Description
API 6A Frac Stack Manufacturer for Hydraulic Fracturing, Acidizing and Refracturing
SGPE manufactures and supplies custom API 6A frac stack systems for hydraulic fracturing, shale oil stimulation, tight oil development, acidizing, refracturing and other high-pressure oil well operations.
Available configurations include 4-1/16″, 5-1/8″ and 7-1/16″ nominal bores with working pressures of 10,000 psi or 15,000 psi. Buyers can select ball-screw manual frac valves, double-acting hydraulic frac valves or a combined operating arrangement.
During treatment, the frac stack creates a temporary full-bore pressure-control path between the frac manifold and the wellbore. Fracturing fluid and abrasive proppant pass through dedicated valves, crosses and spools rather than the permanent production tree.
This arrangement limits direct erosion exposure on permanent wellhead equipment. Upper and lower master valves also provide the isolation barriers required by the approved well-control procedure.
Each SGPE wellhead frac stack is engineered around the actual wellhead connection, minimum bore, treatment pressure, valve sequence, pumping rate, proppant concentration and fluid composition. Before manufacturing begins, the technical review also covers stack height, hydraulic controls, lifting restrictions and available wellsite space.
What Is an API 6A Frac Stack?
An API 6A frac stack, also called a frac tree, fracturing tree or frac valve stack, is a temporary high-pressure assembly installed above the wellhead during oil well stimulation.
A typical system includes upper and lower master valves, a swab valve, a frac head and a lower wellhead adapter. Depending on the pumping program, the assembly may also include a flow cross, spacer spool, crossover spool, hydraulic actuators and a hydraulic control unit.
The equipment provides a full-bore path for treatment fluid and proppant while maintaining the required well-isolation barriers. It also separates severe fracturing service from the permanent production tree.
After the final pumping stage, the field team flushes residual proppant from the bore, depressurizes the equipment and removes the temporary assembly. The production tree can then be reinstalled or reconnected.
Wellhead interfaces vary between fields and equipment manufacturers. The flange size, pressure class, ring groove, stud pattern, minimum bore and available installation height must therefore be confirmed before the final stack-up drawing is released.
API 6A Frac Stack Specifications
| Parameter | Available Configuration |
|---|---|
| Product Name | API 6A Frac Stack |
| Alternative Names | Frac Tree, Fracturing Tree, Frac Valve Stack |
| Equipment Type | High-pressure valve and spool assembly |
| Manufacturer and Supplier | SGPE |
| Applicable Requirements | Applicable API 6A requirements and approved project specifications |
| Working Pressure | 10,000 psi and 15,000 psi |
| Approximate Metric Rating | 68.9 MPa and 103.4 MPa |
| Nominal Bore | 4-1/16″, 5-1/8″ and 7-1/16″ |
| Available Operating Range | -46°C to 121°C, subject to temperature class, materials and seals |
| Fahrenheit Range | Approximately -50.8°F to 249.8°F |
| Product Specification Level | PSL 3 available; final PSL follows the purchase specification |
| Performance Validation | PR2 available when specified and applicable to the selected component design |
| Typical Main Valve Type | Full-bore slab gate frac valve |
| Manual Operator | Handwheel or ball-screw operator |
| Hydraulic Operator | Double-acting hydraulic actuator |
| Main Connections | API flanged or studded connections |
| Flow Direction | Bidirectional options according to valve design |
| Valve Arrangement | Single, dual or multiple master valve configuration |
| Control Method | Manual, hydraulic or combined |
| Primary Service | Oil well hydraulic fracturing |
| Additional Service | Acidizing, refracturing and high-pressure well stimulation |
| Sour-Service Option | Available after review of H₂S, CO₂ and operating data |
| Custom Engineering | Wellhead matching, valve arrangement and stack-height review |
| Inspection | Material, dimensional, NDE, pressure and functional inspection |
| Documentation | Drawings, certificates, test reports, manuals and manufacturing records |
| Third-Party Inspection | Available when required by the purchase order |
| Replacement Support | Complete stacks, valves, actuators, spools, gates, seats and seal kits |
All specifications require technical confirmation.
The approved quotation and manufacturing drawings define the final dimensions, minimum bore, outlet orientation, actuator data, hydraulic control pressure, materials, inspection scope and documentation package.
API 6A Frac Stack Bore Selection
Selecting the correct bore requires more than matching the nominal wellhead size. The review should also consider the maximum pumping rate, proppant concentration, connected flowline, pressure drop and required intervention access.
Customers should state the maximum outside diameter of any wireline, coiled tubing or downhole tool that must pass through the vertical bore.
| Nominal Bore | Decimal Value | Approximate Metric Equivalent | Common Selection Direction |
| 4-1/16″ | 4.0625 in | 103.2 mm | Compact configurations, conventional stimulation, acidizing and selected refracturing projects |
| 5-1/8″ | 5.125 in | 130.2 mm | Balanced flow area, overall dimensions and equipment weight |
| 7-1/16″ | 7.0625 in | 179.4 mm | High-rate pumping, large-bore wellheads and demanding shale oil projects |
These figures are direct nominal conversions. They do not replace the approved minimum bore, drift or critical dimensions shown on the manufacturing drawing.
