The deformation of pipe plate welding form

The adverse effect of welding deformation is resulted from poor sealing of the plate and pulling off of the pipe; the following forms of pipe plate welding deformation are common: 1. Angular deformation of the pipe plate and shell after welding; 2. Arch deformation of the pipe plate surface; 3. Wave deformation of the pipe plate. The angle transformation of the tube plate and shell after welding causes the arch deformation of the tube plate surface and the wave deformation of the tube plate surface.

The pipe plate welding deformation reason

Cylinder and tube plate welding of transverse shrinkage deformation in the thickness direction of the uneven distribution is the primary cause of tube plate welding deformation; tube board and cylinder welding seam is normally a single-sided single-sided v-bevel, in the welding, the back and front of the welding seam of the filling amount of molten metal is not consistent, thereby leading to the deflection of the member plane, so that this is an absolute objective existence of deformation.

Welding angle deformation mainly consists of two kinds of deformation, the cylinder and the tube sheet angle change and the angle distortion of the tube sheet itself, the first is equivalent to the angle deformation induced by the butt welding of two workpieces, the latter is similar to the angle deformation caused by the stack welding on the tube sheet; and the size of the welding deformation mainly depends on the rigidity of the tube sheet, the bevel angle, the shape of the weld cross-section, the welding line energy, the filling amount of the molten metal and the welding operation. The main reasons are the following:

1. welding direction is not implemented in accordance with the specifications;

2. welding parameters are not reasonable, which causes local overheating;

3. The order of assembly and welding is not conducted in accordance with the specifications;

4. Auxiliary measurements are not appropriate.

In accordance with the causes of tube plate deformation and its influencing factors, due to the reality of double-sided welding in the tube plate welding can not be achieved based on the adoption of single-sided welding double-sided shaping, welding with excessive current will cause burn through, injury to the heat exchanger tube, thus, the welding of the tube plate and shell, consideration should be given to the use of small heat input, reduce heat, increasing the rigidity of the tube plate to reduce deformation.

Control of tube plate welding deformation

1. Control the number of layers of welding on the tube plate, in the course of welding on the tube plate, the angular deformation and the number of layers of welding are closely related, the more the number of layers of welding, the greater the deformation.

2. In the process of welding the pipe plate, the bevel perspective should be controlled. In general, the shape of the welding surface and the bevel angle will have a very strong impact on the change of the angle of the welded joint. The amount of transverse shrinkage of the lower and upper portions of the welded joint becomes more significant as the bevel angle gradually becomes larger, so the bevel angle should be reduced as far as possible without affecting the welding quality.

3. Follow the correct installation sequence for the operation. When carrying out assembly, first mount the folded plate, constant distance tube and tension rod to the tube plate, then thread in the heating exchanger tube, pack the tube bundle into the cylinder, team up the tube plate with barrel, then pair up the barrel and tube plate at the other end, guide the tube through the tube plate, and regulate the projection distance to the specified size standard.

4. The parameters of the process of welding are controlled. In the course of the tube plate welding, to prevent deformation caused by high local temperature, it is necessary to use relatively small parameters for welding as soon as possible.

5. In welding the barrel and tube plate, the different areas of the weld seam are to be handled using the segmented welding method. Each individual weld should be separated from each other and welded from both ends to the middle using the cross-welding method. The individual welds are to be staggered 180 degrees apart from each other.

6. The sequence of welding of pipe plate and pipe. While welding the tube and tube plate, the welding should be done from the position in the centre of the welded tube plate first, the number of welded tubes should be more than 1/3 of the total number of welded tubes, where one end of the tube plate is half welded, then the other end is welded, and after the welding is accomplished then the segment just unfinished is finished.

7. For the remaining header welding, weld from the annular seam end of the barrel and tube plate first, and weld outward layer by layer, using the horizontal welding method from both ends to mid-welding, maintaining symmetry during the welding process.

8. Assist method is used during the welding process. There are several secondary methods commonly used in the brazing process: a more rigid part can be used for fixing, and a longer bolt is used in the middle of the pipe plate, and a nut is used to fix the two ends.

9. When welding a hardened metal, in that the distribution size of the welding heat field is reduced to prevent deformation due to uneven heating, the operation can be carried out using forced cooling.