One, seamless pipe and welded pipe comparison:
1, high pressure resistance. Seamless pipe with the same specifications have different optional wall thickness, the pressure of a wide range of applications, but the working pressure of the air conditioning water system, welded pipe will be able to cope with, which is not the reason for the selection;
2, wide caliber. Welded pipe DN100 or more less, while the seamless pipe is more, this is a reason to choose;
3, easy construction. Seamless pipe with welding and flange connection, large-diameter pipe with screw connection installation is difficult, large-diameter pipe is now trench installation, but this method is not suitable for air-conditioning water system. This is the choice of reason two.
Two, seamless pipe mixed with galvanized welded pipe:
Because of the limitations of the construction method, seamless pipe is not galvanized before leaving the factory, the system installs a second galvanized need, plus a second installation, high construction costs (high price of the material itself), and a long period of time. If not the second galvanized on the impact of the system is not the second galvanizing fee so much.
Third, the specification of the welding construction requirements are not high, but welding is not good for the service life of the system has a big impact.
The professional specification for welding construction quality requirements are up to strength and confinement test, the weld is not tested, but the weld in the delivery and warranty period is not leakage, is not equal to the use of the system is not leakage, the actual operation of a number of years of leakage there. Maintenance can only be used to patch welding, is bound to destroy the secondary galvanized layer, the impact on the service life of the system needless to say.
So my point of view, air-conditioning water system should not be used in large quantities of seamless pipe for large caliber, pay attention to the quality of construction, and do the second galvanized.
Speaking of thermal stress release, design considerations, construction practices, and pipe basically has nothing to do.
Seamless steel pipe: seamless steel pipe is made of steel ingot or solid billet by piercing into a bristle tube, and then by hot rolling, cold rolling or cold dialing. The specification of seamless steel pipe is expressed in millimeters of outer diameter * wall thickness. Seamless steel pipe is divided into two categories of hot-rolled and cold-rolled (dial) seamless steel pipe.
Hot rolled seamless steel pipe is divided into general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, petroleum cracking pipe, geological steel pipe and other steel pipe. Cold rolled (dial) seamless steel pipe in addition to general steel pipe, low and medium pressure boiler steel pipe, high pressure boiler steel pipe, alloy steel pipe, stainless steel pipe, petroleum cracking pipe, other steel pipe, including carbon thin-walled steel pipe, alloy thin-walled steel pipe, stainless thin-walled steel pipe, shaped steel pipe. Hot rolled seamless pipe outer diameter is generally greater than 32mm, wall thickness 2.5-75mm, cold rolled seamless steel pipe diameter can be up to 6mm, wall thickness can be up to 0.25mm, thin-walled pipe outer diameter can be up to 5mm wall thickness of less than 0.25mm, cold rolled than hot rolled high dimensional accuracy.
General seamless steel pipe is made of 10, 20, 30, 35, 45 and other high-quality carbon steel 16Mn, 5MnV and other low-alloy structural steel or 40Cr, 30CrMnSi, 45Mn2, 40MnB and other composite steel hot-rolled or cold-rolled. 10, 20 and other low-carbon steel seamless pipe is mainly used for fluid transportation pipeline. 45, 40Cr and other medium carbon steel made of seamless pipe is used to make mechanical parts. Seamless pipes made of medium carbon steel such as 45, 40Cr are used to make mechanical parts, such as automobiles, tractors and other stressed parts. General use of seamless steel pipe to ensure the strength and flattening test. Hot rolled steel pipe to hot rolled state or heat treatment state delivery; cold rolled to hot to heat treatment state delivery.
Low and medium pressure boiler seamless steel pipe: used in the manufacture of a variety of low and medium pressure boilers, superheated steam pipe, boiling water pipe, water-cooled wall pipe and locomotive boilers with superheated steam pipe, large smoke pipe, small smoke pipe and arch brick pipe. Hot-rolled or cold-rolled (dialed) seamless steel pipe made of high-quality carbon structural steel. Mainly with 10, 20 steel manufacturing, in addition to ensure that the chemical composition and mechanical properties to do hydrostatic test, crimping, flaring, flattening and other tests. Hot rolled to hot rolled state delivery, cold rolled (dial) to heat treatment state delivery.
