What Is the Difference Between a Casing Head and a Tubing Head? — JLD Energy

If you're procuring wellhead equipment, one of the first questions you'll face is: what is the difference between a casing head and a tubing head? They look similar, are both mounted on top of casing strings, and both use slip-and-seal suspension mechanisms — but their functions in the wellhead stack are completely different. This article breaks down each component's role, when to use each, and what to specify when ordering.

1. What Is a Casing Head and What Does It Do?

A casing head is the lowermost component of a wellhead assembly. It sits directly on top of the surface casing string and serves two primary functions:

Seals the annulus between the surface casing and the next casing string (intermediate or production casing). This prevents formation fluids from escaping at the surface.

Supports the weight of subsequent casing strings hung inside it. The casing head houses a casing hanger that lands in the bowl profile, transferring the casing string weight to the wellhead.

The casing head also provides side outlets for accessing the casing annulus — used for cement returns during drilling, gas venting, or pressure monitoring during production.

Casing heads are rated per API 6A for the maximum anticipated surface pressure and are typically the highest-pressure-rated component in the wellhead stack.

2. What Is a Tubing Head and What Does It Do?

A tubing head is mounted above the casing head(s) and below the Christmas tree. Its job is to:

Support the tubing string via a tubing hanger that lands inside the tubing head bowl. The tubing hanger seals the tubing-to-casing annulus and carries the weight of the entire production tubing.

Provide access to the tubing-casing annulus through side outlets, which are used for gas lift injection, chemical injection, circulation, or pressure monitoring.

Adapt between the uppermost casing head flange and the Christmas tree bottom flange, often requiring adapter flanges or spools to match different sizes and pressure ratings.

Tubing heads are typically the same or slightly lower pressure rating than the casing head below, as the production tubing provides an additional pressure barrier.

3. Key Differences at a Glance

| Feature | Casing Head | Tubing Head | |---------|-------------|-------------| | Position in stack | Lowest (on surface casing) | Above casing head(s) | | Supports | Casing strings | Tubing string | | Seals | Casing-to-casing annulus | Tubing-to-casing annulus | | Outlet purpose | Cement returns, venting, monitoring | Gas lift, chemical injection, monitoring | | Hanger type | Casing hanger (slip or mandrel) | Tubing hanger (usually mandrel type) | | Typically highest pressure | Yes (bottom of stack) | No (additional barrier above) |

4. Do All Wells Need Both?

Not always. The simplest wellhead assembly — a single casing head with a tubing head adapter bolted directly on top — combines both functions in minimal space. This is common for low-pressure, shallow wells.

For multi-string wells (surface + intermediate + production casing), you need multiple casing heads stacked, with a tubing head on top. Each casing head handles one casing string.

Rule of thumb: One casing head per casing string, plus one tubing head for the production tubing. If you have 3 casing strings, expect 3 casing heads + 1 tubing head.

5. What Specifications Should You Provide When Ordering?

To get an accurate quotation, provide these details for each head:
- Size: Nominal casing size (e.g., 13-3/8 inch for surface casing head)
- Pressure rating: API working pressure class (e.g., 3,000 PSI, 5,000 PSI)
- Material class: AA through HH per API 6A
- PSL level: 1, 2, 3, or 3G
- Top and bottom connection types: Flanged (specify flange type: 6B or 6BX), studded, or threaded
- Number and size of side outlets: Typically 2 outlets, sized 2-1/16 inch or 2-9/16 inch

JLD Energy's engineering team reviews every wellhead specification to ensure all components are compatible and API 6A compliant.

Understanding the difference between casing heads and tubing heads is fundamental to specifying a safe and functional wellhead assembly. JLD Energy manufactures a complete range of both — in sizes from 7-1/16 inch to 21-1/4 inch, pressure ratings from 2,000 to 15,000 PSI, and material classes for sweet and sour service. Contact us with your well design for a compatibility-checked quotation.

Frequently Asked Questions

Can I use a casing head as a tubing head?

No. While they may look similar, casing heads and tubing heads have different bowl profiles and hanger landing shoulders designed for different hanger types. Using one as the other will result in a mismatch — the hanger will not seat or seal properly, creating a safety hazard.

What is a tubing head adapter?

A tubing head adapter (or tubing head spool) connects the uppermost casing head to the Christmas tree when a full tubing head is not needed. It provides the tubing hanger landing profile and side outlets in a compact design. Common in low-pressure or single-string completions.

What is the difference between a slip hanger and a mandrel hanger?

A slip hanger uses wedges (slips) that grip the casing/tubing to support the weight — it's field-adjustable and does not require a pre-threaded connection on the pipe. A mandrel hanger threads onto the top of the casing/tubing and lands on a shoulder in the head. Mandrel hangers provide a better seal but require the pipe to be prepared in advance.

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