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The difference between spiral welded pipe and straight-seam welded pipe

2021/01/20

The difference between spiral welded pipe and straight-seam welded pipe

The primary difference between spiral welded pipe and straight-seam welded pipe lies in their welding processes. Spiral welded pipe is manufactured by rolling low‑carbon structural steel or low‑alloy structural steel strip into a tubular blank at a specific helical angle—also known as the forming angle—and then welding it to form the seam. This method enables the production of large‑diameter pipes from relatively narrow strips. Spiral welded pipe is predominantly represented by spiral submerged‑arc welded pipe (SSAW), which is widely used in China for constructing various gas pipelines. Its dimensions are specified as “outer diameter × wall thickness.” Spiral welded pipes can be either single‑sided or double‑sided welded, and they must meet prescribed requirements for hydrostatic testing, weld tensile strength, and cold‑bend performance.

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What is the significance of pickling large-diameter steel pipes?

2021/01/16

What is the significance of pickling large-diameter steel pipes?

Pickling of large-diameter steel pipes is a process that uses acidic solutions to remove scale and rust from the steel surface. Common pickling acids include sulfuric acid, hydrochloric acid, phosphoric acid, and mixed acids. The primary purpose of pickling is to eliminate surface oxide scales, followed by lubrication—carbon steels are treated with phosphating soap, stainless steels with oil‑lime, and copper or aluminum tubes with oil coating. Subsequently, the traditional copper‑plating process is applied, after which the material undergoes further deep‑drawing operations.

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Welding of Large-Diameter Steel Plate Spiral Pipes

2021/01/13

Welding of Large-Diameter Steel Plate Spiral Pipes

In the welding procedure specification for large-diameter steel plate spiral-welded pipes, specific welding process parameters are defined to ensure the repeatability of welder training. The objective of research and development in welding procedures is to guarantee that welded joints meet relevant standards and satisfy particular application requirements. Thick-walled pipes, as a widely used type of steel pipe, find extensive applications in industry; they are commonly employed as oil‑field drilling pipes and as high‑precision structural steel tubes for automotive and aerospace applications. Each of these end uses can be subject to various influencing factors, and thick-walled pipes may likewise be affected. Let us examine the factors that impact the welding of large-diameter steel plate spiral-welded pipes.

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Corrosion Mechanism of Steel Plate Coiled Pipes

2021/01/11

Corrosion Mechanism of Steel Plate Coiled Pipes

Corrosion that occurs on the surface of steel pipe coils exposed to the atmosphere is referred to as atmospheric corrosion. This phenomenon arises because the atmosphere contains water vapor, which condenses on the pipe surface to form a thin water film. The water film dissolves oxygen and other impurities from the air, leading to electrochemical corrosion. Since the water film is extremely thin and offers low resistance, and oxygen from the air is continuously supplied, the cathodic process is primarily driven by the depolarization of oxygen. The corrosion of steel pipelines in the atmosphere is influenced by factors such as atmospheric conditions, metal composition, surface morphology, orientation, droplet runoff, and operating conditions.

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Causes of Deformation in Steel Plate Coiled Pipes

2021/01/08

Causes of Deformation in Steel Plate Coiled Pipes

Steel plate spiral pipes are typically welded with either straight or helical seams, and the forming process for the coil is essentially the same: shearing (or cutting) — beveling — flipping the steel plate over — pressing rounded arcs at both ends — coiling into a large-diameter roll (including spot welding) — butt-jointing pipe sections (including spot welding) — and welding the circumferential seam (using automatic welding).

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Production process of welded steel pipes

