam welded pipe does not have the corresponding production standard.
Generalspiral welded pipe units are used on-line continuous inspection methodto ensure the welding quality of the weld, which is different from theproduction of spiral welded pipe welded pipe production is anotherimportant feature. Continuous inspection is conducive to the monitoring of weldingdefects, the quality of welding stability, the guarantee of weldinggrade.
Due to thelimitation of the production process, the straight seam welded pipe isextremely difficult to realize the continuous uninterrupted inspection. This will increase the probability of welding problems and qualityproblems, and even affect the overall operational reliability of futurepipeline operation.
Spiral welded pipe manufacturers should hold the country issued by the industrial production permit. Thelicense system requires that the manufacturer of the spiral welded pipeshould first be examined and approved by the competent authority of thestate, and the corresponding production means, the inspection equipmentand the quality assurance system should be run well and the productshould meet the requirements of the national standard and the qualitystandard , By the National Industrial Products Production License Office confirmed after the certificate. So spiral welded pipe manufacturers have a more complete quality assurance system and quality control procedures.
Straight seam welded pipe manufacturers do not have industrial products production license requirements.
Asthe hot-rolled coil material technical performance and productiontechnology requirements are higher, so on the one hand the domesticstandard manufacturers than steel manufacturers to less, on the otherhand its production process and quality level to determine its marketprice is higher than the heat Rolled steel plate. This is the main reason why the market price of spiral welded pipe is higher than that of straight seam welded pipe. For the composition of steel pipe sales price, material prices are dominant and even decisive factors.
Carefullyexamine the spiral welded pipe and straight seam welded pipe pricedifference, spiral welded pipe price slightly higher than the straightseam welded pipe is due to the price difference between the productionof the main material. However, steel pipe production is only part of the project, if takinginto account the overall quality of the project, the project cost andother factors, spiral welded pipe still has the overall advantage.
Length and price
Productionlength of the length of the tube than the average length of the pipeinto the rate of decline is greater, the production enterprises to raisethe price requirements are reasonable. Increase the rate of the enterprise is not consistent, generally based on the base price increase of about 10%. The length of the length should be within the normal length range and is a fixed length dimension required in the contract. Butthe actual operation are cut out the absolute length of the length isnot possible, so the standard length of the length of the provisions ofthe allowable positive deviation. Ifthere is no deviation in the length of the standard deviation andcutting allowance, the supply and demand sides should be negotiated andspecified in the contract. Times the length of the same length with the length of the productionwill bring a significant reduction in production rate, so the productionenterprises to raise the price is reasonable, the increase in the rateof increase with the length of the same length of the same.
Plasma cutting dust
Plasmain the process of cutting the workpiece will produce a lot of metalvapor, ozone, nitrogen oxide dust, will seriously pollute thesurrounding environment. The key to solving the soot problem is how to smoke all the dust intothe dust removal equipment, so as to prevent air pollution.
And for spiral welded pipe plasma cutting, dust is difficult:
1,the plasma gun nozzle in the cutting of the air at the same time to thetwo opposite direction blowing, so that smoke from the ends of thespiral pipe, and installed in the direction of the spiral pipe in thesuction port is very difficult to smoke well recovered The
2, the outside of the suction air from the machine outside the gapinto the suction port and the air volume is very large, so that thetotal amount of dust and cold air in the spiral pipe is greater than theeffective amount of dust inhaled by the dust collector, so that thecomplete absorption of dust can not be completed.
3, due to the cutting part of the dust from the suction inlet fartherto reach the suction port at the wind is difficult to twist the dust.
To this end, the design principles of dust cover is:
1,the dust collector inhalation of the air volume is greater than theplasma generated by the dust and the total amount of air inside thepipeline should be in the spiral pipe to form a certain amount ofnegative pressure chamber, and try not to let the outside air into alarge number of spiral steel pipe, Effectively dust into the dust collector.
2, in the spiral pipe cutting point after the location of the dustwill be blocked, the suction port as far as possible to avoid the coldair into the spiral steel pipe inside the spiral steel pipe to form anegative pressure
Installthe dust baffle on the inside of the spiral pipe and place it at about500mm at the cutting point of the plasma gun. After the helical steelpipe is cut off, it will absorb all the smoke and dust. Note that the dust baffle needs to be positioned precisely after cutting. In addition, in order to support the fume hood of the accompanying carand spiral steel tube rotation consistent with each other, must beaccompanied by the car wheel angle and roller angle consistent.
Forthe diameter of about 800mm large diameter spiral welded pipe plasmacutting, you can use the method; for less than 800mm diameter, smalldiameter pipe can not smoke from the direction of the outlet, do nothave to install the internal baffle. However, there must be an external baffle that shields the cold air from entering the dust inlet of the forming device.