Common terms used in steel pipe
Common terms used in steel pipe
(1) General terminology
1 delivery status
It refers to the state of final plastic deformation or final heat treatment of the delivered product. Generally referred to as hot rolling or cold drawing (rolling) state or manufacturing state without heat treatment; heat treatment delivered by heat treatment, or normalized (normalization), quenching, solid solution, annealing according to the type of heat treatment status. When ordering, the delivery status must be indicated in the contract.
2 delivery according to actual weight or delivery according to theoretical weight
Actual weight - when delivered, the weight of the product is delivered on a weighing (overweight) basis;
Theoretical Weight - When delivered, the weight of the product is the weight calculated from the nominal size of the steel. The calculation formula is as follows (required to be delivered according to the theoretical weight, it must be stated in the contract):
The theoretical weight of steel pipe per meter (the density of steel is 7.85kg/dm3):
W=0.02466(D-S)S
Where: W--Steel pipe theoretical weight per meter, kg / m;
D--the nominal outer diameter of the steel pipe, mm;
S--The nominal wall thickness of steel pipe, mm.
3 guarantee conditions
According to the provisions of the current standards, the inspection and guarantee of compliance with the standards are called guarantee conditions. The guarantee conditions are further divided into:
A. Basic guarantee conditions (also known as mandatory conditions). Whether or not the customer is stated in the contract. The inspection shall be carried out in accordance with the standards and the inspection results shall be in compliance with the standards.
Process performance tests such as chemical composition, mechanical properties, dimensional deviation, surface quality, and flaw detection, hydraulic testing, or flattening or flaring are all mandatory conditions.
B. Agreement guarantee conditions: In addition to the basic guarantee conditions, there are still “in accordance with the requirements of the demander, negotiated by the supplier and the buyer, and marked in the contract?” or “when the demander requests..., it should be noted in the contract. "There are other customers who impose strict requirements on the basic guarantee conditions in the standard (such as composition, mechanical properties, dimensional deviation, etc.) or increase inspection items (such as ellipticity of steel pipes, uneven wall thickness, etc.). At the time of ordering, the supplier and the buyer shall negotiate and sign the supply technical agreement and indicate it in the contract. Therefore, these conditions are also called the agreement guarantee conditions. Products with agreed guarantee conditions are generally subject to price increase.
4 batches
The "batch" in the standard refers to one inspection unit, that is, the inspection lot. If the batch is delivered in batches, it is called the delivery batch. When the delivery quantity is large, one delivery lot can include several inspection lots; when the delivery quantity is small, one inspection lot can be divided into several delivery lots.
The composition of the "batch" usually has the following provisions (see the relevant standards for details):
A. Each batch shall consist of steel pipes of the same grade (steel grade), the same furnace (tank) number or the same master furnace number, the same specification and the same heat treatment system (heating).
B. For high-quality carbon steel structural pipes and fluid pipes, it can be composed of steel pipes of the same grade, the same specification and the same heat treatment system (heating) of different furnaces (tanks).
C. Each batch of welded steel pipe shall consist of the same grade (steel grade) and steel pipe of the same specification.
5 high quality steel and high quality steel
In GB/T699-1999 and GB/T3077-1999 standards, the brand with the word "A" behind it, is high-quality steel, and vice versa.
Premium quality steel is superior to high quality steel in some or all of the following:
A. Reduce the content range of ingredients;
B. Reduce the content of harmful elements (such as sulfur, phosphorus, copper);
C, to ensure higher purity (requires less non-metallic inclusions);
D, to ensure higher mechanical properties and process performance.
6 portrait and landscape
In the standard, the longitudinal direction refers to the direction parallel to the machining direction (ie, the direction of machining); the horizontal direction refers to the direction perpendicular to the machining direction (the machining direction is the axial direction of the steel pipe).
When performing the impact work experiment, the fracture of the longitudinal specimen is perpendicular to the machining direction. Therefore, it is called the transverse fracture; the fracture of the transverse specimen is called parallel to the machining direction, so it is called the longitudinal fracture.
(2) Steel pipe shape, size terminology
1 nominal size and actual size
A. Nominal size: It is the nominal size specified in the standard. It is the ideal size that users and manufacturers hope to obtain, and is the order size indicated in the contract.
B. Actual size: It is the actual size obtained during the production process, and the size is often larger or smaller than the nominal size. This phenomenon of being larger or smaller than the nominal size is called deviation.
