API Standard Thread Connections for Oil Casing

The American Petroleum Institute (API) has established standards for various aspects of the oil and gas industry, including specifications for thread connections used in oil casing. The API standard for thread connections for oil casing is known as API Spec 5B.

Commonly used API-certified threaded connections include the Short Round Thread (STC), Long Round Thread (LTC), and Buttress Thread (BTC).

LTC (Long Round Thread) Type:

This type features a non-bounce design with round threads, consisting of eight dome threads per inch, similar to the STC model.

LTC threads are known for their ease of processing, excellent sealing performance, robust connection strength, straightforward maintenance, and cost-effectiveness.

Widely applied in the oil and gas industry, LTC threads are particularly suitable for scenarios involving some axial loads, provided the overall well conditions do not entail extreme temperatures or pressures.

STC (Short Round Thread) Type:

STC thread type is characterized by a round thread with a runout-free design, comprising eight dome threads per inch.

Capable of withstanding 60% to 80% of the pipe strength, STC threads are well-suited for shorter length casing applications without high axial loads or bending requirements.

BTC (Buttress Thread) Type:

Designed to enhance axial tension or axial compression load capacity while ensuring leak resistance.

BTC threads serve as an excellent connection choice for well conditions that involve high axial loads, along with moderate internal pressures and temperatures.

It's important for manufacturers and users in the oil and gas industry to adhere to these API standards to ensure the reliability and safety of threaded connections in oil casing. Compliance with API Spec 5B helps in maintaining consistency and compatibility across different components in the industry, facilitating efficient and secure operations.