4-1/16″ 10K and 15K Frac Stack
A 4-1/16″ frac stack provides a relatively compact option for conventional well stimulation, acidizing and selected refracturing operations.
The project review must still confirm the treatment rate, connected flowline and minimum internal diameter. A smaller valve size does not automatically suit every pumping program.
Manual and hydraulic 4-1/16″ frac valve packages are available according to the required valve sequence, control distance and expected cycling frequency.
5-1/8″ Manual or Hydraulic Frac Stack
The 5-1/8″ configuration offers a practical balance between flow capacity, stack dimensions and equipment weight.
It can use ball-screw manual master valves, hydraulic master valves or a combined arrangement. This size may suit projects that require more flow area than a compact 4-1/16″ frac tree without moving to the largest available bore.
7-1/16″ Large-Bore Frac Stack
A 7-1/16″ frac stack supports high-rate pumping and large-bore wellhead systems.
Before selecting a 7-1/16″ 15K hydraulic frac stack, the project team should review total stack weight, wellhead loading, actuator clearance, work-platform dimensions and lifting arrangements.
The frac head, master valves, spools and lower adapter must maintain a compatible flow path throughout the complete assembly.
10K and 15K Frac Stack Pressure Ratings
| Pressure Class | Rated Working Pressure | Approximate Metric Rating | Main Engineering Review |
| 10K | 10,000 psi | 68.9 MPa | Treatment pressure, anticipated wellhead pressure, test pressure and operating margin |
| 15K | 15,000 psi | 103.4 MPa | Deep-well stimulation, complete pressure envelope and wellhead compatibility |
Every pressure-containing component must carry a compatible working pressure. This includes the master valves, swab valve, frac head, flow cross, spacer spool, lower adapter, ring gaskets, bolting and connected high-pressure piping.
A lower-rated item can limit the working pressure of the complete system. The technical review therefore covers the entire pressure path rather than individual components in isolation.
A 15K frac stack is not automatically the correct choice for every high-pressure project. The final pressure class should follow the maximum anticipated wellhead pressure, treatment pressure, test pressure and required engineering margin.
Custom API 6A Frac Stack Supply Scope
SGPE is an API 6A frac stack manufacturer and supplier offering complete systems, individual frac valves, hydraulic controls, replacement equipment and spare parts.
| Supply Scope | Available Support |
| Complete Frac Stack | Engineering review, stack-up drawing, valves, spools, frac head and lower adapter |
| Manual Frac Valve Package | Ball-screw or handwheel-operated master and swab valves |
| Hydraulic Frac Stack | Double-acting hydraulic valves, hoses, control panel and optional power unit |
| Frac Head or Goat Head | Custom inlet quantity, direction, connection and pressure class |
| Flow Cross | Equal-size or unequal-size side outlets according to the approved design |
| Spacer Spool | Custom bore, pressure rating and overall height |
| Adapter or Crossover Spool | Matching between the frac stack and existing wellhead interface |
| Hydraulic Control Equipment | Local panel, remote panel, accumulator, HPU, gauges and control valves |
| Replacement Frac Tree | Matching to drawings, nameplates, measurements or used samples |
| Frac Stack Spare Parts | Gates, seats, stem packing, body seals, actuator kits and soft goods |
| Testing and Documentation | ITP, drawings, reports, certificates, manuals and manufacturing records |
Oilfield operators, frac service companies, well service contractors and equipment rental fleets can purchase a complete system or only the components required for an existing package.
Where required, the pressure-control equipment can be supplied together with compatible actuators, hydraulic controls and recommended spare parts. This coordinated supply reduces interface problems between valves, spools and control equipment.
Typical API 6A Frac Stack Components
| Component | Main Function | Common Options | Selection Data |
| Frac Head or Goat Head | Connects pumping lines to the vertical stack | Straight head, studded head, 60-degree goat head or 90-degree cross | Inlet quantity, direction, bore, pressure and connection |
| Swab Valve | Provides vertical wellbore access | Manual or hydraulic full-bore gate valve | Bore, pressure rating and intervention requirements |
| Upper Master Valve | Provides an additional isolation barrier | Ball-screw manual or hydraulic operation | Valve sequence and operating procedure |
| Lower Master Valve | Provides primary isolation above the wellhead | Manual, hydraulic or combined configuration | Well-barrier philosophy |
| Flow Cross | Provides side outlets for monitoring or circulation | Equal or unequal side outlets | Outlet size, direction and connection |
| Spacer Spool | Adjusts stack height and equipment clearance | Custom height and compatible bore | Required overall height and actuator clearance |
| Adapter Spool | Connects the stack to the existing wellhead | Same-size or crossover connection | Flange, pressure class, ring groove and bore |
| Hydraulic Actuator | Opens and closes frac valves remotely | Double-acting actuator | Control pressure, operating time and position indication |
| Hydraulic Control Unit | Supplies and controls hydraulic pressure | Local panel, remote panel, HPU and accumulator | Valve quantity, control distance and power source |
Frac Head or Goat Head
The frac head forms the upper pumping connection.
