API 6A Flanges Selection Guide for High Pressure Oilfield Wellhead Systems
API 6A flanges are critical connection components for oilfield wellhead and high-pressure petroleum equipment. These flanges connect casing heads, tubing heads, Christmas trees, gate valves, choke valves, drilling spools, adapter spools, choke manifolds, kill manifolds and other pressure control equipment.
In drilling, workover, well testing, flowback and production service, a flange does more than join two pieces of equipment. More importantly, it must hold pressure, match the mating connection, seal through the correct RTJ ring gasket and support safe field installation.
Although an API 6A flange may look like a simple forged steel part, real oilfield service is much more demanding. In practice, the connection may face well pressure, vibration, repeated assembly, sour service conditions, field impact, corrosion risk and strict inspection requirements. Therefore, correct selection should include pressure rating, flange type, bore, RTJ ring gasket, bolt pattern, material class, PSL, temperature class and mating equipment details.
Procurement teams should not select API 6A flanges by nominal size alone. For example, a 4-1/16 inch 5000 psi flange still needs the correct API 6A Type 6B or API 6A Type 6BX connection, ring gasket number, bore size, material, documentation and service condition. Otherwise, a small mismatch may delay pressure testing, stop installation or create an urgent replacement requirement at the wellsite.
This guide explains API 6A flanges from an oilfield procurement and engineering point of view. As an oilfield equipment supplier, SGPE supports standard and custom API 6A flange requirements for wellhead, Christmas tree, choke manifold, kill manifold, flowline and pressure control applications. As a result, drilling contractors, wellhead buyers, EPC contractors, oilfield service companies and petroleum equipment distributors can prepare clearer RFQs, reduce technical clarification and improve field connection reliability.
What Are API 6A Flanges?
API 6A flanges are high-pressure oilfield flanged connections for wellhead and Christmas tree equipment. Through a bolted connection and a metal ring gasket sealing system, they connect pressure-containing and pressure-controlling components in upstream oil and gas service.
In practical oilfield applications, these flanges commonly appear on:
- Wellhead assemblies
- Casing heads and tubing heads
- Christmas trees
- Gate valves, check valves and choke valves
- Drilling spools and adapter spools
- Choke manifolds and kill manifolds
- Well testing packages
- Workover pressure control equipment
- High-pressure petroleum flowlines
- Custom oilfield pressure control packages
Oilfield environments create demanding working conditions. For instance, a flange may face high pressure, crude oil, natural gas, drilling fluid, produced water, sour gas, sand, erosion, corrosion and temperature changes. Because of that, API 6A flange selection requires both technical review and field experience.
Moreover, not every flange name describes a separate standard category. Some names, such as API 6A Type 6B Flange, API 6A Type 6BX Flange, API 6A Blind Flange and API 6A Weld Neck Flange, describe common connection or construction types. Meanwhile, other names, including Target Flange, Instrument Flange, Lifting Flange and Custom Machined API 6A Flange, often describe project-specific machining, function or installation needs.
Therefore, a reliable supplier should check the drawing, service condition and mating equipment before confirming the final design.
Why API 6A Flanges Matter in Oilfield Pressure Control
Every oilfield pressure system depends on reliable connections. Therefore, a wellhead valve, spool or manifold can only work correctly when each flange connection fits the equipment and service condition.
When the flange is wrong, several problems may follow. For example, it may fail during hydrostatic testing, leak after installation, mismatch the ring gasket or delay a drilling or workover schedule. In severe cases, an incorrect flange can also create safety and compliance risks.
| Project Goal | How the Right API 6A Flange Helps |
|---|---|
| Pressure integrity | Correct RTJ groove machining, ring gasket fit and bolting help the connection hold pressure during testing and service |
| Equipment compatibility | Matching flange type, bore and bolt pattern reduces mismatch between valves, spools, wellheads and manifolds |
| Faster installation | Correct size, gasket and connection type help the rig crew install the flange without unnecessary rework |
| Schedule protection | Clear flange data reduces urgent machining, replacement delay and repeated technical clarification |
In drilling, workover and production operations, downtime costs money. Therefore, clear API 6A flange specifications help project teams avoid field problems before the equipment reaches the site.
Main API 6A Flange Types and Search Terms
Oilfield projects use different API 6A flange types according to pressure rating, connection design, flow path, sealing method and installation purpose. Before sending an RFQ, identify the flange type and the mating equipment.
| API 6A Flange Type | Common Oilfield Use | Key Selection Focus |
| API 6A Type 6B Flange | Standard wellhead, production tree and manifold connections | Size, pressure rating, bore, RTJ gasket, bolt pattern |
| API 6A Type 6BX Flange | Higher-pressure wellhead and Christmas tree systems | 6BX type, BX gasket, pressure rating, bolting arrangement |
| API 6A Weld Neck Flange | High-pressure piping and flowline transitions | Pipe schedule, bore, weld requirement, NDE |
| API 6A Blind Flange | Closing unused outlets or test connections | Pressure rating, flange face, gasket, lifting requirement |
| API 6A Threaded Flange | Special small-size oilfield connections | Thread type, pressure rating, service condition |
| API 6A Test Flange | Pressure testing, workshop testing and field verification | Test pressure, connection type, sealing method |
| API 6A Companion Flange | Matching a valve, spool, outlet or flowline interface | Mating flange, bolt pattern, gasket, bore |
| API 6A Adapter Flange | Adapting different sizes or connection interfaces | Both-side flange data, bore and overall thickness |
| Double Studded Adapter Flange / DSA Flange | Adapting different flange sizes or pressure ratings | Both-side flange data, studs, bore, thickness |
| RTJ Flange / Ring Type Joint Flange | Metal ring gasket sealing connections | R, RX or BX gasket, ring groove, pressure rating |
| Target Flange | Project-specific impact, flow direction or erosion-related flange design | Drawing, flow direction, erosion area, material |
| Instrument Flange | Gauge, sensor or instrument connection support | Instrument port, thread, orientation, pressure rating |
| Lifting Flange | Large or heavy flange handling and installation support | Lifting hole, pad eye, weight and safety factor |
| Custom Machined API 6A Flange | Non-standard project connection or replacement order | Drawing, dimensions, material and inspection scope |
Standard API 6A Wellhead Flange Types
API 6A Type 6B Flange
API 6A Type 6B Flange, often searched as API 6B Flange or API 6A 6B Flange, serves many standard wellhead, production tree and manifold connections. In general, this connection is used where oilfield pressure control equipment needs a reliable RTJ flange interface.