2 deviations and tolerances
A. Deviation: In the production process, since the actual size is difficult to achieve the nominal size requirement, that is, it is often larger or smaller than the nominal size, the standard specifies that a difference is allowed between the actual size and the nominal size. A positive deviation is a positive deviation, and a negative value is a negative deviation.
B. Tolerance: The sum of the absolute values of the positive and negative deviation values specified in the standard is called the tolerance, also called the “tolerance zone”.
The deviation is directional, that is, it is expressed as "positive" or "negative"; the tolerance is not directional, so it is wrong to call the deviation value "positive tolerance" or "negative tolerance".
3 delivery length
The length of delivery is also known as the length of the user or the length of the contract. There are several provisions for the length of delivery in the standard:
A. Normal length (also known as non-fixed length): Where the length is within the length specified by the standard and there is no fixed length requirement, it is called the normal length. For example, the structural pipe standard stipulates: hot-rolled (extruded, expanded) steel pipe 3000mm ~ 12000mm; cold drawn (rolled) steel pipe 2000mmm ~ 10500mm.
B. Fixed length: The length of the fixed length should be within the normal length and is a fixed length dimension required in the contract. However, it is not possible to cut the absolute length in the actual operation, so the standard deviation length is specified for the length of the rule.
The structural pipe standard is:
The production rate of the length of the tube is larger than that of the normal length tube. It is reasonable for the manufacturer to raise the price. The price increase rate is not consistent with each other, and the price increase is generally about 10% based on the base price.
C. Double-length length: The length of the double-length should be within the normal length. The length of the single-length ruler and the multiple of the total length should be indicated in the contract (for example, 3000mm×3, that is, 3 times of 3000mm, the total length is 9000mm). In practice, the allowable positive deviation of 20 mm should be added to the total length, plus the remaining allowance should be left for each single-length length. Taking the structural tube as an example, the remaining amount of the incision is specified: the outer diameter is ≤ 159 mm is 5 to 10 mm; the outer diameter is > 159 mm is 10 to 15 mm.
If there is no ruler length deviation and cutting allowance in the standard, it shall be negotiated by the supplier and the buyer and specified in the contract. The double length scale is the same as the length of the fixed length, which will bring the finished product rate to the production enterprise to be greatly reduced. Therefore, it is reasonable for the production enterprise to raise the price, and the price increase range is basically the same as the fixed length length increase.
D. Range length: The range length is within the normal length range. When the user requests one of the fixed range lengths, it must be indicated in the contract.
For example, the length is usually 3,000 to 12,000 mm, and the length of the range is 6000 to 8000 mm or 8000 to 10000 mm.
It can be seen that the length of the range is looser than the length of the fixed length and the multiple length, but it is much stricter than the usual length, and it will also bring the reduction of the finished product rate to the production enterprise. Therefore, it is reasonable for the production enterprises to raise the price. The price increase is generally about 4% higher than the base price.
4 uneven wall thickness
The wall thickness of the steel pipe cannot be the same everywhere, and the wall thickness is not uniform in the cross section and the longitudinal pipe body, that is, the wall thickness is uneven. In order to control this unevenness, the allowable index of wall thickness unevenness is specified in some steel pipe standards, and the general regulation does not exceed 80% of the wall thickness tolerance (executed after consultation between the supplier and the buyer).
5 ovality
In the cross section of a circular steel pipe, there is a phenomenon that the outer diameters are not equal, that is, there are maximum outer diameters and minimum outer diameters that are not necessarily perpendicular to each other, and the difference between the maximum outer diameter and the minimum outer diameter is ellipticity (or no Roundness). In order to control the ellipticity, some steel pipe standards specify the allowable index of ellipticity, which is generally specified as not exceeding 80% of the outer diameter tolerance (executed after negotiation between the supplier and the buyer).
6 curvature
The steel pipe is curved in the longitudinal direction, and the degree of curvature is expressed by a number. The bending degrees specified in the standard are generally divided into the following two types:
A. Local bending degree: Use a one-meter long ruler to measure the maximum bending of the steel pipe, and measure the chord height (mm), which is the local bending value, the unit is mm/m, indicating the method is 2.5mm/m. . This method is also applicable to tube end bending.
B. Total length of total bending: Use a string to tighten from both ends of the tube, measure the maximum chord height (mm) of the bent portion of the steel pipe, and then convert it into the length (in meters) as the length of the steel pipe. Full length curvature.
