Blowout Preventer (BOP) Guide: Types, Working Principle & API 16A Selection

Goldenman Technical Guide · Well Control Equipment

Blowout Preventer Fundamentals, BOP Types and Selection

A blowout preventer is not selected as an isolated valve. It is part of an integrated well-control system that must match the wellhead, tubular program, anticipated pressure, ram functions, hydraulic control capacity and choke-and-kill flow path.

API 16AAnnular & Ram BOP scope

2,000-20,000 psiRam BOP range by configuration

Annular + RamCore BOP stack functions

API 16DHydraulic BOP control system

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Quick Answer

A blowout preventer (BOP) is a high-pressure well-control device installed at or near the wellhead to shut in a well when formation fluids enter the wellbore unexpectedly. Annular BOPs use a reinforced elastomeric packing element to seal around different tubular profiles, while Ram BOPs use opposed ram blocks for pipe sealing, open-bore closure or emergency shearing. In a complete BOP stack, these preventers work together with a hydraulic control unit, drilling spool, choke and kill equipment and associated high-pressure lines.

In This Guide

1. What is a blowout preventer?
2. Why BOPs are required
3. How a BOP works
4. Main BOP types
5. Annular BOP
6. Ram BOP
7. Annular vs Ram BOP
8. BOP stack components
9. BOP size & pressure ratings
10. API 16A / 16C / 16D
11. How to select a BOP
12. Frequently asked questions

What Is a Blowout Preventer?

A blowout preventer, commonly shortened to BOP, is pressure-control equipment used during drilling, workover and other well operations to close or restrict the wellbore when normal hydrostatic control is no longer sufficient.

During normal drilling, the drilling fluid column is designed to help control formation pressure. If formation fluids enter the wellbore and create a kick, the crew must detect the influx, stop normal operations and shut in the well according to the approved well-control procedure. The BOP provides the mechanical barrier required to contain pressure while the well is stabilized.

A BOP therefore does more than simply “close a hole.” Depending on the stack configuration, it may seal around drill pipe, tubing or casing, close an open wellbore, shear a specified tubular in an emergency, and provide a controlled pressure path to the choke and kill system.

Why Is a BOP Required During Drilling?

The BOP is one layer in the complete well-control barrier system. It is required because formation pressure can exceed the effective pressure being maintained in the wellbore.

1. Normal ControlDrilling-fluid hydrostatic pressure helps balance formation pressure.

2. Kick OccursFormation fluid enters the wellbore when the pressure balance is disturbed.

3. Well Is Shut InThe correct BOP function is activated to contain well pressure.

4. Pressure Is ManagedChoke and kill equipment supports controlled circulation and pressure management.

A BOP cannot correct poor well-control practices by itself. Successful well control depends on kick detection, the drilling program, properly selected equipment, tested barriers, trained personnel and a verified operating procedure.

How Does a Blowout Preventer Work?

The operating mechanism depends on the BOP type, but modern surface BOPs are normally hydraulically actuated. A BOP control unit stores pressurized hydraulic fluid and directs it to the selected BOP operator.

Kick is identified

The crew recognizes an abnormal influx or pressure condition and follows the approved shut-in procedure.

A BOP function is selected

The operator selects an annular, pipe ram, blind ram or other qualified closing function according to the tubular position and procedure.

Hydraulic pressure moves the operator

Pressurized control fluid moves a piston or ram mechanism to compress the sealing element into the required position.

The well is contained

The selected BOP forms a pressure barrier while well pressure is monitored and controlled through the approved well-control system.

Important engineering distinction: the BOP’s wellbore pressure rating is not the same as the hydraulic pressure used to operate it. A high-pressure BOP may be operated by a much lower-pressure hydraulic control system. The final control-unit pressure and usable fluid volume must be checked against the actual BOP operator data.

