Difference of LSAW and SSAW

Dec 2


Allice S Lee

Allice S Lee

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This artical will explain the difference of LSAW and SSAW in many aspects.


Metallurgical properties of materials
LSAW steel pipe is produced,Difference of LSAW and SSAW Articles and spiral welded pipe is produced by hot-rolled coil. Unit hot strip rolling process has a number of advantages, having access to production of high-quality pipeline metallurgical process capability. For example, the output carriage equipped with a water cooling system to accelerate cooling, which allows the use of low alloy composition to achieve the specific intensity level and low temperature toughness to improve the weldability of the steel. However, this system is basically no steel production plant. Alloy content Coil (carbon equivalent) is often lower than a similar rating plate, which also improves weldability spiral welded pipe.
More needs to be noted that, due to the spiral welded steel coil rolling direction than perpendicular to the axial direction (depending on steel sandwiched solution helix angle) and straight seam steel pipe rolling direction perpendicular to the pipe axis direction, and therefore, spiral crack resistance of the material is better than straight seam welded steel pipe.
· Welding Technology
From the welding process, the welding straight seam steel spiral welded pipe and coherent approach, but inevitably there will be many Longitudinal T-weld, and therefore the probability of the existence of welding defects has greatly improved, and welding residual T welds stress is large, the weld metal are often in three-dimensional stress state, increases the likelihood of cracks.
Furthermore, according to the provisions of submerged arc process, each weld shall have the arc at the place and extinction, but in each Longitudinal seam welding ring, unable to meet the conditions, which may have a place in the extinction more weld defects.
· Strength Features
When the pressure in the pipe to withstand, typically produces two main stress on the wall, that the radial and axial stress stress δY δX. Weld resultant stress δ = δY (l / 4sin2α + cos2α) 1/2, where, α helix spiral welded pipe weld angle.
Helix angle of the spiral weld pipe is generally 50-75 degrees, so the spiral weld resultant stress is 60-85% Longitudinal principal stress. Under the same operating pressure, spiral welded pipe of the same diameter than the Longitudinal wall thickness can be reduced.
According to the above characteristics we can see:
A? Occurs when spiral welded pipe blast, the weld suffered stress and the resultant stress being relatively small, blasting the mouth is generally not originated in the spiral weld, its security Longitudinal high ratio.
B. When there are parallel with the spiral weld near the defect, because the spiral weld force is smaller, so the risk of expansion not as good as straight weld large.
C. when subjected to the maximum load due to the radial stress is present in the maximum stress on the pipe, so the weld in the vertical stress in this direction. That straight seam to bear the load maximum, circumferential welds withstand a minimum load, spiral seam between.
· Hydrostatic burst strength
By the relevant comparison test, to verify the spiral welded pipe and Longitudinal yield pressure and burst pressure measured and theoretical values are basically consistent deviation close. But neither the yield stress or burst pressure, were lower than the Longitudinal spiral welded pipe. Blasting test also shows ring spiral welded pipe blast the deformation rate significantly greater than the Longitudinal mouth. It was thus confirmed, spiral welded pipe Longitudinal superior plastic deformation, blasting the mouth is generally confined to within a pitch, which is spiral weld for expansion gap played a powerful role in binding due.
· Toughness and fatigue strength
Trends in the development of large-diameter pipes, high strength. With the increase of the diameter of the pipe, the steel grade increase, resulting in greater the ductile fracture tip steady expansion trend. According to the test US research institutions showed that spiral welded pipe and Longitudinal although the same as a level, but the spiral welded pipe has a high impact toughness.
Because of the transfer line output volume changes in the actual operation, the steel is subjected to random alternating loads of action. Learn low cycle fatigue strength of steel, judging life of the pipeline is of great significance.
According to measurement results, the fatigue strength of the spiral welded pipe and seamless and ERW pipe the same test data and seamless pipe distribution and resistance in the same area, while Longitudinal submerged arc than the average higher.
· Field weldability
Field weldability mainly by the steel material and port with the dimensional tolerances decision.
Taking into account the requirements of the steel pipe installation and construction, steel processing and production continuity and consistency of shape geometry is particularly important.
Spiral welded pipe production is basically stable continuous flow in the same working conditions: The Longitudinal production process is segmented, including the entire board / indenter / pre-roll / spot welding / welding / finishing / peer group the process of multi-channel processes. This is an important feature different from the Longitudinal spiral welded pipe production production.
Stable production conditions is very easy to control and geometries ensure the welding quality. Because of spiral welded tubular structured, weld uniform, with respect Longitudinal, spiral pipe has a very good mouthpiece ovality and the end vertical, to ensure that the site when steel welding Group Group accuracy.
· Impact on the flow characteristics of the transmission medium
The length of the transfer line in the pressure drop and tube, viscosity coefficient of the fluid, fluid velocity, fluid resistance coefficient is proportional, inversely proportional, and the inner diameter of the tube. The fluid drag coefficient and Reynolds both related, but also with the roughness of the tube wall of the surface. It was determined that affect the surface roughness of the tube wall plays than the local uplift of the area (such as a spiral or longitudinal seam weld, and even includes an inner circumferential weld) on ten times played.
· Production and Management
Spiral welded steel pipe production to reflect the high quality and efficiency advantages. A spiral welded pipe production unit is equivalent to 5-8 Longitudinal station equipment, how to make more than one volume control equipment, production lines are able to achieve the same production standards, ie unified production process specifications and quality assurance system to meet the quality of welding production Requirements and pipe manufacturing grade will be an arduous task.
Long production potential than the increase in the amount of project management and engineering quality supervision. Multiple roll straight seam welding pipe mill and the corresponding devices, operating skills of its operating personnel, quality consciousness, the difference distribution points and control procedures will bring production management, schedule, inspection and acceptance, many difficulties in coordinating other aspects of delivery easily result in quality hectic and manufacturers and construction unit management and coordination of prevarication.
