A Guide To Water Well Casing and Screen Selection   -   23

8.3  Bell and Sigot End

Use of bell and spigot joints overcomes a number of problems inherent in plain ended or threaded and coupled joints. A downhand filet (lap) weld is used to connect the casing and screen sections. Lap welds are easier to make in the vertical position than horizontal butt welds. These joints are also very economical. Their chief disadvantage concerns proper alignment which requires more installation time.

8.4  Welding Collars

Another lap weld connection type that best meets all requirements for six inch and larger casing and screen is the welding collar. Welding collars are factory installed on one end of the joint. Width of the collar ranges from two to six inches with the casing end extending approximately midway through the length of the collar. A properly made welding collar connection is as strong or stronger than the casing. API threaded and coupled joint strength by comparison is less than 70% of casing strength. Removal of casing or screen sections requires only removal of the field weld at the top of the collar. Such sections are easily re-installed since the original faces of the tubes have not changed. Finally transportation and handling damage are reduced. The importance of having a field connection equal in strength to the casing or screen material cannot be overemphasized. Experience has demonstrated this frequently to unwary drilling contractors.

8.5  Stainless Steel to Carbon Steel Connections

Some concern has been expressed regarding the connection of stainless steel material to regular carbon steel in the field. A common thought is that galvanic action between the two dissimilar metals will cause the "less noble" carbon steel to deteriorate rapidly and fail. While galvanic action does take place initially, the carbon steel rusts and polarizes rapidly, effectively inhibiting further deterioration. If stainless steel is welded directly to carbon steel, the carbon steel section should be at least two times the thickness of the stainless section. A connection which may be used to eliminate welding two dissimilar metals is shown below.

Since threaded couplings are usually heavy, no difficulty results when stainless and carbon stell threaded connections are employed together.

Slip mild steel ring A, with machined surface up over end of stainless steel joint Attach stainless steel ring D to top of stainless steel joint with chamfer on bottom. Assemble mild steel rings A,B, and C. B is an open ring. Clamp B around A and C making sure that A and C are snug against D. Tack weld in place. Seam weld B. Fellet weld B to A and C respectively

Back   |   R & D Home   |   Next