API 6A Oilfield Wellhead Equipment Casing Head Foundation Component

Casing Head – API 6A Foundation Component for Wellhead Systems

The casing head is the lowermost component of a wellhead assembly. It is typically installed directly on top of the surface casing and serves as the foundation for the entire wellhead system. Throughout the drilling, cementing, and production lifecycle, the casing head performs several critical functions:

Suspending the weight of subsequent casing strings

Providing a seal between the surface casing and the next casing string

Offering side outlets for well control and annulus access

Serving as a base for mounting blowout preventers (BOPs) during drilling operations

Connecting the surface casing string to either the BOP stack or the wellhead

Our casing heads are designed and manufactured in strict accordance with API Spec 6A, ISO 10423, and GB/T 22513. For customers who require specific configurations, we offer custom manufacturing. We can also produce them to meet NACE MR0175/ISO 15156 requirements for sour service applications.

We have been manufacturing casing heads for decades. The design is proven—solid, stable, and trustworthy. Our products can be found in most oilfields and blocks across China.

Casing Head vs. Casing Spool – Understanding the Difference

In wellhead assemblies, casing heads and casing spools serve distinct purposes, though the terms are sometimes used interchangeably.

Casing Hanger Types – Mandrel vs. Slip-Style

A casing hanger is the assembly that supports the casing string when it is run into the wellhead. There are two basic designs of casing hangers: slip-type and mandrel.

Slip-Type Casing Hanger:

The slip-type hanger is the conventional and most commonly used design. It consists of slip segments that wrap around the casing and bite into the pipe wall to support the casing load. These hangers are installed around the casing after it is run into the wellbore, either before or after the casing is cemented in place.

Mandrel-Type Casing Hanger:

The mandrel-type hanger is threaded directly into the casing. It provides superior well control when landing the hanger and improves the annular seal. This type is normally used when special needs arise during well construction.

Both hanger types are designed to transfer the full weight of the casing string—tens of thousands of pounds—from the drilling rig derrick to the load shoulder in the casing head or spool.

Our casing heads are available with both slip-type and mandrel hangers, and they work interchangeably. This interchangeability is particularly valuable for troubleshooting unexpected problems in the field.

Bottom Connection Methods – Three Configurations for Versatility

Our casing heads can be connected to the surface casing using three distinct methods, allowing customers to choose the configuration that best suits their well conditions and operational preferences.

1. Bottom Slip Connection – Type WD Slip with BT Secondary Seal

This connection method uses Type WD slips to hold the surface casing in place, combined with a BT-type secondary seal structure for leak protection.

Key Characteristics:

Connect surface casing by Type WD slip

Adopt Type BT secondary seal structure

Precise measurement of casing string length is not required, which simplifies installation

Unaffected by surrounding environment or climate conditions

Easy, rapid, safe, and reliable installation

Applicable Casing Sizes: 30", 20", 13-3/8", 12-1/4", 9-5/8", 7", 5-1/2"

2. Bottom Thread Connection – Multiple Thread Types Available

This method connects the bottom of the casing head to the surface casing using various thread types. The threaded connection provides a direct, positive mechanical bond between the casing head and the casing string.

Available Thread Types: CSG, LCSG, BCSG, TM

Key Characteristics:

Convenient and rapid installation

Safe and reliable in operation

Wide range of thread options to match different casing specifications

No welding required, preserving metallurgical properties

3. Bottom Welded Connection – Direct Weld with Pressure Testing

This method involves welding the bottom of the casing head directly to the surface casing.

Key Characteristics:

Bottom of the casing head connects to surface casing by welding

A pressure test hole is provided in the welding annular space to test the welding effect

The weld can be fully inspected before the wellhead is placed into service

Ideal for permanent installations where welding is preferred

Technical Specifications – Comprehensive Configuration Options

Our casing heads are available across a wide range of configurations to suit virtually any well condition, from shallow onshore wells to deep offshore HPHT applications.

Understanding Product Specification Levels (PSL 1–4)

API 6A defines multiple product specification levels, each with increasing technical requirements-:

PSL 1: Standard quality level for general service where additional quality controls are not required.

PSL 2: Additional material chemistry and testing requirements over PSL 1.

PSL 3 / PSL 3G: More stringent material, inspection, and documentation requirements. PSL 3G includes specific gas testing requirements-.

PSL 4: The highest specification level, requiring the most rigorous testing, including 100% nondestructive examination (NDE) of all pressure-containing parts and full documentation traceability-.

