1. Comparison of seamless pipes and welded pipes: 1. High pressure resistance. Seamless pipes have different optional wall thicknesses for the same specification, with a wide range of applicable pressure, but welded pipes can also meet the working pressure of air conditioning water systems, which is not a reason for selection; 2. Wide diameter. There are few welded pipes above DN100, while seamless pipes are more common, which is a reason for selection; 3. Easy construction. Seamless pipes use welding and flange connections, while large diameter pipes use threaded connections which are difficult to install; currently, there is groove installation for large diameter pipes, but this method is not suitable for air conditioning water systems. This is the second reason for selection. 2. Issues with mixing seamless pipes and galvanized welded pipes: Due to construction method limitations, seamless pipes are not galvanized before leaving the factory; if secondary galvanization is needed during system installation along with secondary installation, the construction cost will be high (the material price itself is already high), and the construction period will also be long. If there is no secondary galvanization, the impact on the system will not just be about the cost of secondary galvanization. 3. The standards do not have high requirements for welding construction, but poor welding has a significant impact on the service life of the system. The professional standards require that welding quality meets strength and tightness tests without inspecting welds; however, just because welds do not leak during handover and warranty periods does not mean they won't leak during the service life of the system; there have been cases where leaks occurred after several years of actual operation. Repairs can only be done by patch welding, which inevitably damages the secondary galvanization layer; thus, its impact on the service life of the system goes without saying. Therefore, my opinion is that seamless pipes should not be used extensively in air conditioning water systems; when used in large diameters, attention must be paid to construction quality and secondary galvanization should be performed. Speaking of thermal stress release, design considerations have been made and there are methods in construction that are basically unrelated to pipe materials. SeamlessSteel Pipe: SeamlessSteel Pipe, made from steel ingots or solid pipe blanks through perforation into rough tubes and then processed by hot rolling, cold rolling or cold drawing. SeamlessSteel Pipe's specifications are expressed as outer diameter * wall thickness in millimeters. SeamlessSteel Pipe, divided into hot-rolled and cold-rolled (drawn) seamlessSteel Pipe. Hot-rolled seamlessSteel Pipe, divided into generalSteel Pipe, low and medium pressure boilersSteel Pipe, high-pressure boilersSteel Pipe, alloysSteel Pipe, stainless steelSteel Pipe, petroleum cracking tubes, geologicalSteel Pipe, and others.Steel Pipe(Cold-rolled) seamlessSteel Pipe, besides generalSteel Pipe, low-medium pressure boilersSteel Pipe, high-pressure boilersSteel Pipe, alloysSteel Pipe, stainless steelSteel Pipe, petroleum cracking tubes and others also includes carbon thin-walled tubesSteel Pipe, alloy thin-walled tubesSteel Pipe, stainless thin-walled tubesSteel Pipe, special-shaped ones.Steel PipeHot-rolled seamless pipe generally has an outer diameter greater than or equal to32mm with wall thickness ranging from2.5mm to75mm while cold-rolled seamlessSteel Pipecan reach6mm in diameter with wall thickness down to0.25mm; thin-walled pipe can reach an outer diameter of5mm with wall thickness less than0.25mm; cold-rolled has higher dimensional accuracy than hot-rolled.Steel