Seamless Casing, API Steel Casing Pipe

There are two main types of API oil casing according to the different manufacturing methods: Seamless Casing and ERW Casing. Today we mainly discuss seamless casing.

Seamless Casing - Casing made of seamless steel pipe as raw material;

Seamless steel pipe refers to steel pipe manufactured by four methods: hot rolling, cold rolling, hot drawing and cold drawing. There is no weld on the pipe body itself.

Casing and Tubing:

Casing and Tubing play an important role in oil and gas exploration and production. The casing constitutes the well wall and is a permanent structure, while the tubing is located inside the casing, and the oil or gas is transported to the ground through the casing. Both are key components of oil or gas wells, as failure will result in huge losses. As the depth of the well increases, the requirements will be very strict. Sometimes the well must pass through the rock layer, and sometimes it is in the sea. The size, grade and number of pipes depend on the design of the well, which is based on the product, depth, pressure, volume and environment. As most of the easy exploration areas are exhausted and exploration enters difficult areas, the demand for higher grade and higher quality pipes is increasing every year.

Manufacturing process of seamless casing:

Seamless casing and connections are considered the most commonly used oilfield casing today. Seamless casing is produced by perforation using solid steel billets in a pipe plant.

The manufacturing process of seamless casing includes exposing the billet to high temperatures; using a mandrel to penetrate the billet; feeding the billet to rollers and an internal mandrel to set the shape; heat treating the tube; straightening and final sizing.

Features of seamless casing and connections:

The size and wall thickness specifications of oil well seamless casing range from 1/8 inch to 26 inch OD. It is particularly suitable for high-pressure operations, including oil and gas exploration and drilling, hydrocarbon industries and refineries, and oil and gas transportation.

The threads of seamless casing connections can be completed by the manufacturer or other companies. Ensuring uniform wall thickness of seamless casing is a challenge for manufacturers. The production process may cause the cross-section of the seamless casing wall to be slightly eccentric.

Seamless casing and connections are better than welded types:

Seamless casing and connections are better than welded types. The main advantage of seamless oil well casing is the absence of welds, which are considered weak points that can cause failure and corrosion risks. In addition, seamless casing and connections have better roundness. Finally, the possibility of weak seams is eliminated.

The only weaknesses of seamless casing and oil well connections are wall thickness differences, challenges in the production process, and higher costs. ▶ Learn more about [Seamless vs. ERW Casing: Key Differences & Selection Guide].

Seamless Casing Pipe Specifications & Sizes Chart:

This specification chart lists standard API 5CT seamless casing dimensions, from 4-1/2″ to 20″ OD. For each size and weight, the table indicates compatible API grades (e.g., J55, N80, P110) and available connection types.

* Premium connections are available on request. P - plain end, S - short round thread, B - butress, L - long round thread.

Read more: 

● Steel Grade of Casing Pipe 

● Casing pipe vs Drill pipe

● API Coupling and Threads for Casing & Tubing

● API Tubing Specification