1. Size
(1) Nominal size: It is the nominal size stipulated in the standard, the ideal size desired by users and manufacturers, and the order size specified in the contract
(2) Actual size: It is the actual size obtained during the production process, which is often larger or smaller than the nominal size. This phenomenon of being larger or smaller than the nominal size is called deviation.
(3) Meter weight: weight per meter=0.02466*wall thickness*(outer diameter-wall thickness)
2. Deviations and Tolerances
(1) Deviation: In the production process, because the actual size is difficult to meet the nominal size requirements, that is, it is often larger or smaller than the nominal size, so the standard stipulates that there is a difference between the actual size and the nominal size. If the difference is positive, it is called positive deviation, and if the difference is negative, it is called negative deviation.
(2) Tolerance: The sum of the absolute values of the positive and negative deviation values stipulated in the standard is called the tolerance, also called the "tolerance zone".
The deviation is directional, that is, expressed as "positive" or "negative"; the tolerance has no direction, so it is wrong to call the deviation value "positive tolerance" or "negative tolerance".
3. Delivery length
The delivery length is also called the user's required length or the contract length. The standard has the following regulations on the delivery length:
(1) Normal length (also known as non-fixed length): Any length within the length range specified in the standard and without fixed length requirements is called normal length. For example, the structural pipe standard stipulates: hot-rolled (extrusion, expansion) steel pipe 3000mm~12000mm; cold drawn (rolled) steel pipe 2000mm~10500mm.
(2) Length to length: The length to length should be within the normal length range, which is a certain fixed length dimension required in the contract. However, it is impossible to cut out the absolute cut-to-length length in actual operation, so the standard stipulates the allowable positive deviation value for the cut-to-length length.
(3) Double ruler length: The double ruler length should be within the usual length range, and the single ruler length and the multiple of the total length should be specified in the contract (for example, 3000mm×3, which is a multiple of 3000mm, and the total length is 9000mm). In actual operation, the allowable positive deviation of 20mm should be added to the total length, plus a cut allowance should be left for each single ruler length. Taking the structural pipe as an example, it is stipulated that the incision allowance should be left: 5~10mm for the outer diameter ≤ 159mm; 10~15mm for the outer diameter> 159mm.
If there is no specification for the length deviation and cutting allowance in the standard, it should be negotiated by both the supplier and the buyer and indicated in the contract. The double-length length is the same as the fixed-length length, which will greatly reduce the yield of the production enterprise. Therefore, it is reasonable for the manufacturer to propose a price increase, and the price increase range is basically the same as the fixed-length length increase.
(4) Range length: The range length is within the usual length range. When the user requires one of the fixed range lengths, it must be specified in the contract.
For example: the usual length is 3000~12000mm, while the range length is 6000~8000mm or 8000~10000mm.
4. Uneven wall thickness
The wall thickness of the steel pipe cannot be the same everywhere, and there is an objective phenomenon of unequal wall thickness on its cross-section and longitudinal pipe body, that is, uneven wall thickness. In order to control this unevenness, some steel pipe standards stipulate the allowable index of wall thickness unevenness, which generally stipulates that it does not exceed 80% of the wall thickness tolerance (implemented after negotiation between the supplier and the buyer).
5. Ovality
There are unequal outer diameters in the cross section of circular steel pipes. That is, there is a maximum outer diameter and a minimum outer diameter that are not necessarily perpendicular to each other, and the difference between the maximum outer diameter and the smallest outer diameter is the ellipticity (or out-of-roundness). In order to control the ovality, some steel pipe standards stipulate the allowable index of ovality, which is generally stipulated as not exceeding 80% of the outer diameter tolerance (implemented after negotiation between the supplier and the buyer).
6. Curvature
The steel pipe is curved in the length direction, and the degree of curvature represented by numbers is called curvature. The bending degree specified in the standard is generally divided into the following two types:
(1) Local curvature:Measure the chord height (mm) at the maximum bend of the steel pipe with a one-meter-long ruler, which is the value of the local curvature. The unit is mm/m, and the expression method is 2.5mm/m. This method is also applicable to the curvature of the pipe end.
(2) The total curvature of the whole length:Use a thin rope to tighten from both ends of the pipe, measure the maximum chord height (mm) at the bend of the steel pipe, and then convert it into a percentage of the length (in meters), which is the full-length bending degree of the steel pipe in the length direction.
For example: the length of the steel pipe is 8m, and the measured maximum chord height is 30mm, then the bending degree of the whole length of the pipe should be: 0.03÷8m×100%=0.375%
Tips: Steel pipes have a hollow section whose length is much greater than the diameter or circumference of steel. According to the cross-sectional shape, it is divided into round, square, rectangular and special-shaped steel pipes. According to the material, it is divided into carbon steel pipe, low alloy structural steel pipe, alloy steel pipe and composite steel pipe. According to the purpose, it is divided into steel pipes for pipelines, engineering structures, thermal equipment, octg casing, machinery manufacturing, geological drilling, and high-pressure equipment. According to the production process, it is divided into seamless pipe and welded steel pipe. Among them, seamless steel pipe is divided into hot rolling and cold rolling (drawing), and welded steel pipe is divided into straight seam welded steel pipe and spiral seam welded steel pipe.
