Commonly used terms in steel pipe standards_Wuxi Shangyan Hydraulic Co., Ltd.

Commonly used terms in steel pipe standards

1. General terms

①delivery status

It refers to the state of final plastic deformation or final heat treatment of the delivered product. Generally, those delivered without heat treatment are called hot-rolled or cold-drawn (rolled) manufacturing state; those delivered after heat treatment are called heat-treated state, or normalized (normalized), quenched and tempered, solution, annealed according to the type of heat treatment . When ordering, the delivery status must be indicated in the contract.

②Delivery according to actual weight or delivery according to theoretical weight

Actual weight-at the time of delivery, the weight of the product is delivered according to the weighed (weighed) weight;

Theoretical weight-at the time of delivery, the weight of the product is the weight calculated according to the nominal size of the steel. The calculation formula is as follows (delivery according to the theoretical weight must be indicated in the contract):

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

W=0.02466（D-S）S

Where：

W——Theoretical weight of steel pipe per meter，kg/m；

D——Nominal outer diameter of steel pipe，mm；

S——Nominal wall thickness of steel pipe，mm。

③Guarantee conditions

Performing inspections according to the stipulated items of the current standards and ensuring compliance with the stipulations of the standards are called guarantee conditions. Guarantee conditions are divided into：

A、Basic guarantee conditions (also known as compulsory guarantee conditions). Regardless of whether the customer indicates in the contract. It is necessary to carry out the inspection according to the standard and ensure that the inspection result meets the standard. Such as chemical composition, mechanical properties, dimensional deviation, surface quality, and process performance tests such as flaw detection, hydraulic test, or flattening or flaring, are all guaranteed conditions.（021-57590365）

B、Agreement guarantee conditions: In addition to the basic guarantee conditions in the standard, there is "according to the requirements of the buyer, after negotiation between the supplier and the buyer, and indicating "or" in the contract when the buyer requires..., it should be indicated in the contract"; Other customers put forward stricter requirements on the basic guarantee conditions in the standard (such as composition, mechanical properties, dimensional deviation, etc.) or increase inspection items (such as steel pipe ellipticity, uneven wall thickness, etc.). The above terms and requirements shall be negotiated by the supplier and the buyer when ordering, and the technical supply agreement shall be signed and indicated in the contract. Therefore, these conditions are also called agreement guarantee conditions. Products with agreed guarantee conditions generally have to be increased in price.

④The "batch" in the batch standard refers to an inspection unit, that is, an inspection lot. If the batch is grouped by the delivery unit, it is called the delivery batch. When the delivery lot is large, one delivery lot can include several inspection lots; when the delivery lot is small, one inspection lot can be divided into several delivery lots. The composition of "batch" usually has the following regulations (see relevant standards for details)：

A、Each batch should be composed of steel pipes of the same brand (steel grade), the same furnace (tank) number or the same parent furnace number, the same specification and the same heat treatment system (heat).

B、For high-quality carbon steel structural pipes and fluid pipes, they can be composed of steel pipes of the same brand, specification and heat treatment system (heat) of different furnaces (tanks).

C、Each batch of welded steel pipes shall be composed of steel pipes of the same brand (steel grade) and specifications. (Tianyang Steel Pipe)

⑤High-quality steel and high-quality steel

In the standards of GB/T699-1999 and GB/T3077-1999, those with "A" after their grades are high-quality steels, otherwise they are general high-quality steels. High-quality steel is better than high-quality steel in some or all of the following:

A、Narrow the range of ingredient content；

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

C、Ensure higher purity (requires less non-metallic inclusions)；

D、Ensure high mechanical properties and process performance。

⑥Portrait and landscape

In the standard, the longitudinal direction refers to the one parallel to the processing direction (ie along the processing direction); the transverse direction refers to the perpendicular to the processing direction (the processing direction is the axial direction of the steel pipe)。

When doing the impact energy experiment, the fracture of the longitudinal specimen is perpendicular to the processing direction. Therefore, it is called the transverse fracture; the fracture of the transverse sample is parallel to the processing direction, so it is called the longitudinal fracture.

2. Steel pipe shape and size terms

①Nominal size and actual size

A、Nominal size: the nominal size specified in the standard, the ideal size that users and manufacturers hope to obtain, and the order size specified in the contract。

B、Actual size: the actual size obtained during 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。

②Deviations and tolerances

A、Deviation: In the production process, because the actual size is difficult to meet the nominal size requirement, 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. A positive difference is called a positive deviation, and a negative difference is called a negative deviation.

B、Tolerance: The sum of the positive and negative deviation values specified in the standard is called tolerance, also called "tolerance zone". Deviation is directional, that is, expressed as "positive" or "negative"; tolerance is not directional, so it is wrong to call the deviation value "positive tolerance" or "negative tolerance".

③Delivery length

Delivery length is also called the length required by the user or the length of the contract. The standard has the following regulations on delivery length:

A、Normal length (also known as non-fixed length length): Any length within the standard specified length and no fixed length requirement is called normal length. For example, the structural pipe standard stipulates: hot-rolled (extruded, expanded) steel pipe 3000mm~12000mm; cold drawn (rolled) steel pipe 2000mm~10500mm.

