在焊管生产过程中，只要进行焊接，焊管表面就会产生应力和变形，只是程度不同罢了。焊管在焊接过程中产生的焊接应力和各种变形，往往使焊接产品质量下降，甚至造成裂纹。焊接变形造成焊件尺寸，形状的变化，这种变化超过一定的数值后，可能无法与其他焊管连接或没有足够的加工余量无法进行切削加工。下面我们说下应力和变形。
In the production process of welded pipe, as long as welding is carried out, stress and deformation will occur on the surface of welded pipe, but to varying degrees. Welding stress and various deformations of welded pipes in the welding process often cause the quality of welded products to decline, and even cause cracks. Welding deformation results in the change of weld size and shape. If the change exceeds a certain value, it may not be able to connect with other welded pipes or not have enough machining allowance for cutting. Now let's talk about stress and deformation. 首先是焊管的表面应力，当材料在外力作用下不能产生位移时，它的几何形状和尺寸将发生变化，这种形变就称为应变。材料发生形变时其内部产生了大小相等但方向相反的反作用力抵抗外力，把分布内力在一点的集度称为应力，应力与微面积的乘积即为内力，或物体由于外因(受力、温度变化等)而变形时，在物体内各部分之间产生相互作用的内力，以抵抗这种外因的作用，并力图使物体从变形后的位置回复到变形前的位置。
First is the surface stress of welded pipe. When the material can not produce displacement under external force, its geometry and size will change. This deformation is called strain. When a material is deformed, it produces internal reaction force of equal size but opposite direction to resist external force. The concentration degree of distributed internal force at a point is called stress. The product of stress and micro-area is internal force, or when the object is deformed by external factors (force, temperature change, etc.), the internal force interacts among various parts of the object to resist the effect of external factors. Make the object return from the position after deformation to the position before deformation.
从力学角度来讲，变形是指结构(或其一部分)形状的改变。任何结构都是由可变形固体材料组成，在外力作用下将会产生变形和位移。
From a mechanical point of view, deformation refers to the change of the shape of a structure (or part of it). Any structure is composed of deformable solid materials, which will produce deformation and displacement under the action of external forces.
在焊管生产过程中，即使能矫正，如机械或火焰矫正过来，这也不仅费时费力，而且又增加了焊管的附加应力，对构建使用不利、由此，我们必须对焊接应力和变形的产生原因、大小程度以及如何减小和避免焊接应力和变形进行了解。
In the production process of welded pipe, even if it can be corrected, such as mechanical or flame correction, it will not only take time and effort, but also increase the additional stress of welded pipe, which is unfavorable for construction and use. Therefore, we must understand the causes, magnitude and extent of welding stress and deformation, and how to reduce and avoid welding stress and deformation.
