The Basics of Steel Pipe
The first methods for producing steel pipe were introduced in the early 1800s, and they have steadily evolved into the modern processes used today.
Large-diameter steel pressure pipes for water and wastewater applications are typically made with carbon steel. Steel pipe can be manufactured using three primary methods:
Seamless Steel Pipe
Hot steel is pushed through a die to create the pipe shape. Diameters of up to 20 inches (0.5 meters) can be manufactured this way. This method is expensive but the most reliable for pressurized applications.
Welded Steel Pipe
A sheet of steel is wrapped around a form and then welded at the seam. This method is less expensive but not as reliable as the seamless method for high-pressure situations.
Casting Mold Steel Pipe
Hot liquid steel is poured into a mold. This is an uncommon method but is as reliable as seamless steel pipe. The primary benefit of this type of steel pipe is its strength. These pipes don’t crack from most direct impacts and can operate under high pressure. Under abnormal loads, casting mold steel will bend, rather than break.
The Advantages and Disadvantages of Steel Pipe
Steel pipe is typically used for large-diameter water mains and has several advantages and disadvantages that owners should consider prior to installation.
- High tensile strength
- High compressive strength
- Range of corrosion protection systems available for pipeline integrity
- Wide range of diameters and wall thickness
- Welded joints give continuity
- Prone to external corrosion
- Electrolysis prone
- Jointing requires skilled welders
- Internal/external corrosion protection systems add to price
- Coatings and linings can get damaged during installation and by third parties
How Does Steel Pipe Fail?
Like every pipe material, steel pipe has specific failure modes and indicators that the pipe is nearing failure. Corrosion is the primary cause of failure for any metallic pipe material.
Pitting corrosion that weakens the pipe wall is one way that steel pipe fails. This occurs when pipeline coatings or linings are damaged leading to corrosion of the pipe wall. A failure is typically preceded by a leak on the pipeline. Regular pipeline coating surveys and evaluation of the cathodic protection system can help identify areas susceptible to corrosion before the pipe leaks or fails.
Steel pipe can also fail due to longitudinal cracking, which occurs due to thinning from general corrosion or groupings of smaller pits. An indicator that the pipe is susceptible to longitudinal failure is graphitization, groups of smaller pits and broader areas of wall loss.
Like any pipe material, steel pipe can also fail due to third-party damage during construction.
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