One or more side inlets connect the stack to frac iron, high-pressure flexible lines or a zipper manifold. Their quantity, direction, bore and working pressure must match the pumping layout.
Common arrangements include straight frac heads, studded heads, 90-degree crosses and 60-degree goat heads. The final choice depends on available space, line direction, connection type and required pumping capacity.
Swab Valve
The swab valve provides vertical access to the wellbore.
Depending on the operating procedure, this access may support pressure testing, well cleanout, wireline work or coiled tubing intervention.
Wireline and coiled tubing operations also require an appropriate lubricator, BOP and pressure-control package. The complete intervention system must match the approved well-control procedure.
A standard frac gate valve should remain fully open or fully closed. It should not be used as a choke or flow-regulating valve during abrasive pumping.
Upper and Lower Master Valves
The upper master valve provides an additional barrier below the swab valve or frac head. The lower master valve provides primary isolation above the permanent wellhead.
Many 10K and 15K frac trees use two master valves to support the operator’s barrier philosophy, maintenance program and emergency procedure.
Manual, hydraulic and combined configurations are available according to the required valve sequence and operating frequency.
Flow Cross, Spacer Spool and Lower Adapter
A flow cross provides side outlets for pressure monitoring, circulation, well displacement, kill-line connection or other project piping.
A spacer spool adjusts the total stack height and creates clearance for actuators, work platforms, hydraulic hoses and nearby equipment.
The lower adapter connects the temporary frac stack to the casing head, tubing head or wellhead spool. A verified drawing, equipment nameplate or dimensional report helps prevent flange, ring-groove, bore and stud-pattern mismatches.
Hydraulic Actuation and Control
Double-acting hydraulic actuators use hydraulic pressure for both opening and closing.
Actuator selection depends on valve size, control pressure, operating-time requirement, control medium and position-indication requirements.
A frac stack with hydraulic control equipment may include a power unit, accumulator, local panel, remote station, directional valves, pressure gauges, hoses and emergency controls.
Hydraulic frac stacks suit multi-stage fracturing, zipper-frac projects, multi-well pads and other operations that require frequent valve cycling or remote control.
Manual Frac Stack vs. Hydraulic Frac Stack
| Selection Factor | Manual Frac Stack | Hydraulic Frac Stack |
| Operating Method | Handwheel or ball-screw operator | Double-acting hydraulic actuator |
| Control Position | Directly at the valve | Local or remote control panel |
| Cycling Frequency | Suitable for limited cycling | Suitable for frequent cycling |
| Operating Speed | Depends on manual operation | Faster and more consistent operation |
| Personnel Access | Personnel approach the valve | Remote operation reduces close access |
| Typical Application | Conventional or lower-cycle projects | Multi-stage, zipper-frac and pad operations |
| Control Equipment | Normally not required | Hydraulic power and control equipment required |
| Position Feedback | Visual operator position | Local or remote feedback options |
| Backup Arrangement | Direct manual operation | Manual override may be available according to design |
The final choice depends on the number of treatment stages, operating distance, cycling frequency, required closing time, available hydraulic power and field safety procedure.
A 4-1/16″ 10K manual frac stack may suit a lower-cycle stimulation program. By comparison, a 7-1/16″ 15K hydraulic frac stack is more likely to serve high-rate, multi-stage or multi-well operations.
These examples are general selection directions. The actual project data must confirm the final configuration.
Main Features and Project Benefits
Full-Bore Fracturing Flow Path
A correctly selected full bore supports high pumping rates and efficient proppant transport.
The large passage can also reduce unnecessary pressure loss and localized turbulence. However, the complete flow path must remain compatible with the frac manifold, zipper manifold, high-pressure flowlines and existing wellhead bore.
High-Pressure 10K and 15K Configurations
The available 10,000 psi and 15,000 psi pressure classes cover a wide range of stimulation projects.
Before the system is approved, the pressure rating of each valve, spool, connection, ring gasket and bolting set must be verified.
Manual and Hydraulic Valve Options
Ball-screw manual operators provide a straightforward solution for projects with limited valve cycling.
Hydraulic actuators support faster operation and allow personnel to control critical valves away from the pressurized wellhead. They often suit multi-stage completions, zipper-frac programs and large well pads.
Protection for Permanent Wellhead Equipment
A dedicated wellhead frac stack directs abrasive proppant through equipment selected for stimulation service.
This temporary flow path reduces erosion exposure on the production tree and may reduce the repair work required before the well returns to production.
Replaceable Wear Components
Abrasive fluid can wear gates, seats, stems, packing and internal sealing surfaces.
A maintainable valve design allows technicians to replace critical parts during planned service. Available support can include gate-and-seat sets, stem packing, body seals, bonnet seals, actuator kits and complete soft-goods packages.
Project-Specific Configuration
Wellhead interfaces, pumping layouts and installation heights vary between projects.
The number of valves, outlet direction, spacer height, lower adapter and actuation method can be adjusted around the approved stack-up drawing.
Materials for Abrasive, Acid and Sour Service
Pressure and bore size alone do not determine material suitability.
The review also considers H₂S, CO₂, chloride concentration, acid type, treatment temperature, chemical additives, proppant exposure and expected service duration.