(1) Nominal size: It is the nominal size stipulated in the standard, the ideal size desired by users and manufacturers, and the order size specified in the contract
(2) Actual size: It is the actual size obtained during the production process, which is often larger or smaller than the nominal size. This phenomenon of being larger or smaller than the nominal size is called deviation.
(3) Meter weight: weight per meter=0.02466*wall thickness*(outer diameter-wall thickness)
2. Deviations and Tolerances
(1) Deviation: In the production process, because the actual size is difficult to meet the nominal size requirements, that is, it is often larger or smaller than the nominal size, so the standard stipulates that there is a difference between the actual size and the nominal size. If the difference is positive, it is called positive deviation, and if the difference is negative, it is called negative deviation.
(2) Tolerance: The sum of the absolute values of the positive and negative deviation values stipulated in the standard is called the tolerance, also called the "tolerance zone".
The deviation is directional, that is, expressed as "positive" or "negative"; the tolerance has no direction, so it is wrong to call the deviation value "positive tolerance" or "negative tolerance".
3. Delivery length
The delivery length is also called the user's required length or the contract length. The standard has the following regulations on the delivery length:
(1) Normal length (also known as non-fixed length): Any length within the length range specified in the standard and without fixed length requirements is called normal length. For example, the structural pipe standard stipulates: hot-rolled (extrusion, expansion) steel pipe 3000mm~12000mm; cold drawn (rolled) steel pipe 2000mm~10500mm.
(2) Length to length: The length to length should be within the normal length range, which is a certain fixed length dimension required in the contract. However, it is impossible to cut out the absolute cut-to-length length in actual operation, so the standard stipulates the allowable positive deviation value for the cut-to-length length.
(3) Double ruler length: The double ruler length should be within the usual length range, and the single ruler length and the multiple of the total length should be specified in the contract (for example, 3000mm×3, which is a multiple of 3000mm, and the total length is 9000mm). In actual operation, the allowable positive deviation of 20mm should be added to the total length, plus a cut allowance should be left for each single ruler length. Taking the structural pipe as an example, it is stipulated that the incision allowance should be left: 5~10mm for the outer diameter ≤ 159mm; 10~15mm for the outer diameter> 159mm.
If there is no specification for the length deviation and cutting allowance in the standard, it should be negotiated by both the supplier and the buyer and indicated in the contract. The double-length length is the same as the fixed-length length, which will greatly reduce the yield of the production enterprise. Therefore, it is reasonable for the manufacturer to propose a price increase, and the price increase range is basically the same as the fixed-length length increase.
(4) Range length: The range length is within the usual length range. When the user requires one of the fixed range lengths, it must be specified in the contract.
For example: the usual length is 3000~12000mm, while the range length is 6000~8000mm or 8000~10000mm.
4. Uneven wall thickness
The wall thickness of the steel pipe cannot be the same everywhere, and there is an objective phenomenon of unequal wall thickness on its cross-section and longitudinal pipe body, that is, uneven wall thickness. In order to control this unevenness, some steel pipe standards stipulate the allowable index of wall thickness unevenness, which generally stipulates that it does not exceed 80% of the wall thickness tolerance (implemented after negotiation between the supplier and the buyer).
5. Ovality
There are unequal outer diameters in the cross section of circular steel pipes. That is, there is a maximum outer diameter and a minimum outer diameter that are not necessarily perpendicular to each other, and the difference between the maximum outer diameter and the smallest outer diameter is the ellipticity (or out-of-roundness). In order to control the ovality, some steel pipe standards stipulate the allowable index of ovality, which is generally stipulated as not exceeding 80% of the outer diameter tolerance (implemented after negotiation between the supplier and the buyer).
6. Curvature
The steel pipe is curved in the length direction, and the degree of curvature represented by numbers is called curvature. The bending degree specified in the standard is generally divided into the following two types:
(1) Local curvature:Measure the chord height (mm) at the maximum bend of the steel pipe with a one-meter-long ruler, which is the value of the local curvature. The unit is mm/m, and the expression method is 2.5mm/m. This method is also applicable to the curvature of the pipe end.
(2) The total curvature of the whole length:Use a thin rope to tighten from both ends of the pipe, measure the maximum chord height (mm) at the bend of the steel pipe, and then convert it into a percentage of the length (in meters), which is the full-length bending degree of the steel pipe in the length direction.
For example: the length of the steel pipe is 8m, and the measured maximum chord height is 30mm, then the bending degree of the whole length of the pipe should be: 0.03÷8m×100%=0.375%
Tips: Steel pipes have a hollow section whose length is much greater than the diameter or circumference of steel. According to the cross-sectional shape, it is divided into round, square, rectangular and special-shaped steel pipes. According to the material, it is divided into carbon steel pipe, low alloy structural steel pipe, alloy steel pipe and composite steel pipe. According to the purpose, it is divided into steel pipes for pipelines, engineering structures, thermal equipment, octg casing, machinery manufacturing, geological drilling, and high-pressure equipment. According to the production process, it is divided into seamless pipe and welded steel pipe. Among them, seamless steel pipe is divided into hot rolling and cold rolling (drawing), and welded steel pipe is divided into straight seam welded steel pipe and spiral seam welded steel pipe.
