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In SMAW Welding of Crude storage Tank, Why do we Change the Polarity of the Welding M/C to -ve during root and hot pass and return to +ve later?

<p>It is some times good to challenge our inquisitiveness, when we get to the field and meet a standard procedure that had been written by someone  we just follow it and the job seems going on fine. But on the contrary if you now at very hem of affairs what do you do? because now have to defend your tittle.</p> <p>That is why a community of specialised professional like this is imperative and it is a good place to belong. </p>

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Question ajoutée par ABAYOMI ZACCHEAUS , QA/QC MANAGER , BAYWOOD DEXTRONVENTURE CONTRACTOR TO CHEVRON NIG. LTD.
Date de publication: 2014/10/16
manu varghese
par manu varghese , QC Welding & Painting Inspector , AL ASAB GEN. CONTRACTING EST.

To get proper penetration in root welding,7016, or 8016, (as per the WPS or client requirements) electrodes are normally using for API 650 storage tanks. These electrodes must use in straight polarity (-) to get a better penetration comparatively less slag and an excellent mechanical properties. then for the fillup and cap 7018 or 8018 are the electrodes what we are normally using this must be in reverse polarity (+) for a stable arc. 

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