The final package may include project-specific body materials, trim, elastomers, corrosion-resistant cladding or wear-resistant internal components.
How an API 6A Frac Stack Works
Before installation, the field team checks the valves, spools, connections and gaskets against the approved assembly drawing.
The crew cleans the flange grooves, installs the correct ring gaskets and bolting, aligns the stack and connects the pumping and hydraulic equipment. The required pressure and functional tests are then completed.
During treatment, fluid enters through the frac head and passes through fully open valves into the wellbore. The full-bore passage carries the proppant slurry, while the pressure-containing components maintain the required well barrier.
When isolation is required, the pumping team stops or redirects the flow. The operator then closes the designated master valves in the approved sequence.
After the final treatment stage, the crew flushes the bore and removes residual sand. The system is depressurized and checked for trapped pressure before disassembly.
Before storage or transfer to another well, maintenance personnel should inspect the gates, seats, seals and other erosion-prone components.
API 6A Frac Stack Applications
| Application | Main Operating Demand | Common Configuration Direction |
| Shale Oil Multi-Stage Fracturing | Repeated high-pressure stages and frequent valve cycles | Large-bore hydraulic frac stack |
| Tight Oil Stimulation | High treatment pressure and abrasive slurry | 10K or 15K full-bore frac tree |
| Conventional Oil Well Fracturing | Temporary protection for the production wellhead | Manual, hydraulic or combined stack |
| Mature Well Refracturing | Existing wellhead matching and retrofit requirements | Custom adapter and replacement valves |
| Multi-Well Pad and Zipper Frac Operations | Frequent well switching and manifold integration | Hydraulic master valves and remote control |
| Simultaneous Fracturing Projects | Coordinated pumping and valve sequencing | Project-specific hydraulic control arrangement |
| Oil Well Acidizing and Acid Fracturing | Chemical compatibility and well isolation | Acid-compatible trim and elastomers |
| Sour-Service Stimulation | H₂S and CO₂ exposure | Project-specific sour-service materials |
| Onshore and Offshore Stimulation | Site-specific space, lifting and environmental limits | Custom stack and control arrangement |
Shale Oil and Tight Oil Fracturing
Horizontal shale oil and tight oil wells often require many high-pressure pumping stages.
A large-bore hydraulic frac stack provides the flow capacity, isolation barriers and remote operation needed during repeated proppant pumping cycles.
The technical review should cover the stage count, pumping schedule, proppant concentration, anticipated wellhead pressure and expected valve-cycling frequency.
Conventional Oil Well Fracturing
A temporary frac valve stack may be required when the permanent production tree cannot handle the treatment pressure, pumping rate or proppant concentration.
The temporary assembly provides a suitable full-bore path and protects permanent wellhead equipment throughout the stimulation program.
Mature Well Refracturing
Refracturing can reopen existing fractures or create new flow paths after production has declined.
For these projects, the installed wellhead, existing adapters, available height and previous service history should be reviewed before a replacement or retrofit frac stack is proposed.
Multi-Well Pad, Zipper Frac and Simultaneous Fracturing
Multi-well pads often connect several wells to a shared manifold. During zipper-frac operations, the pumping spread alternates between two or more wells.
Selected simultaneous fracturing programs may involve coordinated pumping and more complex valve sequencing.
Hydraulic master valves support frequent well switching and remote operation. The frac head, side inlets, valve sequence and hydraulic control package must match the manifold layout and approved operating philosophy.
Oil Well Acidizing and Acid Fracturing
Matrix acidizing removes near-wellbore damage, while acid fracturing combines reactive fluid with high pumping pressure.
Both applications require a material compatibility review. Customers should provide the acid type, concentration, additives, temperature, exposure period and maximum treatment pressure.
Sour-Service Frac Stack Applications
A sour-service frac stack requires accurate H₂S and CO₂ data.
The review should include relevant partial pressures, chloride concentration, pH, operating temperature, exposure period and applicable NACE MR0175 or ISO 15156 requirements.
Onshore and Offshore Well Stimulation
Onshore projects may involve truck-mounted pumping equipment, multi-well pads, zipper manifolds and temporary hydraulic control stations.
Offshore stimulation may require compact equipment, controlled weight, defined lifting points, enhanced preservation and detailed documentation.
The final design should reflect available space, platform layout, lifting limits, outlet direction and environmental conditions.
API 6A Frac Stack vs. Frac Tree
The terms “frac stack,” “frac tree” and “fracturing tree” often describe similar high-pressure wellhead assemblies.
A frac tree usually refers to the complete valve assembly installed above the wellhead during stimulation. A frac stack may describe the same assembly or a broader combination of valves, crosses, spacer spools and adapters.
A frac valve stack often refers more specifically to the vertically arranged master and swab valves. The term “wellhead frac stack” emphasizes the connection to the existing wellhead.
Because terminology varies between operators and regions, the component list and stack-up drawing should define the actual supply scope.
The spelling “frack stack” appears in some online searches. However, “frac stack” remains the preferred term in technical specifications and purchasing documents.
