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steel pipe industry-specific terminologies

Oct 26, 2017

Steel pipe terminology

(1) General terms

① delivery status

Refers to the final plastic deformation of the delivery product or the final heat treatment state. It is said that the heat treatment is not heat-treated or it is called hot-rolled or cold-drawn (rolled) state or manufacturing state. The heat treatment is heat-treated, or it is said to be normalized (normalized), quenched and tempered, status. When ordering, delivery status should be indicated in the contract.

② deliver by actual weight or according to the theoretical weight

Actual weight - when delivered, the weight of the product is delivered by weight (weighing)

Theoretical weight - When delivered, the weight of the product is calculated from the nominal size of the steel. The formula is as follows (required by the theoretical weight of the delivery, need to specify in the contract):

The theoretical weight of steel per meter (steel density of 7.85kg / dm3) formula:

W = 0.02466 (D-S) S

Where: W - steel theoretical weight per meter, kg / m;

D - nominal diameter of steel pipe, mm;

S - nominal wall thickness of pipe, mm.

③ guarantee conditions

According to the provisions of the current standard items to test and ensure that meet the standards, called the guarantee conditions. The guarantee conditions are divided into:

A, the basic guarantee conditions (also known as the necessary conditions). Regardless of whether the customer is stated in the contract. Shall be subject to the provisions of the standard inspection, and to ensure that the test results meet the standard requirements. Such as chemical composition, mechanical properties, size deviation, surface quality and flaw detection, water pressure test or flattening or flaring and other process performance experiments are essential conditions.

B, the agreement to ensure that the conditions: the standard in addition to the basic guarantee conditions, there are "according to the demand side, by the supply and demand sides, and in the contract Note" or "when the demand side ... ..., (Such as composition, mechanical properties, size deviation, etc.) or by increasing the inspection items (such as steel pipe oval, uneven wall thickness.) The above terms and requirements, the requirements of the standard, In the order, by the supply and demand sides to negotiate, signed the supply technology agreement and specify in the contract.Therefore, these conditions, also known as the agreement to ensure the conditions of the agreement to ensure that the conditions of the products are generally to increase the price.

④ batch

The "batch" in the standard refers to an inspection unit, that is, inspection lot. If the delivery unit group approved, said the delivery batch. When the delivery quantity is large, a delivery lot may include several inspection lots; when the delivery quantity is small, an inspection lot can be divided into several delivery lots.

The composition of the "batches" usually has the following provisions (see the relevant standards):

A, each batch should be the same grade (steel grade), the same furnace (tank) or the same furnace number, the same specifications and the same heat treatment system (furnace) of the steel pipe composition.

B, for high-quality carbon steel structure pipe, fluid pipe, can be different furnace (tank) the same grade, the same specifications and the same heat treatment system (furnace) of the steel pipe composition.

C, welded steel pipe each batch should be the same grade (steel), the same specifications of the steel pipe composition.

⑤ high quality steel and high quality steel

In GB / T699-1999 and GB / T3077-1999 standard, its grades followed by "A" word, for the high-quality steel, and vice versa for the general high-quality steel.

High-quality steel in the following part or all better than high-quality steel:

A, narrow the content range;

B, reduce the harmful elements (such as sulfur, phosphorus, copper) content;

C, to ensure high purity (requires non-metallic inclusions less);

D, to ensure high mechanical properties and process performance.

⑥ vertical and horizontal

Standard refers to the vertical direction is the direction of processing (that is, along the direction of processing); horizontal refers to the vertical direction with the processing (the direction of the steel pipe).

When the impact work is done, the fracture of the longitudinal specimen is perpendicular to the machining direction. So that transverse fracture; transverse specimen fracture and processing direction parallel, so that the vertical fracture.

(2) steel pipe shape, size terms

① nominal size and actual size

A, nominal size: the standard size specified in the standard, the user and the manufacturer want to get the ideal size, but also the contract specified in the order size.

B, the actual size: the actual size of the production process, the size is often greater than or less than the nominal size. This phenomenon is greater or less than the nominal size of the phenomenon known as the deviation.

② deviation and tolerance

A, Deviation: In the production process, because the actual size is difficult to achieve nominal size requirements, that is often greater or less than the nominal size, so the standard specifies the actual size and nominal size allows a difference between. The difference is positive for the positive deviation, the difference is negative for the negative deviation.

B, tolerance: standard provides positive and negative deviation of the absolute value of the sum called the tolerance, also known as "tolerance zone." The deviation is directional, that is, "positive" or "negative"; tolerance is no direction, therefore, the deviation of the value of "positive tolerance" or "negative tolerance" is wrong.

③ delivery length

Delivery length, also known as the length of the user requirements or contract length. There are several rules for the length of the delivery:

A, usually length (also known as non-length length): Where the length of the standard length of the provisions and no fixed length requirements, are called the usual length. For example, structural pipe standard: hot (extrusion, expansion) steel pipe 3000mm ~ 12000mm; cold drawn

(Rolling) steel pipe 2000mmm ~ 10500mm.

