Gas Handling Systems

Three stages of gas handling

Gas reaches surface from a kick, a well test or production, and each source leads to different equipment.

Gas separators on a drilling rig mainly means the mud gas separator downstream of the choke manifold, plus test separators on well test spreads. Gas processing equipment covers scrubbers, glycol dehydration units, fuel gas skids and H2S removal vessels. Flare and vent systems covers well test burner booms, flare tips, pilots, knock-out drums and vent lines.

Choosing between them

Start from where the gas comes from and where it must go.

• Gas from a kick goes through the choke manifold to a mud gas separator, and the gas leaves through a vent line to a safe point.
• Gas from a well test passes a test separator, is metered, and is burnt at a boom or flared.
• Gas you want to use as fuel or export needs scrubbing, dehydration and often H2S removal before it reaches an engine or pipeline.

A used package sized for one duty rarely suits another. Size each item for your worst-case gas rate, and check that the separator, vent or flare and relief system downstream match.

Standards across the group

• ASME Boiler and Pressure Vessel Code Section VIII governs most vessels, and the nameplate shows the maximum allowable working pressure (MAWP) and temperature.
• API 12J covers oil and gas separators. API 12GDU covers glycol-type gas dehydration units.
• API 521 covers pressure-relieving and depressuring systems, including flare radiation and vent dispersion. API 537 covers flare details such as tips, pilots and ignition.
• API RP 14C sets the safety analysis and shutdown devices for offshore process systems.
• NACE MR0175/ISO 15156 sets materials for service with hydrogen sulphide (H2S).
• IEC 60079 governs electrical equipment in hazardous areas, marked ATEX or IECEx. In the EU, the Pressure Equipment Directive also applies to new equipment placed on the market.

Integration questions that cut across the group

• Back pressure. Vent lines, flare headers and burner lines add friction. The separator upstream must still hold its liquid seal or level against it.
• Relief. Every vessel needs a relief path sized for its worst case, and the relief valves need in-date tests.
• Hazardous areas. Gas equipment sets zones on deck, so motors, heaters and instruments must suit them.
• Layout. Booms, vents and flare tips must keep radiation and gas clouds away from the drill floor, accommodation and air intakes.
• Controls. Packages bring their own PLC, shutdown valves and gas detection, which must tie into the unit's emergency shutdown.

Sourcing used gas handling equipment

Gas equipment is often built for one campaign and then laid up, so its records decide its value.

• Ask for the manufacturer's data book with design code, calculations, material certificates, weld procedures, NDT and hydrotest reports.
• Check the nameplate against the data book, and look for undocumented repairs, re-rating or nozzle changes.
• Ask for the latest wall thickness survey, with readings at inlets, bends and impingement areas where erosion starts.
• Check relief valve test certificates and set pressures against the MAWP.
• Confirm sour service materials in the mill certificates if your field has H2S.

Unused surplus from cancelled projects often comes with a complete data book and only needs a preservation check and retest. Naventr passes your questions on vessel history to the Seller and returns the answers from their records.