The floating collar and shoes are available in different API certificated thread connections, including Short Round Thread (STC), Long Round Thread (LTC) and Buttress Thread (BTC).
Connection strength and tightness are two main coupling technical indicators. Both LTC and STC threads use lead, zinc, copper, graphite or silicone oil composition to improve seals, but those seals only work under temperature of 60 °C to 95 °C. Also for STC coupling, if under huge external pressure and axial tensile stress, when heavy impact or bent happens, the threading will be likely to slippage. Both of those two type of threading are not suitable for heavy oil thermal recovery, ultra deep well and heavy corrosive environment.
LTC (Long Thread) type.
It is also has a non-runout design of round thread. Each has eight round crested thread per inch, which is same as the STC type.
LTC thread is easy to process, good tightness, strong connection strength, simple maintenance and low price.
LTC thread is widely used in oil and gas industry and is well suited for situations where some axial load is encountered but overall well conditions do not include extremes of temperature or pressure.
STC thread type.
It is features with a non-runout design of round thread. Each has eight round crested threads per inch.
STC threads can withstand strength of the tubular 60% to 80% of the pipe strength. STC thread is a good choice for shorter length casing applications that do not involve high axial loads or bending.
It is designed to improve axial tensile or axial compressive load capacity and to provide leakage resistance performance.
It is an excellent connection for use in well situations involving higher axial loads and moderate internal pressures and temperatures.