PipeGenerally speaking, seamless pipe uses10、20、30、35、45 etc., high-quality carbon structural steel16Mn、5MnV etc., low-alloy structural steel or40Cr、30CrMnSi、45Mn2、40MnB etc., alloy steel produced by hot rolling or cold rolling.Steel PipeLow-carbon steel such as10、20 mainly manufactures fluid transport pipelines.Steel PipeMedium-carbon steels like45、40Cr produce mechanical parts such as load-bearing components for cars or tractors.Steel PipeGenerally speaking, ,Steel PipeLow-medium pressure boiler use seamlessSteel PipeHigh-pressure boiler: Mainly used to manufacture high-pressure steam boiler pipelines using quality carbon structural steels alloy structural steels stainless heat-resistant steels seamlessly . These boiler pipelines operate under high temperature high pressure conditions where they may undergo oxidation corrosion due to exposure to hot flue gases steam hence requiring them to possess high durability strength excellent oxidation resistance good organizational stability utilizing grades such as: quality carbon structural steels like20G 、20MnG 、25MnG ; alloy structural steels like15MoG 、20MoG 、12CrMoG 、15CrMoG 、12Cr2MoG 、12CrMoVG 、12Cr3MoVSiTiB etc.; commonly used heat-resistant stainless steels include1Cr18Ni9 、1Cr18Ni11Nb . High-pressure boiler pipelines must ensure chemical composition mechanical properties along with conducting individual hydraulic tests expansion flattening tests.Steel PipeGeological drilling petroleum drilling control use seamlessSteel Pipe以热处理状态交货。此外，对成品Steel Pipe显微组织、晶粒度、脱碳层也有一定要求。 地质钻探及石油钻控用无缝Steel Pipe；为探明地下岩层结构、地下水、石油、天然气及矿产资源情况，利用钻机打井。石油、天然气开采更离不开打井，地质钻控用石油钻探用无缝Steel Pipe是钻井的主要器材，主要包括岩芯外管、岩芯内管、套管、钻杆等。由于钻探用管要深入到几千米地层深度工作，工作条件极为复杂，钻杆承受拉、压、弯曲、扭转和不均衡冲击载荷等应力作用，还要受到泥浆、岩石磨损，因此，要求管材必须具有足够的强度、硬度、耐磨性和冲击韧性，Steel Pipe用钢用“DZ”（地质的汉语拼音字头）加数字一代表钢屈服点表示，常用的钢号有DZ45的45MnB．50Mn；DZ50的40Mn2、40Mn2Si；DZ55的40Mn2Mo、40MnVB；DZ60的40MnMoB．DZ65的27MnMoVB.Steel Pipe都以热处理状态交货。 石油裂化管：用于石油炼厂的炉管、热交换器管和管道用无缝管。常用优质碳素钢（10、20）、合金钢（12CrMo、15CrMo）、耐热钢（12Cr2Mo、15Cr5Mo）、不锈钢（1Cr18Ni9、1Cr18Ni9Ti）制造。Steel Pipe除得证化学成分和各种机械性能外，还要保证水压、压扁、扩口等试验，及表面质量和无损检验。Steel Pipe在热处理状态下交货。 1.GB/T8162-1999（结构用无缝Steel Pipe）。主要用于一般结构和机械结构。其代表材质（牌号）：碳素钢、20、45号钢；合金钢Q345、20Cr、40Cr、20CrMo、30-35CrMo、42CrMo等。 2.GB/T8163-1999（输送流体用无缝Steel Pipe）。主要用于工程及大型设备上输送流体管道。代表材质（牌号）为20、Q345等。 3.GB3087-1999（低中压锅炉用无缝Steel Pipe）。主要用于工业锅炉及生活锅炉输送低中压流体的管道。代表材质为10、20号钢。 4.GB5310-1995（高压锅炉用无缝Steel Pipe）。主要用于电站及核电站锅炉上耐高温、高压的输送流体集箱及管道。代表材质为20G、12Cr1MoVG、15CrMoG等。 5.GB5312-1999（船舶用碳钢和碳锰钢无缝Steel Pipe）。主要用于船舶锅炉及过热器用I、II级耐压管等。代表材质为360、410、460钢级等。 6.GB1479-2000（高压化肥设备用无缝Steel Pipe）。主要用于化肥设备上输送高温高压流体管道。代表材质为20、16Mn、12CrMo、12Cr2Mo等。 7.GB9948-1988（石油裂化用无缝Steel Pipe）。主要用于石油冶炼厂的锅炉、热交换器及其输送流体管道。其代表材质为20、12CrMo、1Cr5Mo、1Cr19Ni11Nb等。 8.GB18248-2000（气瓶用无缝Steel Pipe）。主要用于制作各种燃气、液压气瓶。其代表材质为37Mn、34Mn2V、35CrMo等。 工艺流程简单介绍如下： 1.热轧（挤压无缝Steel Pipe）：圆管坯→加热→穿孔→三辊斜轧、连轧或挤压→脱管→定径（或减径）→冷却→矫直→水压试验（或探伤）→标记→入库 The raw material for rolling seamless pipes is round pipe blanks. The round pipe blanks need to be cut into lengths of about 1 meter by a cutting machine and then transported to the furnace for heating via a conveyor belt. The steel billets are heated in the furnace at a temperature of about 1200 degrees Celsius. The fuel used is hydrogen or acetylene. Controlling the temperature inside the furnace is a critical issue. After the round pipe blank is taken out of the furnace, it must go through a pressure perforating machine for perforation. A common type of perforating machine is the conical roller perforating machine, which has high production efficiency, good product quality, and can accommodate various steel grades with large expansion during perforation. After perforation, the round pipe blank undergoes three-roll slant rolling, continuous rolling, or extrusion