In field applications, Type 6B flanges often connect wellhead valves, casing head outlets, tubing head outlets, production tree components, spool outlets and choke manifold connections.
Even so, a 6B flange still needs full technical confirmation before production. Therefore, a complete RFQ normally includes nominal size, pressure rating, bore, ring gasket number, bolt size, material class, PSL and mating equipment details.
API 6A Type 6BX Flange
For higher-pressure oilfield wellhead and Christmas tree systems, buyers often search API 6A Type 6BX Flange together with 10000 psi, 15000 psi, 6BX RTJ flange and high-pressure wellhead flange.
Unlike a 6B flange, a 6BX flange uses a different connection design. It also needs the correct RTJ gasket, bolt pattern and ring groove geometry. Therefore, 6B and 6BX flanges do not automatically replace each other.
Before production, verify the connection type for high-pressure wellhead service. As a result, the project team can reduce site mismatch and pressure test failure risk.
API 6A Weld Neck Flange
An API 6A Weld Neck Flange connects oilfield pressure piping or equipment through a welded neck. As a result, it provides a strong transition where the system needs welding support and pressure integrity.
In many projects, oilfield teams use API 6A weld neck flanges in high-pressure flowline connections, well testing packages, choke manifold inlet and outlet lines, production flow control skids and petroleum pressure piping transitions.
For weld neck flange inquiries, include pipe size, pipe schedule, bore, material grade, welding requirement, heat treatment, NDE requirement and sour service condition. In addition, if the flange will work in sour oil and gas service, add the NACE MR0175 / ISO 15156 requirement in the RFQ.
API 6A Blind Flange
An API 6A Blind Flange closes a pressure opening in oilfield equipment. Since it has no flow-through bore, it creates a sealed end connection for unused or temporary pressure openings. In the field, crews often install blind flanges on unused wellhead outlets, manifold outlets, test connections and temporary service points.
Because blind flanges support wellhead pressure testing, choke manifold maintenance, kill manifold isolation, production tree outlet closure, workshop hydrostatic testing, site commissioning and temporary field connection closure, selection details matter.
For API 6A blind flange selection, define the flange size, pressure rating, 6B or 6BX type, RTJ gasket, material, PSL, NACE requirement and lifting or handling features.
API 6A Threaded Flange
An API 6A Threaded Flange appears in some smaller oilfield connections or special wellhead equipment designs. Although it allows assembly without welding, the thread type and service condition still need careful checking.
Before ordering threaded API 6A flanges, specify thread type, thread size, pressure rating, material class, fluid medium, temperature range, mating equipment connection and sour service requirement.
If the connection will face sour gas, high pressure or frequent assembly, the supplier should check the threaded design carefully before machining. Otherwise, the connection may not meet the expected pressure or service requirement.
API 6A Test, Companion and Adapter Flanges
API 6A Test Flange
An API 6A Test Flange supports pressure testing, workshop testing, field verification and equipment commissioning. In practice, maintenance teams may use test flanges with wellhead equipment, valves, spools, manifolds and temporary pressure test setups.
Because test pressure may differ from working pressure, a test flange must fit the required test pressure, flange type, gasket, bore and bolting arrangement. Therefore, the inquiry should include both working pressure and test pressure.
For API 6A test flange orders, include the test medium, test pressure, holding time, connection type, material, ring gasket, inspection report and any test port or instrument connection requirement.
API 6A Companion Flange
An API 6A Companion Flange helps match a valve, spool, flowline, wellhead outlet or equipment interface. In many replacement or installation projects, buyers use companion flanges to solve interface matching problems.
Although a companion flange may look simple, it must fit the mating equipment accurately. Therefore, the supplier needs nominal size, pressure rating, flange type, bore, bolt pattern, ring gasket number and material requirement. For replacement projects, a drawing or clear photo of the mating equipment can save several rounds of clarification.
API 6A Adapter Flange
An API 6A Adapter Flange connects different sizes, pressure ratings or connection interfaces in oilfield pressure control systems. For example, it may connect a wellhead outlet to a valve, a spool to a manifold, or a flowline connection to a pressure control package.
Compared with a standard flange order, adapter flange selection requires more detail. The inquiry should include both-side connection data, overall thickness, bore size, gasket type, bolt size, material class, PSL and service condition.
When an adapter flange connects equipment from different suppliers, the engineering team should check drawings before production. Otherwise, small dimensional differences can create major field installation problems.
Double Studded Adapter Flange / DSA Flange
A Double Studded Adapter Flange, also called a DSA Flange, connects two different oilfield flange interfaces with studs on both sides. In other words, it can adapt one size to another size, one pressure rating to another pressure rating, or one compatible connection design to another.
In practice, DSA flanges are often used for wellhead upgrades, Christmas tree modification, choke manifold conversion, kill manifold connection adjustment, BOP stack interface matching, workover equipment adaptation, well testing package connection and replacement equipment installation.
