Thu. Jun 30th, 2022

The imported alloy tube is rolled with a solid tube billet after being pierced.  ;

1. Manufacturing methods    can be divided into hot-rolled tubes, cold-rolled tubes, cold-drawn tubes, extruded tubes, etc. according to different production methods.

1.1. Hot-rolled P91 alloy tubes are generally produced on automatic tube rolling mills. The solid tube blank is inspected and cleaned of surface defects, cut to the required length, centered on the perforated end surface of the tube blank, and then sent to the heating furnace to be heated and pierced on the punching machine. When the perforation continuously rotates and advances at the same time, under the action of the roller and the plug, a cavity is gradually formed inside the tube blank, which is called a capillary tube. Then it is sent to the automatic rolling mill to continue rolling. Finally, the whole wall thickness is uniformed by the whole machine, and the diameter is sizing by the sizing machine to meet the specification requirements. It is a more advanced method to produce hot-rolled P91 alloy pipes using continuous pipe rolling mills.

1.2. If you want to obtain a smaller size and better quality seamless pipe, cold rolling, cold drawing or a combination of the two methods must be used. Cold rolling is usually carried out on a two-high rolling mill. The steel pipe is rolled in an annular pass formed by a variable cross-section circular hole groove and a stationary tapered plug. Cold drawing is usually carried out on a single-chain or double-chain cold drawing machine of 0.5 to 100T.

1.3. The extrusion method is to put the heated tube blank in a closed extrusion cylinder, and the perforated rod and the extrusion rod move together to extrude the extruded part from the smaller die hole. This method can produce steel pipes with smaller diameters.

2, use   2.1, P91 alloy tube has a wide range of uses. The general-purpose P91 alloy pipe is rolled by ordinary carbon structural steel, low-alloy structural steel or alloy structural steel, and has the largest output. It is mainly used as pipelines or structural parts for conveying fluids.

2.2. According to different purposes, it can be supplied in three categories: a. According to chemical composition and mechanical properties; b. According to mechanical properties; c. According to water pressure test. Steel pipes supplied according to categories a and b, if used to withstand liquid pressure, shall also be subjected to a hydraulic test.

2.3. P91 imported alloy pipes for special purposes include P91 alloy pipes for boilers, P91 alloy pipes for geology and seamless pipes for petroleum.

3. Classification of P91 imported alloy tubes. The main alloying elements of alloy tubes are silicon, manganese, chromium, nickel, molybdenum, tungsten, vanadium, titanium, niobium, zirconium, cobalt, aluminum, copper, boron, rare earth and other alloy steel tubes in steel. In addition to iron, carbon and a small amount of inevitable silicon, manganese, phosphorus, and sulfur elements, it also contains a certain amount of alloying elements. The alloying elements in steel include silicon, manganese, molybdenum, nickel, sulphur, vanadium, titanium, niobium, One or more of boron, lead, rare earth, etc. This kind of steel is called alloy steel. The alloy steel system differs according to their respective resource conditions, production and use conditions. In the past, nickel and steel systems were developed abroad. In China, it has been discovered that alloy steel systems dominated by silicon, manganese, vanadium, titanium, niobium, boron, lead, and rare earths account for more than ten percent of the total output of steel. They are generally smelted in electric furnaces according to their purpose. Alloy steel pipes can be divided into 8 categories, which are: alloy structural steel pipes, spring steel pipes, bearing steel pipes, alloy tool steel pipes, high-speed tool steel pipes, stainless steel pipes, heat-resistant non-skin steel pipes, and electrical silicon steel pipes with good PC/ABS Formability, can process large-scale automobile parts, such as automobile fenders, with a high cost performance. Alloy steel pipe is a classification of iron-carbon alloy steel pipe formed by adding an appropriate amount of one or more alloying elements on the basis of ordinary carbon steel : Steel pipes are divided into P91 alloy pipes and welded steel pipes.

4, specifications and appearance quality   P91 alloy tube according to GB/T8162-87 regulations

4.1, specifications: hot-rolled tube outer diameter 32 ~ 630mm. The wall thickness is 2.5~75mm. The outer diameter of cold rolled (cold drawn) pipe is 5~200mm. The wall thickness is 2.5-12mm.

4.2. Appearance quality: The inner and outer surfaces of the steel pipe must not have cracks, folds, folds, delamination, hair lines and scarring defects. These defects should be completely removed, and the wall thickness and outer diameter must not exceed the negative deviation after removal.

4.3. Both ends of the steel pipe should be cut at right angles and burrs should be removed. Gas cutting and hot saw cutting are allowed for steel pipes with wall thickness greater than 20mm. After the agreement between the supply and demand parties, it is not necessary to cut the head.

4.4, cold-drawn or cold-rolled precision P91 alloy pipe “surface quality” refers to GB3639-83.

5. Chemical composition inspection

5.1. Domestic P91 alloy pipes supplied according to chemical composition and mechanical properties, such as No. 10, 15, 20, 25, 30, 35, 40, 45 and 50 steel, shall have chemical composition in accordance with GB/T699-88 Provisions. Imported P91 alloy pipes shall be inspected according to the relevant standards stipulated in the contract. The chemical composition of 09MnV, 16Mn, 15MnV steel should meet the requirements of GB1591-79.

5.2. Refer to the relevant part of GB223-84 “Methods for Chemical Analysis of Steel and Alloy” for specific analysis methods.

5.3. The analysis deviation refers to GB222-84 “Permissible deviation of chemical composition of steel samples and finished products for chemical analysis”.

6P91 alloy tube welding process

In order to increase the argon gas protection zone and enhance the protection effect, a large diameter welding gun porcelain nozzle can be used to increase the argon gas flow of the welding gun. When there are splashes attached to the nozzle that obviously hinder the flow of argon gas. Spatter must be removed or the nozzle must be replaced. When the tungsten tip is contaminated, the shape is irregular, etc., it must be repaired or replaced. The tungsten electrode should not stick out of the nozzle. The control of welding temperature is mainly the control of welding speed and welding current. The test results show that high current and fast welding can effectively prevent the generation of pores. This is mainly due to the faster penetration of the weld during the welding process, the short heating time of the molten metal, and the less opportunity for gas absorption.

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