Dear Mr. Asghari,
Change of polarity for SMAW is a supplementary essential variable as per ASME Sec-IX(QW-409.4). The definition of this change is illustrated below:-
· A change from AC to DC, or vice versa; and in DC welding, a change from electrode negative (straight polarity) to electrode positive (reverse polarity), or vice versa.
Generally speaking E-7018/7018-1 electrodes are designed and formulated to operate in DCEP or AC .That's the recommendations put forth in ASME Sec-II,Pt-C, SFA 5.1.Operating them with DCEN may not be advisable unless it it recommended and certified by the electrode manufacturers.
Change of polarity alters burning rate of SMAW electrodes, increases tendency for overheating/ stub losses and it could lead to increase of weld defect rates, due to changes in burning characteristics.
Qualifying WPS is only one part of the project activities. If there is no requirement of impact test in the design/ construction code, then the contractor's point may be valid, within the rules of ASME Sec-IX.
However looking at the broader picture , it would be advisable to select polarity as recommended by electrode manufacturer so as to get quality levels required by project specification. I would think you need to discuss this with the contractors and come to some reasonable understanding.
The attached guide would be of help.
I would think, the viewpoints of the other members of the forum, especially from electrode manufacturers would be more appropriate.
Thanks.
Welding & Metallurgical Engineer/Specialist
Component Integrity Section.
Engineering and Training Services
Ontario Power Generation Inc.
Res:-88,Garth Trails Crescent
Hamilton,Ontario, L9B2X1,Canada
Tel-905-679-9677
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Ali Asghari
Sent: Saturday, February 20, 2010 6:50 AM
To: materials-welding@googlegroups.com
Subject: [MW:4350] DCEN in E7018-1
Dear All
our contractor have procured E7018-1,that manufacture recommended DCEP/AC.but they use DCEN in PQR(accepted) and production.
according to this has conflict with AWS A5.01 and manufacture's recommendation. is it true or not?
regards
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