For example, a site may need to connect a 4-1/16 inch 5000 psi wellhead outlet to a 3-1/8 inch 10000 psi valve connection. A properly designed double studded adapter flange can solve this interface problem. However, both sides must be checked before production.
RTJ, Instrument, Lifting and Custom API 6A Flanges
RTJ Flange / Ring Type Joint Flange
An RTJ Flange, also called a Ring Type Joint Flange, uses a metal ring gasket to create a high-integrity sealing connection. Because RTJ sealing suits high-pressure wellhead, Christmas tree and manifold service, most API 6A flanges for oilfield pressure control equipment use this design.
The correct RTJ flange must fit the gasket type, ring gasket number, ring groove, pressure rating and mating flange. Otherwise, a wrong RTJ gasket can cause leakage, pressure test failure or ring groove damage.
Buyers usually need R, RX or BX ring gaskets depending on the flange type and pressure class. For high-pressure 6BX connections, the ring gasket details become especially important.
Target Flange
A Target Flange usually refers to a project-specific flange design used where flow direction, impact area, erosion risk or internal geometry needs special review. In oilfield equipment, this term may appear in choke manifold service, high-velocity flow, test packages or custom pressure control assemblies.
Because “target flange” can mean different things in different projects, the buyer should share the drawing, flow direction, bore, pressure rating, material, erosion allowance and inspection requirement. Otherwise, a supplier cannot confirm the item correctly by name alone.
Instrument Flange
An Instrument Flange supports pressure gauges, sensors, transmitters or small instrument connections on wellhead, manifold, test or pressure control equipment. In some designs, it may include a threaded port, special outlet, small-bore connection or project-specific machining.
For instrument flange orders, specify the pressure rating, port size, thread type, instrument orientation, bore, material, NACE requirement and test requirement. In addition, if the instrument connects to sour service equipment, material and hardness control need extra attention.
Lifting Flange
A Lifting Flange helps with handling, lifting or installation of heavy oilfield components. For large API 6A blind flanges, adapter flanges, test flanges and custom machined flanges, lifting holes, lifting lugs or other handling features may be required.
For lifting flange design, include flange weight, installation method, lifting point requirement, space limitation and any site safety standard. Also, the supplier should check the lifting arrangement together with the flange drawing.
Custom Machined API 6A Flange
A Custom Machined API 6A Flange supports non-standard oilfield projects, replacement orders, special interfaces and equipment modifications. Usually, buyers need custom machining when old equipment has a special bore, non-standard thickness, unique bolt layout, instrument port, lifting feature or special material requirement.
When a drawing is available, include it in the RFQ. If no drawing exists, send old flange photos, nameplate data, bolt hole measurements, bore size, thickness, gasket number, material requirement and service condition.
Custom machining can solve many field connection problems. At the same time, it increases the need for careful dimensional checking and inspection.
API 6A Flange Pressure Ratings
Pressure rating is one of the most important selection points for API 6A flanges. In oilfield projects, common pressure ratings range from 2000 psi to 20000 psi. The table below gives a practical overview for preliminary selection.
| Pressure Rating | Approx. MPa | Common Oilfield Use | Typical Selection Notes |
| 2000 psi | 13.8 MPa | Low-pressure wellhead outlets and light-duty petroleum flow control | Check production pressure and outlet use |
| 3000 psi | 20.7 MPa | Production wellhead equipment and field service connections | Match gasket type and mating flange |
| 5000 psi | 34.5 MPa | Wellhead valves, casing heads, tubing heads and choke manifold connections | Common in many wellhead packages |
| 10000 psi | 69 MPa | High-pressure wellhead, Christmas tree and drilling-related pressure equipment | Check 6B or 6BX type carefully |
| 15000 psi | 103.5 MPa | Severe high-pressure wellhead and pressure control systems | Review material, PSL and sour service |
| 20000 psi | 138 MPa | Special high-pressure oilfield and critical well control projects | Requires strict engineering and document control |
The flange pressure rating must fit the complete pressure system. For example, a 5000 psi flange cannot safely replace a 10000 psi flange only because the bolt holes look similar. Likewise, a higher-rated flange does not make the connection safe if the mating valve, gasket, studs, nuts or spool has a lower rating.
For accurate selection, check working pressure, test pressure, equipment rating and project specification before ordering.
Common API 6A Flange Sizes
API 6A flanges come in many sizes for oilfield wellhead and pressure control equipment. Common sizes include 1-13/16 inch, 2-1/16 inch, 2-9/16 inch, 3-1/8 inch, 4-1/16 inch, 5-1/8 inch, 7-1/16 inch, 9 inch, 11 inch, 13-5/8 inch, 16-3/4 inch, 18-3/4 inch, 20-3/4 inch and 21-1/4 inch.
| Common Size | Common Oilfield Equipment | Typical Inquiry Focus |
| 1-13/16 in | Small wellhead valves, test outlets, instrument connections | Pressure rating, gasket, thread or outlet type |
| 2-1/16 in | Gate valves, choke valves, tubing head outlets | 5000 psi or 10000 psi requirement |
| 2-9/16 in | Wellhead valves and production tree components | Bore, flange type, RTJ gasket |
| 3-1/8 in | Choke manifold, kill manifold and tree connections | 6B/6BX type and pressure rating |
| 4-1/16 in | Wellhead valves, spools and manifold outlets | Common 5000 psi and 10000 psi applications |
| 5-1/8 in | Casing head, tubing head and spool connections | Bore, material class and PSL |
| 7-1/16 in | Large-bore wellhead and BOP-related connections | Pressure rating, bolt pattern, gasket |
| 9 in and above | Large wellhead, drilling spool and pressure control equipment | Drawing approval, lifting details and packing |
These sizes appear on wellhead valves, casing heads, tubing heads, drilling spools, adapter spools, BOP-related connections and choke manifold equipment.