For example, if the length of the steel pipe is 8m and the maximum chord height is 30mm, the full-length bending of the pipe should be:
0.03÷8m×100%=0.375%
7 size is out of tolerance
The size is out of tolerance or the size exceeds the standard tolerance. The "size" here mainly refers to the outer diameter and wall thickness of the steel pipe. Usually, some people use the size tolerance to be called "tolerance". This kind of equating the deviation and tolerance is not strict, and it should be called "deviation". The deviation here may be "positive" or "negative", and it is rare that the "positive and negative" deviations are out of the same batch of steel tubes.
(3) Chemical analysis terminology
The chemical composition of steel is one of the important factors that affect the quality and end-use performance of steel. It is also the main basis for the preparation of steel and even the heat treatment system of the final product. Therefore, in the technical requirements of the steel standard, the first item usually specifies the grade (steel grade) and its chemical composition applicable to the steel, and is included in the standard in the form of a table. It is the chemical composition of the steel and steel for the inspection of the production enterprise and the customer. An important basis.
1 steel melting component
The chemical composition specified in the general standard refers to the smelting component. It refers to the chemical composition of steel in the middle of smelting and pouring. 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 small ingots in the sample mold, and the sampling chips are shaved or drilled thereon according to the prescribed standards. The method (GB/T223) is analyzed, and the results must conform to the standard chemical composition range, which is also the basis for customer acceptance.
2 finished ingredients
The finished product component is also called the verification analysis component. It is a chemical component obtained by drilling or planing the sampling chips from the finished steel according to the specified method (GB/T222) and analyzing according to the specified standard method (GB/T223). In the crystallization and subsequent plastic deformation of steel, due to the uneven distribution (segregation) of the alloying elements in the steel, there is a deviation between the finished product component and the standard component range (melting component), and the deviation value should meet the requirements of GB/T222. .
The finished components of steel are mainly used by the use department or the quality inspection department for the acceptance of steel quality. The production enterprises generally do not perform finished product analysis (except for user requirements), but the finished product analysis should meet the standard requirements.
3 arbitration analysis
Since the results of the two laboratories analyzing the same sample are significantly different and exceed the allowable analytical error of the two laboratories, or when the manufacturer and the use department, the demander and the supplier have different opinions on the same sample or the finished product analysis of the same batch of steel, It can be reanalyzed by an authoritative unit with rich analytical experience (such as China Iron and Steel Research Institute or inspection department with qualification for commodity inspection), which is called arbitration analysis. The result of the arbitration analysis is the final judgment basis.
(4) Terminology of mechanical properties
The mechanical properties of steel are important indicators to ensure the ultimate performance of steel (mechanical properties), which depends on the chemical composition of the steel and the heat treatment system. In the steel pipe standard, tensile properties (tensile strength, yield strength or yield point, elongation), hardness and toughness indexes, and high and low temperature properties required by users are specified according to different use requirements.
1 tensile strength (σb)
The maximum force (Fb) of the specimen during the drawing process, the stress (σ) obtained from the original cross-sectional area (So) of the specimen, called the tensile strength (σb), in N/mm2 (MPa). It represents the maximum ability of a metal material to resist damage under tensile forces.
2 yield point (σs)
The metal material with yielding phenomenon, the force of the sample does not increase (maintains constant) during the stretching process, and the stress at the time of elongation can be continued, which is called the yield point. If the force drops, the upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa).
Upper yield point (σsu): the maximum stress before the sample yields and the force drops for the first time;
Lower yield point (σsl): The minimum stress in the yielding phase when the initial transient effect is not counted.
3 elongation after break (σ)
In the tensile test, the percentage of the length increased by the gauge length after the sample is broken and the length of the original gauge length is called the elongation. Expressed in σ, the unit is %.
4 section shrinkage rate (ψ)
In the tensile test, the percentage of the maximum reduction in the cross-sectional area of the reduced diameter after the sample is broken and the original cross-sectional area is called the reduction ratio of the section. Expressed in ψ, the unit is %.
5 hardness index
The ability of a metal material to resist the indentation of a hard object 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, microhardness and high temperature hardness. Commonly used for pipes are Brinell, Rockwell and Vickers hardness.
