Dur O Lok^® Couplings

Designed like a coupling. Performs like a flange.
Made in the USA. Designed to ASME BPVC.

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Benefits & Features

Specifications

Installation Instructions

Assembly Clamp

Resources

Save on maintenance, downtime, material costs, and space.

For decades, top refineries and industrial processors have trusted BETE DUR O LOK couplings to keep their piping systems running safely, efficiently, and dependably. Engineered to replace bulky ANSI flanges, DUR O LOKs are all-purpose, lightweight connectors delivering reliability across a wide range of operating temperatures. The compact, boltless design saves space, reduces installation time, eliminates the need for hardware, and minimizes alignment effort. It features a threadless, self-energizing seal and offers a wide range of material options for a thermally stable, corrosion-resistant, and low-maintenance solution.

The heart of the DUR O LOK design is a system of wedge-shaped, circumferential teeth on the outside diameter of the hubs and the inside diameter of the mating split coupler. When assembled, the teeth generate a wedging action that compresses the gasket and brings the hub ends together. The split coupler’s tapered outside diameter accepts a matching tapered retaining ring that slides over the split coupler ring segments, forcing them together and holding them securely in place with a set screw. The entire connection process can be completed in under a minute, without wrenches.

By significantly reducing installation time, space requirements, and overall system weight without sacrificing strength, DUR O LOK couplings offer numerous advantages over traditional flanges. These benefits make them the preferred solution for many pipe-connecting applications, particularly in petrochemical processing and refining.

How It Works

The heart of the DUR O LOK design is the system of wedge-shaped, circumferential teeth located on the outside diameter of the hubs and the inside diameter of the mating split coupler. The wedging action of the teeth compresses the gasket and brings the hub ends into contact with each other. The outside diameter of the split coupler is tapered. A ring with a tapered inside diameter slides over the split coupler ring segments, forcing them together and holding them firmly in place. The tapered retaining ring is secured with a set screw. Without wrenches, the entire connection process can be accomplished in less than a minute.

Benefits

Reduce maintenance

Reduce materials cost

Reduce space requirements for pipe racks

Features

The DUR O LOK coupling meets the requirements of the following codes:

• ASME Boiler and Pressure Vessel Code, Section VIII
• ASME B31.1, Code for Pressure Piping
• ASME B31.3, Code for Process Piping

Compact - length and outside diameter reduced by 30% - 50%, compared to flanges. Allows double the number of pipes per rack and improves external flow distribution for immersed couplings. It will reduce shadowing for couplings used in process vessels.

Lightweight - weight reduced by 60% - 90%, compared to flanges.

Simple - Number of parts reduced by 55% - 75% per connection, compared to flanges.

Fast - Save up to 10-15 minutes to make or break each connection.

Non-restrictive - Full port inside diameter eliminates pressure drop and allows "pigging".

Smooth interior bore - Minimizes flow disturbances. It eliminates attrition in catalyst and other solids conveying applications.

Boltless and threadless - Only safety set screws required. No torque measurements are required. No bolt holes to align. No need to tighten connections after thermal cycling. Simplifies painting and insulating.

Thermally stable - Design minimizes thermal expansion effects on sealing. It will tolerate very rapid changes in external or internal temperatures.

No interference fits or metal-to-metal sealing - Higher reliability. Less susceptible to damage.

Benefits

Reduce installation labor and downtime with fast, easy assembly and disassembly
Improve flow efficiency in piping systems
Suitable for use in corrosive, high-temperature, and abrasive environments
Minimize flange leakage and maintenance issues

Features

Compact – 30-50% reduction in overall length and outside diameter
Lightweight – 60-90% lighter than flanges
Simple – 55-75% fewer parts
Fast – saves up to 10-15 minutes per connection
Non-restrictive – full-port inside diameter
Smooth interior bore – minimizes flow disturbances
Boltless and threadless – set screws only; no torquing, re-tightening, or bolt alignment – simplifies painting & insulating
Self-energized seal – less chance of leaks
Thermally stable – withstands rapid temperature changes
No interference fits – high reliability, reduced damage risk

The DUR O LOK coupling meets the requirements of the following codes:

