Stainless steel hydraulic fittings for offshore platforms and drilling rigs

Where are hydraulics concentrated offshore?

• Lifting equipment: deck cranes, pipe and material cranes, and their pressure, return and pilot lines.
• Pipe handling systems: cylinder and motor connections on the moving systems that rack drill pipe and transfer it to the derrick.
• Deck machinery: windlasses, mooring winches and towing gear.
• Hydraulic power units: pump outlets, filter blocks, accumulator lines and distribution manifolds.
• Auxiliary control circuits: remote-controlled valves, measurement and sampling lines, and control panel connections.
• Support vessels: deck hydraulics on the offshore support vessels serving platforms and drillships.

Safety-critical systems such as well control equipment are subject to their own design and certification requirements. For the auxiliary lines around these systems as well, the specification that governs each connection should be clarified together with the operator's engineering team at the quotation stage.

For the control, injection and measurement lines of onshore wellheads, refineries, petrochemical plants and pipeline stations, see our “Oil & Gas” sector page.

Material: 316L and the specification

Thanks to its molybdenum content, AISI 316L offers a much longer service life in marine atmospheres than carbon steel and grade 304; its carbon content of no more than 0.03% also gives it an advantage against intergranular corrosion in welded parts. That said, some offshore specifications may call for higher-alloy materials (such as 6Mo or super duplex) instead of 316L, particularly for small-bore tubing exposed to direct sun and spray in hot climates. Since GÜNEYSS works with AISI 316/316L raw material, if your project specification defines a different material class, stating it in your quote request ensures that the right solution is discussed from the outset.

Fluid and seal compatibility matter as much as the material. In systems that use environmentally friendly, biodegradable hydraulic fluids, the compatibility of the O-ring and seal material with the fluid should be checked separately.

Fitting selection: pressure, vibration and installation orientation

Pressure, vibration, line size and installation orientation determine the type of fitting, hose or flange. The most common pairings in offshore applications:

Using different connection families one after another on the same pressure line creates an additional leak point at every transition. A line should be built with a single connection family wherever possible, and conversion adapters should be used only where the equipment port makes them unavoidable.

Maintenance: removability and spare parts planning

Offshore, maintenance windows are short and tool access is limited. The following should therefore be planned into the connection layout in advance:

• Removable connections should be positioned where a wrench can reach them, with enough clearance for seal replacement.
• Seal, O-ring and hose assembly sizes for every critical line should be recorded in the spare parts list.
• A suitable anti-seize compound should be used on stainless steel threads during assembly to prevent galling; otherwise the threads may be damaged at the next disassembly.
• Clamp spacing on hose lines should be set according to vibration, and hoses should be kept from chafing against sharp edges.
• If carbon steel clamps or supports have been used on stainless steel lines, corrosion can start at the contact point; support and clamp materials should also be selected to suit the environment.
• A controlled leak check should be carried out at initial commissioning and after every intervention.

Power unit and control panel side

In offshore power units, a large number of connections, from the pump outlet to the manifold and from the manifold to the distribution lines, are concentrated on a compact skid. At this density, it is important that every connection can be reached with a wrench and that filters and accumulators can be serviced without dismantling the line. Control panels use small-bore stainless steel tubing and twin-ferrule instrumentation fittings; a clean, square tube cut, the correct wrench turns and tube supports placed with vibration in mind determine sealing performance. Where a panel carries different fluids or pressure levels, labeling the lines and choosing connection types that cannot be mixed up reduce intervention errors in the field.

Lead times and shipping

Standard sizes in stock are ready to ship within 1-3 business days on average; standard production items are scheduled within 5-10 business days on average, hose assemblies made up to length within 5-15 business days on average, and custom-size and project manufacturing within 10-20 business days on average after technical approval. For offshore shipments, parts are packed separately by size and order group; threads and ports are closed off with protective caps, and quantities, product types and a final visual check are verified before dispatch. The logistics point where the packages will be transferred to the vessel or platform, and the delivery terms, are agreed when the order is placed.