What are the terms of seamless steel pipe

Seamless steel pipe refers to a steel pipe that is made of a single piece of metal and has no seams on the surface. According to the production method, seamless tubes are divided into hot-rolled tubes, cold-rolled tubes, cold drawn seamless tubing, extruded tubes, jacked tubes, etc. According to the cross-sectional shape, seamless steel tubes are divided into two types: round and special-shaped, and special-shaped tubes have various complex shapes such as square, oval, triangular, hexagonal, melon-shaped, star-shaped, and finned tubes. The maximum diameter is 650mm, and the minimum diameter is 0.3mm. Depending on the application, there are thick-walled tubes and thin-walled tubes. Understanding the following steel pipe terminology concepts can effectively help us avoid unnecessary losses and misunderstandings.

(1) Nominal size and actual size:

①. The nominal size of the seamless steel pipe is the nominal size stipulated in the standard. It is the ideal size that users and manufacturers want to obtain, and it is also the order size specified in the contract.

②Actual size: It is the actual size obtained in 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.

(2), deviation and tolerance

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 used as a tolerance, also called "tolerance zone".

The deviation is homogeneous, that is, expressed as "positive" or "negative"; the tolerance has no directionality, so it is wrong to call the deviation value "positive tolerance" or "negative tolerance".

(4), ellipticity:There is a phenomenon of unequal outer diameters on the cross-section of circular seamless steel pipes, that is, there are maximum outer diameters and minimum outer diameters that are not necessarily perpendicular to each other, and the difference between the largest outer diameter and the smallest outer diameter is the ellipticity. In order to control the ellipticity, some seamless steel pipe standards stipulate the allowable index of the roundness, which is generally stipulated as not exceeding 80% of the outer diameter tolerance (implemented after negotiation between the supplier and the buyer).

(5) Curvature: The seamless steel pipe is curved in the length direction, and the curvature expressed 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 length of the bending degree:Use a thin rope to tighten from both ends of the pipe, measure the maximum chord height (mm) at the bend of the seamless 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 full-length bending degree of the pipe should be: 0.03÷8mx 0100%=0.375%.

(6) Size out of tolerance: The size of the seamless pipe is out of tolerance or the size exceeds the allowable deviation of the standard. The "size" here mainly refers to the outer diameter and wall thickness of the pipe. Usually, some people call the habit of dimensional out-of-tolerance "out of tolerance". This kind of equating deviation and tolerance is imprecise and should be called "out of tolerance". The deviation here may be "positive" or "negative". It is rare that both "positive and negative" deviations are out of line in the same batch of steel pipes.

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