High-pressure boiler steel pipe: mainly used to manufacture high-pressure and above the pressure of steam boiler piping and other high-quality carbon structural steel, alloy structural steel and stainless heat-resistant steel seamless steel tube, these boiler tubes by the party at high temperature and high pressure work, tube in the role of high temperature smoke and water vapor will also be oxidized and corroded, so the requirements of the steel tube has a high enduring strength, high oxidation resistance, and has a good organizational stability. Good organizational stability, the use of steel are: high-quality carbon structural steel steel number 20G, 20MnG, 25MnG; alloy structural steel steel steel number 15MoG, 20MoG, 12CrMoG, 15CrMoG, 12Cr2MoG, 12CrMoVG, 12Cr3MoVSiTiB, etc.; rust-resistant and heat-resistant steel commonly used 1Cr18Ni9, 1Cr18Ni11Nb high-pressure boiler tube in addition to ensuring the chemical composition and mechanical properties, to do root by root hydraulic test, to be flared, flattened test. Steel pipe heat treatment state delivery. In addition, the finished steel pipe microstructure, grain size, decarburization layer also has certain requirements.
Geological drilling and oil drilling control seamless steel pipe; in order to explore the underground rock structure, groundwater, oil, natural gas and mineral resources, the use of drilling rigs to drill wells. Oil, natural gas extraction is even more inseparable from the drilling, geological drilling and control of oil drilling with seamless steel pipe is the main equipment for drilling, mainly including core outer pipe, core inner pipe, casing, drill pipe and so on. Due to the drilling pipe to work deep into the depth of several thousand meters of stratum, the working conditions are extremely complex, the drill pipe is subjected to tensile, compressive, bending, torsion and unbalanced impact load and other stresses, but also by the mud, rock abrasion, so the requirements of the pipe must be sufficient strength, hardness, abrasion resistance and impact toughness, the steel pipe with steel with "DZ" (geology of the Hanyu Pinyin prefix) plus the number one on behalf of the yield point of steel, commonly used steel number DZ45 45MnB, 50Mn; DZ50 40Mn2, 40Mn2Si; DZ55 40Mn2Mo, 40MnVB; DZ60 40MnMoB, DZ65 27MnMoVB. steel pipe are delivered in a heat-treated state.
Petroleum cracking pipe: used in petroleum refineries, furnace pipe, heat exchanger pipe and pipeline seamless pipe. Commonly used high-quality carbon steel (10, 20), alloy steel (12CrMo, 15CrMo), heat-resistant steel (12Cr2Mo, 15Cr5Mo), stainless steel (1Cr18Ni9, 1Cr18Ni9Ti) manufacturing. In addition to the chemical composition and various mechanical properties of steel pipe, but also to ensure that the water pressure, flattening, flaring and other tests, and surface quality and non-destructive testing. Steel pipe in the heat treatment state delivery.
Stainless steel pipe: hot rolled with a variety of stainless steel, cold rolled stainless steel pipe, widely used in petroleum, chemical equipment, piping and various uses of stainless steel structural parts, in addition to the chemical composition and mechanical properties should be guaranteed, where used to withstand the pressure of fluids to ensure that the pipe is hydrostatic test pass. A variety of special steel pipe to ensure that the conditions in accordance with the provisions.
Seamless steel pipe is divided into hot-rolled (extruded) seamless steel pipe and cold-drawn (rolled) seamless steel pipe because of its different manufacturing processes. Cold-drawn (rolled) tube is also divided into two kinds of round tube and shaped tube. Seamless steel pipe, and because of its different uses and is divided into the following varieties:
1.GB/T8162-1999 (structural seamless steel pipe). Mainly used for general structure and mechanical structure. Its representative materials (grades): carbon steel, 20, 45 steel; alloy steel Q345, 20Cr, 40Cr, 20CrMo, 30-35CrMo, 42CrMo and so on.
2.GB/T8163-1999 (seamless steel pipe for transportation of fluids). Mainly used in engineering and large-scale equipment for the transportation of fluid pipelines. Representative material (grade) for 20, Q345, etc..
3.GB3087-1999 (low and medium pressure boiler seamless steel pipe). Mainly used for industrial boilers and domestic boilers to transport low and medium pressure fluid piping. The representative material is 10, 20 steel.
4.GB5310-1995 (high-pressure boiler seamless steel pipe). Mainly used in power stations and nuclear power plant boilers on the high temperature, high pressure transportation fluid container and piping. The representative materials are 20G, 12Cr1MoVG, 15CrMoG and so on.
5.GB5312-1999 (carbon steel and carbon manganese steel seamless steel pipe for ships). Mainly used for ship boilers and superheaters with I, II level pressure-resistant tubes and so on. Representative materials for 360, 410, 460 steel grade.