2020/03/25

Production process of welded steel pipes

The development of steel pipe manufacturing technology began with the rise of the bicycle industry, the early‑19th‑century oil boom, shipbuilding, boiler and aircraft production during the two world wars, and, after World War II, the manufacture of thermal power plant boilers. Additionally, advances in the chemical industry, as well as the drilling, extraction, and transportation of oil and natural gas, have all strongly propelled the steel pipe industry forward in terms of product variety, output, and quality. Steel pipes are typically classified into two main types based on their manufacturing process: seamless steel pipes and welded steel pipes. This discussion will focus primarily on welded steel pipes. Welded steel pipes, also known as seam‑welded pipes, are produced by bending and rolling tube blanks—made from steel plates or strips—into the desired cross‑sectional shape and dimensions using various forming methods, followed by welding along the seam to create the finished pipe. Compared with seamless steel pipes, welded pipes offer higher dimensional accuracy, especially in wall thickness; simpler primary equipment; a smaller footprint; the ability to operate continuously; greater production flexibility; and a broader range of products that can be manufactured on a single production line. I. The general production process for spiral welded steel pipes is as follows: 1. Raw materials include steel strip coils, welding wire, and flux. 2. Prior to forming, the steel strip undergoes leveling, edge trimming, edge planing, surface cleaning, conveying, and pre‑bending operations. 3. A weld gap control device is used to ensure that the weld gap meets welding requirements, with strict control over pipe diameter, misalignment, and weld gap dimensions. 4. After cutting into individual pipe lengths, the first three pipes of each batch undergo rigorous initial inspection, assessing weld mechanical properties, chemical composition, fusion quality, and surface finish. Nondestructive testing is also performed to confirm compliance with manufacturing standards before the pipes are officially put into production. II. Longitudinal Submerged Arc Welded Pipes (LSAW): Longitudinal submerged arc welded pipes are generally manufactured from steel plates. Through various forming processes, including double‑sided submerged arc welding and post‑weld expanding, these pipes are produced. Key equipment includes edge milling machines, pre‑bending machines, forming machines, pre‑welding units, and expanding machines. There are several distinct forming methods for LSAW pipes, such as UOE, RBE, and JCO (JCOE). In the UOE process, the steel plate is first pressed into a U‑shape, then further formed into an O‑shape, followed by internal and external submerged arc welding. Post‑weld expansion is typically applied either at the ends or along the entire length, resulting in what is called a UOE pipe; if no expansion is performed, it is referred to as a UO pipe. For RBE pipes, the steel plate is rolled and bent into shape, then subjected to internal and external submerged arc welding, with subsequent expansion. If no expansion occurs, it is designated as an RB pipe. In the JCO process, the steel plate is sequentially formed into J‑, C‑, and O‑shapes, followed by post‑weld expansion, yielding a JCOE pipe; without expansion, it becomes a JCO pipe. UOE longitudinal submerged arc welded pipe forming process: The three primary forming steps in UOE pipe production involve pre‑bending the edges of the steel plate, forming a U‑shape, and finally forming an O‑shape. Each step employs a dedicated forming press, sequentially completing edge pre‑bending, U‑shaping, and O‑shaping to transform the steel plate into a circular tubular form. As shown in the figure: JCOE longitudinal submerged arc welded pipe forming process: During forming, the JC0 machine performs multiple incremental stamping operations—first pressing half of the steel plate into a “J” shape, then shaping the other half into a “C” shape, and finally applying pressure at the center to produce an open “0”‑shaped blank. Comparison between JCO and UO forming methods: JCO forming uses progressive pressure, transforming the pipe‑forming process from the two steps of UO formation into multiple stages. Throughout this process, the steel plate deforms uniformly, residual stresses remain minimal, and the surface remains free of scratches. The resulting pipes exhibit greater flexibility in diameter and wall‑thickness specifications, allowing for both large‑scale and small‑batch production. They can manufacture high‑strength, thick‑walled pipes of large diameters as well as small‑diameter, thick‑walled pipes. Particularly when producing high‑grade, thick‑walled pipes—especially medium and small diameters—JCO offers advantages unmatched by other processes, satisfying users’ diverse requirements for pipe specifications. Investment is relatively low, but production efficiency is comparatively modest, with annual output typically ranging from 100,000 to 250,000 tons. UO forming, which employs both U‑ and O‑shaped pressure steps, is characterized by its high capacity and substantial output, often reaching 300,000 to 1 million tons per year, making it suitable for large‑volume production of a single specification. However, the capital investment required is considerable, often beyond the reach of developing countries. III. Longitudinal Electric Resistance Welded Pipes (ERW): Longitudinal electric resistance welded pipes are produced by taking hot‑rolled coil stock, forming it through specialized machinery, and then utilizing the skin effect and proximity effect of high‑frequency currents to heat and melt the edges of the pipe blank. Under pressure from the rolling mill, the heated edges are fused together, completing the weld. Welded steel pipes, also known as weld pipes, are manufactured by rolling steel plates or strips into shape and then welding them together. Their production process is simple, highly efficient, and offers a wide variety of grades and specifications, requiring relatively little equipment. However, their overall strength is generally lower than that of seamless steel pipes. Since the 1930s, with the rapid advancement of continuous rolling technology for high‑quality steel strips and improvements in welding and inspection techniques, weld quality has steadily improved, leading to an increasing diversity of welded pipe grades and specifications. Consequently, welded pipes have increasingly replaced seamless pipes across many applications. Welded pipes are categorized according to weld type into longitudinal welded pipes and spiral welded pipes. By manufacturing method, they are further divided into arc‑welded pipes, resistance‑welded pipes, gas‑welded pipes (high‑frequency and low‑frequency), and furnace‑welded pipes. Longitudinal welded pipes feature a straightforward production process, high efficiency, low cost, and rapid development. Spiral welded pipes generally exhibit higher strength than longitudinal welded pipes, enabling the use of narrower blanks to produce larger‑diameter pipes, and even allowing the same‑width blanks to yield pipes of different diameters. Nevertheless, compared with longitudinally welded pipes of equal length, spiral welded pipes typically have weld seams that are 30%–100% longer, while their production speed tends to be slower. Product Standards: Common materials used for welded pipes include Q235A, Q235C, Q235B, 16Mn, 20#, Q345, L245, L290, X42, X46, X60, X80, 0Cr13, 1Cr17, 00Cr19Ni11, 1Cr18Ni9, 0Cr18Ni11Nb, among others. The raw material for welded pipes is steel plate or steel strip, which, depending on the welding process, is classified into furnace‑welded pipes, electric‑welded pipes (resistance‑welded), and automatic arc‑welded pipes. Based on the welding configuration, they are further divided into longitudinal welded pipes and spiral welded pipes. Depending on the end‑shape, they may also be categorized as round‑ended welded pipes or irregular‑shaped welded pipes (square, flat, etc.). According to material and intended application, welded pipes can be grouped into the following categories: GB/T 3091‑2001 (galvanized steel for low‑pressure fluid conveyance).

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Canghai Steel Pipe: Production is bustling, and sales are booming.

2020/03/24

Canghai Steel Pipe: Production is bustling, and sales are booming.

On March 24, the factory’s production workshop was bustling with activity. In recent days, Canghai has been simultaneously prioritizing epidemic prevention and ramping up production, accelerating the fulfillment of spiral steel pipe orders to meet demand across multiple regions both within and outside the province. In the first quarter of this year, order volumes not only held steady but actually increased, with sales rising by 100% year over year.

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Maintenance methods for spiral steel pipes

2020/03/16

Maintenance methods for spiral steel pipes

Solvents and emulsions are used to clean the steel surface, removing oil, grease, dust, lubricants, and similar organic contaminants; however, they cannot eliminate rust, scale, welding flux, or other surface imperfections. Therefore, in corrosion protection, they serve only as auxiliary methods.

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