ASME Boiler and Pressure Vessel Code, Section VIII
ASME B31.1, Code for Pressure Piping
ASME B31.3, Code for Process Piping

DUR O LOK Materials

Carbon steel
Stainless steel – 304, 316, 321
Other materials available on request
Material traceability available

DUR O LOK/Flange – Weight and Dimension Comparison

DUR O LOK					Weld Neck Flanges
Pipe Size	Pipe Schedule	Overall Diameter (in)	Overall Length (in)	Approx Weight (lb)	Flange Class	Flange OD (in)	Flange Assembly Length (in)	Flange Assembly Weight (lb)
1.00	80	2.50	3.50	1.99	2500	6.25	7.00	26.60
1.25	80	2.85	3.50	2.61	600	5.25	5.20	13.10
1.50	XXS	3.13	4.00	4.82	2500	8.00	8.80	57.00
2.00	80	3.55	5.00	5.25	2500	9.25	10.00	83.30
2.50	160	4.21	6.00	9.19	600	7.50	6.20	38.00
3.00	80	4.95	6.50	11.20	1500	10.50	9.20	102.50
3.50	80	5.45	7.00	13.64	600	9.00	6.80	63.20
4.00	160	5.95	7.50	20.54	2500	14.00	15.00	301.20
6.00	80	8.47	9.50	41.51	600	14.00	9.20	173.50
8.00	80	10.65	9.50	60.84	600	16.50	10.50	259.10

DUR O LOK drawing

Please note that weight and dimensions information are approximate.
Please call if you have questions.

DUR O LOK® Pipe Couplings – Dimensions (in), Ratings (psi), and Assumed Moments (ft-lb)

Data provided below is for the o-ring design. Similar information is available upon request for the high temperature gasket seal design.

Pipe Size	Pipe Sched.	"D" Pipe O.D.	"B" Pipe I.D.	"A" Overall Diameter	"C" Tapered Ring Length	"L" Overall Length	"W" Nominal Wall	Approx. Weight (lbs.)	Pressure Rating (PSI)^† Carbon Steel	Pressure Rating (PSI)^† 304 Stain. Steel	Assumed Moment (ft-lb)
1	40	1.32	1.05	2.50	1.47	3.50	0.14	1.99	1475	1229	33
1	80	1.32	0.96	2.50	1.47	3.50	0.18	2.10	2850	2374	33
1¼	40	1.66	1.38	2.85	1.47	3.50	0.14	2.41	1550	1291	59
1¼	80	1.66	1.28	2.85	1.47	3.50	0.19	2.61	2800	2332	59
1¼	160	1.66	1.16	2.85	1.47	3.50	0.25	2.81	4650	3873	59
1½	40	1.90	1.61	3.13	2.00	4.00	0.15	3.71	2250	1874	82
1½	80	1.90	1.50	3.13	2.00	4.00	0.20	4.00	3850	3207	82
1½	160	1.90	1.34	3.13	2.00	4.00	0.28	4.38	5900	4915	82
1½	XXS	1.90	1.10	3.13	2.00	4.00	0.40	4.82	8100	6747	82
2	40	2.38	2.07	3.55	2.00	5.00	0.16	4.70	1850	1541	140
2	80	2.38	1.94	3.55	2.00	5.00	0.22	5.25	3350	2791	140
2	160	2.38	1.69	3.55	2.00	5.00	0.35	6.19	5600	4665	140
2½	40	2.88	2.47	4.21	2.00	6.00	0.21	7.16	2100	1749	266
2½	80	2.88	2.32	4.21	2.00	6.00	0.28	8.10	3500	2916	266
2½	160	2.88	2.13	4.21	2.00	6.00	0.38	9.19	4700	3915	266
3	40	3.50	3.07	4.95	2.00	6.50	0.22	9.81	1600	1333	431
3	80	3.50	2.90	4.95	2.00	6.50	0.30	11.20	2900	2416	431
3	160	3.50	2.62	4.95	2.00	6.50	0.44	13.23	3900	3249	431
3½	40	4.00	3.55	5.45	2.00	7.00	0.23	11.75	1650	1374	599
3½	80	4.00	3.36	5.45	2.00	7.00	0.32	13.64	2850	2374	599
4	40	4.50	4.03	5.95	2.00	7.50	0.24	13.70	1550	1291	804
4	80	4.50	3.83	5.95	2.00	7.50	0.34	16.21	2400	1999	804
4	120	4.50	3.62	5.95	2.00	7.50	0.44	18.55	2700	2249	804
4	160	4.50	3.44	5.95	2.00	7.50	0.53	20.54	2700	2249	804
5	40	5.56	5.05	7.35	3.10	8.50	0.26	26.27	1750	1458	1363
5	80	5.56	4.81	7.35	3.10	8.50	0.37	30.45	2450	2041	1363
6	40	6.63	6.07	8.47	3.10	9.50	0.28	34.25	1600	1333	2124
6	80	6.63	5.76	8.47	3.10	9.50	0.43	41.51	2350	1958	2124
8	40	8.63	7.98	10.65	3.10	9.50	0.32	49.72	1350	1125	4202
8	80	8.63	7.63	10.65	3.10	9.50	0.50	60.84	1825	1520	4202

