Split Steel Casing Pipe vs. One-Piece Steel Casing

Split steel casing and one-piece steel casing perform the same protective function. Their structural design, installation method, and typical applications differ significantly.

Selection is primarily determined by installation conditions. New pipeline projects generally use one-piece casing, while existing pipelines and rehabilitation work often require split casing. This article compares the two designs from the perspectives of structure, installation, applications, maintenance, and selection criteria.

In this article, the term carrier pipe refers to the operating pipeline installed inside the protective steel casing.

1. What Is a Split Steel Casing Pipe?

A split steel casing pipe is a steel casing manufactured in two longitudinal halves rather than as a single continuous section. After positioning around the carrier pipe, the two halves are joined by welding or mechanical fasteners to form a complete protective casing.

The split design retains the same basic function as a conventional steel casing while allowing the casing to be assembled in the field. Joint details, plate thickness, diameter, and length can be manufactured to suit project specifications.

Figure 1. Typical split steel casing assembled around an existing carrier pipe.

2. Why Was Split Steel Casing Developed?

A one-piece steel casing must be installed before the carrier pipe is fully connected or before surrounding structures restrict access. In many rehabilitation and maintenance projects, these installation conditions no longer exist.

Split steel casing was developed to solve this construction constraint. By assembling the casing around an existing pipeline, installation can be completed without removing the carrier pipe or creating a larger excavation area. Common applications include water main repairs, utility crossings, pipeline rehabilitation, and other projects where the carrier pipe remains in service.

The Term "Steel Casing" Can Refer to Different Products

The term steel casing is used across several industries and may refer to different products depending on the application.

This article focuses on protective steel casing for pipeline applications. If you are looking for API 5CT casing used in oil and gas wells, see our API 5CT Casing & Tubing page.

3. One-Piece vs Split Steel Casing Pipe: Key Differences

Engineering Tip: 

Split steel casing is not intended to replace one-piece casing in new construction. It is an engineering solution developed for projects where a continuous casing cannot be installed because of existing pipelines or restricted site conditions.

Split casing is specified only when installation constraints prevent the use of a continuous casing. If a continuous casing can be installed before the carrier pipe is placed, a one-piece casing is normally preferred.

4. How Is a Split Steel Casing Installed?

Split steel casing is assembled after the carrier pipe has been positioned.

4.1 Typical Installation Process

1)Excavate and expose the section of pipeline requiring protection.

2)Position the lower casing half beneath the carrier pipe.

3)Place the upper casing half and align both longitudinal joints.

4)Connect the casing sections by welding or mechanical fasteners in accordance with the project specification.

5)Inspect joint alignment, weld quality, and dimensional accuracy.

6)Apply corrosion protection where specified and complete backfilling.

4.2 Installation Inspection Checklist

Before the casing is placed into service or backfilled, the following items should be verified:

1)Longitudinal joint alignment

2)Weld quality or bolt tightness, as applicable

3)Casing roundness and dimensional accuracy

4)Corrosion protection or coating condition

5)Clearance between the carrier pipe and casing, where specified

6)Compliance with project drawings and construction specifications

5. Typical Applications

6. Advantages and Limitations

7. How to Choose Between One-Piece and Split Steel Casing?

Selection is generally based on installation feasibility rather than casing performance. One-piece casing is preferred where a continuous section can be installed during construction. Split casing becomes the practical solution when existing pipelines, limited access, or rehabilitation requirements prevent the use of a continuous casing.

8. Frequently Asked Questions

Q1. When should split steel casing be used?

It is typically specified for existing pipelines, rehabilitation projects, utility crossings, and locations where a continuous one-piece casing cannot be installed.

Q2. Can split steel casing be installed around an existing pipeline?

Yes. The casing is manufactured in two longitudinal sections that are assembled around the existing carrier pipe and connected by welding or mechanical fasteners.

Q3. Can split steel casing be welded or bolted?

Both welded and bolted designs are widely used. Welded joints are generally specified for permanent installations, while bolted connections are selected where future removal or inspection may be required.

Q4. Is split steel casing as strong as one-piece steel casing?

Not exactly. A one-piece steel casing has a continuous structure without longitudinal joints, while split steel casing transfers load through welded or bolted connections. Properly designed split casing provides reliable structural protection for applications where continuous installation is not possible.

Q5. Can split steel casing be used for new pipeline construction?

Generally not. New pipeline construction normally allows installation of a continuous one-piece casing before the carrier pipe is placed.