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   Site:Home >> Steel Tube >> Steel Tube Knowledge >> Usual Glossary In Steel Tube Norm


一、General terms

①Delivery state

      
Delivery state means the state of the final plastic deformation or final heat treatment of delivered product. Generally, the products delivered without heat treatment are called hot-rolled or cold-drawn (rolled) state; the products delivered with heat treatment are called heat treatment state, or they can be called as normalizing, quenching and tempering, solution, annealing states. Delivery state should be indicated in the contract when ordering.

②Delivering according to actual weight or theoretical weight

      
Actual weight — the product is delivered according to the measured weight (on the scales);

      
Theoretical weight — when delivering, the weight of product is calculated according to the nominal size of steel material. The calculation formula is as follows (if the products are delivered according to theoretical weight, it should be indicated in the contract)
     
Calculation formula for the theoretical weight (the density of steel is 7.85 kg/dm3) per meter of steel tube:
      W=0.02466(D-S)S
      In the formula:
      W——theoretical weight per meter of steel tube,kg/m;
      D——nominal external diameter of steel tube,mm;
      S——nominal thickness of wall of steel tube,mm。

③Guarantee conditions

      
Under the provisions in current standard, testing the products and ensuring to comply with the provisions of standard is known as the guarantee conditions. Guarantee conditions can also be divided into:

A、Basic guarantee conditions (also known as necessary conditions). No matter whether they are specified in the contract by the customer, you should inspect this item according to the provisions in standard, and ensure that the test results meet the provisions in standard. For example, chemical compositions, mechanical properties, dimensional deviation, surface quality, damage detection, water pressure test or technological experiments such as pressing flat and tube end expansion are all necessary conditions.

B、Agreement guarantees conditions: in addition to basic guarantee conditions, there are still "according to the requirements of buyer, the conditions should be negotiated by both sides, and the conditions should be indicated in contract" or "if the buyer requires ..., it should be indicated in the contract"; some customers have stricter requirements on basic guarantee standard conditions (such as compositions, mechanical properties, dimensional deviation, etc.) or increase the testing items (such as ellpticity, uneven wall thickness, etc.). Above provisions and requirements should be negotiated by the both sides of supplier and buyer, an Availability Technology Agreement should be signed, and the requirements should be indicated in the contract. Therefore, these conditions are also called agreement guarantee conditions. In general, the prices of the products with agreement guarantee conditions should be increased.

④"Batch" in the “batch standard” means an inspection unit, ie. inspection batch. The batch divided by the delivery unit is called "delivery batch". If the batch amount of delivery is large, a delivery batch may include several inspection batches; if the batch amount of delivery is small, an inspection batch may include several delivery batched. The compositions of "batch" are usually regulated as follows (see related standards):

A、Each batch should be composed of the steel tubes of the same model (steel grade), the same boiler (tank) number or the same mother boiler number heaters, the same specifications and the same heat treatment system (boiler number).

B、As to the quality carbon steel pipe and fluid tube, the batch can be composed of the same model, the same specification and the same heat treatment system (boiler number) of different boilers (tanks).

C、Each batch of welded steel tubes should be composed of the same model (steel grade) and the same specification.

⑤Quality steel and senior quality steel

      
In the GB/T699-1999 and GB/T3077-1999 standards, the steel whose model accompanied with "A" is senior quality steel, on the contrary, the steel is general quality steel. Senior quality steel is in advance of quality steel on the following aspects partially or wholly:

A、Reduce the range of composition content;

B、Reduce the content of harmful elements (such as sulfur, phosphorus and copper);

C、Assure higher cleanliness (the content of non-metal inclusions should be small);

D、Assure higher mechanical properties and technological properties.

⑥Longitudinal direction and transverse direction

     
In the standard, the longitudinal direction is parallel with the processing direction (ie. along the processing direction); transverse direction is vertical with the processing direction (processing direction is the axial direction of steel tube).

      
During the impact test, the fracture of longitudinal specimen should be vertical with processing direction, thus it is called transverse fracture; the fracture of transverse specimen should be parallel with processing direction, thus it is called longitudinal fracture.

二、Steel tube appearance and size terms

①Nominal size and actual size

A、Nominal size: it is the nominal size regulated in the standard, and is the ideal size expected by the user and manufacturer, and is also the ordered size indicated in the contract.

B、Actual size: it is the actual size obtained during production, and this size is usually larger or smaller than the nominal size. The phenomena are called deviation.

②Deviation and tolerance

A、Deviation: during production, as the actual size is hard to achieve the requirements of nominal size, ie. the actual size is often larger or smaller than nominal size, an allowable difference between actual size and nominal size. The positive difference is called positive deviation, while the negative difference is called negative deviation.

B、Tolerance: the sum of the absolute values of positive deviation and negative deviation regulated in the standard is called tolerance, also called “tolerance zone”.

③Delivery length

      
Delivery length is also called user required length or contract length. In the standard, there are several regulations on the delivery length in the standard, as following:

A、Common length (also called random length): the length within the length range regulated in standard and without fixed length requirements is called common length. For example, it is regulated in the structural tube standard that: the common length of hot rolled (extruded, expanded) steel tube is 3000 mm -12000mm; while the common length of cold-drawn (rolled) steel tube is 2000 mm-10500mm.

B、Cut length: cut length is often within the range of common length, and is the certain fixed length size required in contract. However, it is impossible to cut out absolute cut length always in the actual operation, thus allowable positive deviation of cut length is regulated in the standard.

Take structural tube as an example:

      
The finished product rate of cut-to-length tube is greatly lower than the common-length tube, thus the price increasing request brought out by the manufacturer is reasonable. The price increasing rates of each enterprise are not consistent; generally, the price can be increased by 10% on the basis of basic prices.