*DUR O LOK® Pipe Couplings - Note: Values for dimensions and weights are nominal; please contact Customer Service for exact values. Maximum Temperature: 400°F (204°C) with Viton o-ring, 450°F (232°C) with silicone rubber o-ring. Please note: Grafoil® limit in air or oxygen 850°F (454°C).

DUR O LOK^® COUPLINGS INSTALLATION PROCEDURE

GENERAL INSTALLATION INFORMATION

For the installation of DUR O LOK couplings in catalyst lift lines or similar services involving long piping runs, tack weld the assembled coupling to both pieces of pipe, positioned horizontally along a flat surface. Care must be taken to ensure that the two pieces of pipe are straight and properly aligned before welding. 80 feet of (shop floor) space is required to position and weld two 40-foot sections of pipe to a DUR O LOK coupling. The tacked coupling may be disassembled prior to completing the circumferential weld.
For pipes employing precision bends (e.g., CCR catalyst transfer lines and related applications), trial installation in the shop is highly recommended, as it allows for final adjustments to be made. DUR O LOK couplings have higher installation tolerances than standard flanges, and extra care must be taken during final alignment. Pipe sections must be match-marked after the trial fit-up is complete and on-spec. This will facilitate trouble-free installation of the pipe assemblies in the field.
DUR O LOK couplings are available in both standard and high-temperature designs. Standard design couplings employ an elastomeric type O-ring seal and are used for applications typically below 450 °F (232 °C). The O-ring material determines the temperature limit. Materials of construction for O-rings include Viton^®, silicone, Kalrez^®, and many others, depending on the application requirements. Although O-rings are typically reusable if not damaged, it is strongly recommended that a used O-ring be replaced with a new one.
The high-temperature design utilizes a graphite-type flat gasket for nominal service temperatures exceeding 450 °F (232 °C). A DUR O LOK installation clamp may be required to compress the installed gasket and properly assemble the high-temperature DUR O LOK coupling. These custom-sized gaskets are not reusable and only available through BETE. Please specify DUR O LOK coupling pipe size and pipe schedule when ordering.

Warning: Low-temperature (OR70) and high-temperature (GRF100) design DUR O LOK couplings and their gaskets are not interchangeable.

BETE offers an assembly clamp (purchased separately) for fast and easy installation, ensuring proper alignment of the coupling hubs. If this clamp is to be used, refer to the attached DOL Clamp Instructions for more details.

STEP-BY-STEP INSTALLATION PROCEDURE

STEP 1. PREPARE DUR O LOK^® COUPLING FOR WELDING

The welding surfaces of the coupling and the mating pipe must be cleaned and prepared for welding. Be sure to remove any dirt, grease, or other surface contaminants prior to welding. Also, be sure to remove plastic protective caps, as they will melt. If the coupling has a black oxide finish, lightly grind or sand off the black oxide coating from the welding surfaces of the coupling. Removal of the black oxide coating from the coupling’s welding end may have already been done at the factory for your convenience.
For applications involving catalyst transfer (e.g., CCR Platforming), it is recommended that the black oxide coating be removed from the entire inner surface of the coupling.
Remove the gasket or O-ring.

