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Friday, August 12, 2011

Re: [MW:12204] welding procedure for distortion control

Dear Purvin :

The following Rules can help minimize distortion during welding

 

  • 1. Design fabrications so that welds are balanced each side of the neutral axis.
  • 2. Do not over specify fillet weld sizes.
  • 3. Use double sided welds rather than single sided, and minimum bevel angles, to reduce the amount of weld metal.
  • 4. Use minimum gap sizes.
  • 5. In non-fatigue sensitive areas use intermittent fillet welds where possible.
  • 6. Use double fillet welds where possible, rather than full penetration T butt welds.
  • 7. Use clamps, strong backs, jigs or fixtures.
  • 8. Use welding positioners so that welding can be carried out in the flat or horizontal-vertical positions with high deposition rates.
  • 9. Deposit a few weld runs alternately on each side of the joint in double V butt welds.

  • 10. Weld a large construction from the center outwards.
  • 11. Use high speed welding processes where possible, eg, iron powder MMA electrodes, MIG welding or mechanized welding. 
  • 12. Use frequent tacking. 
  • 13. Balance welding on each side of the neutral axis, i.e. do not weld all one side before starting the other.
  • 14. Weld fabrications clamped back to back and preset if possible; alternatively stress relieve before releasing from the clamps. 
  • 15. Use block welding to prevent movement. 
  • 16. When block welding thick plate, butter the sides of the preparation and build up the buttering progressively towards the center of the joint, so that most of the joint can contract transversely before the joint is bridged. 
  • 17. Weld first the joints that cause the most contraction.
  • 18. Make use of sub-assemblies.  
  • 19. Make frequent dimensional checks during welding, and if distortion is evident change the welding sequence or the clamping arrangements accordingly.
Regards
Ramin  Kondori
   QC/Welding Engineer 
         IWE AT 0070
   



On Thu, Aug 11, 2011 at 3:58 PM, Himangshu Das <himangshu_das123@rediffmail.com> wrote:
The welding procedure adopted does not actually matter for distortion
control in structural welding.The shape of the structure and the heat
input involved during welding is what causes distortion. For example,
if built up sections with thickness greater than 16 mm with lengths
varying from 5M to 10M are to be welded it is always advisable to use
GMAW/FCAW or SAW for both Quality and production. But these being high
heat input processes and the nature of welds being straight lengthy
beads, it is advisable that the sections be placed on LEVEL PLATFORMS,
FIT UP BE CHECKED FOR STRAIGHTNESS,WARPS IN PARENT METALS CAUSED BY GAS
CUTTING. These checks are a must.Thereafter one could clamp down the
sides to be welded to the platform and a staggered sequence of welding
from both sides involving 2 to 4 welders(depending on the weld length)
may be adopted. 2 welders from opposite ends on opposite sides may
start welding simultaneously and weld progression may be towards center
or start from center and proceed towards ends.Alternately staggered
weld areas may be marked on opposite sides and welders may weld
alternate staggered areas on their own sides but from opposite ends.
The idea is to achieve EVEN HEAT DISTRIBUTION. AFTER WELDING, CLAMPS
SHALL NOT BE REMOVED TILL THE WELDED AREAS HAVE COOLED TO AMBIENT.
In case of rolled sections like trestles, purlins etc. where continuous
welding is not involved SMAW can be safely used.Electrode dia should
not be allowed to exceed 3.15mm.
This is a general overview. If some details of structure type is known
I can be more specific.













On Thu, 11 Aug 2011 15:25:03 +0530 wrote

>
Dear friends,



By adopting which welding procedure (SMAW/GMAW/FCAW) we can reduce
distortion in structural welding





Regards,



Purvin Bhatt



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