Understanding Material Classes (AA through HH)

The material class defines the suitability of materials for different service environments:

Higher material classes impose stricter hardness controls, more rigorous NDE requirements, and tighter chemistry specifications to prevent sulfide stress cracking (SSC) in H₂S environments.

Understanding Performance Requirements (PR1 vs PR2)

Key Design Features – Engineering for Reliability

45° Load Shoulder Design

Our casing heads feature a straight-bore bowl with a 45° landing shoulder. This design avoids damage to sealing areas by drilling tools and prevents test plug and bowl protector wedging problems when pressure is applied. The 45° shoulder is designed to support the full weight of the casing string transmitted by the casing hanger.

Interchangeable Hanger Compatibility

The bowl design accepts both slip-type and mandrel casing hangers without modification. This flexibility simplifies inventory management and allows field personnel to adapt to changing well conditions quickly.

Side Outlet Options

Our casing heads are equipped with two side outlets. These outlets serve multiple purposes:

Dynamic liquid level measurement during production

Casing gas venting for pressure management

Hot washing and chemical injection operations

Annulus access for monitoring and intervention

Outlets are available in multiple configurations, including line pipe outlets and flanged (studded) outlets.

Secondary Sealing Capability

Casing head spools are provided with a seat for secondary sealing, which can include a secondary supplementary ring gasket that allows the maximum pressure build-off with one stage.

Installation and Field Service

Recommended Installation Procedure

Step 1 – Preparation

Verify that the casing head specifications match the well design (pressure rating, material class, PSL)

Inspect all sealing surfaces, flange faces, and threads for damage or debris

Ensure all required seals, gaskets, lockdown screws, and accessories are available

Confirm that the casing head is compatible with the surface casing size and connection method

Step 2 – Positioning and Connection

Lower the casing head onto the surface casing using the selected bottom connection method (slip, thread, or weld)

For slip connections: Install WD slips and BT secondary seal

For threaded connections: Make up threads to specified torque values using appropriate thread compound

For welded connections: Complete the weld and allow to cool before pressure testing

Verify alignment and level

Step 3 – Flange Connection

Align the top flange bolt holes with the mating flange

Install stud bolts and nuts with appropriate ring gaskets (Type R, RX, or BX depending on pressure rating)

Tighten bolts to specified torque values in a cross-pattern sequence

Step 4 –Pressure Testing

Perform hydrostatic pressure test to 1.5x rated working pressure for shell testing (minimum hold time 5 seconds)-

Perform seat/seal test to 1.1x rated working pressure

For welded connections: Use the pressure test hole to verify weld integrity

Record all test results for well records and regulatory compliance

Step 5 – Final Assembly

Install the casing hanger and run the next casing string

Install BOP stack or subsequent wellhead components

Perform final system-level pressure test

Quality Assurance – 100% Testing Before Delivery

Before any casing head leaves our manufacturing facility, it undergoes comprehensive testing in accordance with API Spec 6A requirements:

Full testing reports are provided with every shipment, including material test reports (MTRs), NDE reports, and pressure test records.

Selection Guide – How to Choose the Right Casing Head

Why Choose Sunrise for Casing Heads

As a specialized trading company with strong API-certified manufacturing partnerships, Sunrise offers:

API Spec 6A certified casing heads – Full compliance with the latest edition of API Spec 6A, including PSL 1 through PSL 4

NACE MR0175 sour service compliance – Materials selected and heat-treated per NACE MR0175/ISO 15156 for H₂S environments

Wide pressure range – 2,000 psi to 20,000 psi to suit any well condition

Flexible bottom connections – Slip (WD + BT seal), thread (CSG, LCSG, BCSG, TM), or welded connection with test port

Complete hanger options – Both slip-type and mandrel casing hangers available

Full material class coverage – From AA (general service) to HH (extreme sour service)

Two-stage and multi-stage casing heads – Available for complex casing programs with multiple intermediate and production strings

Decades of proven field experience – Our products are installed in oilfields and blocks across China

Custom manufacturing – Special sizes, thread types, or configurations available on request

Complete documentation – Mill test reports, NDE reports, pressure test records, and API compliance certification included with every shipment

Global logistics support – Export documentation, sea/air freight, and delivery to remote drilling locations worldwide

Contact Sunrise to order the right casing head for your well construction program. We provide the correct pressure rating, connection type, material class, and PSL level for your specific well conditions — with full API 6A compliance, NACE MR0175 sour service capability, and on-time delivery.