Welds backing rings

Figure 6.10 A perforated carbon steel pipe at a weld-backing ring. The gaping pit was caused by sulfate-reducing bacteria (see Case History 6.1).

A weeping leak developed in a carbon steel emergency service water pipe at a circumferential weld emplo3nng a weld-backing ring. A rubberized saddle clamp was used to plug the leak temporarily. After several weeks the section was cut out of the system and the failure was examined. 

Figure 6.21 A longitudinally split carbon steel emergency service water pipe, as in Fig. 6.10. Note the circumferential weld-backing ring, which is consumed on one side.

Corrosion associated with weld backing rings... 

Fig. GR-3.4.3(f) Geometry of Weld Joint Detail Single Vee Groove Butt, Continuous Flat Backing Ring...

The susceptibility of the piping material to crevice corrosion under backing rings, in threaded joints, in socket-welded joints, and in other stagnant, confined areas. 

G External weld reinforcement and internal weld protrusion shall be fused with and shall merge smoothly into the component surface. The thickness of external weld reinforcement and internal weld protrusion (when no backing ring is used) shall not exceed the following ... 

BACKING RING - Backing in a form of a ring, generally used in welding of piping. 

Backing rings are sometimes used when welding pipe. It is neeessary that the backing ring insert is consumed during the welding process to avoid a crevice. 

Ultrasonic Uses high-frequency sound waves to locate defects. Very sensitive can detect very fine surface and subsurface cracks. Equipment is portable Personnel must be trained to interpret equipment response. Not effective on rough surfaces or welds with backing rings. 

For most fans, blades are riveted to the back plate or hub respectively. For centrifugals, the blades are usually welded to the shroud however, they can be welded to both shroud and backplate. For some designs and classes of service, an extra reinforcing ring is welded to the blades between the backplate and the shroud. This is particularly necessary for large heavy-duty units see Figure 12-120B. 

---