C、Double length: double length should be within the range of common length usually, the individual double length and the multiple to compose the total length should be indicated in the contract (for example, 3000 mm × 3, that is triple of 3000 mm, with a total length of 9000mm). In the actual operation, an allowable positive deviation of 20mm should be added to the total length, as well as plus the cutting margin of each double length. Take structural tube as an example, the required cutting margin is 5 - 10mm for the steel tube with a diameter ≤159mm; 10-15mm for the steel tube with a diameter >159mm.

      
If there are no regulations in the standard, the double length deviation and cutting margin should be negotiated by both supplier and buyer and indicated in the contract. The same as cut length, double length can reduce the finished product rate of the enterprise greatly, thus the price increasing request brought out by the manufacturer is reasonable, and the price increasing rate is essentially the same as the price increasing rate of cut length.

D、Range length: range length is usually within common length range; in the case that the user requires the length in a fixed length range, it should be indicated in the contract. For example: that of common length is 3,000-12000mm, while that of cut length is 6000-8000mm or 8000 ~ 10000mm.

      
It may be seen that, the requirements on range length is easier than the cut length and double length, but stricter than the common length a lot, and it may reduce the finished product rate of enterprises. Therefore, the price increasing request brought out by the manufacturer is reasonable; generally, the price can be increased by about 4% on the basis of basic prices.

④Uneven wall thickness

      
Steel tube wall thickness is impossible to be the same, uneven wall thicknesses may exist on the cross-section and longitudinal tube objectively, ie. uneven thickness. To control this uneven phenomenon, the allowable indexes of uneven thicin the steel tube standard; generally, it is regulated not to exceed 80% of the tolerance of wall thickness (which should be imkness are regulated plemented after negotiating between the supply and the buyer).

⑤Ellipticity

      
The external diameter of the cross section of round steel tube may be uneven, that is the maximum external diameter and the minimum external diameter may be not perpendicular to each other, the difference between the maximum external diameter and the minimum external diameter is ellipticity (or non-round degree). In order to control the ellipticity, the allowable indexes of ellipticity are regulated in some steel tube standard; generally, it is regulated not to exceed 80% of the tolerance of external diameter (which should be implemented after negotiating between the supply and the buyer).

⑥Curvature

      
The steel tube is curvilinear along the length direction, and the bending degree indicated with figures is called curvature. The curvature regulated in the standard can be divided into two categories as follows:

A、Local curvature: 1-meter long ruler can be used to measure the chord height (mm) at the maximum bending location, ie. local curvature value, its unit is mm/m, for example: 2.5 mm / m. The method is also applied to the curvature of tube end.

B、Overall curvature of the total length: tighten a cord at both sided of the tube to measure the maximum chord height (mm) of the bending location of the steel tube, and then convert it into the percentage of length (m), that is the overall curvature along the length direction of the steel tube.

Example: the length of steel tube is 8m, and the maximum chord height is measured as 30mm, thus the overall curvature of the tube should be:
0.03÷8m×100%=0.375%

⑦Size exceed

      
Size exceed can also be called as allowable deviation of the size exceeding the standard. Here the "size" mainly refers to the external diameter and wall thickness of steel tube. Usually, someone calls the size exceed as “tolerance exceed”, but this way of equate deviation to tolerance is not rigorous, and it should be called as "deviation exceed". Here the deviation may be "positive" or "negative", the "positive" deviation and "negative" deviation hardly exceed the standard simultaneously in the same batch of steel tube.

三、Terms for chemical analysis

      
The chemical composition of steel is one of the important factors related to the quality of steel material and ultimate usage performance, as well as the primarily basis of steel establishment and the heat treatment system of final products. Therefore, as to the technical requirements in the steel standard, the applicable model (steel grade) and its chemical compositions are often regulated in the first item and included into the standard in tabular form, which is an important basis for the manufacturer and customer to accept steel and the chemical compositions of steel.

①Smelting composition of steel

      
The chemical composition regulated in the general standard refers to smelting composition. It refers to chemical compositions when finishing smelting the steel and at the medium period of pouring and casting. To ensure a certain representation (ie. representing the average compositions of boiler and tank), it is regulated in the standard methods of sampling that, cast the molten steel to small ingots in the die, and then plane or dig them to take samples; analyzing according to the regulated standard (GB/T223), the results must meet standard chemical composition range, it is also the basis for customer acceptance.

②Finished product composition

      
Finished product composition is also called the testing analyzing composition, ie. plane or dig the finished steel to take samples according to the regulated methods (GB/T222), and then analyze the chemical compositions according to the regulated methods (GB/T223). During the crystallization and subsequent plastic deformation of steel, as a result of uneven distribution (segregation) of alloy elements in the steel, there may be a deviation between the allowable compositions of finished products and the standard compositions (smelting ingredients), the deviation should meet the regulations in GB/T222.

      
The compositions of finished steel is mainly adopted for inspecting the steel quality by the using departments or quality inspection & acceptance departments, and the manufacturer do not perform finished product analysis (except as required by the users) generally, but it should ensure that the finished product analysis complies with the standard.

③Referee analysis

      
If there is a significant difference between the analysis results of two laboratories and the difference exceeds the allowable analysis differences of the two laboratories, or there are different opinions on the finished product analysis of the same sample or the same batch of steel among the manufacturer, using departments, buyer and supplier, the products should be analyzed further by the third party, ie. an authorized unit with rich experience in analysis (such as the Central Iron & Steel Research Institute of China, or the inspection departments with commodity inspection qualification), that is the arbitration analysis. The results of arbitration analysis are the basis of final determination.

 
 
 
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