Wednesday, November 26, 2014

Roll pass desigh of welded steel pipe

Hole is made by the tank formed by a pair (or more) rolls rolling. Steel strip deformation to a certain shape (rolled) through the hole, and through a series of successive deformation molded into a cylindrical tube. For the series of grooved shape and size selection, calculation and determination, and finally drawn into roll chart, the whole process is called the roll pass design. The basic requirements for roll pass design of welded steel pipe (LSAW and SSAW steel pipe)are:
(1) with a minimum passes (i.e., the shortest length of the deformation zone) to complete the forming and deformation process;
(2) the generated edge extending as small as possible when molding without creating ridges and folds;
(3) the edges are fully deformed and tube joints for no beak-shaped;
(4) stable strip forming in the hole;
(5) uniform deformation, roll small and uniform wear;
(6) low energy consumption;
(7) ensure the pipe dimensions and surface quality meet standard requirements;
(8) roll processing convenient, easy to manufacture, pass design can be combined with added processing;
(9) the pass design is with the characteristic of standardization, which can fit the unit with the same type of product specifications;
(10) can make use of computer-aided design (CAD).

DWTT of pipeline steel

DWTT (drop weight tear performance) is an important performance parameters of pipeline steel. Pipeline steel pipe includes seamless steel pipe and welded steel pipe (LSAW and SSAW steel pipe) and for the pipeline steel used for the production of oil pipeline, it not only requires a certain strength, but also a certain toughness, so the production pipeline are all required a DWTT test, and this parameter has a close relationship to its body ferrite.
For the impact of ferrite type on DWTT: pipeline generally form the inner polygonal ferrite or acicular ferrite.
The role of polygonal ferrite is:
1) coordination deformation. Due to the polygonal ferrite belongs to a low strength and good ductility phase, there is an appropriate amount of polygonal ferrite can improve coordination among various organizations deformation capacity, in addition, the presence of grain boundaries of pearlite also makes coordination ferrite deformation limited, the deformation resistance to increase, and expansion work successfully shaped crack increases, thereby improving toughness.
2) passivation crack tips. Polygonal ferrite belong to the toughness organization with low strength, it can make a greater plastic deformation in the crack tip, impeding crack propagation, meanwhile the crack tip stress gets relaxed and the crack tip passivated. In addition, a certain amount of polygonal ferrite grains will continue to force the crack go through the pearlite structure and polygonal ferrite, a large number of the interface suppresses the crack propagation, so that the toughness is improved.

long-distance slurry pipeline pipe

Particularity research with long-distance slurry pipeline pipe technology
The principle in the application of Long-distance slurry pipeline and oil and gas transmission pipelines is the same, but the delivery media is different, thus forming their own transportation technology. The main parameters of Kunming Dahongshan iron ore pipeline system has been put into production last year are as follows:
Transmission capacity 2.3 million t / a
Conveyor length 171Km
Pipe material API 5L GrX65
Pipe wall thickness 7.9 --- 14.7mm
Pipe diameter 244.5mm
Working pressure 24.4mpa / max
Pulp density of 65%
Transport velocity 1.5m / s
Concentrate fineness 80-0.043mm
According to its transmission medium and process, it puts forward specific technical requirements for the welded steel pipe, especially the technology selection of steel pipe.
In theory, the long-distance slurry pipeline selection can be a seamless steel pipe, high-frequency straight seam resistance welded steel pipe (ERW steel pipe), double-sided straight seam submerged arc welded steel pipe (LSAW steel pipe), but considering the economic pipeline investment and delivery amount break-even point, the length of the 100km pipeline is the most economical, ERW steel pipe and LSAW steel pipe are generally used. Information from the project abroad, pipe diameter minimum 114.3mm, wall thickness of 7.1-12.7mm, the largest pipe is 660mm and maximum wall thickness of 23.01mm, steel grade for x52-x70. Owners tend to choose ERW steel pipe, but ERW steel pipe limited to the wall thickness and grade, the majority uses LSAW steel pipe. From pipe technology, ERW steel pipe through the weld heat treatment process is better than the LSAW steel pipe with wide weld.

Tuesday, November 25, 2014

Why the ERW steel pipe aces in the city gas pipeline network construction

"Town Gas Design Code" provides the gas pipeline with pressure greater than 0.4Mpa. The pressure is less than 0.4Mpa pressure and low-pressure gas pipeline should use polyethylene pipe, mechanical interface ductile iron pipe, steel steel or steel skeleton plastic pipe. For pipeline for urban transport, the ERW steel pipe more than 0.4Mpa pressure is with undisputed status compared to other materials used in the steel pipe. Therefore, ERW steel pipe is the preferred city gas pipeline network construction.
1, In terms of the safety, for the city gas pipeline network main pipe, the bearing capacity, tensile strength and elongation of ERW steel pipe are all far greater than cast iron pipe, and bearing capacity, tensile strength and the ability to adapt to the temperature difference are far greater than "PE "pipe; and in terms of the interface rigors, ERW steel pipe weld interface is far much more closely than the cast iron pipe, and much more solid;
2, in terms of the adaptability, ERW steel pipe is suitable for gas, LNG, LPG, liquefied natural gas and air mixture, and cast iron pipe on the ability to adapt to LNG and natural gas is much less; ERW steel pipe capacity to adapt to temperature and pressure range is much greater than the "PE" pipe.
3, In terms of the economic aspect, ERW steel pipe is cheaper than ductile iron pipe. And when more than φ160, ERW steel pipe is also cheaper than the "PE" pipe (generally speaking, most of the city gas main pipe φ300 or so).
4, corrosion resistance of ERW steel pipe is not as good as cast iron pipe and "PE" pipe, which is an important issue to be sure to take a good anti-corrosion measures in the design and construction.

