The TT (Thru Tubing) Series AST has been in service since 2006 and is aimed at eliminating motor stalls as well as reducing drilling vibrations and stick-slip with downhole motors.
In recent years, the TT series tools have been upgraded with all the features found on the larger drilling series tools, so as to safely accommodate the stronger motors in use as well as drilling using foam, gas or air.
The tools are also being used for open-hole coiled tubing drilling where the electric line is pulled straight through the tool. The advantage of using the AST is reduced stalls and longer fatigue life for the tubing. The AST also allows for longer motor life, especially when the weight transfer becomes critical.