Main Types of Blowout Preventers

The two principal BOP families used in drilling and workover stacks are Annular BOPs and Ram BOPs. Ram BOPs can then be equipped with different ram assemblies for different well-control functions.

BOP / Ram Type	Sealing Method	Seal Around Pipe	Close Open Bore	Shear Pipe	Typical Role
Annular BOP	Reinforced elastomeric packing element	Yes	Model dependent	No	Flexible sealing across tubular profiles
Fixed Pipe Ram	Opposed fixed-size ram blocks	Yes	No	No	Dedicated seal around one tubular OD
Variable-Bore Ram	Variable sealing geometry	Yes	No	No	Qualified range of tubular ODs
Blind Ram	Opposed blind ram faces	No	Yes	No	Open-bore shut-in with no tubular across cavity
Shear Ram	Qualified cutting blades / ram assembly	No	Function dependent	Yes	Emergency tubular shearing
Blind-Shear Ram	Cutting plus sealing assembly	No	Yes	Yes	Emergency shearing followed by bore isolation

BOP Type 01

Annular BOP: Flexible Sealing Around Different Profiles

An Annular Blowout Preventer uses a reinforced elastomeric packing element that is compressed inward by a hydraulic piston. This allows one BOP to seal around several approved tubular outside diameters without changing fixed-size ram blocks.

Goldenman API 16A annular blowout preventer in oilfield equipment factory — Goldenman Annular BOP – flexible wellbore sealing using a reinforced packing element.

Sealing MethodReinforced packing element

Bore RangeApprox. 179.4-539.7 mm

Pressure Range2,000-10,000 psi by model

Depending on the selected model and operating procedure, an annular BOP may seal around drill pipe, tubing, casing, drill collars, tool joints and other approved profiles. Open-bore closure and controlled stripping capability must be verified for the exact packing element and BOP design.

Goldenman Annular BOP product data currently covers spherical and tapered designs. Final bore, working pressure, connection, temperature class and elastomer selection should be confirmed from the project datasheet.

View API 16A Annular BOPs

BOP Type 02

Ram BOP: Positive Sealing, Open-Bore Closure and Shearing Functions

A Ram Blowout Preventer uses two opposed ram assemblies that move horizontally toward the center of the bore. The installed ram type determines whether the cavity seals around pipe, closes an open bore or provides a qualified shear function.

Goldenman API 16A double ram blowout preventer for drilling well control — Goldenman Double Ram BOP with two independently operated ram cavities.

Ram FunctionsPipe / VBR / Blind / Shear

Bore RangeApprox. 4-1/16 to 26-3/4 in

Pressure Range2,000-20,000 psi by configuration

A Double Ram BOP contains two independent ram cavities, allowing two different functions in one pressure-containing body. For example, one cavity can use a pipe or variable-bore ram while the second cavity uses a blind or blind-shear ram.

Final selection depends on nominal bore, rated working pressure, tubular OD, tool-joint profile, required shear data, connection type, temperature and service conditions.

View Double Ram BOP Configurations

Annular BOP vs Ram BOP: What Is the Difference?

Annular and Ram BOPs are complementary rather than interchangeable. A typical BOP stack uses the flexibility of an annular preventer together with the dedicated barrier functions provided by ram preventers.

Comparison	Annular BOP	Ram BOP
Primary sealing element	Reinforced elastomeric packing element	Metal ram block plus sealing packer
Pipe-size flexibility	High within approved packing range	Fixed-size or qualified variable-bore range
Open-bore sealing	Available on approved configurations	Requires blind or blind-shear ram
Shearing capability	No	Available with qualified shear ram
Typical advantage	Versatile first closure around different profiles	Dedicated positive barrier functions
Key selection input	Packing range, tool-joint OD, stripping conditions	Ram type, tubular OD, shear data and cavity arrangement

System View

What Is a BOP Stack?

A BOP stack is the assembled pressure-control system installed above the wellhead. The exact sequence depends on the drilling program, but a surface stack can combine annular and ram preventers with drilling spools, choke and kill outlets and the hydraulic control system.

