Cladded pipe is a steel pipe with a corrosion-resistant alloy layer metallurgically bonded to its internal or external surface. Carbon steel or low alloy steel is used as the base material. Clad pipes meet the most stringent strength and corrosion resistance requirements. The carbon steel outer pipe (backing steel or base metal) meets static strength and durability requirements, whereas the high alloyed inside pipe protects against corrosion. As more pipelines are operated under highly corrosive conditions, the use of CRA cladded pipe in the pipeline industry, particularly in offshore areas, is increasing.
Applications of cladded Pipe
An internal layer of corrosion-resistant alloy material, known as a cladding material, is economically appropriate because the thinner layer improves corrosion resistance while increasing cost. As a result, Cladded Pipe is widely used in subsea pipelines and natural gas industries for conveying sour oil and gas, saltwater pipelines, water reinjection systems, chemical industry process pipes, saltwater pipes, Water injection pipelines, Interfield pipelines, Riser pipelines, Flow-lines, power plants, and marine applications.
CRA Materials for Cladded Pipe
As cladded pipe material, a wide range of stainless steel and nonferrous alloy materials suitable for the temperature requirements can be used. In typical industrial applications, the following materials are found to be suitable for cladding.
- Duplex Stainless Steel, Stainless Steel 304, 316, 317, 410,
- Alloy Steel 254 SMO 904,
- Inconel alloy 59, Inconel alloy 625, Incoloy alloy 825
- C-276 Hastelloy,
- C-22 Hastelloy,
- Alloy 20, Monel alloy 400, AL6NX
- Zirconium
- Titanium
The cladding material must meet ASTM A265, B898, B424, B443, B619, A240, A263, A264, B622, B675, B265, B551, and other standards. The CRA layer is typically 0.25 mm to 6 mm thick.
Manufacturing of CRA Cladded Steel Pipes
There are two common pipe cladding processes for bonding the CRA cladding pipe layer to the steel pipe:
Cladding pipe metallurgical bonding:
Weld Overlay, explosion bonding, hot rolling, coextrusion, powder metallurgy, and other methods can be used to metallurgical bond the cladding. As raw materials, clad plates are used. However, the main issue with metallurgical bonding is the high costs associated with such a complex and demanding manufacturing process of metallurgical bonding the plates due to a limited number of suppliers.
Weld Overlay Method
The most common metallurgical bonding process for pipe cladding is a weld overlay. Weld Overlay is another name for cladding, weld cladding, hard facing, or weld overlay cladding. One or more metals are joined together as a layer to the surface of a base metal (backing steel) in this process. Weld overlay surfaces can even be highly customized by layering and alloying multiple different materials together.
The weld overlay process is appropriate for both small and large-diameter pipe spools, flanges, and fittings. The following are the primary advantages of weld overlay pipe cladding:
- For complex requirements, the weld overlay process can be used.
- It offers long-term corrosion resistance and high reliability in harsh environment applications.
- Weld overlay is a cost-effective method of providing excellent corrosion resistance for steel without jeopardizing design thickness.
Other Metallurgical Bonding Methods
Two dissimilar materials are bonded using the pressure and heat produced by the explosion to create a cladded pipe by explosion bonding. The clad material is placed on top of the base material, and the explosive material is then applied to it. When the explosive is ignited, the resulting thrust bonds the clad plate to the base plate beneath. Various combinations of the clad plate and base plate thickness can be bonded depending on the job requirements.
The roll bonded cladding technique is typically used for pipe sizes ranging from 16′′ to 24′′. The following are some of the benefits of Roll-bonded metallurgical bonding cladding methods:
- When compared to overlay welding, it produces a smoother surface.
- Roll-bonded clad plates are a less expensive alternative to high-alloy solid plates. The mechanical properties of the base material and the corrosion resistance of the cladding material combine to form an optimal combination.
- It has thinner wall thicknesses and better workability than solid plates.
- When compared to explosion cladding, it has more homogeneous bonding and a wider range of dimensions.
Mechanical bonding of Cladding Pipe:
Spring back variation using a Hydroforming or full-length pipe expander is used to mechanically bond the CRA pipe and the base steel pipe. Hydroforming costs more than a full-length pipe expander.