Monday, November 24, 2014

12Cr1MoV high alloy seamless steel pipe

              GB5310 standard 12Cr1MoV high alloy seamless steel pipe 
               bearing capacity parameters allowable stress lookup table
                            Chemical composition of high-pressure alloy steel pipe
           Chemical composition%
                         Mechanical properties of alloy seamless steel pipe



                          Alloy seamless steel pipe allowable stress
Allowable stress (Mpa) under the following temperature (℃)

Seamless steel pipe for low and medium pressure boiler

Pressure seamless steel pipe because of its special purpose, a series of tests must be made before using. If not, it is likely to leave hidden problem for future safety production. Because of the working pressure of low and medium pressure boiler seamless steel pipe is less than 5.88Mpa, operating temperature is below 450 ℃; this is a rough range, as long as the low and medium pressure boiler seamless steel pipe is produced according to the standards, there is no problem to use it normally. Of course, it has no problem also for the medium pressure boiler seamless steel pipe to be pressurized to about 7,8MPA, but if it is long-term work under this pressure, seamless steel amounted to less than its normal life. Leakage may occur and cause accidents in advance.
(1) flattening test
For outside diameter D> 22 mm, wall thickness S≤10 mm pipe, flattening test should be carried out, flat pitch h following formula
h = (1 + α) S / (α + S / D) where S --- pipe wall thickness, mm;
D --- pipe diameter, mm;
α --- unit length deformation coefficient, 0.08; when the S / D≥0.125 0.07.
(2) Bending test
D≤22mm outer diameter pipe bending test should be carried out. Bending angle is 90 °, the apex radius of 6 times the pipe diameter. Not bend cracks and cracks.
(3) hydraulic test
Should be carried out by the root test, the test pressure P (MPa) is calculated as follows, but 10 steel maximum pressure 7 MPa; 20 steel maximum pressure 10 MPa, the regulator for not less than 5 s.
P = 2SR / D where S --- nominal pipe wall thickness, mm;
D --- nominal diameter pipe, mm;
R --- allowable stress, provides 60% of the yield point, MPa.
Supplier eddy current testing can be used instead of hydraulic tests.

How to choose the way to weigh the steel pipe

The weight of the steel pipe is the most important parameter in the trade, which determines the steel trade fair and just. In general, there are two ways to weigh the steel pipe: the theoretical weight and weighing weight. Theoretical weight of steel is through the theoretical data (actual measured pipe outside diameter, wall thickness and length) and calculate the weight by a mathematical formula, the formula is: = weight per meter of pipe (OD - Wall Thickness) * wall thickness * 0.02466, the unit value is KG; weighing platform weight is hanging pounds or so on the actual weighed weighing tool steel weight. But in the steel industry, for different steel tend to have their own "hidden rules."

Whether seamless steel pipe, straight seam steel pipe or forged steel pipe, their theoretical weight formula is :(OD - wall thickness ) * wall thickness * 0.02466 = KG per meter of pipe. Generally speaking, this theoretical approach is a little less than the actual weight of the seamless steel pipe, is approximately equal to the actual weight of the forged steel pipe, but a little greater than the actual weight of lsaw steel pipe, ssaw steel pipe or erw steel pipe. In view of this, the seller will take a different approach to weight in the actual process. Straight seam steel pipe is generally taken as the theoretical weight mode, seamless generally uses the weighing weight way. For which way to choose, we can find the cause in the steel manufacturing process.

Longitudinal steel pipe is made with open flat plate or roll, and the actual thickness of the plate or a plate generally have a lower differential, about 0.25mm-0.5mm less than the theoretical thickness, so the weight of the theoretical weight way is to be greater than weighting way; while for the actual thickness of the seamless steel pipe is generally poor, the small thin-walled seamless steel pipe, seamless steel pipe, 20MM thick seamless steel pipe above it on the poor big, can reach 1-2MM, if 40MM or 50MM thick, seamless steel pipe, seamless steel pipe wall thickness can be the difference between some manufacturers to 3-5MM, and the next is almost no difference, so as to ensure that only weigh the seller does not lose tons. Same as for forging steel, because of its very high precision product processing, diameter and wall thickness fairly standard, so conducive to the theoretical formula worked out important and weighing weight.