However, size alone does not identify the correct API 6A flange. For instance, a 4-1/16 inch flange may have different pressure ratings, 6B or 6BX connection type, RTJ gasket, bore size and bolt pattern. Therefore, combine size with pressure rating, flange type and gasket information.
API 6A Type 6B Flange vs API 6A Type 6BX Flange
Many buyers search for API 6B Flange vs API 6BX Flange. In a professional API 6A context, a more accurate way to describe them is API 6A Type 6B Flange and API 6A Type 6BX Flange. Both appear in oilfield wellhead equipment, but they use different connection designs.
| Item | API 6A Type 6B Flange | API 6A Type 6BX Flange |
| Common Search Term | API 6B Flange, API 6A 6B Flange | API 6BX Flange, API 6A 6BX Flange |
| Common Use | Standard wellhead, tree and manifold connections | Higher-pressure wellhead and Christmas tree systems |
| Gasket Type | Usually R or RX, depending on design | Usually BX, depending on connection requirement |
| Pressure Focus | Common in medium and high-pressure oilfield service | Common in higher-pressure applications |
| Interchangeability | Cannot automatically replace 6BX | Cannot automatically replace 6B |
| Buyer Focus | Size, pressure, bore, gasket, bolt pattern | 6BX type, BX gasket, bolting, ring groove |
| Risk if Wrong | Leakage, gasket mismatch, site delay | Pressure test failure, connection mismatch, rework |
A 6B flange often works in standard wellhead, production tree and manifold connections. In contrast, a 6BX flange usually appears in higher-pressure systems and uses a different RTJ gasket and bolting arrangement.
Before choosing 6B or 6BX, check the existing wellhead connection, mating valve flange type, working pressure, bore size, RTJ gasket type, ring gasket number, bolt hole pattern, project standard and end user specification.
For replacement jobs, photos help but rarely tell the full story. Therefore, a clear drawing, nameplate photo, ring gasket number, bolt hole quantity, bolt size and bore size can save several rounds of technical clarification.
RTJ Gaskets for API 6A Flanges
Most API 6A flanges use RTJ sealing. RTJ means ring-type joint. In this design, a metal ring gasket sits inside the machined groove between two flange faces. After the installer tightens the studs and nuts, the gasket creates a metal-to-metal pressure seal.
| RTJ Gasket Type | Common Use in Oilfield Flange Connections | Selection Focus |
| R Ring Gasket | Some standard RTJ connections | Match ring number and material |
| RX Ring Gasket | Pressure-energized RTJ sealing in suitable designs | Check flange groove and pressure rating |
| BX Ring Gasket | Common in API 6A Type 6BX high-pressure connections | Match 6BX flange and exact ring number |
Oilfield flange connections often use R, RX or BX ring gaskets. Therefore, the correct gasket depends on flange type, pressure rating, ring groove design and mating equipment.
For API 6A flange inquiries, define the RTJ gasket type, ring gasket number, gasket material, flange type, pressure rating, sour service requirement and mating equipment connection.
In many cases, buyers order API 6A flanges together with matching RTJ ring gaskets, studs and nuts. As a result, this approach reduces connection mismatch and makes field installation easier.
Materials for API 6A Flanges
API 6A flanges for oilfield service usually require forged steel materials. Because these parts work under pressure, the material must support pressure load, impact load, temperature changes and petroleum service conditions.
Common material options may include forged alloy steel such as AISI 4130, AISI 4140 or equivalent grades, depending on the project specification. In addition, sour oil and gas service may require NACE MR0175 / ISO 15156 compliance.
| Material Factor | Why It Matters for API 6A Flanges |
| Working pressure | Affects strength requirement and flange rating |
| Operating temperature | Affects material toughness and temperature class |
| Sweet or sour service | Determines whether NACE compliance may apply |
| H2S and CO2 content | Helps evaluate sour service and corrosion risk |
| Heat treatment | Supports mechanical properties and hardness control |
| Hardness control | Critical for sour service applications |
| Low-temperature impact | Important for cold-weather and offshore projects |
| Material traceability | Supports inspection, approval and final acceptance |
Material traceability matters in oilfield projects. Each flange should link back to its heat number, material test report and inspection record. As a result, the buyer can pass project review, third-party inspection and final acceptance more smoothly.
API 6A Material Classes for Petroleum Service
API 6A equipment may use material classes such as AA, BB, CC, DD, EE and FF. These classes help define material suitability for different oilfield service environments.
| Material Class Topic | Buyer Should Check |
| Sweet service | Crude oil or gas without sour service requirement |
| Sour service | H2S condition, NACE requirement and hardness limit |
| CO2 condition | Corrosion risk and material suitability |
| Chloride content | Corrosion control for harsh service |
| Temperature class | Low or high temperature operating condition |
| End user specification | Final project requirement and document scope |
A sweet oil production well may require a different material class from a sour gas well. Likewise, an offshore production platform may require stricter material control and documentation than a simple non-sour replacement order.
If the buyer does not know the material class, the well condition, end user datasheet or project specification should guide the final choice.
PSL and Inspection Requirements
PSL means Product Specification Level. API 6A equipment may involve different PSL requirements according to product type and project specification. In many oilfield tenders, buyers may require PSL 1, PSL 2, PSL 3 or higher levels for certain equipment.
