Enclosures for Wellhead Control Systems

Enclosures are usually made of 316 stainless steel to withstand the corrosive environment of offshore platforms or the workover conditions around the wellheads. As a minimum, all the hardware must be made of 316 stainless steel. This includes hinges, latches, handles, bolts, and nuts.

Enclosures may be made to withstand such things as windblown rain, sand, and dust; splashing water; hose-directed water; and spray from wellhead workover activities. External icing may also be a problem, but it is usually handled by the use of buildings or shelters.

Specifications may be written to describe the enclosure construction required to withstand operating conditions, but the use of NEMA-type enclosures, developed for electrical equipment, can match the right cabinet or enclosure to the operating conditions. Some of the NEMA types are as follows.

NEMA 13 — indoor use, protection against dust, spraying of water, oil, and noncorrosive fluids.

NEMA 12 — indoor use, protection against dust, falling dirt, and dripping noncorrosive liquids.
NEMA 3 — outdoor use, protection against windblown dust, rain and external icing.
NEMA 3R — outdoor use, protection against falling rain, external icing, and only rust resistant
NEMA 4 or 4X — outdoor use, protection against windblown dust and rain, splashing water, hose-directed water, and external icing. (The “4X” means corrosion-resistant, but “316 stainless steel” should be added to this description.)

Following are some other important requirements for construction.
• Tubing runs between components should be designed to allow easy removal of components or in-place maintenance to replace “O” rings and gaskets.
• Stacking or double layering of tubing runs should not be allowed.
• Longer tubing runs should be clamped with solid stainless steel spacers.
• All tubing should be reamed and blown clean with dry air before installation.
• Pipe-to-tube fitting adapters should be used to connect components instead of pipe nipples and unions.
• All penetrations or bulkhead fittings should be on the sides, back, or bottom. No penetrations should be allowed into the top of the enclosure.
• No internal components should be mounted from the top or bottom of the enclosure.
• When height or width exceeds 36 inches, then construction should be with at least 12-gage stainless steel. Otherwise 16-gage metal is satisfactory.
• Gaskets should be made of oil- and water-resistant material such as neoprene.
• Gaskets should be secured with an oil-resistant adhesive and supported by continuous stainless steel retainer strips.
• The bottom should be sloped, with a 1/2-inch flush-mounted half-coupling for draining.
• Lifting eyes with reinforced plates should be provided to support the entire weight of the completed panel for installation.
• Mounting brackets or stands (including nuts and bolts) should be provided for small enclosures that are less than 48 inches tall.
• Integral legs should be provided for free standing enclosures 48 inches or taller, including hardware to bolt the legs to the floor.
• If earthquake requirements exist, brackets should be provided for securing tall enclosures.
• Number and size of doors should be specified and should depend on the width of the enclosure. If it is wider than 36 inches, multiple doors are required, with a maximum width for each door of 30 inches.
• If the type of door latch is not specified as NEMA 4X, three-point latches made of stainless steel are typically used.
• Locks or other features should be provided for security.
• Mounting and bracing of all internal components should be provided to prevent damage during shipment and installation and from operating conditions such as vibration. These supports and shelves are usually made from a corrosion-resistant material such as stainless steel.
• All clips, clamps, straps, bolts, nuts, washers, screws, etc., should be made of 316 stainless steel, nylon, or some other durable, corrosion-resistant material.
• It may be desirable to have a panel or even individual compartments to separate hydraulic systems from pneumatic systems.
• When potentially hazardous or corrosive gasses are being handled, the design of the control system should prevent them from entering any panels or enclosures.

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