Annular Blowout Preventer

Upper Ram BOP / Pipe or Variable-Bore Ram

Lower Ram BOP / Blind or Shear Function

Drilling Spool + Choke / Kill Outlets

Wellhead / Casing Head System

The stack must be reviewed as a system. Bore alignment, rated working pressure, connections, ram functions, outlet locations, opening and closing volumes, maintenance clearances and hydraulic controls all have to be compatible.

Goldenman stacked blowout preventer system with annular and ram BOP components — Example stacked well-control arrangement. Final BOP stack configuration must follow the approved well program.

Core Components Around the BOP Stack

Annular BOP

Provides flexible sealing around multiple approved tubular profiles.

View Annular BOPs

Ram BOP

Provides pipe, variable-bore, blind, shear or blind-shear functions.

View Double Ram BOPs

Drilling Spool

Provides stack spacing and, where specified, pressure outlets or connection transitions.

View Drilling Spools

Choke & Kill Manifold

Provides the high-pressure flow path used for controlled well pressure management.

View API 16C Manifolds

Choke & Kill Hose

Connects pressure-control equipment where flexible high-pressure routing is required.

View API 16C Hoses

BOP Control Unit

Stores and distributes hydraulic energy for BOP and associated well-control functions.

View API 16D Control Units

BOP Size and Pressure Rating Reference

BOP selection must match both nominal bore and rated working pressure. The bore has to provide sufficient clearance for the largest tubular and tool-joint profile expected to pass through the stack. The working pressure has to satisfy the well-control design and project requirements.

The following table summarizes representative availability from Goldenman’s current Annular and Double Ram BOP product data. It is a sourcing reference, not a substitute for an approved BOP datasheet.

Nominal Bore	Approx. Metric Bore	Annular BOP Reference	Double Ram BOP Reference	Engineering Note
7-1/16 in	179.4 / 180 mm	3,000 / 5,000 / 10,000 psi by model	5,000 psi standard; higher ratings available by configuration	Common compact drilling / workover bore
9 in	228.6 / 230 mm	3,000 / 5,000 psi by model	5,000 psi standard; project-specific options	Check tool-joint and completion OD
11 in	279.4 / 280 mm	3,000 / 5,000 / 10,000 psi by model	3,000 / 5,000 / 10,000 / 15,000 / 20,000 psi by configuration	Broad pressure-class availability
13-5/8 in	346.1 / 350 mm	3,000 / 5,000 / 10,000 psi by model	3,000 / 5,000 / 10,000 / 15,000 psi by configuration	Confirm stack height and side clearance
18-3/4 in	Approx. 476 mm	Model-specific	5,000 / 10,000 and higher project-specific configurations	Large-bore stack engineering required
21-1/4 in	Approx. 540 mm	Large-bore annular models available by series	2,000 / 5,000 / 10,000 psi by configuration	Verify exact connection and project scope

Not every bore, pressure class, connection, ram arrangement and material class is available as one standard product. Final availability is confirmed through the approved technical datasheet and general arrangement drawing.

API Standards Used Across a BOP Well-Control System

Procurement teams often use the phrase “API BOP” broadly, but different equipment within the well-control package falls under different product scopes. The purchase specification should identify the applicable standard for each item.

API Spec 16AApplies to blowout-prevention drilling equipment such as Annular and Ram BOPs within the applicable product scope.

API Spec 16CApplies to choke-and-kill equipment and associated pressure-control components within the applicable product scope.

API Spec 16DApplies to control systems used for land-based and surface-mounted BOP stacks within the applicable product scope.

For sour-service projects, material and elastomer selection may also need to address specified H2S conditions and applicable NACE MR0175 / ISO 15156 requirements. The final compliance package should follow the purchase order, operator specification and project quality plan.