STEP 2. WELD DUR O LOK COUPLING TO MATING PIPE

It is highly recommended that the DUR O LOK coupling be welded to the mating pipes as an assembled unit whenever possible, as this ensures proper alignment and protects machined surfaces. Be sure to take extra care during welding alignment as DUR O LOK couplings have higher installation tolerances than standard flanges.

Warning: Do not have a gasket or O-ring in place while welding, as damage will occur.

For pipes involved in catalyst transfer, a smooth transition at the inside surface for all circumferential welds is mandatory. The inside diameters of the pipes and welded DUR O LOK coupling may require grinding to remove all ledges in order to produce a flush transition in the area of the circumferential welds. The final wall thickness of the pipes and the coupling must not be less than the minimum required wall thickness.
For non-horizontal coupling installations, ensure that the female hub (the hub with a gasket cavity) is positioned as the lower half of the coupling, so that the gasket cannot fall out of place during assembly.

Warning: Protect the machined surfaces of the coupling from weld splatter.

STEP 3. POSITION TAPERED RETAINING RING

Place the tapered retaining ring over the male hub end and slide it past the grooves on the hub for the split coupler. The end with the larger inside diameter must be oriented toward the mating (gasket) surface of the coupling. The two set screw holes should be located in the half of the tapered retaining ring closest to the mating surface of the coupling.
Bring the two hub ends welded to the pipe segments into an approximate assembled position.

STEP 4. INSTALL GASKET

Closely examine the gasket cavity of the female hub. Ensure the cavity is free from oil, debris, scratches, or any other contaminants that may compromise the seal’s quality.
Place the gasket in the cavity of the female hub.
Handle gaskets with care in order to avoid damage.

Warning: Damaged gaskets must not be used, as they will not seal properly. Always replace used gaskets to ensure a proper seal. High-temperature (GRF100) gaskets are for one-time use only.

STEP 5. ASSEMBLE COUPLING

With the gasket in place, draw the hub ends together. If the welded pipes are not aligned properly, a clamp will be required to draw the two halves of the DUR O LOK coupling together. BETE offers a special clamp to simplify this process, but, if desired, a clamp can be constructed in your shop using standard riser clamps.
Couplings that are excessively out of alignment will require removal, repositioning, and rewelding. It is best to take care to align the piping and couplings prior to welding.
Place the two split couplers in position. Ensure that the set screw grooves in the split couplers are aligned over the female hub (the hub with the gasket).
Slide the end with the larger inside diameter over the split couplers until the tapered retaining ring aligns with the set screw holes directly over the set screw grooves in the split couplers. Use a soft-faced hammer (e.g., nylon or rubber) to drive the tapered retaining ring into a fully engaged position.

DUR O LOK coupling assembly with clamp — BETE-made clamps are available for purchase. Refer to attached DOL Clamp Instructions.

Warning: The tapered retaining ring must be fully engaged to attain the design compression and pressure rating for the desired service. The tips of the set screws must fit completely inside the split coupler’s set screw grooves. The coupling could become inadvertently disassembled due to vibration during use if not assembled properly. This may result in process material leakage.

STEP 6. SECURE COUPLING

Install and hand-tighten the set screws with the supplied 3/16” hex key (Allen wrench). The function of the set screws is to prevent the tapered collar from disengaging. The set screws do not function to pull the tapered retaining ring into position. Do not overtighten, as this may cause damage to the threads.
Install the safety wire through the holes in both set screws and wrap the wire once around the coupling.
Twist the safety wire a minimum of five times, ensuring the set screws cannot work loose during operation. Safety wire twisting and cutting pliers are available for this purpose.
The presence of the safety wire is generally indicative that a gasket is in place. DUR O LOK couplings can also be tagged or marked to indicate “gasket installed.”

BETE offers an assembly clamp for fast and easy installation, ensuring proper
alignment of the coupling hubs.

Key Benefits

Corrects minor hub misalignment
Ensures proper gasket compression and pressure rating
Helps fully engage split couplers and retaining ring
Reduces installation rework

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Resources

BETE Dur O Lok^® PDF

Download PDF

Dur O Lok^® Couplings Installation Procedure

Download PDF

Contact an Engineer

A illustration of a BETE TF full/hollow cone nozzle.

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