1. Double layer board casing
The middle of the double layered casing male and female joints is a double layered structure consisting of an outer plate and an inner plate. Insert another layer of padding between the outer and inner panels. The thickness of the joint part (T) is almost the same as the thickness of the outer plate+pad+inner plate (t1+t2+t3=t4). The characteristics of double-layer casing are good rigidity, low deformation and good recovery, strong and durable, but the disadvantages are heavy weight and high cost.

2. Single layer casing
The middle of the male and female joints is a whole board, and there is a step between the pipe body and the male and female joints. The characteristic of single-layer casing is that it is lightweight and inexpensive, but it is prone to deformation and difficult to restore after deformation.

At present, there are many manufacturers of casing used in the market for full rotation full casing drilling rigs, and the dimensions of casing joints, wall thickness, etc. are often inconsistent. The commonly used ones are shown in the table below.

Diameter of casing				1.0m	1.2m	1.5m	1.6m	1.8/2.0m	2.4/2.5m	2.6m	2.8/3.0/3.2m
Knife head	Model		Quantity	18	21	24	24	27/30	36	39	42/45/45
	45 angle expansion knife is used for rocks below 80Mpa	50 expansion angle knife can cut steel bars above 80Mpa in rocks
Bolt	Model		Quantity	Double row 12 sets （5T）	Double row 12 sets （5T）	Double row 16 sets （5T）	Double row 16 sets （5T）	Double row 20 sets （5T）	Double row 24 sets （7T）	Double row 30 sets （7T）	Double row 28/32/32 groups （9T）
	NCB Code of Ethics	M90	Male female combination height	700mm	700mm	700mm	700mm	700mm	760mm	760mm	760mm
			Thickness	50	50	50	50	50/（60 customization）	60	60	70
Wall thickness				t25 t30	t25 t30	t30	t30	t30 t40	t40	t40	t40

The connection of the male and female joint parts of the casing is fastened with bolts. The complete set of fastening bolts consists of three parts: male wedge head, female wedge head seat, and female wedge head. They are fastened with a conical surface to prevent loosening. It should be noted that if foreign objects such as soil and sand are mixed into the cone surface, it may cause deformation of the cone surface, welding fracture, insufficient fastening, and inability to loosen during disassembly. It must be cleaned thoroughly before use.

1. The length of the casing includes various types such as 2, 3, 4, 5, and 6 meters. A 6 meter long casing is commonly used, and the quantity of each length of casing should be prepared according to the needs during construction. The length of the bottom section casing with a bottom casing can be appropriately extended.
2. The bottom sleeve (the sleeve at the bottom end with the blade installed) is generally a single-layer pipe made of thick plate. The length is usually around 8m.
3. The casing connected to the bottom casing is susceptible to hammer impact or heavy hammer impact, resulting in deformation of the inner plate and frequent replacement of positions with other casings.
4. The upper joint bears the load in the joint section.
5. If the joint part is deformed or damaged, it should be replaced in a timely manner. If it needs to be reused, it should be connected to the lower part because the lower part has a relatively small acceptance capacity, which is not easy to loosen and ensures safety.
6. Even if the shape and diameter of the casing, casing joint, and joint bolt are the same, the machining dimensions of the casing and casing joint parts from different manufacturers may also be different. Therefore, when using them, the non universality of products from different manufacturers should be considered.