Materials and Service Conditions
| Service Condition | Information Required | Main Engineering Review |
| Standard Fracturing Service | Pressure, temperature, pumping rate, fluid and proppant data | Body material, trim, seals and wear exposure |
| Abrasive Proppant Service | Proppant type, size, concentration and total pumped volume | Gates, seats, bore and replaceable wear parts |
| Sour Service | H₂S, CO₂, partial pressures, pH, chlorides and temperature | Material class, hardness, trim, bolting and seals |
| Acidizing Service | Acid type, concentration, additives and exposure time | Wetted materials, cladding and elastomers |
| Low-Temperature Service | Minimum ambient and fluid temperature | Temperature class, body material and seals |
| Offshore Service | Salt exposure, humidity and preservation period | Coating, preservation, bolting and lifting arrangement |
| High-Cycle Hydraulic Service | Expected valve cycles and required operating time | Actuator sizing, controls, seal kits and maintenance |
For standard fracturing service, provide the working pressure, test pressure, temperature, fluid composition, proppant type, proppant size, concentration, water chemistry and chemical additives.
The number of treatment stages, total pumped volume and expected valve cycles help determine likely wear and the recommended spare-parts package.
For sour or acid service, material selection should follow complete operating data rather than a general service description.
Project-specific options may include sour-service materials, corrosion-resistant cladding, wear-resistant gates and seats, low-temperature seals, acid-resistant elastomers and special coating systems.
API 6A Frac Stack Selection Guide
1. Confirm the Pressure Class
Provide the maximum anticipated wellhead pressure, maximum pumping pressure and required test pressure.
The selected 10K or 15K pressure class must cover the treatment program with an appropriate engineering margin.
2. Select the Required Bore
Provide the maximum pumping rate, fluid density, proppant concentration and minimum required internal diameter.
Also state the outside diameter of any intervention equipment that must pass through the vertical bore.
3. Verify the Wellhead Interface
Send the existing wellhead drawing, equipment nameplate and verified connection dimensions.
Required details include the flange size, pressure class, ring groove, stud pattern, internal bore and available installation height.
4. Define the Valve Arrangement
Confirm the required number of master valves, swab valve configuration, frac head arrangement, flow-cross requirements and side outlet directions.
The well-barrier philosophy should identify the primary and secondary isolation valves.
5. Choose Manual or Hydraulic Operation
State whether the project requires ball-screw manual operators, double-acting hydraulic actuators or a combined arrangement.
For hydraulic valves, provide the control pressure, operating distance, opening and closing time and position-indication requirements.
6. Review the Pumping Program
Provide the number of treatment stages, maximum pumping rate, proppant type, maximum concentration and estimated total pumped volume.
These details support the flow-path, wear and spare-parts review.
7. Confirm the Service Environment
State the operating temperature, H₂S, CO₂, chlorides, acid data and chemical additives.
Also provide the installation location, lifting limitations, work-platform dimensions and required outlet direction.
8. Define Quality and Documentation Requirements
Identify the required PSL, performance-validation scope, material certificates, NDE reports, pressure testing, third-party inspection, drawings and manuals.
API 6A Frac Stack Price Factors
The price of an API 6A frac stack depends on the complete equipment scope rather than the product name alone.
| Price Factor | Effect on the Quotation |
| Nominal Bore | Larger bores require larger valves, bodies, flanges and actuators |
| Working Pressure | A 15K system normally requires heavier-duty components than a 10K system |
| Valve Quantity | Additional master, swab or side valves increase the supply and testing scope |
| Actuation Method | Hydraulic actuators, panels, hoses and feedback equipment add to the package |
| Frac Head Design | Inlet quantity, angle, bore and connection affect design and machining |
| Stack Height | Custom spacer and crossover dimensions affect material and manufacturing |
| Service Materials | Sour, acid and low-temperature service require additional material control |
| Trim and Cladding | Wear-resistant trim and corrosion-resistant cladding add manufacturing processes |
| PSL and PR2 Scope | Additional inspection, documentation and validation affect price and schedule |
| Hydraulic Controls | Valve quantity, control distance, accumulator and redundancy affect the scope |
| Inspection and Documents | Third-party witness points and detailed records require added work |
| Packing and Preservation | Offshore shipment or long-term storage may require enhanced protection |
SGPE does not use one fixed frac stack price because wellhead connections, valve arrangements and service conditions vary between projects.
A 7-1/16″ 15K hydraulic frac stack with remote controls and sour-service materials has a different cost structure from a 4-1/16″ 10K manual frac stack.
A complete wellhead drawing and treatment specification allow the engineering and sales teams to prepare a more accurate API 6A frac stack quotation.
Replacement and Retrofit Frac Stack Solutions
SGPE can review an existing frac tree for replacement, upgrade or retrofit.
Replacement may become necessary when the original manufacturer no longer supports the equipment, the current valve arrangement cannot meet a new pumping program or the stack requires extensive repair.
The supply can cover a complete replacement frac tree or only the affected master valve, swab valve, frac head, flow cross, spacer spool or lower adapter.
Retrofit options can include manual-to-hydraulic actuator conversion, a lower stack-height arrangement or a new local or remote control system.