For API 6A flanges, define the exact PSL requirement before ordering. As PSL levels become stricter, manufacturing control, inspection scope and documentation requirements usually increase.
| Inspection Item | Common Purpose |
| Raw material review | Confirms material source and heat number |
| Forging inspection | Checks forging quality before machining |
| Heat treatment verification | Confirms required mechanical properties |
| Hardness test | Supports material and sour service review |
| Dimensional inspection | Confirms size, bore, bolt pattern and thickness |
| Ring groove inspection | Helps verify the RTJ sealing area |
| Visual inspection | Checks surface condition and obvious defects |
| MPI / LPI when required | Detects surface flaws |
| UT when required | Checks internal soundness |
| Hydrostatic test when applicable | Confirms pressure integrity for applicable products |
| Final document review | Supports end user and third-party approval |
For projects with strict end user approval, request an ITP before production. In this way, both parties can define inspection stages, witness points and acceptance criteria before manufacturing starts.
API 6A Flange Dimensions Buyers Should Check
Many buyers search for API 6A flange dimensions because they need to replace old wellhead components or connect new oilfield equipment to existing systems. However, one or two measurements from site photos can lead to mistakes.
| Item | Why It Matters |
| Nominal flange size | Confirms basic connection size |
| Pressure rating | Confirms system pressure compatibility |
| Flange type | Distinguishes 6B, 6BX, blind, weld neck, threaded, test, companion, adapter or DSA design |
| Bore size | Confirms flow path compatibility |
| RTJ gasket type | Helps prevent sealing mismatch |
| Ring gasket number | Matches the correct sealing component |
| Bolt hole quantity | Confirms bolting pattern |
| Bolt size | Matches studs and nuts |
| Bolt circle diameter | Confirms mating flange alignment |
| Flange thickness | Affects strength and installation |
| Overall length | Important for adapter flanges and spools |
| Instrument port | Important for instrument flange or test flange designs |
| Lifting feature | Important for heavy blind flanges or large custom flanges |
| Material grade | Supports pressure and service condition |
| Surface protection | Helps prevent corrosion during storage and transport |
When possible, send a drawing. If no drawing exists, clear photos, nameplate details, bolt hole measurements, bore size and mating equipment information can help the supplier check the connection more accurately.
SGPE recommends sharing drawings, photos, nameplate information and mating equipment details together. This helps reduce quotation assumptions and improves the accuracy of technical confirmation.
Oilfield Applications of API 6A Flanges
API 6A flanges support many upstream petroleum systems. Each application has its own selection focus.
| Oilfield Application | Common API 6A Flange Use | Selection Focus |
| Wellhead equipment | Casing heads, tubing heads, outlets and valves | Bore, pressure rating, material class |
| Christmas tree assemblies | Master valves, wing valves, swab valves and crosses | RTJ gasket, PSL, sour service |
| Choke manifolds | Choke valves, gate valves, crosses, tees and outlets | Pressure rating, erosion risk, gasket fit |
| Kill manifolds | High-pressure well control lines | Bore, working fluid, test requirement |
| Drilling spools | Wellhead and BOP-related connections | Top and bottom flange data, drawings |
| Workover equipment | Temporary pressure control connections | Existing interface and delivery schedule |
| Well testing packages | Test manifolds, choke valves and temporary production lines | Test pressure, flow medium, sand content |
| Offshore platforms | Wellhead and production control equipment | Documentation, coating, packing, traceability |
| Instrument connections | Gauge, sensor or transmitter ports | Thread, orientation, pressure rating |
| Custom replacement jobs | Old wellhead or manifold interface matching | Photos, drawings, dimensions and gasket data |
Wellhead Equipment
Wellhead equipment uses API 6A flanges to connect casing heads, tubing heads, outlets, valves and spools. Because the wellhead forms the main pressure boundary at the surface, these flanges must match the well pressure, bore, material class and service condition.
In wellhead applications, these connections appear on casing head outlets, tubing head adapters, wellhead valves, test outlets, production outlets and adapter spools. Therefore, flange selection must follow the project specification carefully.
Christmas Tree Assemblies
Christmas trees use API 6A flanges between master valves, wing valves, swab valves, crosses, tees, chokes and adapters. These connections control oil and gas flow after well completion.
For Christmas tree service, verify working pressure, bore size, valve connection type, RTJ gasket, material class, PSL, temperature class and sour service condition. Therefore, a correct flange connection helps the Christmas tree maintain stable production control.
Choke Manifolds
Choke manifolds control flow and pressure during drilling, well testing, flowback and production operations. In these systems, API 6A flanges may connect choke valves, gate valves, crosses, tees, outlets and adapter components.
Because choke manifold service can involve high-pressure flow, vibration, pressure changes and abrasive fluids, flange quality, gasket fit and bolting accuracy matter a lot. In some projects, a Target Flange or Custom Machined API 6A Flange may help address a special flow path, erosion area or connection interface.
Kill Manifolds
Kill manifolds help pump fluid into the well during pressure control operations. Since these systems support well control procedures, they need reliable high-pressure connections.
For kill manifold flange connections, review pressure rating, bore size, valve connection, working fluid, test requirement and field installation layout. Otherwise, a connection mismatch can delay rig operations.
Drilling Spools and Adapter Spools
Drilling spools and adapter spools often use API 6A flanges to connect wellheads, BOP stacks, valves and pressure control equipment. Because these products may need different flange sizes or pressure ratings on each end, drawings are often required for approval.
When buying spools with API 6A flanges, check top flange size and pressure, bottom flange size and pressure, bore size, overall length, side outlet details, ring gasket type, material, PSL and NACE requirement. Before production, confirm the connection data carefully.
Workover Equipment
Workover operations use API 6A flanges on pressure control equipment, temporary wellhead connections, test adapters and service valves. Since workover sites often need fast installation, reliable sealing and correct connection matching, accurate flange data is important.
For workover service, check the existing wellhead connection, equipment interface, pressure test requirement, handling space and delivery schedule. With accurate flange data, the workover team can reduce downtime and complete pressure testing faster.
