Plates, Pipes and Structural Profiles

Transcription

1 Plates, Pipes and Structural Profiles Metals, especially steel and its alloys, are produced in a wide variety of shapes and cross-sections. While steel is initially produced as pellets or ingots which can then be casted as parts of any desired shape, steel plants also produce steel in different shapes and cross-sections such as plates, rods, pipes, and different structural profiles. These different cross-sectional shapes of steel products can be used as is in many applications (such as in steel structures) or they can be further processed to reach the final desired shape. Plates, Sheets and Foils Plates, sheets (also known as sheet metal) and foils are flat in shape and have a thickness that is very small relative to the other two dimensions. They are mainly produced by rolling processes (hot or cold) and the main difference between them is the thickness range (the thickest is plate, then sheet, then foil). Plates and sheets are used in structural and mechanical applications (they are thick enough to carry loads) while foils are used in other types of applications, such as food industries for instance. Thickness is the most important dimension used to designate plates sheets and foils. The typical thickness ranges vary between different standards, but the most common are: Plates: from 6 mm to 300 mm Sheets: from 0.25 mm to less than 6 mm Foils: from 0.01 mm to less than 0.25 mm Plates come in a variety of standard sizes (Length x Width) where the most common size is 3 m x 1.5 m. Sheets (or sheet-metal) can either come as flat sheets of different sizes or they can come in the form of coils (as seen in the figure) of up to 1.8 m width, and then they are cut to the desired length. Foils come as rolls of different widths. Foils are not made of steel, usually they are made of metals such as aluminum, stainless steel, silver, gold, etc. Plates, Pipes and Structural Profiles Page 1 of 6

2 There is a wide variety of standard thicknesses of plates and sheets: ISO standard uses the actual thickness to designate plates and sheets and the standard thicknesses are chosen from the preferred numbers. ANSI standard uses gauge numbers for designating thicknesses less than ¼ inch (they are referred to as sheets) while plates of thickness ¼ inch and higher are designated by the actual thickness. Pipes and Tubes Pipes and tubes are sometimes confused with each other because they look somehow similar (having hollow circular cross-section). However, pipes and tubes are basically different since each is intended to be used for a different purpose. Pipes: are used for the transport of fluids (water, oil, gas, etc.). The inside diameter is the most import property of a pipe since it determines its capacity, and thus pipes are specified by their inside diameter. Tubes: are mostly used in structures to carry loads (force, moment, torque, etc.). The nominal dimensions of tubes are based on the outside diameter. Also, tubes come with cross-sections other than the circular, such as square or rectangular tubes. Pipes and tubes are commonly produced using one of two different methods: Welded pipes: are produced by rolling a plate in the shape of a pipe and welding its ends using resistance welding. This type of process is usually used for steel pipes and it is generally a low cost process. Seamless pipes: are produces using the extrusion process where the heated material is pushed through a die with a mandrill inside. This process can be used for most types of materials including metals and polymers and it produces a better quality pipes. The tolerances on the dimensions of pipes are looser compared with those of tubes and thus pipes are generally less expensive to produce. Plates, Pipes and Structural Profiles Page 2 of 6

3 Pipes Pipes are available in a wide variety of material choices ranging from metals (steel, stainless steel, aluminum, etc.), to polymers (PVC, CPVC, PEX, etc.) to concrete. The most commonly recognized and widely used standard for pipes is the ANSI standard where standard sizes start from ⅛ inch up to 48 inches. The ANSI standard uses the so called NPS (Nominal Pipe Size) to identify pipe sizes. The NPS is a nominal value corresponding to the inside diameter of a pipe for sizes up to 12 inches (for sizes larger than 12 inches, the NPS corresponds to the outer pipe diameter). For example the inside diameter of a standard wall thickness NPS 2" pipe is close to 2 inches (2.067 inch), while the outside diameter is inch. The ISO standard adapted the standard ANSI pipe sizes but instead of using the NPS for identifying the sizes, it uses a metric equivalent called DN (Diametre Nominel). Each of the standard pipe sizes has different choices for the wall thickness. The outside diameter of a single nominal pipe size needs to be kept constant in order for the pipe to fit into the different types of pipe connectors (elbows, fittings, etc.). Thus, ANSI standard keeps the outside diameter constant, and the inside diameter varies with wall thickness. The pipe standard wall thicknesses can be specified using one of two methods: Standard, XS and XXS: The wall thickness is specified as; Standard, XS (Extra-Strong) and XXS (Double Extra-Strong). This is the older system of designation and it is still being used. Schedule Numbers: The wall thickness is specified using a schedule number (such as: Schedule 5, Schedule 10, Schedule 40, etc.). This is the newer designation system and it was added because it has more choices and it is more convenient to use. Schedule 40 is the most commonly used wall thickness where it is same as the Standard wall thickness, while Schedule 80 is the same as the XS. A pipe is designated by its NPS (or DN) and schedule number (example: 2" SCH 40) and they usually come as 6 m long pieces. The table gives the standard ANSI pipe sizes (from ½ inch to 6 inch) along with the equivalent ISO-DN number. For each size some of the common wall thicknesses are listed. Plates, Pipes and Structural Profiles Page 3 of 6

4 Circular Tubes The term circular tube is simply used to refer to hollow circular cross-sections having nominal dimensions based on the outside diameter. As mentioned earlier, tubes in general are mostly used to carry loads, but sometimes circular tubes are used to transport fluids such as the copper tubes used in air conditioning and refrigeration. Circular tubes are seamless (not welded) and they are usually made of metals. The most commonly used standard for circular tubes is the ANSI standard which is also adapted by ISO. A circular tube is specified by its outside diameter and wall thickness (example: mm). Bars The term bar is used to refer to a piece having a simple geometric cross-section with its crosssectional dimensions much smaller than its length. Bars have a solid section (i.e., no hollow) and Plates, Pipes and Structural Profiles Page 4 of 6

5 they can come in a variety of shapes (circular, square, rectangular, hexagonal, etc.), as seen in the figure. Bars come in a variety of standard sizes and they may either be used as is in some applications or they can be machined to achieve certain shape and size (for instance stepped shafts are made by turning a circular bar using lathe). Structural Profiles Structural profiles are widely used for making strong and relatively light structures in a wide variety of applications. Structural profiles come in different shapes and sizes as seen in the figure. The unique property of such shapes is that; it has small wall thickness compared to the overall dimensions of the cross-section where that provides high resistance to bending moments with relatively light weight. The standard ISO structural steel profiles are shown in the figure below and they can be divided in two groups: Open sections: I-shape, T-shape, C-shape and L-shape. Closed sections: usually referred to as tubular sections and they are usually circular, square or rectangular. Plates, Pipes and Structural Profiles Page 5 of 6

6 Standard structural profiles are usually designated by the profile type or code and their major dimension or dimensions. The different sizes of structural profiles are listed in tables which give the dimensions, weight and section properties. Examples: o Unequal Leg Angle : refers to an angle with 50 mm height, 30 mm width, and 5 mm thickness. o Rectangular Tube : refers to a tube with 50 mm height, 30 mm width, and 3.2 mm thickness. o C-Channel - CH : refers to a channel with 100 mm height, and 10 kg/m weight. o I-Beam (wide flange) - SC 120: refers to a beam with 120 mm height. Standard structural profiles are usually supplied as long sections of 6 m length then they are cut to the desired length (or joined together when necessary). Other lengths may be available in some cases. The table shows an example of the tables used to list the different sizes along with dimensions, weight, and section properties for standard steel structural profiles (This table is for IPN regular I-beam "DIN standard"). Plates, Pipes and Structural Profiles Page 6 of 6