For worn equipment, replacement gates, seats, seals, stem packing and actuator kits are available. Where service conditions have changed, the review can also cover sour-service materials, acid-resistant elastomers or corrosion-resistant cladding.
Existing drawings, nameplate photographs, dimensional reports, service histories and used samples can support the matching process.
These services address requirements such as replacement frac tree manufacturing, obsolete frac valve replacement, hydraulic frac stack upgrades and custom wellhead adapter supply.
Inspection, Testing and Project Documentation
| Inspection or Document | Typical Scope | Availability |
| Material Certificates | Material grade, heat number and traceability | According to purchase requirements |
| Visual Inspection | Surface condition, workmanship and marking | Available |
| Dimensional Inspection | Bore, flange, ring groove and interface dimensions | Available |
| Nondestructive Examination | UT, MT, PT or RT according to component requirements | As specified |
| Hardness Testing | Verification according to material and PSL requirements | As specified |
| Hydrostatic Body Test | Pressure integrity of pressure-containing components | Available |
| Seat Leakage Test | Valve sealing performance | Available |
| Functional Test | Manual or hydraulic opening and closing | Available |
| Actuator Test | Stroke, hydraulic integrity and operation | Available |
| Final Assembly Inspection | Stack arrangement, interfaces and marking | Available |
| Third-Party Inspection | Witness or hold points by an approved agency | Optional |
| Manufacturing Record Book | Approved manufacturing and inspection records | As required |
| Operation and Maintenance Manual | Installation, operation and maintenance guidance | Available |
The inspection program can include material identification, traceability review, dimensional checks, visual examination and the required nondestructive examinations.
When specified, the scope can also include hardness verification, hydrostatic body testing, seat leakage testing and actuator functional checks.
Before shipment, the final assembly inspection confirms the stack arrangement, main interfaces, nameplates, markings, preservation and packing.
Customers can define review, witness and hold points in the approved inspection and test plan. Independent third-party inspection can also be coordinated when required.
The document package can include the general arrangement drawing, stack-up drawing, wellhead interface drawing, sectional drawing, product data sheet and bill of materials.
Material certificates, NDE reports, dimensional records, pressure test reports, leakage test reports and actuator test records can form part of the final manufacturing file.
Depending on the contract, the project package may also include a certificate of conformity, manufacturing record book, installation instructions, operation and maintenance manual, recommended spare-parts list and preservation records.
Installation, Operation and Maintenance
Only trained personnel should install and operate high-pressure frac wellhead equipment.
Before installation, verify the working pressure, internal bore, connection type, ring groove, studs, nuts and ring gasket against the approved drawing.
Keep flange grooves and sealing surfaces clean. Damaged gaskets, bolting or sealing surfaces should not be installed.
Align the stack vertically and provide adequate structural support. External piping and frac iron should not transfer excessive bending loads to the valves or wellhead flanges.
Connect hydraulic hoses according to the approved control schematic. Confirm the actuator opening and closing ports before applying hydraulic pressure.
Complete the required pressure and functional tests before pumping begins.
During treatment, keep standard frac gate valves fully open or fully closed. Do not use a master valve as a choke or flow-regulating device.
After pumping abrasive proppant, flush the bore according to the approved procedure. Residual sand can damage gates, seats and seals during the next operating cycle.
Depressurize and isolate the equipment before inspection, maintenance or disassembly.
Maintenance intervals depend on pumping rate, proppant concentration, total treatment volume, pressure cycles, fluid chemistry and valve-cycling frequency.
Regular inspection can reduce leakage, unplanned downtime and emergency repair costs.
Available frac stack spare parts include gate-and-seat sets, stem packing, body seals, bonnet seals, seat seals, wear rings and stem bearings. Manual valve support can also include ball-screw operator components and handwheels.
Hydraulic valve support may include actuator seal kits, position indicators, hydraulic fittings and control-system components. Ring gaskets, studs, nuts, complete soft-goods kits and major repair packages are also available.
When requesting replacement parts, provide the valve model, nominal bore, pressure class, serial number, part number, drawing or existing component dimensions.
Why Choose SGPE as Your API 6A Frac Stack Manufacturer?
Project-Specific Engineering
The technical team reviews the actual wellhead interface, pumping program, service conditions and installation limits before confirming the configuration.
This process reduces connection risks and helps prevent unsuitable valves, spools or sealing materials from entering the final design.
Complete Supply Capability
SGPE supplies frac valves, frac heads, goat heads, flow crosses, spacer spools, adapters, hydraulic actuators, control equipment, gaskets, bolting and replacement parts.
Customers can purchase a complete package or only the components required for an existing system.
Existing Wellhead Matching
Drawings, nameplates, photographs, dimensional reports and used samples can support the matching of an existing casing head, tubing head or wellhead spool.
This service supports both new custom systems and replacement frac tree projects.
Manual and Hydraulic Configurations
Manual, hydraulic and combined arrangements are available according to the required valve sequence and wellsite control philosophy.
Local controls, remote controls and valve-position feedback can also form part of the project.
Testing and Documentation Support
The supply can include project drawings, material records, test reports, operating manuals and manufacturing documentation according to the approved requirements.
Independent third-party inspection can form part of the project when specified.