B、Cut-to-length length: The cut-to-length length should be within the usual length range, which is a certain fixed length dimension required in the contract. However, it is impossible to cut out the 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：

The yield rate of production of fixed-length pipes is much lower than that of normal-length pipes, and it is reasonable for manufacturers to request price increases. The rate of price increase varies from company to company. Generally, the price increase is about 10% on the basis of the base price. (Shanghai Tianyang)

C、Length of multiple ruler: The length of the multiple ruler should be within the range of normal length. The contract should indicate the length of the single ruler and the multiple of the total length (for example, 3000mm×3, which is 3 multiples of 3000mm, and the total length is 9000mm). In actual operation, the allowable positive deviation of 20mm should be added to the total length, plus a margin for the incision of each single ruler length. Take the structural pipe as an example, the allowance for cutting is stipulated: 5-10mm for outer diameter ≤159mm; 10-15mm for outer diameter >159mm.

If there is no double-length deviation and cutting allowance in the standard, it should be negotiated by the supplier and the buyer and indicated in the contract. The double-length scale is the same as the fixed-length length, which will bring about a substantial reduction in the yield rate of the manufacturer. Therefore, it is reasonable for the manufacturer to raise the price, and the price increase is basically the same as the fixed-length length.

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 indicated in the contract. For example: Usually the length is 3000~12000mm, and the range cut-to-length length is 6000~8000mm or 8000~10000mm.

It can be seen that the range length is looser than the fixed-length and double-length length, but it is much stricter than the usual length, which will also reduce the yield of production enterprises. Therefore, it is reasonable for the manufacturer to raise the price, and the price increase is generally about 4% above the base price.

④Uneven wall thickness

The wall thickness of steel pipes cannot be the same everywhere, and there are objectively unequal wall thicknesses in the cross section and longitudinal pipe body, that is, uneven wall thickness. In order to control this non-uniformity, some steel pipe standards stipulate the allowable index for uneven wall thickness, which is generally specified not to exceed 80% of the wall thickness tolerance (implemented after negotiation between the supplier and the buyer).

⑤Ovality

There is a phenomenon of unequal outer diameters in the cross-section of the round steel pipe, that is, there are large and small outside diameters that are not necessarily perpendicular to each other. The difference between the large and small outside diameters is the ellipticity (or non Roundness). In order to control the ovality, some steel pipe standards stipulate the allowable index of ovality, which is generally specified as not exceeding 80% of the outer diameter tolerance (implemented after negotiation between the supplier and the buyer).

⑥Curvature

The steel pipe is curved in the length direction, and the degree of curve is called the degree of curvature, which is indicated by numbers. The curvature specified in the standard is generally divided into the following two types:

A、Local curvature: Measure the chord height (mm) with a one-meter straight ruler on the bend of the steel pipe, which is the value of local curvature. The unit is mm/m, and the expression method is 2.5mm/m. This method is also suitable for tube end curvature.

B、全长总弯曲度：用一根细绳，从管的两端拉紧，测量钢管弯曲处大弦高（mm），然后换算成长度（以米计）的百分数，即为钢管长度方向的全长弯曲度。

例如：钢管长度为8m，测得大弦高30mm,则该管全长弯曲度应为：
0.03÷8m×100%=0.375%

⑦尺寸超差

尺寸超差或叫尺寸超出标准的允许偏差。此处的“尺寸”主要指钢管的外径和壁厚。通常有人把尺寸超差习惯叫“公差出格”，这种把偏差和公差等同起来的叫法是不严密的，应叫"偏差出格"。此处的偏差可能是"正"的，也可能是“负”的，很少在同一批钢管中出现“正、负”偏差均出格的现象。

三、化学分析术语

钢的化学成分是关系钢材质量和终使用性能的重要因素之一，也是编制钢材，乃至终产品热处理制度的主要依据。因此，在钢材标准的技术要求部分，往往规定了钢材适用的牌号（钢级）及其化学成分，并以表格形式列入标准中，是生产企业和客户验收钢及钢材化学成分的重要依据。(www.steeltube-cn.com)

①钢的熔炼成分

一般标准中规定的化学成分即指熔炼成分。它是指钢冶炼完毕、浇注中期的化学成分。为使其具有一定代表性，即代表该炉或罐的平均成分，在取样标准方法中规定，将钢水在样模内铸成小锭，在其上刨取或钻取样屑，按规定的标准方法（GB/T223）进行分析，其结果必须符合标准化学成分范围，也是客户验收的依据。

②成品成分

成品成分又叫验证分析成分，是从成品钢材上按规定方法（GB/T222）钻取或刨取样屑，并按规定的标准方法（GB/T223）进行分析得来的化学成分。钢在结晶和以后塑性变形中，因钢中合金元素分布的不均匀（偏析），因此允许成品成分与标准成分范围（熔炼成分）之间存在有偏差，其偏差值应符合GB/T222之规定。

钢材的成品成分主要是供使用部门或质量检验部门验收钢材质量使用的，生产企业一般不做成品分析（用户要求者除外），但应保证成品分析符合标准规定。

③仲裁分析

由于两个实验室分析同一样品的结果有显著差别并超出两个实验室的允许分析误差，或者生产企业与使用部门、需方与供方对同一样品或同一批钢材的成品分析有分歧意见时，可由第三方具有丰富分析经验的权威单位（如中国钢铁研究总院或具有商检资格的检验部门）进行再分析，即称之谓仲裁分析。仲裁分析结果即为终判定依据。

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