·Quality assurance
Spiral welded pipe production standards in accordance with the provisions of spiral welded steel pipe of the main inspection / control items include:
Dimensions: pipe diameter, wall thickness, ovality, bending, tube end squareness,
Length appearance quality: weld reinforcement, the wrong side, steel surface, delamination, inclusions, weld defects determination
chemical composition
Tensile testing of welded joints
Hydrostatic Testing
Etch test
Nondestructive Inspection
The Longitudinal no corresponding production standards.
General spiral welded pipe mill line continuous test methods are used to ensure the quality of welding seam, which is another important feature of the spiral welded pipe production distinguish Longitudinal production. Continuous monitoring test in favor of welding defects, welding quality and stability, the welding grade guarantee.
Due to limitations of the production process, Longitudinal extremely difficult to achieve uninterrupted inspection. This will increase the probability of occurrence of welding hidden quality problems, and even affect the overall reliability of the future pipeline operation.
· Production Qualification
Spiral welded pipe manufacturer should hold the national industrial production permit issued. Licensing requirements of spiral welded pipe manufacturer should first review the assessment by the national institutes of recognized authority, with the appropriate means of production, testing equipment, good and effective quality assurance system, the product should meet the national standard level and quality standard requirements , after the country's industrial production permit issuing office confirmed. So spiral welded pipe producers have better quality assurance system operational procedures and quality control.
Longitudinal manufacturers no industrial production permit requirements.
· Price Analysis
Due to the high technical performance of hot-rolled coil material and production technology requirements, so the one hand, domestic manufacturers meet the standards than the steel plate manufacturer less the other hand, their production processes and quality level to determine its market price is also higher than the heat rolled steel sheet. This is the main reason for the spiral welded pipe market price is higher than the Longitudinal. For the composition of the steel pipe sales price, the price of materials is the dominant or even the decisive factor.
Conscientiously study and Longitudinal spiral welded pipe price differences, the price slightly higher than the Longitudinal spiral welded pipe price difference is due to the production of primary materials due. However, steel production is only one part of the project but, if taking into account the overall quality of the project, the project total cost and other factors, spiral welded pipe still has the overall advantage.
Cut length and price
Production cut length tube timber rate is usually lower than that of the length of the tube by a big margin, the company proposed fare increase request is reasonable. Companies are not consistent markups, usually based on the base price increase of about 10%. Cut length should be within the usual length, size is a fixed length contract requirements. But the actual operation are absolute cut-length cut is unlikely, and therefore the standard length for a predetermined length of positive deviation allowed. If the standard deviation is no double length and cutting margin provisions negotiated by both parties and specified in the contract. Times longer scale length with the same length, the company will bring a significant reduction in the rate of finished product, so the company proposed increases are reasonable, its rate of increase with the length of the rate of increase is substantially the same length.
Plasma cutting dust
Plasma cutting a workpiece process will produce large amounts of metal vapor, ozone, nitrogen oxides, soot, will seriously pollute the surrounding environment. The key to solve the dust problem is how to put all the plasma dust sucked into the dust removal device, thus preventing air pollution.
As for the spiral welded pipe plasma cutting, dust difficulty is:
1, the plasma gun nozzle air is blown simultaneously to both reverse direction during cutting, so that the smoke coming out from both ends of the spiral steel pipe, and spiral steel pipe installed in a direction of the intake port is very difficult to recycle the fine dust .
2, the inlet peripheral cold air into the inlet from the space outside of the machine and a large amount of wind, so that the total inner spiral pipe smoke and cold air is greater than the effective amount of dust inhaled air, thus cutting soot absorption becomes completely impossible.
3, due to the cutting site distant from the dust suction port, the suction port of the wind to reach the difficult twitch smoke.
For this reason, the design principles dust cover are:
1, the dust inhaled air volume is greater than the total amount of plasma cutting and pipe smoke generated inside the air should be inside the spiral steel pipe of a certain amount of negative pressure chamber, and try not to let outside air poured into the spiral steel pipe, in order to effectively dust sucked into the dust collector.
2, the spiral steel pipe cutting point position after smoke blocked the entrance to avoid the cold air sucked into the internal spiral steel pipe, spiral steel pipe in the internal space to form a negative pressure
The dust baffle is mounted inside the spiral steel pipe accompanying trolley and placed plasma cutting point gun at about 500mm, spiral pipe cut after staying at, to absorb all the dust. Note that the smoke baffle must accurately positioned at the position after cutting. In addition to the support smoke baffle accompanying car and spiral pipe rotation coincide with each other, we must be allowed to take the accompanying car wheel angle and roll angle within consistent.
For large diameter spiral welded pipe diameter of about 800mm, plasma cutting, this method can be used; for diameter less than 800mm, small diameter pipe smoke can not emerge from the direction, without having to install an internal baffle. But in the former dust suction port, must have blocked cold air into the outer bezel.
Development Direction editor
Due to increasingly higher bearing pressure pipelines, using increasingly harsh conditions, and to try to extend the life of the pipeline, the main development direction of the spiral welded pipe is:
(1) the production of large diameter thick-walled tube to increase pressure resistance;
(2) design and production of new steel structure, such as a double spiral welded pipe, that is half the thickness of the wall of steel welded into a double tube, not only the intensity is higher than the same thickness of the single-pipe, and will not appear brittle failure;
(3) development of new steel grades, improve smelting technology level, extensive use of controlled rolling and after rolling heat treatment process, to continuously improve the pipe body toughness and weldability;
(4) to develop coated pipes, such as the inner wall of the tube is coated with the coating, not only extend life and improve the smoothness of the wall, reducing fluid friction, reducing accumulated wax and dirt, reducing pigging frequency, lower maintenance cost.