Well Testing Equipment
Well testing packages may use API 6A Test Flanges, API 6A Adapter Flanges and RTJ flanges on flow control equipment, test manifolds, choke valves, separator inlet connections and temporary production lines. Therefore, the flange must handle expected well pressure and test flow conditions.
For well testing service, define test pressure, flow medium, sand content, temperature range, connection orientation and service duration. Because well testing conditions can change quickly, a reliable flange connection helps keep the package stable.
High-Pressure Oilfield Flowline Connections
High-pressure oilfield flowlines may use API 6A Weld Neck Flanges, API 6A Companion Flanges, adapter flanges and RTJ flanges at connection points between valves, manifolds, adapters and wellhead equipment. In addition, flowline service can involve crude oil, gas, drilling fluid, produced water or mixed petroleum fluids.
For oilfield flowline flange selection, review pressure rating, flow direction, bore, material, corrosion condition, erosion risk and RTJ gasket type.
Offshore Petroleum Platforms
Offshore oil and gas platforms often use API 6A flanges on wellhead and production control equipment. Because replacement at sea costs more, offshore projects usually need stricter documentation, coating, packing and inspection.
For offshore petroleum service, the order may require complete MTR, NDE reports, coating records, NACE compliance, third-party inspection, seaworthy packing, clear marking and traceability. Because of this, offshore API 6A flange orders should include full documentation requirements from the beginning.
How to Select the Right API 6A Flange
A practical selection process helps avoid costly mistakes. Before ordering, follow these steps.
| Step | What to Check | Why It Matters |
| 1 | Equipment type | Defines the connection purpose |
| 2 | Size and pressure rating | Sets the basic flange requirement |
| 3 | 6B, 6BX or other flange type | Prevents interface mismatch |
| 4 | Bore size | Confirms flow path and equipment compatibility |
| 5 | RTJ gasket type and number | Prevents sealing problems |
| 6 | Material class and service condition | Supports sweet or sour service selection |
| 7 | PSL and inspection scope | Matches project approval requirements |
| 8 | Documents and packing | Supports delivery, inspection and installation |
| 9 | Special features | Covers test port, instrument port, lifting feature or target area |
| 10 | Custom machining requirement | Confirms non-standard dimensions before production |
Step 1: Identify the Equipment
Start with the equipment. First, identify whether the flange will connect to a wellhead, Christmas tree, choke manifold, kill manifold, spool, valve, workover package or well testing system.
Step 2: Check Size, Pressure and Flange Type
Next, check size and pressure rating. These two points create the basic selection, but they do not complete it. After that, define the flange type. The project may require an API 6A Type 6B Flange, API 6A Type 6BX Flange, API 6A Blind Flange, API 6A Weld Neck Flange, API 6A Threaded Flange, API 6A Test Flange, API 6A Companion Flange, API 6A Adapter Flange, DSA Flange or custom machined flange.
Step 3: Verify Sealing and Working Conditions
Then, verify the sealing system. The RTJ gasket type, ring gasket number and groove requirement must fit the mating equipment. In addition, evaluate the working condition. Sweet oil, sour gas, drilling fluid, produced water, abrasive flow and mixed petroleum fluids may require different material and inspection controls.
Step 4: Review Documents, Delivery and Packing
Finally, check material, documents, delivery and packing. As a pressure-related oilfield component, an API 6A flange needs material traceability, inspection records, ring groove protection, rust prevention, thread protection and strong export packing.
Common Mistakes When Buying API 6A Flanges
Oilfield buyers can avoid many problems by improving inquiry details.
| Common Mistake | Possible Result | Better Practice |
| Only sending size and pressure | Wrong flange type or gasket | Add 6B/6BX type, bore and ring gasket |
| Ignoring mating equipment | Bolt pattern or bore mismatch | Send drawing, nameplate and photos |
| Mixing 6B and 6BX | Site installation failure | Verify connection type before order |
| Forgetting sour service | Material or hardness issue | Share H2S, CO2 and NACE requirement |
| Missing special features | Wrong test port, lifting point or instrument port | Send drawing and installation need |
| Buying without documents | Project inspection delay | Request MTR, COC and inspection reports |
Only Sending Size and Pressure
An inquiry such as “API 6A flange 4-1/16 inch 5000 psi” does not give enough information. Therefore, the supplier still needs flange type, bore, gasket, material class and service condition.
Ignoring the Mating Equipment
A flange must fit the equipment it connects to. Before ordering, check the valve, spool, wellhead outlet or manifold connection.
Mixing 6B and 6BX Connections
6B and 6BX flanges do not automatically match. As a result, buyers should verify the exact connection type from the drawing, nameplate or previous purchase record.
Forgetting Sour Service
If the well contains H2S, the flange may require NACE MR0175 / ISO 15156 compliance. Consequently, this requirement affects material, heat treatment, hardness and documentation.
Ignoring Custom Features
A test flange, instrument flange, lifting flange or target flange may need more details than a standard API 6A flange. Therefore, share the instrument port, lifting point, test port, target area, flow direction or custom machining drawing when the project requires it.
Buying Without Traceable Documents
Low-cost flanges without proper documents may fail project inspection. For oilfield service, request material reports, dimensional reports and compliance documents when the project requires them.
