Product Overview
The Knuckle Joint, also named downhole universal joint, is an essential flexible accessory specially designed for full-series coiled tubing well intervention operations. It is assembled between the upper weighted tool string (weight bar) and lower working tools including hydraulic setting tools, bridge plugs, jetting subs and perforating guns.
The core design value of knuckle joint is to add extra flexibility to the whole downhole tool string. It solves two major construction pain points in oilfield industry: tool string sticking and difficult running in narrow restricted boreholes and high-angle deviated/horizontal wells. With reliable internal sealing structure, this knuckle joint supports two core motion functions simultaneously: the lower connected tool string can complete free 360° full rotation, and the joint body allows maximum 15° angular deflection to fit irregular wellbore trajectory.
All standard models of knuckle joint adopt STD standard carbon steel as base material, with complete outer diameter specifications ranging from 1-11/16" to 2-7/8", matched with three mainstream oilfield connection thread standards: 1" AMMT, 1-1/2" AMMT and 2-3/8" PAC. The overall assembly length increases synchronously with outer diameter size, forming a full-size product series to cover slim, medium and large size coiled tubing tool string matching demands. The integral sealed structure has no vulnerable internal moving parts, featuring stable downhole performance, low wear rate and minimal daily maintenance requirements.
Complete Technical Specification Table
| PN Part Number | Outer Diameter OD | Internal Through Bore ID | Overall Make-Up Length | Working Condition Grade | Connection Thread |
|---|---|---|---|---|---|
| L4031690120 | 1-11/16" | 0.33" | 12" | STD Standard Carbon Steel | 1" AMMT |
| L4031750120 | 1-3/4" | 0.33" | 12" | STD Standard Carbon Steel | 1" AMMT |
| L4032125120 | 2-1/8" | 0.5" | 15" | STD Standard Carbon Steel | 1-1/2" AMMT |
| L4032250120 | 2-1/4" | 0.55" | 15" | STD Standard Carbon Steel | 1-1/2" AMMT |
| L4032500120 | 2-1/2" | 0.67" | 15" | STD Standard Carbon Steel | 1-1/2" AMMT |
| L4032875120 | 2-7/8" | 0.94" | 17" | STD Standard Carbon Steel | 2-3/8" PAC |
Note: Custom outer diameter size, internal through bore size, overall assembly length and special non-standard thread specifications are available upon engineering consultation. Besides standard STD carbon steel grade, NACE MR0175 compliant H₂S sour service anti-sulfide corrosion alloy version can be customized for high-hydrogen-sulfide corrosive well environments. All standard models support seamless matching with weight bar, hydraulic setting tool and bridge plug tool string assembly standards for global coiled tubing operations.
Core Features & Advantages
Dual Motion Design: Max 15° Angular Deviation + Full 360° Rotation
This knuckle joint realizes two independent flexible movements in one sealed unit. The maximum 15° angular deflection can compensate the angle change of wellbore build-up sections in deviated and horizontal wells, preventing rigid tool string from colliding or sticking on borehole wall. The full 360° free rotation eliminates torsion resistance generated during tripping operation, ensuring smooth and straight running of lower working tools to target reservoir depth.
Fully Sealed Internal Structure, Stable Downhole Service Performance
The internal movable joint component is wrapped by high-performance integrated sealing assembly, effectively isolating downhole formation fluid, completion brine and solid debris from internal rotating and deflection parts. It avoids internal component corrosion, sand jamming and motion failure under long-term downhole working conditions, greatly extending the service cycle of the knuckle joint and reducing on-site tool replacement frequency.
Full-Size Standard Thread Matching System
The complete knuckle joint product line is configured with standardized oilfield connection threads corresponding to different outer diameter sizes. Small OD models match 1" AMMT thread, medium OD models adopt 1-1/2" AMMT thread, and large-size models support 2-3/8" PAC thread. All thread sizes follow unified industry processing standards, enabling direct plug-and-play assembly with coiled tubing strings, weight bars, hydraulic setting tools and bridge plug assemblies without secondary modification or extra adapter conversion.
Greatly Improves Tool String Passing Performance in Complex Wellbores
When deployed in restricted narrow boreholes, highly deviated wells and horizontal wells, the flexible structure of knuckle joint effectively buffers the contact friction between rigid tool string and irregular borehole wall. It drastically reduces the risk of tool string blockage, stuck pipe and running failure, improving the overall construction success rate and operation efficiency of coiled tubing well intervention projects.
Complete Standard Size Series, Wide Compatibility with Tool String
The product portfolio covers all mainstream outer diameter specifications from 1-11/16" to 2-7/8", with matched inner through bore and unified assembly length design for each size. The full-size range can perfectly match slim small-bore coiled tubing strings, conventional medium-size tool strings and heavy-duty large-diameter downhole tool assemblies, realizing full-scene coverage of global onshore and offshore coiled tubing intervention operations.
Low Maintenance & Simple On-Site Assembly Operation
There are no fragile spring parts or easily worn sealing components inside the knuckle joint main body. The overall structure is sturdy and impact-resistant. On-site assembly only requires standard torque tightening of upper and lower connection threads, which greatly shortens tool string pre-assembly time before well operation. After finishing downhole service, only simple surface cleaning and appearance inspection are needed, cutting down after-sales maintenance labor cost and spare parts inventory pressure.