SSAW pipe played a significant role in conveying gas, transportation. With the planning and construction of a number of major domestic and international pipeline projects, large deformation steel, high-strength levels and heavy-gauge hot simmer elbow pipe temperature high value-added products, showing a good market competitiveness and greater market demand , while domestic enterprises in the development of the series products relatively slow progress, should be developed for industrial applications with high added value large deformation pipeline as soon as possible, the heat and simmer bend steel, pipeline stations with low-temperature steel pipe, X100 straight seam submerged arc welded pipe, spiral submerged arc welded pipe and spiral welded pipe heat simmer bend.

Perform standard editing
Pressure fluid transport spiral submerged arc welded pipe SY5036-83 mainly used to transport oil, natural gas pipelines; pressure fluid delivery with spiral seam high frequency welded steel pipe SY5038-83, high frequency lap welding method, with the in the pressure spiral seam high frequency welded steel pipe fluid delivery. Strong pressure steel, plastic, and easy welding and machining molding; general low pressure liquid delivery spiral submerged arc welded pipe SY5037-83, using double-sided automatic submerged arc welding or welding into the legal system for water, gas, air and steam and other general low pressure liquid delivery SAW pipe.
Commonly used spiral steel pipe standards are generally divided into: SY / T5037-2000 (Ministry of standard, also known as general fluid pipes with spiral submerged arc welded pipe), GB / T9711.1-1997 (GB, also known as the oil and gas industries - Steel pipe Technical delivery conditions for the first part: A grade steel (demanding a GB / T9711.2 B grade steel)), API-5L (American Petroleum Institute, also known as line pipe; which is divided into two levels PSL1 and PSL2), SY / T5040-92 (pile with spiral submerged arc welded pipe).
Equipment editor
Uncoiler: Double Cone head uncoiler, removable 32 tons heavy steel coils.
Flat steel cutter machine: seven flat roller cutter, thickness of up to 20mm
Shears: You can cut 2000mm * 20mm Coil
Welder: welding just lead end
Disc cut: cut steel edges reach a predetermined size
Milling Machine: processed into the desired groove of the steel sheet ≥10mm
Edger means: to ensure delivery of steel running along the line
Delivery machine: two roll forming machine for the delivery of the main power
Guides: ensure balance plate into the molding machine
Molding machines and Bridge, output roller, three club curved plate, outside roller sizing
Molding machine can be shaped pipe Φ219-Φ2520mm
Inside and outside the welding equipment: welding monofilament inner and outer double wire welding, the choice of Lincoln
Welder, and infrared thermal imaging within the welding tracking control system
Flux recovery: recovery after welding flux
Automatic welding equipment outside: repair weld defects
Flat head to edge machine: to ensure requirements meet the standard tube end
Hydraulic test machine: 100% of the hydrostatic test
Weighing measuring devices: Weighing and measuring the length of pipe