How to Prevent the De-formation of Base Plate Due to Welding

I would wish you would give enough information to know what you are dealing with.......

Thickness of material,

type of material?

thickness of material?

what the heck is 2mtr....is that 2 meters? diameter?

Control your heat, with a heat sink if you can, even use a vortex tube

Break up your weld, and give it a chance to cool,

and stop posting on numerous categories, it as though your panicking.

p911

the vertical shell thickness is 8mm and the bottom plate is 10mm thk. the diameter of the tank is 2 meter. height is 3meter.it is normal carbon steel plate. after the circular welding with the bottom plate to vertical shell, buckling is forming on the center of bottom plate.

Mcnutty,

Could this be the first tank that you have ever welded ?

Do you have any experience with large weldments ?

If you are aware of the problem, why are you not aware of the solution?

So, the problem is heat application. You could weld with two welders 180° apart.

Or, just be careful. Any experienced welder should know this.

Like p911 said. Control the heat!

You can prevent most of the deformation with spot welding or clamping the bottom on a stiff - heat absorbent base. We used a 2" thick base plate. After the tank is finished cut it loose. If deformation is still unacceptable, you'll need to crimp the "bulbs' down with heat and cooling. Many good practices are show here and this is just supplementary.

Try making a number of smaller welds around the perimeter of the shell before welding the final seam.

I usually preheat a surface like this with acetylene torche so that the heat of the welding process doesnt shock the metal and cause it to curve/warp while welding. Tack weld the piece your going to affix to the surface while the base material that you want to stay flat is evenly heated with torch, then add your full weld bead. Then cool the metal slowly and it should not warp.

Distortion is caused by unequal heating and cooling of a metallic body during welding. It is caused by contraction of the weld metal during solidification and contraction of surrounding parent metal as it cools from high temperature. When the portion contract, they try to pull the parts together and the result is distortion.

In any lengthy and complex welds, sequence welding and direction in which each pass is made are very important. An incorrect sequence in welding causes distortion and some times cracks in the weld metal due to stress concentration at some point in the fabrication. A correct welding sequence distributes and balance the forces and stress developed by weld contraction.

An metallic body does not distort if it is heated as whole uniformly and is cooled as a whole uniformly and freedom expand and contract freely in all directions . But during the welding it does not happen and unequal heating and cooling rise to stress in the weld and it finds its relief in its distortion. Consequently the shape and dimensions of the welded fabrication will have changed when it returns to room temperature.

So, the fabricator has to choose in between distortion (dimensional changes occurs in light structures) or locked up stresses leading to cracks (mostly in higher thickness due to restraint) in the weld at times.

To avoid distortions to large extent, the whole length of the weld is dived into equal segments ( say 200 mm or so), and each fresh starting done away from the start of the weld and ending at the starting point of earlier weld. This is known as Back step method or you can skip in between and balance the heat and know as skip back method.

For circumferential joints, it is important to distribute contraction stresses evenly around the circumference as shown above. The bottom plate is divided into 8 to 12 parts and weld on area 1 is followed by, weld on area 2 diagonally opposite. Weld on area 3 is followed by a weld on area 4 and like wise. . . .

Further the distortion can be minimized in fillet welds by using, large size electrodes and less no. passes, reducing the fillet size (use minimum weld metal and avoid over welding) or change to better welding processes like GMAW in place of SMAW as the amount of heat input at any given unit length will be less comparatively due to higher travel speeds.

Trust above details will help to avoid distorting in your bottom plate welding.

Sridhar.