I have used ceramic backing extensively in fabrication of Box Girders, Plate Girders and Nodes for Off-shore platforms. But never used it on storage tanks. I feel it would be a good idea to use it on tanks as well.
AWS does not prohibit the use of ceramic backing and thus we have used it for structural welding. You can use the same for tanks provided you carry out the procedure qualification as per the applicable specifications.
Hi Ajoy:
Thanks for the encouraging info. Infact we have developed special Flexible Heat Resistant cord ( 10 mm dia) which is snuggly fitted in the Double V groove ( with min 3 mm root gap) from one side and then held in position with self adhesive 75 mm wide Aluminum tape. Root run is made from the open side . On completion of the root run the Aluminum tape and cord is removed and a shinning weld bead is obtained which neither requires back chipping nor grinding. Its ready for further capping runs.
The flexible cord makes it possible to cover both vertical joints and and horizontal joints of tanks as per API 650. The procedure is qualified and the quality of weld generally depends on the welder skill but generally with a little bit of practice we get good results.
For single V joints of 6 mm and 8 mm thk plates we use a flat cord and get full penetration weld on the back side after removal of tape and the cord.
This method has been found useful in SAW and GTAW as well. In case of GTAW no Argon purging is required
Prakash
Prakash,
can you tell me the manufacturer of the heat resistant flexible cords. we have used ceramic backing for single and double vee from NST and GULLCO only. we have used it on 1G and 2G but never on 3G.
Hi Ajoy:
As I said , we have developed this cord. Our team has already taken trials in Dubai for the new tankage job. Our teams will be visitng Dubai again shortly. If you desire , samples and trials can be conducted for you in Dubai.
Regards
Hi Ajoy:
Last week I was in Kuwait and this flexible chord was tested extensively in one of the big steel fabricators' shop. Tests were conducted in 3 G position and were successful for SMAW and MIG ( with flux cored wire). The test was also successful in 1G position for SAW. Can I have your e mail id so that I can meet you when I am in Dubai.
Prakash
Hi Prakash,
Iam in the business of laying Pipelines and we do it mostly with STT/FCAW process combinations. The back-up process is always cellulose SMAW. So from marketing point of you I may not be able to help you but I may direct you to some potential clients.
call me up when you are in Dubai : 050-4789300.
Prakash Chopde
Welcome to the forum. How is backing used on a double-V-groove weld? Or did you mean single V, and bevel groove welds?
By -
Date 08-03-2004 03:52
Third Eye,
Ceramic backing used on a double V groove is generally for when there is a large root gap fitup condition. Keeping in mind the various code/WPS provisions regarding gaps, if permissible it can be used to weld against. After the first side is complete, the backing is removed and the weld backgouged and welded as normal.
Mankenberg
Kip,
That makes sense. I've seen spacer bars or strips used often to bridge wide double V root gaps on mining equipment. I never thought about using a nonmetal material. Thanks.
Hi thirdeye:
I have replied to ajoy and that answers your question as well. In this method most important part is to have a root gap of min 3 mm and vertical joints are done in steps ( upwards) to avoid closing of the gap due to welding contractions.
We have used ceramic backing for many applications, including full penetration seam welds on tank shells. In our situation, we have access to both sides of the joint and are able to backgouge and repair any weld segments that are not as they should be. (The welds often do not penetrate the tack welds and must be feathered out and welded from the second side. This is normal when not using submerged arc and is part of our procedures.) The ceramic saves a lot of time and labor and the welds easily pass radiographic examination when the welder does his/her job correctly.
You might want to reference AWS D1.1-2004, section 5.10. In the situation you are describing, you are using the ceramic backing to prevent melt through and to shape the weld bead on the root side. The seam is treated as welding from 2 sides. The ceramic backing is not replacing a one sided groove weld with steel backing.
Chet Guilford
I agree with Chet. Also see paragrah 2.27.2, which prohibits the use of backing other than steel, unless you qualify your procedure and welders to section 4 of AWS D1.1.
Hello Chet:
Thanks for sharing your experience. We use a different material which is non metallic and non ceramic. My reply to Ajoy describes the method.
Could you please tell me projects, countries where you have used backing strips for tank welding. I will go thru the AWS spec indicated by you and revert back.
Prakash
Wow, I'm not sure I can remember all the times I have seen ceramic backing used.
I first saw it used about 24 years ago and have seen it used frequently ever since. The only job that was outside the United States was shipped to Venezuala (the correct spelling escapes me at the moment) for bauxite processing. I don't remember who the owner was. Panel sections for large diameter tanks were spliced with ceramic backing.
As a matter of routine, we use ceramic for any situation where melt thru could be a problem and where we have access to the root side.
It even works well for plugging holes if you clamp a bar over the ceramic to hold it. (The foil overheats and ceramic falls off if you don't)
We have used ceramic successfully on carbon steel, stainless, and aluminum.
Your backing as described is essentially the same thing. Basically, a material that does not melt at high temperatures is used to hold molten metal in place until it solidifies. It also excludes atmospheric contamination on the root side.
I don't know what else I can tell you that will help you out. I'm thinking that the manufacturers of the backing can give you much better information.
Chet Guilford
OK, you have a cord. AWS D1.1 will not accept this cord as prequalified. You, Mr. Chopde, must qualify your procedures.
Very best regards,
Vonash
Hi Vonash:
You are right. We use it only after Procedure Qualification and Welder Qualification.
Hi Prakash:
can this non metallic backing strips(ceramic as well as glass) procedure be used in the manufacturing of pressure vessels? when we are engaged in the welding of tanks,we usually use bronze backing strips for root runs with the root gap of 2-3 mm.the bronze backing strips is moving along with the welding gun on the other side.
hope to get ur response soon.thanks.
best regards.
Hi:
Yes we have used this for pressure vessels. Needless to say that Procedure Qualification and Welder Qualification is to be done prior to usage of such materials as backing for butt welds.
As regards root runs for tanks, is the bronze strip water cooled. I have read literature of systems for Vertical welds where water cooled copper backing moves parallely( vertically) and with flux cored wire the complete gap is filled up in one go. In my opinion Flexible Cord is much easier to use and there is no need for any back gouging, grinding . A shining finish is obtained on the back side - ready to receive further capping runs.