Documents for API 6A Flanges
Oilfield projects often require a complete documentation package. These documents help buyers pass end user review, third-party inspection and final acceptance.
| Document | Why Buyers Need It |
| Certificate of conformity | Confirms product supply scope and compliance |
| Material test report | Shows chemical and mechanical properties |
| Heat treatment report | Confirms heat treatment process |
| Hardness test report | Supports material and NACE review |
| Dimensional inspection report | Confirms final machined dimensions |
| Ring groove inspection record | Helps verify RTJ sealing area |
| NDE report when required | Supports surface or internal defect inspection |
| Hydrostatic test report when applicable | Confirms pressure test result |
| NACE compliance statement when required | Supports sour service approval |
| Final inspection report | Summarizes final QC result |
| Packing list and photos | Supports shipment and receiving inspection |
For tender projects, confirm the document list before placing the order. This step helps avoid missing certificates after production.
API 6A Flange Marking and Traceability
Marking helps field crews and inspectors identify the flange. A clear marking system may include size, pressure rating, material, heat number, manufacturer information, flange type and standard reference.
Traceability also matters. Each flange should connect back to its forging record, material test report and inspection record. Consequently, the buyer can answer end user questions and pass inspection faster.
Before shipment, request photos of flange marking, ring groove condition, flange face protection, stud hole condition, thread protection for studded products, packing details and label information. In this way, both sides can reduce delivery disputes and site confusion.
API 6A Flanges for Sour Oil and Gas Service
Sour service requires careful material control. In oil and gas wells, H2S can create sulfide stress cracking risk if the material does not meet the service requirement. Therefore, sour service API 6A flanges need suitable material, controlled heat treatment, hardness control and complete documentation.
| Sour Service Data | Why It Helps Selection |
| H2S content | Determines sour service risk |
| CO2 content | Helps evaluate corrosion condition |
| Chloride content | Supports corrosion review |
| Operating pressure | Affects pressure-containing design |
| Operating temperature | Affects material and temperature class |
| Fluid type | Defines oil, gas, water or mixed service |
| Material class | Guides material selection |
| Hardness limit | Supports NACE-related review |
| End user specification | Defines final acceptance standard |
With these details, the supplier can review the working condition and recommend a suitable material and manufacturing route.
API 6A Flange Inquiry Checklist
To receive a faster and more accurate quotation, include the following information in the RFQ:
| Required Information | Example |
| Product type | 6B flange, 6BX flange, blind flange, test flange, companion flange, DSA flange |
| Nominal size | 2-1/16 inch, 3-1/8 inch, 4-1/16 inch |
| Pressure rating | 5000 psi, 10000 psi, 15000 psi |
| Bore size | Full bore or specified bore |
| RTJ ring gasket | R, RX or BX type with ring number |
| Material class | AA, BB, CC, DD, EE or FF |
| PSL | PSL 1, PSL 2, PSL 3 if required |
| Temperature class | As per project requirement |
| Service condition | Sweet oil, sour gas, drilling fluid, produced fluid |
| NACE requirement | Required or not required |
| Special feature | Test port, instrument port, lifting feature or target area |
| Quantity | Number of pieces |
| Drawing | Available or not available |
| Documents | MTR, COC, NDE, dimensional report |
| Inspection | Buyer inspection or third-party inspection |
| Delivery requirement | Required delivery date and destination |
A complete inquiry helps the supplier quote faster and reduce technical clarification before production. In addition, it helps the engineering team confirm material, gasket, drawing and document requirements before manufacturing starts.
When sending an inquiry to SGPE, please include the flange type, pressure rating, size, bore, RTJ ring gasket, material class, service condition, quantity, drawing and required documents. If the drawing is not available, photos and key dimensions can also help with preliminary confirmation.
Why Choose SGPE for API 6A Flanges?
Technical Review Capability
SGPE can help check flange type, bore, RTJ ring gasket, bolt pattern, material class, PSL, NACE requirement and mating equipment details before production. This technical review is especially important for replacement orders, urgent wellsite demand, custom machined flanges and end user approval projects.
Standard and Custom Flange Support
SGPE can support API 6A wellhead flange supply, API 6A Type 6B flange supply, API 6A Type 6BX flange supply, API 6A Weld Neck Flange, API 6A Blind Flange, API 6A Threaded Flange, API 6A Test Flange, API 6A Companion Flange, API 6A Adapter Flange and Double Studded Adapter Flange / DSA Flange requirements.
In addition, project-specific requirements may involve RTJ ring groove machining, Target Flange review, Instrument Flange machining, Lifting Flange features and Custom Machined API 6A Flange solutions.
Documentation and Export Support
For petroleum projects, communication also matters. SGPE can support forged material traceability, NACE sour service document review, dimensional inspection, NDE coordination when required, export packing and technical document preparation. As a result, the buyer can reduce approval delays and installation risk.
FAQ About API 6A Flanges
1. What is an API 6A flange?
An API 6A flange is a high-pressure oilfield flange connection for wellhead and Christmas tree equipment. In practice, it connects casing heads, tubing heads, gate valves, choke valves, adapter spools, drilling spools, choke manifolds and other petroleum pressure control equipment.
In most oilfield systems, this flange works with an RTJ ring gasket, studs and nuts to create a strong metal-to-metal sealing connection. Therefore, the specification should include flange type, bore, ring gasket, material class, PSL, temperature class and sour service requirement.
2. What API 6A flange types are commonly used in oilfield equipment?
Common types include API 6A Type 6B Flange, API 6A Type 6BX Flange, API 6A Weld Neck Flange, API 6A Blind Flange, API 6A Threaded Flange, API 6A Test Flange, API 6A Companion Flange, API 6A Adapter Flange and Double Studded Adapter Flange / DSA Flange.
In addition, some projects need Target Flange, Instrument Flange, Lifting Flange or Custom Machined API 6A Flange solutions. Because these custom names can mean different things, they usually require a drawing, service description and mating equipment information before quotation.
3. Where are API 6A flanges used in oilfield equipment?
These flanges serve upstream oil and gas operations, especially wellhead systems, Christmas trees, choke manifolds, kill manifolds, drilling spools, adapter spools, workover equipment, well testing packages and high-pressure petroleum flow control systems.
