Stainless steel instrumentation and hydraulic fittings for oil and gas

From wellhead to terminal: where the fittings work

• Wellheads and wellhead control panels (WHCP): hydraulic control lines for surface and subsurface safety valves, accumulator and pump connections, and emergency shutdown (ESD) circuits.
• Land drilling rigs: power unit and rig equipment hydraulics, and auxiliary lines around the BOP control unit.
• Chemical injection units: dosing lines for corrosion and scale inhibitors, methanol, glycol and paraffin inhibitors.
• Refineries and petrochemical plants: transmitter impulse lines, sampling points, analyzer systems and control lines for actuated valves.
• Pipelines and stations: compressor and pump stations, natural gas RMS (pressure reduction and metering) and pigging stations, and actuator and pressure-sensing connections on line valves.
• Storage and terminals: measurement, sampling and valve control lines at tank farms and loading terminals.

This page focuses on onshore fields, refineries, petrochemical plants and pipelines; offshore platforms and drillships are covered on our “Offshore & Drilling” sector page. Wellhead equipment (API 6A) and BOP control systems (API 16D) are subject to their own standards and certification requirements; we make no claim to supply parts for this equipment itself. For auxiliary lines, confirm the applicable specification in writing before ordering.

Instrumentation lines: fittings, needle valves and check valves

Control panels, injection lines and measurement points are built with small-bore stainless steel tubing. Twin-ferrule (double ferrule) fittings grip the tube without welding, in a controlled and repeatable way; needle valves are used for flow adjustment and gauge isolation, and check valves to prevent backflow. The main points to watch:

• Tube outside diameter, wall thickness and hardness should be selected according to the design pressure and compatibility with the fittings; inch and metric sizes should not be mixed on the same line.
• Bodies, nuts and ferrules should come from the same system; parts from different manufacturers should not be used in the same connection.
• A check valve at the injection point stops backflow but does not provide safe isolation; a separate isolation valve should be planned for maintenance and, where the specification requires it, a double block and bleed (DBB) arrangement upstream of the instrument.
• On high-pressure lines such as subsurface safety valve control lines, the pressure rating of the fittings, tubing and valves should each be confirmed separately against the system's design pressure.

H2S-containing environments (sour service) and chlorides: the limits of 316L

AISI 316L is a common material in hydrocarbon service and against atmospheric corrosion; however, its use is limited in H2S-containing environments and in hot, chloride-bearing water. Material requirements for these environments are defined by NACE MR0175 / ISO 15156 in oil and gas production and, in refineries, mostly by NACE MR0103 / ISO 17945. ISO 15156 accepts austenitic stainless steels within limits that depend on temperature, chloride content, H2S partial pressure, pH and the presence of elemental sulfur; it also sets requirements for heat-treatment condition and hardness. Whether a line stays within these limits is decided by the project specification; if this requirement applies, it should be stated clearly in the order.

In chloride environments, pitting resistance is compared using PREN (Cr + 3.3 Mo + 16 N); on this scale, 316L is clearly below duplex and super duplex steels, and as temperature rises it becomes more susceptible to localized corrosion and stress corrosion cracking. For this reason, specifications may call for duplex, super duplex, 6Mo or nickel alloys under severe conditions. Since our raw material is AISI 316/316L, state any different material class in your quote request; whether the request can be met will be stated clearly before the order.

Material documentation, traceability and testing

In oil and gas projects, documentation is part of the delivery. The purchase specification may call for an EN 10204 3.1 material certificate, positive material identification (PMI), hardness values, a pressure test or specific marking. Raw material batches are recorded at receiving and kept traceable; parts undergo dimensional, thread and surface inspection before dispatch. State your documentation, testing or inspection requirements in writing at the quotation stage; the scope that can be provided is clarified before the order.

Pipelines and stations: actuator and control lines

Hydraulic or gas-over-oil actuators on line valves, their control blocks, hand pumps and pressure-sensing lines are connected with small-bore stainless steel tubing and fittings. Most line valve stations are unmanned and operate outdoors in every season; reducing the number of connections, supporting the tubing against vibration and positioning valves where they can be reached for maintenance all lower the risk of leaks. In the hydraulic power units of compressor and pump stations, large-bore pressure lines are mostly built with SAE flanges, and moving connections with hose assemblies with stainless steel ends. A manifold block machined to a technical drawing can replace a chain of elbows and adapters. If there is an additional requirement for connections and installation in hazardous (explosive atmosphere) areas, it should be stated in the specification.

Preparing for a refinery turnaround

Refinery turnarounds are planned in advance; the earlier the requirements list is finalized, the more orderly the shipments. Before the turnaround, we recommend listing the fittings, valves and tubing to be replaced together with their size family (inch or metric), thread standard (NPT, BSPP, BSPT), material and documentation requirements. Parts are packed separately by order and size group; open threads and ports are protected with caps. The delivery plan is communicated before the order, taking documentation and testing requirements into account.