Hydraulic Control

The BOP Control Unit Must Be Sized From Actual Operating Volumes

The BOP control unit is the hydraulic power and control system that opens, closes and regulates the required well-control functions. It should not be selected only by the number of accumulator bottles.

Goldenman API 16D BOP control unit with hydraulic accumulator bottles — BOP Control Unit: hydraulic energy storage and function control for the BOP stack.

Reference Pressure3,000 psi / 207 bar hydraulic system

Sizing BasisActual opening and closing volumes

ConfigurationAccumulator, pumps, reservoir, remote control

Engineering inputs should include the opening and closing volumes of each Annular and Ram BOP, hydraulic ram locks, choke and kill valves, minimum operating pressure, emergency sequence, usable accumulator fluid volume and required reserve.

Goldenman’s current API 16D BOP Control Unit reference configuration uses a 3,000 psi / 207 bar hydraulic system and can be configured with different accumulator banks, pump packages, reservoirs and remote control functions.

View API 16D BOP Control Units

How to Select the Correct Blowout Preventer

Buying a BOP only by diameter and pressure class creates a high risk of mismatch. Goldenman reviews the complete well-control application before confirming a model and manufacturing datasheet.

1. Define the operationDrilling, workover, well servicing, HPHT, sour-service or replacement application.

2. Confirm maximum anticipated surface pressureUse the well-control design basis rather than selecting pressure class from habit.

3. Confirm nominal boreCheck the wellhead bore plus the largest tubular, tool-joint and downhole profile passing through the stack.

4. Define ram functionsSpecify fixed pipe, variable-bore, blind, shear or blind-shear requirements for each ram cavity.

5. Verify shear dataProvide OD, wall thickness, grade, material strength and tool-joint information for any required shear function.

6. Confirm top and bottom connectionsDefine flange, studded or hub interfaces, ring grooves, studs and stack-height restrictions.

7. Define service conditionsTemperature, drilling fluid, H2S, CO2, chloride exposure and elastomer requirements affect configuration.

8. Check control-system capacityUse opening / closing volumes and required operating pressures from the final BOP datasheets.

9. Define choke and kill interfacesConfirm outlet size, orientation, working pressure, valves, manifolds, hoses and flow-path requirements.

10. Agree documentation and testingConfirm API certificates, material traceability, NDE, pressure tests, FAT and third-party witness requirements before production.

Example Selection Logic

Example: 7-1/16 in, 5,000 psi Surface BOP Stack

For a project requiring a 7-1/16 in bore and 5,000 psi working pressure, the equipment package might include an FH18-35 Annular BOP, a 2FZ18-35 Double Ram BOP, a compatible drilling spool, choke and kill equipment and an API 16D control unit. The final ram arrangement, connections, control volumes and pressure-control flow path still have to be engineered from the actual well program.

FH18-35 Annular BOP
2FZ18-35 Double Ram BOP
API 16D Control Unit

Common BOP Procurement Mistakes

Selecting only by bore and pressureTwo BOPs with the same nominal bore and pressure rating can have different connections, dimensions, hydraulic volumes and spare parts.

Ignoring tool-joint ODThe largest profile passing through the BOP may be larger than the nominal drill pipe body OD.

Assuming any shear ram will cut any pipeShear capability depends on pipe OD, wall thickness, grade, material strength, operator force and available hydraulic pressure.

Matching control pressure to BOP pressure ratingWellbore pressure rating and hydraulic operating pressure are different engineering values.

Treating H2S service as a simple optionSour-service materials and elastomers must be selected from actual pressure, temperature and fluid-composition requirements.

Leaving documentation until shipmentAPI scope, material certificates, NDE, FAT, pressure test records and witness points should be agreed before manufacturing.

Goldenman BOP Manufacturing, Testing and Project Support

For Goldenman, a BOP quotation is not complete until the pressure-containing equipment, ram or packing functions, hydraulic controls and project documentation have been reviewed together. Our current product range includes Annular BOPs, Double Ram BOPs, BOP Control Units, Choke and Kill Manifolds, high-pressure hoses, drilling spools and replacement sealing parts.

