1.any type of kelly bar combined and all advantage together 2.durable steel material for longtime use 3.drilling depth is deep

Combined type kelly bar is a kind of combination drill, which is formed by mechanical locking type, full interlocking type, frictional type and other various forms. There are a variety of combinations. Generally speaking, the kelly bar may drill the hard layer in the range of 0-50 meters. It can be used for construction of soft layer formation when the hole depth is in the range of 50-70 meters. According to the need of the configure or the operating condition, the drill pipe chooses the way of transmission of pressure. Such as ,the first section of the mechanical locking kelly bar. According to the machine-locking driving force set, and other are full interlocking kelly bar.  In order to achieve a certain depth of drilling and enhance the effect of drilling hard layer, it can be chosen the full interlocking or mechanical locking kelly bar outside and inner is resistance kelly bar, comprehensive situations for difference kelly bar specifications. Generally, there are: mechanical lockingX1 +full interlocking X3 or mechanical lockingx4+grinding resistance X1, full interlockingX4 + grinding resistance X1 and other kind of of combination.

Combined type kelly bar for drilling rig
Type	O.Dia.(MM)	Section	Depth(m)	Torque(KN.M)
JT12 340-3x13	340	3	36	120
JT12 356-3x13	356	3	36	120
JT15 377-4x14	377	4	52	150
JT20 406-4x14	406	4	52	200
JT22 406-4x14	406	4	52	220
JT25 445-4x15	445	4	56	250
JT25 445-3x15 (Reinforced)	445	3	42	250
JT25 470-4x15	470	4	56	250
JT25 508-4x15	508	4	56	250
JT28 508-5x15	508	5	70	280

Combined type kelly bar for drilling rig