Replacement and Retrofit Support
The engineering team can evaluate an existing system and supply replacement frac valves, actuator packages, crossover spools, sealing components or a complete upgraded assembly.
Frequently Asked Questions About API 6A Frac Stacks
1. What is an API 6A frac stack?
An API 6A frac stack is a temporary high-pressure valve and spool assembly installed above the wellhead during hydraulic fracturing, acidizing, refracturing and other oil well stimulation operations. It is also commonly called a frac tree, fracturing tree, frac valve stack or wellhead frac stack.
During treatment, the assembly creates a full-bore pressure-control path between the frac manifold and the wellbore. Fracturing fluid and abrasive proppant pass through dedicated master valves, spools and the frac head rather than through the permanent production tree.
This arrangement helps protect permanent wellhead equipment from erosion and repeated pressure cycles. At the same time, the upper and lower master valves provide the isolation barriers required by the approved well-control and pumping procedure.
2. What components does a complete frac stack include?
A typical API 6A frac stack includes an upper master valve, lower master valve, swab valve, frac head and lower wellhead adapter. Depending on the pumping layout and available installation height, the system may also include a goat head, flow cross, spacer spool or crossover spool.
Hydraulic frac stack packages can include double-acting hydraulic actuators, control hoses, a local control panel, a remote station, an accumulator and a hydraulic power unit. Manual frac stack configurations generally use handwheel or ball-screw operators and may suit projects with fewer valve cycles.
The final component arrangement depends on the wellhead interface, working pressure, required bore, valve sequence, pumping rate and field operating procedure. A stack-up drawing should define the complete supply scope before manufacturing begins.
3. Does a frac stack replace the production wellhead?
A frac stack does not normally replace the casing head, tubing head or other permanent pressure-containing wellhead equipment. Instead, the operator removes or isolates the production tree and installs the temporary fracturing assembly on a verified wellhead connection.
During hydraulic fracturing, the temporary frac tree handles the high-pressure treatment fluid and abrasive proppant. After the final pumping stage, the equipment is flushed, depressurized and removed so that the production tree can be reinstalled or reconnected.
Before selecting an adapter or crossover spool, the supplier should verify the flange size, pressure class, ring groove, stud pattern, internal bore and available stack height. This review is especially important for mature wells, refracturing projects and existing wellheads from different manufacturers.
4. What is the difference between a frac stack and a frac tree?
The terms “frac stack” and “frac tree” are often used for the same temporary high-pressure wellhead assembly. Both terms can describe a system containing master valves, a swab valve, a frac head and the adapter used to connect the equipment to the existing wellhead.
In some specifications, “frac tree” refers mainly to the complete valve assembly above the wellhead. “Frac stack” may describe a broader package that also includes flow crosses, spacer spools, crossover spools, hydraulic actuators and control equipment.
A “frac valve stack” often refers more specifically to the vertically arranged master and swab valves. Because terminology varies between operators, service companies and regions, the component list and approved stack-up drawing should always define the actual equipment scope.
5. What API 6A frac stack bore sizes are available?
SGPE supplies API 6A frac stack configurations with 4-1/16″, 5-1/8″ and 7-1/16″ nominal bores. Each bore size can be engineered around the required pressure class, wellhead connection, pumping program and valve-operating method.
A 4-1/16″ frac stack provides a relatively compact solution for conventional well stimulation, acidizing and selected refracturing projects. A 5-1/8″ frac stack offers a balance between flow area, overall dimensions and equipment weight. A 7-1/16″ large-bore frac stack is commonly considered for high-rate pumping, shale oil stimulation and large-bore wellhead systems.
The nominal bore alone does not determine whether a configuration is suitable. The technical review should also consider the minimum drift, maximum pumping rate, proppant concentration, connected flowline and the outside diameter of any wireline, coiled tubing or intervention equipment that must pass through the stack.
6. What is the difference between a 10K and 15K frac stack?
A 10K frac stack has a rated working pressure of 10,000 psi, which is approximately 68.9 MPa. A 15K frac stack has a rated working pressure of 15,000 psi, or approximately 103.4 MPa.
The correct pressure class should be selected according to the maximum anticipated wellhead pressure, maximum treatment pressure, required test pressure and the engineering margin defined by the project. A 15K configuration is not automatically necessary for every high-pressure fracturing operation.
Every pressure-containing item in the system must have a compatible rating. This includes the master valves, swab valve, frac head, flow cross, spacer spool, lower adapter, ring gaskets, bolting and connected high-pressure piping. One lower-rated component can limit the working pressure of the complete frac stack.
7. Should I choose a manual or hydraulic frac stack?
A manual frac stack uses handwheel or ball-screw operators and may suit conventional stimulation projects with limited valve cycling and direct access to the wellhead. It can provide a straightforward solution when remote operation and rapid valve sequencing are not required.
A hydraulic frac stack uses double-acting hydraulic actuators for opening and closing the master or swab valves. Hydraulic operation supports faster and more consistent valve movement and allows personnel to control critical valves from a local or remote panel.