For example, a wellhead assembly may use API 6A wellhead flanges to connect casing heads, tubing heads and valves. Meanwhile, a choke manifold may use API 6A RTJ flanges to connect choke valves, crosses, tees and outlets.
4. What is the difference between API 6A Type 6B Flange and API 6A Type 6BX Flange?
API 6A Type 6B Flange and API 6A Type 6BX Flange use different connection designs. A 6B flange often appears in standard wellhead, production tree and manifold connections. However, a 6BX flange usually appears in higher-pressure oilfield systems and uses a different RTJ gasket and bolting arrangement.
Before ordering 6B or 6BX flanges, check the mating equipment, pressure rating, bore size, bolt pattern, ring gasket type and ring gasket number. As a result, the buyer can avoid field mismatch during installation or pressure testing.
5. Are API 6A flanges the same as ASME flanges?
No. API 6A flanges and ASME flanges serve different connection systems. Generally, API 6A flanges suit oilfield wellhead, Christmas tree and high-pressure petroleum pressure control equipment, while ASME flanges usually serve general piping systems.
Although both products may look similar, their dimensions, pressure ratings, sealing designs and application standards can differ. Therefore, do not replace an API 6A wellhead flange with an ASME flange unless the project drawing and engineering team clearly approve the connection.
6. What pressure ratings are common for API 6A flanges?
Common pressure ratings include 2000 psi, 3000 psi, 5000 psi, 10000 psi, 15000 psi and 20000 psi. In replacement and project supply, oilfield buyers often search for API 6A 5000 psi flange, API 6A 10000 psi flange, API 6A 15000 psi flange and high-pressure wellhead flange.
The correct pressure rating depends on the wellhead system, working pressure, test pressure and end user specification. However, a higher-rated flange does not automatically make the system safe if the mating valve, spool, gasket, studs or nuts have a lower rating.
7. What sizes are common for API 6A wellhead flanges?
Common API 6A flange sizes include 1-13/16 inch, 2-1/16 inch, 2-9/16 inch, 3-1/8 inch, 4-1/16 inch, 5-1/8 inch, 7-1/16 inch, 9 inch, 11 inch, 13-5/8 inch, 16-3/4 inch, 18-3/4 inch, 20-3/4 inch and 21-1/4 inch.
However, size alone cannot identify the correct API 6A flange. For accurate selection, provide flange size, pressure rating, flange type, bore and ring gasket information together.
8. What RTJ gasket should I use for API 6A flanges?
Most API 6A flanges use an RTJ ring gasket sealing system. Common oilfield ring gasket types include R, RX and BX. Therefore, the correct gasket depends on flange type, pressure rating, ring groove design and mating equipment.
For example, an API 6A Type 6B flange may require a different ring gasket from an API 6A Type 6BX flange. Because of this, the RFQ should include RTJ gasket type, ring gasket number, gasket material and sour service requirement. Many buyers also purchase API 6A flanges with matching ring gaskets, studs and nuts to reduce installation risk.
9. Can API 6A flanges work in sour oil and gas service?
Yes. These flanges can work in sour oil and gas service when the material, heat treatment, hardness control and documents meet the required sour service conditions. In many oilfield projects, NACE MR0175 / ISO 15156 compliance is required when H2S exists in the well fluid.
For sour service API 6A flanges, share H2S content, CO2 content, chloride content, operating pressure, operating temperature, fluid type, material class and hardness requirement. With these details, the supplier can select suitable forged material and prepare proper documents for project approval.
10. What information should I provide for an API 6A flange inquiry?
A clear API 6A flange inquiry helps the supplier quote faster and avoid wrong assumptions. The RFQ should include product type, nominal size, pressure rating, 6B or 6BX flange type, bore size, RTJ gasket type, ring gasket number, material class, PSL, temperature class, service condition, NACE requirement and quantity.
For replacement orders, also send the mating equipment drawing, old flange photos, nameplate information, bolt hole quantity, bolt size, bolt circle diameter and required documents. In addition, if the project needs a test flange, instrument flange, lifting flange, target flange or custom machined flange, include the special feature and drawing.
11. What documents are usually required for API 6A flanges?
Common documents for API 6A flanges include certificate of conformity, material test report, heat treatment report, hardness report, dimensional inspection report, ring groove inspection record, NDE report when required, hydrostatic test report when applicable, NACE compliance statement and final inspection report.
For tender projects, confirm the document list before placing the order. This step helps avoid missing certificates after production. Moreover, it helps the end user, third-party inspector and project team review the API 6A flange package more smoothly.
12. How can I choose a reliable API 6A flange supplier?
A reliable supplier should understand oilfield wellhead equipment, pressure control systems and real field connection problems. Therefore, the supplier should review flange type, bore, RTJ gasket, material class, PSL, NACE requirement, documents and mating equipment details before production.
When sourcing API 6A flanges, choose a supplier that can support standard and custom oilfield flange requirements, including 6B, 6BX, weld neck, blind, threaded, test, companion, adapter, DSA, RTJ and custom machined flange solutions. SGPE can support these requirements with technical confirmation, document coordination and export supply support.
Conclusion
API 6A flanges are essential components in oilfield wellhead, Christmas tree, choke manifold, kill manifold, workover, well testing and high-pressure petroleum flow control systems. Although they may look simple, they directly affect pressure integrity, field installation, equipment compatibility and project safety.
To select the right API 6A flange, define more than size and pressure rating. Instead, review flange type, 6B or 6BX connection, bore, RTJ ring gasket, material class, PSL, temperature class, sour service condition, NACE requirement, special machining needs and inspection documents.
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