General term for seamless steel pipe

General term for seamless steel pipe

1 Delivery status

Refers to the final plastic deformation or final heat treatment state of the delivered product. Generally, delivery without heat treatment is called hot-rolled or cold-drawn (rolled) state or manufacturing state; delivery after heat treatment is called heat treatment state, or according to the type of heat treatment, it is called normalizing (normalization), quenching and tempering, solid solution, annealing state. When ordering, the delivery status must be indicated in the contract.

2 Delivery by actual weight or delivery by theoretical weight

Actual weight - at the time of delivery, the weight of the product is delivered according to the weighed (weighted) weight;
Theoretical weight - at the time of delivery, the product weight is the weight calculated according to the nominal size of the steel.

3 Guarantee conditions

Inspection according to the specified items of the current standard and ensuring compliance with the standard are called guarantee conditions. Guarantee conditions are further divided into:
A Basic guarantee conditions (also known as mandatory guarantee conditions). Regardless of whether the customer specifies it in the contract. It is necessary to carry out the inspection according to the standard regulations, and ensure that the inspection results meet the standard regulations. Such as chemical composition, mechanical properties, dimensional deviation, surface quality, flaw detection, hydraulic test, or process performance tests such as flattening or flaring, are all mandatory conditions.
B Agreement guarantee conditions: In addition to the basic guarantee conditions in the standard, there are "according to the requirements of the buyer, after negotiation between the supplier and the buyer, and indicate in the contract" or "when the buyer requires..., it should be indicated in the contract" ; Some customers put forward stricter requirements on the basic guarantee conditions in the standard (such as composition, mechanical properties, dimensional deviation, etc.) or increased inspection items (such as steel pipe ovality, uneven wall thickness, etc.). The above terms and requirements, when ordering, shall be negotiated by both the supplier and the buyer, and the supply technology agreement shall be signed and specified in the contract. Therefore, these conditions are also called agreement guarantee conditions.

4 Batches

The "batch" in the standard refers to an inspection unit, that is, an inspection batch. If the batch is grouped by the delivery unit, it is called the delivery batch. When the delivery batch is large, one delivery batch can include several inspection batches; when the delivery batch is small, one inspection batch can be divided into several delivery batches.
The composition of "batch" usually has the following regulations (see relevant standards for details):
A Each batch shall consist of steel pipes of the same designation (steel grade), same furnace (tank) number or parent furnace number, same specification and same heat treatment system (heating number).
B For high-quality carbon steel structural pipes and fluid pipes, they can be composed of steel pipes of the same brand, the same specification and the same heat treatment system (heat) in different furnaces (tanks).
C Each batch of welded steel pipes shall consist of steel pipes of the same designation (steel grade) and the same specification.

5 Portrait and landscape

In the standard, the longitudinal direction refers to those parallel to the processing direction (that is, along the processing direction); the transverse direction refers to the vertical to the processing direction (the processing direction is the axial direction of the steel pipe). When doing the impact energy test, the fracture of the longitudinal sample is perpendicular to the processing direction. Therefore, it is called transverse fracture; because the fracture of transverse specimen is parallel to the processing direction, it is called longitudinal fracture.

Terminology of steel pipe dimensions


1 Nominal and actual dimensions
A Nominal size: It is the nominal size stipulated in the standard, it is the ideal size desired by users and manufacturers, and it is also a reasonable size.
    Dimensions specified in order.
B Actual size: It is the actual size obtained in the production process, which is often larger or smaller than the nominal size. this big
The phenomenon of being larger or smaller than the nominal size is called deviation.


2 Deviations and tolerances
A 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.
B 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:
A Normal length (also known as non-fixed length): where the length is within the length range specified by the standard and there is no fixed length requirement,
Both are 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.
B. 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.
Take the structural pipe standard as an example: the yield rate of the production of fixed-length pipes is much lower than that of ordinary length pipes, and it is reasonable for manufacturers to ask for price increases. The price increase range varies from company to company, and generally increases by about 10% on the basis of the base price.
C Multiple ruler length: The double ruler length should be within the normal 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, an 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 margin is 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.
D 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-specific length is 6000-8000mm or 8000-10000mm.
It can be seen that the range length is looser than the fixed length and double length, but much stricter than the usual length.


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 does not exceed 80% of the wall thickness tolerance (implemented after negotiation between the supplier and the buyer).


5 Ovality
There is a phenomenon of unequal outer diameters on the cross section of circular steel pipes, that is, there are maximum outer diameters and minimum outer diameters that are not necessarily perpendicular to each other, then the difference between the largest outer diameter and the smallest outer diameter is the ellipticity (or not 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:
A Local bending degree: Use a one-meter-long ruler to measure the maximum bending point of the steel pipe, and measure its chord height (mm), which is the value of the local bending degree. 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.
B The total bending degree 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 length of the steel pipe. Full length flex. 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÷8m×100%=0.375%
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7 size out of tolerance
The size 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 steel pipe. 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.


 Chemical Analysis Terminology


The chemical composition of steel is one of the important factors related to the quality and end-use performance of steel, and it is also the main basis for formulating the heat treatment system of steel and even the final product. Therefore, in the technical requirements section of steel standards, the first item often stipulates the applicable steel grade (steel grade) and its chemical composition, and it is listed in the standard in the form of a table. important basis.  


1 Melting composition of steel
The chemical composition specified in the general standard refers to the smelting composition. It refers to the chemical composition of steel after smelting and mid-casting. In order to make it representative, that is, to represent the average composition of the furnace or tank, it is stipulated in the sampling standard method that the molten steel is cast into a small ingot in the sample mold, and the sample chips are planed or drilled on it, according to the specified standard. Method (GB/T223) for analysis, the results must meet the standard chemical composition range, which is also the basis for customer acceptance.


2 Finished ingredients
Finished product composition is also called verification analysis composition, which is the chemical composition obtained by drilling or planing sample chips from the finished steel according to the specified method (GB/T222), and analyzing according to the specified standard method (GB/T223). During the crystallization and subsequent plastic deformation of steel, due to the uneven distribution (segregation) of alloying elements in the steel, there is a deviation between the composition of the finished product and the standard composition range (smelting composition), and the deviation value should comply with the provisions of GB/T222 .


3 Arbitration analysis

When there are significant differences in the results of the analysis of the same sample by two laboratories and exceed the allowable analysis error of the two laboratories, or when the manufacturer and the user department, the buyer and the supplier have different opinions on the analysis of the same sample or the finished product of the same batch of steel , can be re-analyzed by a third-party authoritative unit with rich analysis experience, which is called arbitration analysis. The results of the arbitration analysis shall be the basis for the final judgment.