Black steel is a term given to steel pipe with a black oxide scale on the surface. This black oxide scale is formed when the pipe is forged and is typically sealed with a protective oil to prevent corrosion. Because of this oxide scale and protective film, black steel pipe requires little maintenance and is used for a wide variety of applications, including in water, steam, air and gas services. Black steel pipes are typically cut and threaded in the field. Black steel pipe has high tensile strength, making it suitable for a variety of demanding applications. The toughness of black steel pipe guards against cracks and allows high loading capacities. A critical property of black steel pipe is its uniformity. Black steel's tensile strength is uniform along the entire length of pipe, which ensures consistent and predictable diameters. Compared to bolted lattice structures, installation of black steel pipe can be quicker and easier. Threaded ends, flanges or welded construction allows designers the ability to make adjustments as required. In addition to strength, black steel pipe can be field-fabricated and easily worked to any length. The availability of multiple components and black steel fittings reduces costs and can speed up structural fabrication. Depending on the application and diameter, black steel pipe can be threaded or welded. Once installed, black steel pipe has superior rust and corrosion resistance; without exterior damage such as nicks, scrapes or cuts, black steel is virtually maintenance-free. In addition, black steel piping does not shrink and retains its shape and strength. This eliminates any need to retighten or repair broken welds. This material is impervious to insects, rot or fire and, if required, can be further protected by painting or galvanizing, a powder coat or liquid application of zinc.

Modern steel production has three major categories, namely, welded pipe, seamless pipe and seamless steel pipe. Welded pipe is a metal strip into a tube by deformation processing, welding in the weld area forming, welding pipe welding process can be divided according to the furnace welding, high frequency resistance welding, TIG and plasma welding, etc; can be divided according to the form of the weld straight seam welding and spiral welding. Pipe injuries have common natural slag, cracks, holes, Weld and so on. Seamless round tube is perforated or extruder processed into a capillary, and then rolling machine rolling forming small diameter pipes and thin-walled tube also repeated cold rolling - annealing process. Common injuries seamless nature are longitudinal, transverse cracking, warping and folding the inner and outer walls, pits, pitting and delamination. The seamless pipe is heated primarily by reducing rolling, pickling, lubrication, drawing heat treatment and thermal annealing processes produce seamless steel pipe, steel pipe production of this same inevitably exist Weld Weld inclusions, such as welding and overheating problems. Whether welded steel pipe, seamless steel pipe or seamless steel pipes, cracks are the most common natural defects.

Pickling of carbon steel is chemically pickled pipeline, container oxides, rust and oil on the surface is removed, to obtain a metallic luster surface, to ensure the cleanliness of the pipe wall, while after pickling rust treatment also makes the bottom wall of the metal to be protected, to prevent further corrosion, pipeline pickling is a key pipeline construction. Pipeline pickling method more pickling method currently used in the construction site and has trough pickling acid cycle, the cycle is divided pickling pickling line and off-line pickling. Circulation pickling is a pipe or hose coupling union constitute a loop with an acid pump acid into the circulating pipe pickling. It can be installed without removing the pipe, as long as the hydraulic components can be carried out even better off with a hose, which is called pickling line cycle. As some of the short tube or pipe fittings should not form a loop in the installation position detached, local loop circulating pickling connected with a hose or fitting, which is called pickling line outside the circle. General requirements for circulating acid leaching as follows: (1) The right formula, that formula pickling solution to be able to fully clear the wall oxide by chemical action, and because they can not make the wall excessive corrosion and rust again. (2) Reasonable pickling loop, to ensure every part of the wall can be thoroughly and evenly pickling clean. (3) Rational process and strict rules and special operations team with timely processing problems pickling process, to ensure the smooth progress of the work of pickling. (4) Pickling and after the water should be thoroughly purged, and promptly flushed with hydraulic oil to ensure oil evenly throughout the inner tube, to produce the inner tube to flush out all the flying objects and when pickling.

After cold expansion for lsaw steel pipe , steel tube and pipe end diameter will increase by about one percent difference in diameter of the diameter, roundness, and the pipe ends are greatly improved, also have greatly improved the straightness of the steel pipe, steel pipea length of about 0.5% reduction in wall thickness decreases by about 0.8%. Fully develop LSAW process should consider these changes, to determine the pipe plate width, length and thickness, and the pipe diameter in front of the enlarged diameter, in order to avoid the enlarged diameter steel pipe geometry reach the final requirements caused by substandard.  The purpose of cold expansion for lsaw steel pipe has the followings: (1) Improve pipe end geometric dimensional accuracy of LSAW steel pipe, so that the diameter of the steel tube and pipe end, roundness, and the diameter of the pipe ends Poor meet the standard requirements, facilitate field welding construction.  (2) Reduce inhomogeneous deformation of LSAW steel pipe forming and welding process and decrease the residual stress of forming and welding of tube, and improve its distribution, improve the overall mechanical properties of the steel pipe.  (3) Inspect the steel pipe overall performance comprehensively and effectively.  (4) Improve the straight degree of lsaw steel pipe, especially for the smaller diameter LSAW pipe straight is more obvious.

Steel is considered to be carbon steel when no minimum content is specified or required for chromium, cobalt, niobium, molybdenum, nickel, titanium, tungsten, vanadium or zirconium, or any other element to be added to obtain a desired alloying effect; when the specified minimum for copper does not exceed 0.40 percent; or when the maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper 0.60. Different types of carbon steel pipes Classes of carbon steel Carbon content % Ultra-high carbon steel 1.00 – 2.00 High carbon steel 0.60 – 0.99 Medium carbon steel 0.30 – 0.59 Low carbon steel 0.16 – 0.29 Mild carbon steel 0.05 – 0.15 Black steel pipe is uncoated and made without steam, and therefore, it is widely used for transporting gas like propane and natural gas to residential and commercial building. Black steel pipe is manufactured as seamless which makes it a better type for gas transportation. It can be used for fire sprinkler system since it can prevent fire better than galvanized pipe. Since it has a dark color surface that is form by iron oxide during the manufacturing process, it is called black steel pipe.