Backing rings are used while welding Pressure Pipes or tubes. They will avoid irregular penetration of weld metal inside the pipe or tube, creating extra friction losses.
Typically Backing rings are less expensive than buying a 150# slip on flange for stainless steel pipe. We use stub ends and 150# backing rings on our piping, but we do not have any situations where we have high pressures going through the stainless steel lines. For carbon lines we just use weld necks or slipons.
our weldprocedure mandate the use of backing strip to welding aluminum pipe. we dont require it for cs and ss pipe welding. the intent is to prevent burnthrough, oxidation or contaminant during the root pass - & ensure you have a good root.
if the done on vessel or large bore dia pipe, you may just perfrom a backweld, ground out, then do the other side for the hot pass followed by fill and cap.
It is not necessary on SS pipe provided you can argon purge during the root pass. It is not necessary at all for the cs pipe irrespective of wehter youre using tig or stick or the joint is slipon or sowcket.
Here is some information on using consumable backing rings.
Consumable Backing Ring Welding
Backing Rings are inserted into the beveled pipe end with the spacer nubs flush against the pipe land and the ring gap positioned in the area of first bead deposition. The beveled end of the adjoining pipe is slipped onto the backing ring until the edge of the pipe land is firmly abutted against the spacer nub. Depending upon the Ring Style chosen, the welder has the choice of "striking off" the nubs or leaving them intact.
The welder can either weld the split making a solid ring or weld away from the split allowing the heat of the molten metal to expand the ring forcing it tightly against the inner surface of the pipe. This eliminates gaps, openings, or crevices between the Backing Ring and the pipe, tube, valve or fitting. Flat outer surfaces afford immediate access to the root of the weld and allow complete penetration. The 1/16" lands on the outer ring edges prevent curling. The internal bevels and flat inner land minimize flow turbulence on the downstream side to a nearly incalculable degree.
During welding, the arc should be directed as to penetrate the backing ring and inner edges of the pipe or fitting. The molten metal should penetrate into the Backing Ring approximately forty to fifty percent of the cross-sectional dimension thereby forming an integral welded joint.
The benefit of a backing ring is that it virtually guarantees full penetration of the weld without the worry of burn through. The root pass of an open butt joint is typically the most difficult part of the weld to create because the welder has to pay detailed attention to the amount of heat applied, to much and the weld blows out, to little and penetration is not achieved. One of the many reasons GTAW becomes a prefered method of root passing.
The negatives (besides added cost) are that backing rings can and have broken free after the piping goes into service causing havoc in the system. It can also boost a welders confidence to high and negatively affect the interpretation of various forms of NDE.
The decision is yours but I find them to be more trouble than they are worth for the more basic materials. Lane Baker
Baker Quality Services
LaneBQS@att.net