Hydraulic configurations are commonly selected for multi-stage fracturing, shale oil development, zipper-frac operations, simultaneous fracturing programs and multi-well pads. The final choice should consider the number of treatment stages, operating distance, expected valve cycles, required closing time, available hydraulic power and the site safety procedure.
8. Can SGPE match a frac stack to an existing wellhead?
SGPE can engineer a custom wellhead frac stack around an existing casing head, tubing head or wellhead spool. The review normally begins with the original wellhead drawing, equipment nameplate, flange details and verified field dimensions.
Important connection data includes the nominal flange size, pressure class, ring-groove type, stud pattern, internal bore and available installation height. Photographs, dimensional reports and previous equipment data sheets can support the matching process when the original drawing is unavailable.
This service is particularly useful for replacement frac tree projects, mature well refracturing, obsolete equipment replacement and manual-to-hydraulic upgrades. Where necessary, a custom adapter spool, crossover spool or reduced-height arrangement can be developed for the existing installation.
9. Where can an API 6A frac stack be used?
API 6A frac stacks are used in shale oil fracturing, tight oil stimulation, conventional oil well fracturing, mature well refracturing, acidizing and acid-fracturing operations. They can also support deep-well stimulation and selected intervention work when the complete pressure-control package is properly configured.
Large-bore hydraulic frac stacks are often used on multi-stage horizontal wells, multi-well pads and zipper-frac projects that require frequent valve cycling. Selected simultaneous fracturing operations may require additional hydraulic controls and coordinated valve sequencing between several wells.
Onshore projects may use truck-mounted pumping equipment, temporary control stations and shared manifolds. Offshore stimulation projects may require compact stack dimensions, controlled equipment weight, defined lifting points, enhanced corrosion protection and a detailed manufacturing document package.
10. Can SGPE supply sour-service or acid-service frac stacks?
Sour-service and acid-service frac stack configurations are available after the actual operating conditions have been reviewed. A general statement such as “sour service” or “acid service” is not sufficient to confirm the final material and seal selection.
For sour-service applications, the technical review should consider the H₂S and CO₂ content, relevant partial pressures, chloride concentration, pH, operating temperature and expected exposure period. The applicable NACE MR0175 or ISO 15156 requirements should also be identified in the purchase specification.
For acidizing or acid-fracturing service, customers should provide the acid type, concentration, chemical additives, temperature and expected contact time. Depending on these conditions, the equipment may require project-specific body materials, trim, elastomers, corrosion-resistant cladding or wear-resistant internal components.
11. Are PSL 3 and PR2 available for API 6A frac stacks?
PSL 3 and PR2 options are available when required by the purchase specification and supported by the selected component design. The final quality level, inspection scope and documentation package should be confirmed before the quotation and manufacturing drawings are approved.
PSL requirements affect material traceability, inspection, nondestructive examination, testing and documentation. The required scope may include material certificates, dimensional reports, NDE records, hydrostatic pressure tests, seat leakage tests and functional inspection.
PR2 applies to the relevant validated valve or component design. It does not automatically apply to every custom combination of valves, spools, adapters and controls as one complete frac stack assembly. The quotation should clearly identify which components and validation requirements are included.
12. What information is required for an API 6A frac stack quotation?
An accurate API 6A frac stack quotation requires the nominal bore, working pressure, required test pressure, maximum pumping pressure and operating temperature range. The inquiry should also include the existing wellhead drawing or nameplate, top and bottom connections, minimum bore and available installation height.
The required valve arrangement should identify the number of master valves, swab valve, frac head or goat head, flow cross, spacer spool and lower adapter. For a hydraulic frac stack, the customer should also provide the control pressure, operating distance, required opening and closing time and position-indication requirements.
Pumping information should cover the maximum treatment rate, proppant type, proppant size, maximum concentration, estimated total pumped volume and number of fracturing stages. Where acid or sour service applies, the fluid composition, acid data, H₂S, CO₂ and required material class should also be provided.
The inquiry should finally state the required PSL, PR2 or performance-validation scope, NACE requirements, inspection plan, third-party inspection, document package, quantity, requested delivery date and preferred Incoterms. Complete project data allows SGPE to prepare a more accurate 10K or 15K frac stack quotation, hydraulic control proposal and custom stack-up drawing.
Request an API 6A Frac Stack Quotation
Available options include 4-1/16″, 5-1/8″ and 7-1/16″ nominal bores with 10,000 psi or 15,000 psi working pressures. Configurations can include ball-screw manual frac valves, double-acting hydraulic valves, frac heads, goat heads, flow crosses, spacer spools, wellhead adapters, hydraulic controls and replacement parts.
For an accurate quotation, provide the required bore, working pressure, test pressure, maximum pumping pressure and operating temperature. Please also include the existing wellhead drawing or nameplate, top and bottom connections, valve arrangement and available stack height.
For hydraulic systems, state the control pressure, operating distance, required opening and closing time and position-indication requirements.
Pumping data should include the maximum rate, proppant type, concentration, estimated total pumped volume and number of treatment stages. For acid or sour service, provide the fluid composition, acid data, H₂S, CO₂ and required material class.
Please also confirm the required PSL, performance-validation scope, NACE requirements, inspection plan, documentation, quantity, delivery date and Incoterms.
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