B, length of length: length should be within the length of the length of the contract is required in a fixed length of the size. But the actual operation are cut out the absolute length of the length is not possible, so the standard length of the specified length of the allowable positive deviation. It is not possible to cut out the absolute length of the length, so the allowable positive deviation is specified for the length of the scale.

The structural pipe standard is:

Production length of the length of the pipe than the usual length of the pipe into the rate of decline is greater, the production enterprises to raise the price requirements are reasonable. Increase the rate of the enterprise is not consistent, generally based on the base price increase of about 10%.

C, the length of the length: the length of the length should be within the normal length range, the contract should be marked with a single length and the length of the total length of the composition (for example, 3000mm × 3, that is, 3000mm 3 times the total length of 9000mm). In practice, should be based on the total length of the base

Plus the allowable positive deviation of 20mm, plus the length of each monogon should stay incision margin. To structural tube, for example, to set the incision

Balance: Outer diameter ≤159mm is 5 ~ 10mm; diameter> 159mm is 10 ~ 15mm.

If the length of the standard without the length of the deviation and cut the provisions of the provisions of the supply and demand sides should be negotiated and specified in the contract. Times the length of the same length with the length of the production will bring a significant reduction in production rate, so the production enterprises to raise the price is reasonable, the rate of increase with the length of the increase in the length of the same.

D, the length of the range: the length of the range in the normal length range, when the user requires a fixed range of length, the need to specify in the contract.

For example: usually length of 3000 ~ 12000mm, and the length of the length of 6000 ~ 8000mm or 8000 ~

10000mm. It can be seen that the length of the length is longer than the length and length of the length requirements, but much more than the usual length, but also to the production enterprises to bring the yield reduction. Therefore, the production enterprises to raise the price is justified, the increase in the price increase in the base price of about 4%.

④ uneven wall thickness

Steel pipe wall thickness can not be the same everywhere, in its cross-section and vertical pipe body on the objective of the existence of wall thickness, that is, uneven wall thickness. In order to control this non-uniformity, in some steel pipe standards in the provisions of the wall thickness of the allowable indicators, the general provisions of not more than 80% of wall thickness tolerance (after consultation between the supply and demand sides to implement).

⑤ ellipticity

In the cross section of the circular steel pipe there is a phenomenon in which the outer diameter is not equal, that is, there is not necessarily perpendicular to each other, the maximum outer diameter and the minimum outer diameter, the difference between the maximum outer diameter and the minimum outer diameter is ellipticity Roundness). In order to control the ellipticity, some steel pipe standard provides the allowable index of ellipticity, the general provisions of not more than 80% of the outer diameter tolerance (after consultation between the supply and demand sides).

⑥ bending degree

Steel pipe in the length of the direction of a curve, with the number that the curvature of the curvature that is called. The curvature specified in the standard is generally divided into the following two types:

A, local bending degree: with a meter long ruler by the maximum bending in the steel pipe, measuring the chord height (mm), that is, local bending value, the unit is mm / m, that method such as 2.5mm / m The This method also applies to the curvature of the pipe end.

B, the total length of the total curvature: with a string, from the tube at both ends of tension, measuring the maximum bending height of steel pipe (mm), and then converted into length (in meters) percentage, The length of the curvature.

For example: steel pipe length of 8m, measured the maximum string height 30mm, then the tube full length of curvature should be:

0.03 ÷ 8 m x 100% = 0.375%

⑦ size tolerance

Size tolerance or size of the standard deviation beyond the standard. The "size" here refers mainly to the outer diameter and wall thickness of the pipe. Often it is the size of the tolerance is called "tolerance outrageous", this deviation and tolerance is equivalent to the name is not tight, should be called "deviation". Where the deviation may be "positive", it may be "negative", rarely in the same batch of steel pipe in the "positive, negative" deviation are out of the phenomenon.

(3) Chemical analysis terminology

The chemical composition of steel is one of the important factors in the quality and end use performance of steel, and the main basis for the preparation of steel and even the final product heat treatment system. Therefore, in the technical requirements of the steel standard part, often the first item on the provisions of the steel grades (steel grade) and its chemical composition, and in tabular form included in the standard, is the production enterprises and customers acceptance of steel and steel chemical composition The important basis.

① steel smelting ingredients

The chemical composition specified in the general standard refers to the melting component. It refers to the steel smelting finished, pouring the middle of the chemical composition. In order to make it a representative, that is, the average composition of the furnace or tank, in the sampling standard method provides that the molten steel in the mold into the ingot, in which to dig or drill shrimp, according to the provisions of the standard Method (GB / T223) for analysis, the results must meet the standard chemical composition range, but also the basis for customer acceptance.