in sequence. After extrusion, it needs to be sized.Steel PipeThe inner diameter is determined by the outer diameter length of the sizing machine's drill bit.Steel PipeAfter sizing, it enters a cooling tower where it is cooled by water spray.Steel PipeAfter cooling, it needs to be straightened.Steel PipeAfter straightening, it is sent via conveyor belt to a metal flaw detector (or hydraulic test) for internal inspection.Steel PipeIf there are internal issues such as cracks or bubbles, they will be detected.Steel PipeAfter quality inspection, there will also be strict manual selection.Steel PipeAfter quality inspection, paint will be sprayed on with numbers, specifications, production batch numbers, etc., and then lifted into storage by a crane.Steel Pipe2. Cold drawn (rolled) seamless : Round pipe blank → Heating → Perforation → Heading → Annealing → Pickling → Oiling (Copper plating) → Multiple cold drawing (cold rolling) → Blank pipe → Heat treatment → Straightening → Hydraulic test (flaw detection) → Marking → Storage.Steel PipeCold drawn (rolled) seamless 's rolling method is more complex than hot rolling (extruded seamless).Steel PipeTheir production process flow is basically the same for the first three steps. The difference starts from the fourth step; after being hollowed out, the round pipe blank must undergo heading and annealing. After annealing, it must be pickled with a special acidic liquid. After pickling comes oiling. Then follows multiple cold drawing (cold rolling) before becoming a blank pipe and undergoing specialized heat treatment. After heat treatment, it needs to be straightened.Steel PipeWeldingSteel PipeIf there are internal issues such as cracks or bubbles, they will be detected.Steel PipeAfter quality inspection, there will also be strict manual selection.Steel PipeAfter quality inspection, paint will be sprayed on with numbers, specifications, production batch numbers, etc., and then lifted into storage by a crane.Steel Pipe2. Cold drawn (rolled) seamless : Also known as welded pipes; they are made from steel plates or strips that are bent into shape and then welded together. They can be classified into straight seam welded pipes and spiral welded pipes based on seam type. According to their use, they can also be divided into general welded pipes, galvanized welded pipes, oxygen-blowing welded pipes, electrical wire conduits, metric welded pipes, roller support pipes, deep well pump pipes, automotive pipes, transformer tubes, electric welding thin-walled tubes and electric welding special-shaped tubes as well as spiral welded tubes.Steel PipeGeneral welded pipes: General welded pipes are used for transporting low-pressure fluids and are made from Q195A.Q215A.Q235A steel. Other easily weldable soft steels can also be used for manufacturing. 's specifications require water pressure tests as well as bending and flattening tests with certain surface quality requirements; typical delivery lengths range from 4-10m with often specific length requirements (or multiples thereof). The specifications of welded pipes are indicated by nominal diameter (in millimeters or inches), which differs from actual dimensions; according to specified wall thicknesses there are ordinarySteel Pipe,Steel Pipe, thickened types;Steel Pipe, according to end form they can also be divided into threaded and non-threaded types.Steel Pipe. With improvements in welding technology and ease of processing now some seamless pipes have been replaced by welded ones; welding 's capabilities have reached production sizes over219mm(8 inches).Steel Pipe: To improve corrosion resistance performance against generalSteel Pipe(black pipe), galvanization is applied. Galvanization can either be hot-dip galvanizing