Viking Johnson FlexLock Restrained Coupling for Steel Pipe

A compact restrained coupling for steel and ductile iron pipe

The Viking Johnson FlexLock Coupling is a restrained coupling sized to the exact outside diameter of steel and ductile iron pipe, rather than a wide-tolerance band. Stainless-steel gasket gripper teeth bond the gasket to the pipe so the joint resists pull-out. The datasheet lists 15 pipe size entries from DN50 (60.3 mm OD) to DN300 (323.9 mm OD), each with its own end ring, bolt set and gasket mould.

It is a narrow-tolerance product, so the pipe OD must match the table. Choose it for rigid pipe runs where a restrained joint is wanted but space is tight, for example pipe racks, valve chambers and plant rooms.

FlexLock technical data

Size table from the datasheet (OD and lengths in mm; L = overall length, A = end ring OD, S = sleeve length x thickness).

Limits and design notes from the datasheet

• Only for ductile iron, steel and coated steel; coating over 500 microns DFT stops the teeth from gripping.
• Stainless steel pipe is excluded: because of the surface characteristics the grippers cannot achieve a guaranteed grip.
• If the coupling is taken apart, fit a new gasket on reassembly because the teeth may be dislodged; spares are ordered by gasket mould number and compound.
• Two entries exist for some sizes (steel and ductile iron OD), so state the pipe material when ordering.

Selection and installation

Choose by actual pipe OD, for example 114.3 mm steel or 118 mm ductile iron for DN100, rather than the nominal size alone. Specify EPDM or nitrile gaskets and keep within the 40 C maximum printed for the gasket. Tighten M12 bolts at 55-65 Nm and M16 at 95-120 Nm. The datasheet lists no single order code, so quote size, OD, pipe material and gasket compound for confirmation.

Applications in Oman and the GCC

Steel pipe is the standard material for many industrial and fire water systems, and FlexLock gives a restrained joint where welding or flanging would be slow. Typical locations are above-ground manifolds in pump houses, plant room risers and valve chambers. Keep operating temperature within +40 C and check that the pipe coating is below 500 microns.

From the size table, the sleeve length and thickness grow with diameter: the DN50 entry has an 80 x 5.5 mm sleeve, while the DN250 and DN300 entries use 178 mm sleeves with M16 bolts at up to 275 mm length. That is why the two largest sizes drop to 10 bar for water. Weights run from 2.7 kg to 33.7 kg, which matters when a joint has to be lifted into a trench or an overhead rack by hand.

When you enquire about the FlexLock, state the pipe material, steel or ductile iron, the outside diameter within the DN50 to DN300 range, and whether the medium is water at up to 16 bar or gas at up to 6 bar, so that the restrained size and gasket can be confirmed from the datasheet.

Selection and installation notes

Pipe couplings and clamps must be chosen from the actual pipe outside diameter, the pipe material, the working pressure and the joint movement expected, so measure the pipe before ordering and compare the reading with the size range on the data sheet. Clean the pipe surface and remove dirt, scale and sharp edges, mark the insertion depth, centre the coupling over the joint and tighten the bolts evenly in a cross pattern to the torque in the installation instructions. Check the joint again after the line has been pressurised, and do not use a coupling outside its stated pressure rating.

Information needed for a quotation

Send the full model code, the quantity, the delivery location in Oman or the GCC, the intended use and any accessories needed, so that the complete package can be quoted together.

Documents and supply information

The manufacturer data sheet is attached to this page and should be read together with the project specification and the site risk assessment before a purchase is confirmed. Ratings, standards and dimensions are quoted as printed on that sheet. Lead time, stock position and certificates available with the shipment are confirmed in the quotation, and we supply to Oman and the wider GCC region for industrial, utility and building services projects.

Related items and documents

See the pipes and fittings category for UltraGrip and MaxiFit couplings. The official datasheet is attached; Seven Star LLC can quote by pipe OD.