Material TraceabilityHeat-number and material-certificate review for specified pressure-containing components.

Dimensional InspectionBore, connections, ring grooves, ram cavities, hydraulic interfaces and overall dimensions.

NDE & HardnessInspection scope defined by the product specification, material class and approved quality plan.

Hydraulic Function TestOpening, closing, locking and control functions verified according to the selected configuration.

Pressure & Seal TestingBody pressure, sealing, pressure-holding and leakage checks according to the agreed test procedure.

Third-Party InspectionCustomer or third-party witness and hold points can be built into the inspection and test plan.

Frequently Asked Questions About Blowout Preventers

What does BOP stand for in drilling?

BOP stands for Blowout Preventer. It is pressure-control equipment used to shut in and control a well during drilling, workover and related operations.

What is the main purpose of a blowout preventer?

Its main purpose is to contain well pressure when formation fluids enter the wellbore unexpectedly. Different BOP functions can seal around pipe, close an open bore or shear a specified tubular in an emergency.

What are the two main types of BOP?

The two main BOP families are Annular BOPs and Ram BOPs. Ram BOPs can use fixed pipe, variable-bore, blind, shear or blind-shear ram assemblies.

What is the difference between an Annular BOP and a Ram BOP?

An Annular BOP uses a deformable packing element and can seal around several approved tubular profiles. A Ram BOP uses opposed ram blocks to perform more specific functions such as fixed-pipe sealing, open-bore closure or tubular shearing.

Can an Annular BOP seal an open hole?

Open-bore sealing is available on approved annular configurations, but it must be confirmed for the exact model, packing element and operating procedure.

Can a shear ram cut any drill pipe?

No. Shearing capability depends on pipe OD, wall thickness, steel grade, material strength, connection or tool-joint position, BOP operator force and available hydraulic pressure. The exact tubular data must be reviewed.

What is a BOP stack?

A BOP stack is the assembled well-control equipment installed above the wellhead. It can combine one or more Annular and Ram BOPs with drilling spools, choke and kill outlets, hydraulic control equipment and associated pressure-control components.

What API standard applies to blowout preventers?

Annular and Ram Blowout Preventers fall within the applicable API Spec 16A product scope. Related well-control equipment can fall under other standards, such as API Spec 16C for choke-and-kill equipment and API Spec 16D for BOP control systems.

How do I choose the correct BOP pressure rating?

The rated working pressure should be selected from the well-control design basis, maximum anticipated surface pressure, stack pressure class, test requirements and applicable operator or regulatory requirements. Every pressure-containing component in the required flow path must be compatible.

What information should I provide when requesting a BOP quotation?

Provide nominal bore, working pressure, top and bottom connections, tubular sizes, tool-joint OD, required ram functions, shear tubular data, service temperature, drilling-fluid conditions, H2S requirements, existing stack drawing, control-unit details, inspection requirements and destination.

Need a BOP Configuration for a New or Replacement Stack?

Send Goldenman your bore size, working pressure, BOP stack drawing, tubular program, ram functions, shear requirements, connection details, service conditions and required API / inspection documentation. We can review the system and prepare the recommended BOP configuration and technical quotation.

Request a Technical Quote
Email info@goldenman.com

Related BOP & Well Control Resources

Well Control Equipment Systems →
API 16A Annular BOP →
API 16A Double Ram BOP →
API 16D BOP Control Unit →
API 16C Choke & Kill Manifold →
Blowout Preventer Price Guide →

What Is a Blowout Preventer? Complete BOP Guide for Drilling Well Control

Table of Contents

Blowout Preventer Fundamentals, BOP Types and Selection

In This Guide

What Is a Blowout Preventer?

Why Is a BOP Required During Drilling?