② finished ingredients

(GB / T222) is obtained from the finished product (GB / T222), and the chemical composition is analyzed according to the standard method (GB / T223). In the plastic and later plastic deformation of steel, due to the uneven distribution of alloying elements in the steel (segregation), thus allowing the finished product composition and the standard composition range (melting composition) between the existence of partial

Poor, the deviation should be consistent with the provisions of GB / T222.

The finished product composition of steel is mainly for the use of departments or quality inspection departments to accept the quality of steel use, the production enterprises generally do not do product analysis (except for user requirements), but should ensure that the finished product analysis in line with standards.

③ arbitration analysis

As the two laboratories analyzed the results of the same sample with significant differences and exceeded the allowable analytical errors of the two laboratories, or when the production and use departments, the demand side and the supplier had different opinions on the same sample or the finished product analysis of the same batch of steel , Which may be reanalyzed by an authoritative unit with a rich analytical experience from a third party (such as the China Iron and Steel Research Institute or the inspection department with a commodity inspection qualification), which is called arbitration analysis. The result of arbitration is the final judgment basis.

(4) mechanical properties

The mechanical properties of steel are important indicators to ensure the ultimate use of steel (mechanical properties), which depends on the chemical composition of steel and heat treatment system. In the steel pipe standard, according to different requirements, the tensile properties (tensile strength, yield strength or yield point, elongation) and hardness, toughness indicators, as well as the user requirements of high and low temperature performance.

① Tensile strength (σb)

The maximum force (Fb) of the specimen during the drawing process is the tensile strength (σb), expressed in terms of the stress (σ) of the original cross-sectional area (So) N / mm2 (MPa). It means that the metal material under the action of resistance to break

Bad the greatest ability. The formula is: where: Fb - the maximum force that the specimen is pulled off, N (Newton); So - the original cross-sectional area of the specimen, mm2.

② yield point (σs)

With the yield phenomenon of metal materials, the specimen in the tensile process does not increase (to maintain a constant) can continue to stretch the stress, called the yield point. If the force falls, it should distinguish between the upper and lower yield points. The unit of yield point is N / mm2 (MPa). (Σs): the maximum stress in the yield phase when the initial instantaneous effect is not counted.

The yield point is calculated as:

Where: Fs - the tensile strength of the sample during the test (constant), N (Newton); So - the original sample cross-sectional area, mm2.

③ elongation after breaking (σ)

In the tensile test, the length of the gauge length after the specimen is pulled off is the percentage of the length of the original gauge length, called the elongation. Expressed in σ, in%. The formula is:

Where: L1 - after the specimen cut off the length of the gauge length, mm; L0 - the original sample length length, mm.

④ section shrinkage (ψ)

In the tensile test, the maximum reduction of the cross-sectional area at the reduced diameter and the percentage of the original cross-sectional area after the specimen is broken is called the section shrinkage. Expressed in ψ, in%. The formula is as follows: Where: S0 - the original cross-sectional area of the sample, mm2;

S1 - the minimum cross-sectional area of the specimen after the specimen is broken, mm2.

⑤ hardness indicators

The ability of a metal material to resist a hard object's crushing surface is called hardness. According to the test method and the scope of application, the hardness can be divided into Brinell hardness, Rockwell hardness, Vickers hardness, Shore hardness, micro hardness and high temperature hardness. For the pipe commonly used are Brinell, Rockwell, Vickers hardness of three.

A, Brinell hardness (HB)

(F) is pressed against the pattern surface with a predetermined test force (F) with a certain diameter ball or carbide ball, and the test force is removed after the specified holding time. The indentation diameter (L) of the sample surface is measured. Brinell hardness values are calculated by dividing the test force by the indentation spherical surface area. Expressed in HBS (steel ball), the unit is N / mm2 (MPa).

The formula is:

Where: F - the test force on the surface of the metal sample, N;

D - test ball diameter, mm;

d - indentation average diameter, mm.

Determination of Brinell hardness is more accurate and reliable, but the general HBS only applies to 450N / mm2 (MPa) the following metal materials, for hard steel or thin plate is not applicable. In the steel pipe standard, Brinell hardness is the most widely used, often with indentation diameter d to represent the hardness of the material, both intuitive and convenient.

Example: 120HBS10 / 1000130: indicates a Brinell hardness value of 120 N / mm2 (MPa) measured for 30 seconds (seconds) under a test force of 1000 Kgf (9.807 KN) with a diameter of 10 mm.

B, Rockwell Hardness (HK)

Rockwell hardness test with the Brinell hardness test, are indentation test method. The difference is that it is the depth of the indentation measured. That is, under the influence of the initial test force (Fo) and the total test force (F), the indenter (gold steel cone or steel ball) is pressed into the surface of the specimen, and after the specified holding time, The test force is calculated using the measured residual indentation depth increment (e). Its value is an unknown number, expressed in symbol HR,