Application Scenarios
1. Conventional onshore and offshore oil & gas well coiled tubing intervention operations, including bridge plug setting, jetting perforation, wellbore cleaning, reservoir stimulation and sand removal construction.
2. Highly deviated wells and horizontal well intervention projects, using 15° angular deflection function to adapt wellbore trajectory and avoid tool string sticking during running.
3. Restricted narrow borehole coiled tubing construction, providing flexible buffer to reduce friction resistance between rigid tool string and borehole wall.
4. Conventional low-sulfur oil and gas well maintenance, well plugging, well abandonment and secondary reservoir reconstruction intervention operations.
5. Matching assembly with weight bar, hydraulic setting tools and jetting subs to form complete standardized coiled tubing downhole tool combination.
6. Slim small-diameter coiled tubing service jobs for slim hole and compact wellhead oilfield projects.
Standard Delivery Package
Complete pre-assembled integral knuckle joint unit with factory precision thread finishing and surface anti-rust protective treatment.
Hard plastic thread protective caps and anti-collision packaging accessories for safe transportation and long-term warehouse storage.
Factory full dimensional tolerance inspection report, base material chemical composition analysis report and mechanical property tensile test certificate.
Official product installation operation guide and tool string matching assembly manual for on-site construction reference.
Optional customized thread precision inspection report and third-party independent material certification for overseas oilfield project bidding document requirements.
Quality Warranty & After-Sales Service
Warranty Coverage: 12 months after factory shipment or 500 times cumulative downhole tripping operation cycles, whichever condition comes first.
Strict full factory inspection: Every knuckle joint passes dimensional tolerance detection, thread precision inspection, sealing performance test and surface defect visual inspection before leaving factory.
Free professional global technical support: Tool string matching consultation, size selection guidance and working condition material grade recommendation for all overseas and domestic clients.
Long-term stable spare parts supply: Full complete size series inventory supports bulk wholesale order and fast global sea & air delivery arrangement.
Customized engineering service: Support non-standard outer diameter, internal bore size, assembly length, special connection thread and H₂S anti-sulfide corrosion alloy material customization according to client technical drawings and actual downhole well working conditions.
FAQ
Q1: What is the core function of coiled tubing knuckle joint?
A1: The knuckle joint is a flexible key accessory for coiled tubing downhole tool string. It is installed between weight bar and lower working tools to increase overall tool string flexibility. It provides maximum 15° angular deflection and full 360° rotation, solving tool sticking and difficult running problems in restricted boreholes, highly deviated wells and horizontal wells, ensuring smooth delivery of downhole working tools to target reservoir depth.
Q2: What working condition material grades are available for this knuckle joint?
A2: Standard finished products adopt STD standard carbon steel, cost-effective and suitable for conventional low-sulfur, low-corrosion oil and gas wells. We support customized NACE MR0175 compliant H₂S sour service anti-sulfide corrosion alloy version, which can resist sulfide stress cracking and severe formation fluid corrosion, specially applied to high-hydrogen-sulfide sour gas wells and acidizing corrosive downhole environments.
Q3: What standard connection threads does the knuckle joint support?
A3: Our full-series knuckle joints are equipped with three mainstream oilfield standard connection threads matched with different outer diameter sizes: 1" AMMT for small OD models, 1-1/2" AMMT for medium OD models, and 2-3/8" PAC for large OD models. All thread specifications follow unified industry processing standards, realizing direct matching with weight bar, hydraulic setting tool, coiled tubing string and other downhole intervention tools without extra adapter conversion.
Q4: Why choose sealed integral knuckle joint for coiled tubing deviated well operation?
A4: The integral sealed structure fully protects internal movable deflection and rotation components from downhole solid debris and corrosive formation fluid, avoiding sand jamming, internal corrosion and motion failure. Its dual-motion design (15° deflection + 360° rotation) can perfectly adapt irregular wellbore trajectory in deviated and horizontal wells, greatly reducing tool string sticking risk and improving construction success rate, which cannot be replaced by rigid straight pipe connectors.
Q5: Do you accept customized non-standard knuckle joint specifications?
A5: Yes, we provide full customized engineering solutions for global clients. We can manufacture non-standard outer diameter, internal through bore size, overall assembly length, special non-standard connection thread and H₂S anti-sulfide corrosion alloy material knuckle joints strictly according to client technical drawings, field well parameters and actual downhole working conditions.
Get Custom Datasheet & Factory Quote
We are a professional OEM & ODM manufacturer specializing in full series oilfield coiled tubing well intervention tools, supplying high-performance sealed knuckle joints, solid weight bars, hydraulic setting tools, bridge plugs and complete sets of supporting downhole service tools for global onshore and offshore oil & gas field projects. All our products adopt standardized forging and precision machining process with strict multi-stage factory testing, featuring stable long-term downhole working performance and excellent cost performance ratio. Whether you need standard-size STD carbon steel knuckle joints or customized H₂S sour service anti-corrosion versions with non-standard specifications, please feel free to contact our professional engineering team. We will provide targeted tool string matching solutions, complete detailed technical datasheets and competitive factory bulk wholesale quotations within 24 working hours.
