9.2 Ram Preventers: Pipe Rams, Variable Bore, Blind Shear Rams & Locking Devices

Ram-type blowout preventers represent the definitive heavy-duty mechanical containment barrier in drilling well control. While annular preventers provide flexible closure over variable shapes and facilitate stripping, ram preventers are built to withstand maximum wellbore pressures (up to $15,000\text{ to }20,000\text{ psi}$), severe mechanical hang-off loads exceeding $600,000\text{ lbs}$, and high-velocity abrasive gas-and-sand flow without loss of structural containment.

Supervisors and drilling engineers must master ram BOP operating mechanics, including the differences between fixed and variable bore configurations, the physics of drillstring shearing, mechanical and hydraulic locking systems, and diagnostic leak-detection pathways.

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Ram BOP Architecture: Body, Bonnets, and Dynamic Seals

A modern ram preventer consists of a monolithic forged alloy steel body with a vertical wellbore drift and opposing horizontal ram guideways (cavities). Bonnets containing the hydraulic operating cylinders are mounted on opposite sides of the body via high-tensile studs or boltless hydraulic latch mechanisms.

┌─────────────────┬───────────────────┬─────────────────┐
│ Operating Piston│ Ram Block Cavity  │ Operating Piston│
│ ═══════════════ │ ═════════════════ │ ═══════════════ │
│ [Close Chamber] │ [Upper Pipe Ram]  │ [Close Chamber] │
│   Connecting    │  ┌───┐     ┌───┐  │   Connecting    │
│    Rod ───────► │  │   │  │  │   │  │ ◄─────── Rod    │
│ [Open Chamber]  │  └───┘     └───┘  │ [Open Chamber]  │
│                 │    Wellbore Bore  │                 │
│  Weep Hole (•)  │                   │  Weep Hole (•)  │
└─────────────────┴───────────────────┴─────────────────┘

The Intermediate Flange and Weep Hole (Tell-Tale Hole)

The connecting rod (ram shaft) transmits axial force from the hydraulic piston inside the bonnet to the ram block in the wellbore cavity. This rod must traverse two completely separate pressure environments: the hydraulic operating fluid in the bonnet cylinder (up to $3,000\text{ psi}$) and the drilling fluid/hydrocarbons in the wellbore (up to $15,000\text{ psi}$).

To isolate these fluids, the intermediate bonnet flange houses two distinct sets of dynamic packings separated by an atmospheric cavity vented to the outside through a small diagnostic port known as the weep hole (or tell-tale hole):

• Wellbore Rod Packing: Facing inward toward the wellbore cavity, sealing against drilling mud, sour gas ($H_2S$), and hydrocarbons.
• Hydraulic Piston Rod Seal: Facing outward toward the operating cylinder, sealing hydraulic control fluid.

Diagnostic Leak Identification via Weep Hole

1. Drilling Mud or Gas Discharging from Weep Hole: The inner wellbore rod packing has failed. Wellbore pressure is escaping to atmosphere. Assess the compromised barrier and secure the well using the available verified barriers. Use an emergency secondary-packing procedure only if fitted and appropriate for that model.
2. Hydraulic Oil Discharging from Weep Hole: The outer operating cylinder piston rod seal has failed. Hydraulic closing/opening fluid is leaking to atmosphere. Assess the loss of operating-fluid containment and control capability, secure as necessary, and arrange repair/reverification before relying on the affected equipment.

Secondary Emergency Rod Packing

Some ram preventers have an emergency secondary rod-packing system. Its activation, hydraulic-pressure state and subsequent repair requirements follow that model's procedure. For example, the NOV SL manual describes a specific emergency secondary-seal operation and prompt service follow-up. Do not turn a generic injection bolt while assuming every BOP has the same pressure conditions or repair method.

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Ram Preventer Types: Capabilities and Limitations

┌────────────────────────────────────────────────────────┐
│                 RAM PREVENTER TYPES                    │
├──────────────────┬──────────────────┬──────────────────┤
│ Fixed Pipe Rams  │  Variable Bore   │   Blind Shear    │
│                  │    Rams (VBR)    │    Rams (BSR)    │
├──────────────────┼──────────────────┼──────────────────┤
│ • Machined single│ • Pivoting steel │ • Hardened blade │
│   pipe diameter  │   inserts        │   shears string  │
│ • Highest hangoff│ • Multi-diameter │ • Integrated seal│
│   rating         │   coverage       │   shuts in hole  │
│ • Extended life  │ • Faster wear    │ • Pipe body only │
└──────────────────┴──────────────────┴──────────────────┘

1. Fixed Bore Pipe Rams

Fixed pipe rams feature machined semi-circular steel recesses fitted with molded rubber face packers and top seals designed specifically for a single outer diameter of drillpipe, casing, or tubing (e.g., 3-1/2", 5", or 5-1/2").