or electro-galvanizing; hot-dip galvanizing has thicker coatings while electro-galvanizing has lower costs. Oxygen-blowing welding tube: Used as oxygen-blowing tubes in steelmaking processes generally made from small diameter welds with specifications ranging from3/8 inchto2 inches across eight types using08、10、15、20orQ195-Q235steel strips manufactured; some undergo aluminum diffusion treatment for corrosion prevention.Steel PipeElectrical wire conduits: Also ordinary carbon steel electric welds used in concrete and various structural distribution projects commonly have nominal diameters ranging from13-76mmwith thinner walls often coated or galvanized before use requiring cold bending tests.Steel PipeMetric welded tube: Specifications expressed in seamless tube form using outer diameter * wall thickness millimeters indicating welds made using ordinary carbon steel high-quality carbon steels or low-alloy steels through hot band cold band welding methods or hot band followed by cold drawing methods produced metric welds categorized into ordinary thin-walled structures like drive shafts fluid transport thin-walled furniture lighting etc., ensuringSteel Pipestrength along with bending tests.Steel PipeSupport roller tube: Used in belt conveyor support rollers generally manufactured usingQ215、Q235A.Bsteel along with20steel having diameters63.5-219mmwith certain requirements regarding curvature end face perpendicularity ovality typically undergoing water pressure flattening tests. Transformer tube: Used for manufacturing transformer cooling tubes along with other heat exchangers made using ordinary carbon steel requiring flattening flaring bending hydraulic testing.Steel Pipedelivered at specific lengths or multiples thereof while maintaining certain curvature requirements. Special-shaped tubes: Made from ordinary carbon structural steels along with16Mnand other steel strips forming square rectangular cap-shaped hollow rubber door window frames.Steel Pipe，用在混凝土及各种结构配电工程，常用的公称直径从13-76mm.电线套套管壁较薄，大多进行涂层或镀锌后使用，要求进行冷弯试验。 公制焊管：规格用无缝管形式，用外径*壁厚毫米表示的焊接Steel Pipe，用普通碳素钢、优质碳素钢或普能低合金钢的热带、冷带焊接，或用热带焊接后再经冷拨方法制成。公制焊管分普能和薄壁、普通用作结构件，如传动轴，或输送流体，薄壁用来生产家具、灯具等，要保证Steel Pipe强度和弯曲试验。 托辊管：用于带式输送机托辊电焊Steel Pipe，一般用Q215、Q235A．B钢及20钢制造，直径63.5-219.0mm.对管弯曲度、端面要与中心线垂直、椭圆度有一定要求，一般进行水压和压扁试验。 异型管：由普通碳结结构钢及16Mn等钢带焊制的方形管、矩形管、帽形管、空胶钢门窗用Steel PipeMainly used for agricultural components, steel windows and doors, etc. Electric welded thin-walled pipes: mainly used for making furniture, toys, lamps, etc. In recent years, thin-walled pipes made of stainless steel strips have been widely applied in high-end furniture, decoration, railings, etc. Spiral welded pipes: are made by rolling low carbon structural steel or low alloy structural steel strips into pipe blanks at a certain spiral angle (called the forming angle), and then welding the pipe seams together. They can produce large diameters with narrower strips.Steel PipeSpiral welded pipes are mainly used for oil and natural gas transmission pipelines, with specifications expressed as outer diameter * wall thickness. Spiral welded pipes can be single-sided or double-sided welded. The welded pipes must ensure that water pressure tests, weld tensile strength, and cold bending performance meet the requirements. The choice mainly depends on the design working pressure! The two serve different purposes and are used in different places. SeamlessSteel Pipeis used for high pressure; pipelines with a pressure of over 0.8MPa generally require seamlessSteel Pipe; while galvanizedSteel Pipeis used for corrosion resistance; for example, galvanized is used in water gas pipelines.Steel PipeAs for prices, I see that galvanizedSteel Pipeseems to be more expensive than seamless.Steel Pipe贵。 |