6.GB1479-2000 (high-pressure fertilizer equipment with seamless steel pipe). Mainly used for fertilizer equipment to transport high temperature and high pressure fluid pipeline. The representative materials are 20, 16Mn, 12CrMo, 12Cr2Mo and so on.
7.GB9948-1988 (seamless steel pipe for petroleum cracking). Mainly used in petroleum refineries, boilers, heat exchangers and their pipelines for transporting fluids. Its representative materials are 20, 12CrMo, 1Cr5Mo, 1Cr19Ni11Nb and so on.
8.GB18248-2000 (seamless steel pipe for gas cylinder). Mainly used for making all kinds of gas, hydraulic cylinders. Its representative materials are 37Mn, 34Mn2V, 35CrMo and so on.
In addition, there are GB/T17396-1998 (hot-rolled seamless steel pipe for hydraulic strut), GB3093-1986 (high-pressure seamless steel pipe for diesel engine), GB/T3639-1983 (cold-drawn or cold-rolled precision seamless steel tubes), GB/T3094-1986 (cold-drawn seamless steel pipe for profiled steel tubes), GB/T8713-1988 (Seamless Steel Tubes with Precision Inner Diameter for Hydraulic and Pneumatic Cylinders), GB13296-1991 (Seamless Stainless Steel Tubes for Boilers and Heat Exchangers), GB/T14975-1994 (Seamless Stainless Steel Tubes for Structural Use), GB/T14976-1994 (Seamless Stainless Steel Tubes for Fluid Conveyance) GB/T5035-1993 (Seamless Steel Tubes for Automotive Semi-axle Casing), APISPEC5CT-1999 (Specification for Casing and Tubing), etc.
The process is briefly described as follows:
1. Hot rolled (extruded seamless steel pipe): round billet→heating→piercing→three-roll tilting, rolling or extruding→stripping→dimensioning (or reduction)→cooling→straightening→hydraulic test (or flaw detection)→marking→stocking
The raw material for rolling seamless pipe is round billet, and the round embryo tube should be processed through the cutter's cutting into a billet with the length of about 1 meter billet, and conveyor belt to the furnace heating. The billet is sent to the furnace to be heated at a temperature of about 1200 degrees Celsius. The fuel is hydrogen or acetylene. Temperature control in the furnace is a critical issue. After the round billets are removed from the furnace, they are hollowed out by a pressure piercing machine. Generally more common piercing machine is the conical roller piercing machine, this piercing machine production efficiency, product quality, piercing and expansion of a large amount, can wear a variety of steel. After piercing, the round billet is successively three-roll tilt rolling, continuous rolling or extrusion. After extruding, the pipe should be taken off and calibrated. Sizing machine through the conical drill bit rotating at high speed into the steel embryo perforation, the formation of steel pipe. The inner diameter of the steel pipe is determined by the length of the outer diameter of the drill bit of the sizing machine. After sizing, the steel pipe enters a cooling tower and is cooled by spraying water. After cooling, the steel pipe is straightened. After straightening, the steel pipe is sent by conveyor belt to the metal flaw detector (or water pressure test) for internal flaw detection. If there are cracks, bubbles and other problems inside the steel pipe, they will be detected. After the quality inspection, the steel pipe is also passed through strict hand selection. After quality inspection, the steel pipe is sprayed with paint with number, specification, production lot number, etc.. And lifted into the warehouse by a crane.
2. Cold-drawn (rolled) seamless steel pipe: round billet→heating→piercing→heading→annealing→acid cleaning→oil coating (copper plating)→multiple cold-drawn (cold-rolled)→billet→heat treatment→straightening→hydraulic test (flaw detection)→marking→storage.
The rolling method of cold drawn (rolled) seamless steel pipe is more complicated than that of hot rolled (extruded seamless steel pipe). The first three steps of their production process are basically the same. Differences from the fourth step, round pipe billets are hollowed out, to hit the head, annealed. After annealing, it is pickled in a specialized acidic liquid. After pickling, it is oiled. Then immediately followed by a number of cold-drawn (cold-rolled) and then billet pipe, specialized heat treatment. After heat treatment, it is to be straightened. Steel pipe after straightening by the conveyor belt sent to the metal flaw detection machine (or water pressure test) for internal flaw detection. If there are cracks, bubbles and other problems inside the steel pipe, they will be detected. After the quality inspection, the steel pipe is also passed through strict hand selection. After the quality inspection of steel pipe, it is sprayed with paint with number, specification, production lot number, etc.. And lifted into the warehouse by a crane.
