Pipeline Corrosion Resistant Alloy Material
Tuesday, February 16, 2016
In order to prevent corrosion defects, over the past ten years there have been several manufacturing methods developed for producing Corrosion Resistant Alloy (CRA) clad/lined pipes. API (1993) has developed a specification for the CRA clad and lined pipe. CRA clad or lined pipes may be classified into two basic categories (Urband, 2001):
- Metallurgically Bonded Pipes: They are those in which there is a metallurgical bond between the structural outer pipe and the corrosion resistant inner pipe.
- Mechanically Lined Pipes: The simplest and most economical method of producing clad pipe is to internally line carbon steel pipes.
CRA steel is often used to
replace carbon steel for corrosive applications. But CRAs are normally more
expensive than carbon steel. Thus, whether or not CRAs should be useddepends
upon overall economics. But in subsea application, the very critical, high
impact components, like trees, jumpers, and manifolds, are often made of CRAs.
But pipelines, especially long pipelines, are often made of carbon steel and
continuous corrosion inhibitor injection is utilized to protect the pipeline.
Depending on alloy contents, CRA
pipe can be broken into follows:
- Stainless steel: 316L, 625 (Inconel), 825, 904L, etc.
- Chrome based alloy: 13 Cr, Duplex (22 Cr), Super Duplex (25 Cr), etc.
- Nickel based alloy : 36 Ni (Invar) for cryogenic application such as LNG (liquefied natural gas) transportation (-160oC)
- Titanium: Light weight (56% of steel), high strength (up to 200 ksi tensile), high corrosion resistance, low elastic modulus, and low thermal expansion, but high cost (~10 times of steel). Good for high fatigue areas such as riser touchdown region, stress joint, etc.
- Aluminum: Light weight (1/3 of steel), low elastic modulus (1/3 of steel), high corrosion resistance, but low strength (only up to 90 ksi tensile). Applications can include casing, air can, and risers.
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Source:
Lee, Jaeyoung. Introduction to Offshore Pipelines and Risers. 2007.
Guo, Boyun, Shanhong Song, Jacob Chacko, Ali Ghalambor. USA. 2005.
Bai, Yong and Bai, Qiang. Subsea Pipelines And Risers. USA: Elsevier Inc. 2005.
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