• Hang-Off Capability: A qualified pipe ram can support a specified suspended load by landing the appropriate tool-joint shoulder on the ram. Verify the actual ram, pipe, tool-joint and load ratings, space-out and approved load-transfer sequence; fixed-pipe geometry alone does not establish hang-off capacity.
• Fatigue Life: Extremely high; capable of hundreds of pressure test and functional cycles.

2. Variable Bore Rams (VBRs)

Variable Bore Rams utilize a specialized elastomeric packer reinforced with segmented radial steel inserts that pivot inward like an iris diaphragm when the rams close.

• Operational Envelope: A single pair of VBRs can seal across a range of pipe and casing sizes (e.g., $3\text{-}1/2"\text{ to }5"$, $5"\text{ to }7"$, or $7"\text{ to }9\text{-}5/8"$). They can also seal across the hexagonal body of a kelly or tapered drillstrings.
• Hang-Off Limitations: VBR hang-off capacity is significantly lower than fixed rams (typically limited to $200,000\text{ to }350,000\text{ lbs}$, depending on pipe size). Landing maximum string weight on a VBR on its smallest rated pipe diameter can plastically deform the pivoting steel inserts.
• Elastomer Degradation: Because the rubber undergoes extreme elastomeric deformation during each closure, VBR packing elements experience rapid fatigue and must be inspected and replaced more frequently than fixed rams.

3. Blind Shear Rams (BSRs) and Casing Shear Rams (CSRs)

Blind Shear Rams feature high-tensile alloy steel shearing blades (typically modified double-V or curved guillotine profiles) with integrated elastomeric blade and side seals. Upon activation, BSRs perform two sequential functions in a single stroke:

1. Sever the Drillstring: Upper and lower blades shear cleanly through the drillpipe body.
2. Isolate the Wellbore: As the blades overlap at the end of the stroke, the transverse blade seal mates with the opposing blade while the side seals contact the body cavity, establishing an absolute, pressure-tight hydraulic barrier across the open wellbore.

Casing Shear Rams (CSRs): Heavy-duty non-sealing rams fitted with deep-profile hardened blades designed exclusively to cut thick-walled high-strength casing (such as 9-5/8", 10-3/4", or 13-3/8" casing) or heavy drill collars. A non-sealing casing-shear ram needs a separate, suitably positioned sealing element to isolate the well after the cut. Verify the actual tubular, ram capabilities and space-out; do not assume every component called a casing shear can cut any collar or casing.

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Drillpipe Shearing Mechanics and Non-Shearable Zones

Required shearing force depends on the actual tubular dimensions/metallurgy, blades, position, axial load and well conditions. Use the installed ram's qualified shear-and-seal data and available hydraulic pressure at the actuator; a generic tensile-strength multiplier is not a shear qualification.

Hydraulic piston force follows pressure × effective area. Opposing well-pressure forces, friction and the actuator/booster design affect the net force available to cut and seal. A booster adds effective force, but neither an assumed doubled area nor a 3,000 psi supply guarantees a successful cut at maximum well pressure.

Record the qualified tubular combinations, pressure conditions and space-out on the rig's shear plan. Distinguish cutting capability from sealing capability after the cut.

Non-Shearable Wellbore Components

Standard Blind Shear Rams cannot cut everything in the hole. Drilling supervisors must maintain strict tallies of non-shearable items, which include:

• Drillpipe Tool Joints: The heavy, thick-walled forged steel box and pin connections cannot be severed by standard BSRs. Attempting to shear across a tool joint will stall the blades, deform the ram blocks, destroy the shearing edge, and prevent wellbore shut-in.
• Drill Collars and Heavy-Weight Drillpipe (HWDP) tool joints.
• Bottom-Hole Assembly (BHA) components: Mud motors, MWD/LWD pulser collars, rotary steerable tools, jars, and stabilizers.
• Unqualified casing/tubing combinations: Some blind/shear designs can cut tubing or specified casing, while others cannot. Use the installed shear table; tubing does not categorically require a separate non-sealing casing-shear ram.

Mechanical and Hydraulic Ram Locking Mechanisms

Once a ram preventer closes under hydraulic pressure, API Standard 53 requires a positive mechanical lock to prevent the ram from creeping open if hydraulic closing pressure is vented, lost due to accumulator failure, or severed by fire.

Manual Locks

Manual locking screws mechanically retain the closed rams. Before hydraulic opening, release both locks as the installed procedure requires and verify they are disengaged. Do not apply opening pressure against engaged or partly engaged locks. Any reset movement is model-specific, not a universal quarter-turn rule.

Hydraulically Actuated Mechanical Locks

Examples include Cameron Wedgelock and NOV/Shaffer Poslock and Ultralock arrangements. Hydraulic commands actuate the locking/release mechanism, but retention is mechanical rather than dependence on trapped closing fluid alone. Follow the correct circuit sequence and confirm the lock state before relying on closure or commanding opening. Do not infer engagement, release pressure or travel range from the trade name alone.