Welding

1.- Prepare a welding sequence ( Don´t make a continiuos weld)

2.- Use bridges ( Like Chicago´s)

3.- For the same seam weld use 2 or more welders at the same time.

4.- Contrl Heat input.

Note: Avoid distorsion in 5 mm stainless steel is not easy. Keep and eye during works.

You are using a 12 gage (2.6 mm) coated electrode for welding. Try using 14 gage(2.0 mm) coated electrodes. This is an available size. Also S.S. expands more than Carbon steels. The co-efficient of expansion for C.S. is approx. 13X10^-6 m/m and that of S.S. 17x10^-6 m/m. This causes more distortion in SS than ordinary mild steel when heated. Therefore it is important to keep heat input low in welding S.S. Let the weld cool down more frequently and avoid weld weaving. The discoloration can be removed by pickling the weld and adjacent areas by brushing with a 20% solution of Nirtic Acid. The discoloration is usually on the surface. After cleaning the weld shines bright white.

In welding of lowered thicknesses of stainless steel like 5 mm, we used to use GTAW (TIG) welding (with shielding gas like Argon) using small diameter wires with a little pit of amperage and inturn a little heat input. Or we use semi-automatic arc welding GMAW (MIG/MAG), using small diameters of electrodes which produce a little heat input to avoid distortion of workpiece.

It is one of the serious problem in welding. We can not eliminate it fully, It is either distortion or locked up stresses. So we can reduce it to maximum possible extent by adopting a suitable sequence (do not weld continuously) like back-step or skip back or a combination of both as sheets and thinner plates like 5 mm distort easily than a thicker plates.

Distortion can be minimized by lower heat in put (check heat in put formula) during welding. This could be done by by depositing minimum number of layers and avoid using lower size electrodes & weaving. Avoid SMAW process once for all for thin sheets as heat input is high due to low travel speeds. The same is true with normal TIG process also.

We prefer a Pulsed TIG Welding process than a normal TIG or GMAW process (both with Argon or Argon (+) 2% O₂ shielding for SS) and distortion could be controlled within one to 2 degrees.

Since you are using 5 mm plate and with a re-gouge and a seal pass, you can think of using a vertical down welding position as weld travel speeds in V-down is 1.5 more than in flat position. As in GMAW, Pulsed TIG, V-down with higher travel speeds give lesser heat input comparatively.

You can also think of using chill bars, i.e., use copper or Aluminum strips (10 thk*25 mm width & with a 0.50 *2.00 mm groove at the center for root penetration) underneath the weld through a proper clamping system or fixtures.

Sridhar

Thanks shridhar

We are welding with SMAW with 2 passes using 2.6 electrode both sides ( it is very difficult to change any variables), there is any acceptability limit for this distortion or only it is based on the apperance acceptance by client

i need technical guidance in avioding the distortion of the plate by welding using the above mentioned method and we are strictly monitoring the welder performance in achieving the joint without distortion.

thanks

As such, there is no acceptable standards of limits in distortion control. If it is a circumferential joint, you should get proper alignment. It should not be wavy and able to provide a good aesthetic look. But distortion can be be controlled if you can not make it zero.

One of the easiest way to control/reduce the distortion in SS and thin sheet fabrication (as you can not change the process at present) is do the welding using a copper base plate. it could be 10 or 12 mm thick, and a suitable size to your job, so that, what ever the heat generated during the welding gets dissipated immediately and continuously leaving the job with no (or) little which will pass through inspection.

If you want to minimize cost on copper plate procurement, you can make a welding fixture (with or without water cooling system) size 50 width*15 mm thick, made of copper or MS base snug-fitted with copper in it (dove-tail cut) and with provision to pass argon gas for purging and it will help you to do distortion free welds in any thin sheet including SS . Make sure that the it is held tightly underneath and through out the length of the weld joint by proper spiders spaced at intervals.

Alternatively you can think of vertical down welding and with above fixture arrangement, you will surely get a distortion less assembly.

In future, you please change the process to pulsed TIG and get it accepted through a new WPS/PQR so that will help to control the distortion fully.

Sridhar.