BL6/BL8 are non-coupling direct connections with inner diameter matching the pipe body. Two thread pitches are available for optimized field performance and make-up speed:
BL6: 6 threads per inch for superior stress relief and connection performance.
BL8: 8 threads per inch for faster make-up.
With low-flank-angle thread profile and low/straight taper, they deliver outstanding service performance.
As a product series with broad applications, BL6/BL8 feature specially engineered thread structures. Under complex loading, their load capacity reaches 100% of the pipe body’s actual internal yield strength.

BL6/BL8 Structure
Connection strength equals pipe body strength; gas sealing capacity reaches pipe inner wall yield pressure; allows repeated make-up & break-out; non-tapered thread fit; long upset section.

BL6/BL8 Thread Design

1. Two-stage hook-type threads with a 7.5° load flank, resisting thread galling and providing high connection strength.
2. 20° lead angle for easy stabbing and threading.
3. Optimized thread pitch diameter reduces interference, improving joint efficiency and stress corrosion resistance.
4. BL6: 6 threads/inch; BL8: 8 threads/inch. BL6 offers better stress distribution; BL8 achieves faster make-up.
5. Two-stage straight taper simplifies stabbing, prevents cross-threading and doubles make-up speed.

Optimized pitch diameter reduces thread interference, concentrating tightening torque on the torque shoulder to boost connection efficiency and corrosion resistance.
BL6 (6RD) delivers better stress relaxation; BL8 (8RD) enables faster make-up.
Two-stage straight taper doubles threading speed.

BL6/BL8 Shoulder Design
Multi-stage mixed right-angle / negative-angle shoulders:

1. Optimized pitch diameter lowers thread interference. Torque acts mainly on shoulders to improve joint efficiency and stress corrosion resistance.
2. Primary right-angle shoulder forms cone-cone interference fit with main sealing surface.
3. -30° reverse self-locking negative shoulder enhances bending resistance.
4. Secondary right-angle shoulder adjacent to secondary seal provides effective auxiliary sealing under torque.
5. Large fillet at primary shoulder root reduces stress concentration and rationalizes strain distribution under over-torque.
6. Three-shoulder design delivers far higher torsional strength than other premium connections. Suitable for high-pressure wells, fracturing, acidizing, fishing and well remediation.

BL6/BL8 Seal Design
Two-stage metal-to-metal sealing plus three-stage shoulder auxiliary sealing.
Main seal adopts cone-on-cone profile with advantages:
(1) Cone-on-cone line contact creates high contact pressure over a short seal length for easy machining control.
(2) Large sealing area plus shoulder-assisted sealing maintains stable contact pressure and sealing performance under combined tension, bending and high internal pressure.
(3) Cone-cone interference metal seal forms one secondary seal and three auxiliary seals at torque shoulders. The joint’s critical pressure capacity reaches 100% of pipe body internal yield strength.