Welded steel pipe: also called welded pipe, is made of steel plate or steel strip after bending and molding, and then made by welding. According to the form of welded seam is divided into straight seam welded pipe and spiral welded pipe. According to the use is divided into general welded pipe, galvanized welded pipe, oxygen blowing welded pipe, wire casing, metric welded pipe, roller pipe, deep well pump pipe, automotive pipe, transformer pipe, electric welded thin-walled pipe, electric welded profiled pipe and spiral welded pipe.
General welded pipe: general welded pipe is used to transport low-pressure fluids. With Q195A, Q215A, Q235A steel manufacturing. Can also be easy to weld other soft steel manufacturing. Pipe to water pressure, bending, flattening and other experiments, there are certain requirements for surface quality, usually delivery length of 4-10m, often require fixed-foot (or times the foot) delivery. Welded pipe specifications expressed in nominal caliber (millimeters or inches) nominal caliber is different from the actual, welded pipe according to the specified wall thickness of ordinary steel pipe and thickening of two kinds of steel pipe according to the form of the pipe end is divided into two kinds of threaded and unthreaded.
With the welded steel pipe technology to improve improve and easy to process, now welded pipe instead of part of the seamless pipe, welded steel pipe has been able to produce more than 219mm (8 inch).
Galvanized steel pipe: in order to improve the corrosion resistance of steel pipe, general steel pipe (black pipe) galvanized. Galvanized steel pipe is divided into hot-dip galvanized and electric steel zinc two kinds of hot-dip galvanized galvanized layer is thick, electric galvanized low cost.
Oxygen blowing welded pipe: used as a steel blowing oxygen pipe, generally with a small diameter welded steel pipe, specifications from 3/8 inch -2 inch eight. Made of 08, 10, 15, 20 or Q195-Q235 steel strip. In order to prevent corrosion, some of the aluminum treatment.
Wire casing: also ordinary carbon steel welded steel pipe, used in concrete and a variety of structural power distribution projects, commonly used nominal diameter from 13-76mm. wire casing sleeve wall is thinner, most of the coating or galvanized for use after the requirement of cold bending test.
Metric welded pipe: specifications in the form of seamless pipe, with the outer diameter * wall thickness in millimeters expressed in the welded steel pipe, with ordinary carbon steel, high-quality carbon steel or universal low alloy steel hot strip, cold strip welding, or hot strip welding and then made by cold dialing method. Metric welded pipe sub-puneng and thin-walled, ordinary used as structural parts, such as drive shafts, or to transport fluids, thin-walled used to produce furniture, lamps and lanterns, etc., to ensure that the strength of the steel pipe and bending test.
Roller tube: used for belt conveyor rollers welded steel pipe, generally with Q215, Q235A.B steel and 20 steel manufacturing, diameter 63.5-219.0mm. on the pipe bending, end face to be perpendicular to the center line, oval degree has certain requirements, generally hydrostatic and flattening test.
Transformer tube: used in the manufacture of transformer heat pipes and other heat exchangers, made of ordinary carbon steel, the requirements for flattening, flaring, bending, hydraulic test. Tubes are delivered in fixed or multiple sizes, and there are certain requirements for tube bending.
Shaped tubes: square tubes, rectangular tubes, cap-shaped tubes, hollow rubber steel doors and windows with steel tubes welded by ordinary carbon structural steel and 16Mn and other steel strip, mainly used as agricultural machinery components, steel windows and doors.
Thin-walled welded tube: mainly used to make furniture, toys, lamps and lanterns. In recent years the thin-walled tube made of stainless steel belt is widely used, advanced furniture, decoration, fences and so on.
Spiral welded pipe: is a low carbon carbon structural steel or low alloy structural steel steel strip according to a certain angle of the helix (called the molding angle) rolled into a billet, and then welded the pipe seam made of it, it can be a narrower strip to produce large-diameter steel pipe. Spiral welded pipe is mainly used for oil and natural gas transportation pipelines, its specifications are expressed in terms of outer diameter * wall thickness. Spiral welded pipe has a single-side welding and double-sided welding, welded pipe should ensure that the hydrostatic test, the tensile strength of the weld and the cold bending properties to comply with the provisions.
As for the choice is mainly based on the design working pressure!
The two have different roles and are used in different places. Seamless steel pipe for high-pressure, pressure 0.8MPa above the pipeline generally have to use seamless steel pipe; and galvanized steel pipe for rust resistance, such as water and gas pipelines with galvanized steel pipe. As for the price, I see as if galvanized steel pipe is more expensive than seamless steel pipe.
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