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Connection Types of Pup Joints

Date:2024-07-01View:445Tags:pup joints, casing pipe, drill pipe,

Connection Types of Pup joints


Pup joints


Pup joints are short tubular sections used to finely adjust the length of casing and tubing strings during oil and gas drilling operations. The American Petroleum Institute (API) defines several standardized connection types including API threaded, EUE, NUE, BTC, and STC.


Understanding the distinguishing features and applications of each joint variant enables optimal selection for specific well architecture requirements.


API Threaded Pup Joints


The most common pup joint connections conform to API 5CT specifications. API threaded joints use tapered threading that provides high strength and pressure resistance for casing and tubing strings. The tapered thread form consists of symmetric V-shaped wedges that create tight seals under increasing loads. This self-locking characteristic prevents joints from loosening over repeated thermal cycles in harsh downhole environments.


API connections are available in different thread pitches and diameters. Common designs include BUTTRESS, NEW VAM, and rotary-shouldered threads denoted as LTC, STC, and LTC-SR. API pup joints can be mated with matching API couplings to extend string lengths as needed. They are manufactured from API steel grades such as J55, K55, and N80 to provide required strength ratings.


EUE Pup Joints


The EUE or external flush threaded connection uses exterior male threads on the pin end that mate with female threads on the box coupling.This design provides a flush outer diameter without recessed threads for unobstructed string installation. EUE threads minimize flow restrictions and turbulence for optimal hydraulic performance.


They are preferable for applications that require frequent stabbing and re-stabbing during drilling or workover operations. The flush joint profile prevents hang up and damage compared to protruding wedge threads. EUE connections also reduce the risks of cross-threading damage. They are available in common API grades and incorporate premium triangular thread geometries.


NUE Pup Joints


NUE joints feature female threads machined on the interior walls of the pin end. Corresponding male wedge threads on the coupling provide the sealing force. The smooth outer pin nose facilitates alignment and initial engagement during stabbing.


NUE threading provides superior pressure integrity for critical casing and tubing applications. The design also enables a thicker pin nose for increased section strength. NUE joints are often selected for shallow, large-diameter hole sections where alignment is challenging and damage risks are high. They are manufactured in a range of API steel grades for different strength requirements.


BTC Pup Joints


Buttress threaded connections or BTC represent another common joint variant defined by API 5CT standards. BTC threads utilize angled flanks with substantially increased clamping force and interference compared to API round threads. This provides superior resistance to axial loads and internal pressures.


The wedge thread profile also enables rapid assembly and disassembly for efficient rig operations. BTC joints can be applied in large-diameter hole sections where high compression strength is needed. They are typically mated with BTC couplings and available in various API casing and tubing grades.


STC Pup Joints


Shoulder threaded connections or STC joints use a multi-stepped thread profile. The design alternates between larger and smaller diameter sections which create axial shoulders. This step profile allows rapid initial mating followed by high torque final tightening to achieve strong sealing and assembly integrity.


The dimensional steps act as pressure seals without excessive makeup torque and galling. STC threads are advantageous in highly deviated wellbores and high-temperature, high-pressure (HTHP) environments. They maximize the reliability of premium connections where re-runs would be very costly. STC joints are manufactured in top API grades and premium alloys.


Understanding the different connection types enables optimal selection for specific casing and tubing string requirements. Key factors include strength, hydraulic efficiency, damage resistance, and relibility.