A, Brinell hardness (HB)
Press the steel ball or carbide ball of a certain diameter into the surface of the sample with the specified test force (F). After the specified holding time, remove the test force and measure the indentation diameter (L) on the surface of the sample. The Brinell hardness value is the quotient obtained by dividing the test force by the spherical surface area of the indentation. It is expressed by HBS (steel ball) and the unit is N/mm2 (MPa).
Determination of Brinell hardness is more accurate and reliable, but generally HBS is only suitable for metal materials below 450N/mm2 (MPa), not suitable for harder steel or thinner plates. Among the steel pipe standards, Brinell hardness is the most widely used, and the hardness of the material is often expressed by the indentation diameter d, which is both intuitive and convenient.
Example: 120HBS10/1000130: It means that the Brinell hardness value measured by holding a 10mm diameter steel ball under the test force of 1000Kgf (9.807KN) for 30s (second) is 120N/mm2 (MPa).
B, Rockwell hardness (HK)
The Rockwell hardness test, like the Brinell hardness test, is an indentation test method. The difference is that it measures the depth of the indentation. That is, under the action of the initial test force (Fo) and the total test force (F), the indenter (the steel plant cone or steel ball) is pressed into the surface of the sample, and after the specified holding time, the main body is removed. Test force, the hardness value was calculated using the measured residual indentation depth increment (e). Its value is an unnamed number, represented by the symbol HR. The scale used has 9 scales such as A, B, C, D, E, F, G, H, and K. The scales commonly used for steel hardness testing are generally A, B, C, ie HRA, HRB, HRC.
The Rockwell hardness test is currently a widely used method in which HRC is used second only to Brinell hardness HB in steel pipe standards. Rockwell hardness can be applied to the determination of metal materials from very soft to very hard, which makes up for the Brinell method. It is simpler than the Brinell method and can directly read the hardness value from the dial of the hardness machine. However, the hardness value is not as accurate as the Brinell method because of its small indentation.
C, Vickers hardness (HV)
The Vickers hardness test is also an indentation test method in which a positive quadrilateral pyramid diamond indenter with an opposite face angle of 1360 is pressed into the test surface with a selected test force (F), and the test is performed after the specified holding time. Force, measure the length of the two diagonals of the indentation.
The Vickers hardness value is the quotient of the test force divided by the surface area of the indentation.
The Vickers hardness test force F is 6 (49.03), 10 (98.07), 20 (196.1), 30 (294.2), 50 (490.3), 100 (980.7) Kgf (N), etc., and the hardness value can be measured. The range is 5 to 1000 HV.
An example of the expression method: 640 HV30/20 indicates that the Vickers hardness value measured by holding a test force of 30 Hgf (294.2 N) for 20 seconds (second) is 640 N/mm 2 (MPa).
The Vickers hardness method can be used to determine the hardness of very thin metal materials and surface layers. It has the main advantages of the Brinell and Rockwell methods, and overcomes their basic shortcomings, but is not as simple as the Rockwell method. The Vickers method is rarely used in steel pipe standards.
6 impact toughness index
Impact toughness is the resistance of the metal to the external impact load. It is generally expressed by the impact toughness value (ak) and the impact energy (Ak). The units are J/cm2 and J (Joule).
Impact toughness or impact energy test (referred to as "impact test"), divided into normal temperature, low temperature and high temperature impact test due to different test temperatures; if it is according to the notch shape of the sample, it can be divided into "V" shaped notch and "U" There are two types of notched impact tests.
Impact test: a sample of a certain size and shape (10 × 10 × 55 mm) (with a "U" or "V" type notch in the middle of the length direction, a notch depth of 2 mm) is subjected to impact load on a specified test machine. The experiment of breaking at the gap.
A. Impact absorption work Akv (u) - a metal pattern having a certain size and shape, which is absorbed when broken under the impact load. The unit is Joule (J) or Kgf. m.
B. Impact toughness value avv (u) - The quotient of the impact absorption work divided by the bottom cross-sectional area at the notch of the sample. The unit is joules/cm 2 (J/cm 2 ) or kilograms force. m/cm 2 (Kgf . m/cm 2 ).
The normal temperature impact test temperature is 20±50C; the low temperature impact test temperature range is <15～-1920C; the high temperature impact test temperature range is 35～10000C.
The cooling medium used in the low temperature impact test is generally a non-toxic, safe, non-corrosive metal and liquid or gas that does not solidify at the test temperature. Such as anhydrous ethanol (alcohol), solid carbon dioxide (dry ice) or liquid nitrogen atomizing gas (liquid nitrogen).