What is Cladded Pipe? Difference Between Clad and Lined Pipe

In my 20 years of managing piping systems in offshore oil platforms and chemical processing plants, I have seen many engineers make costly mistakes when selecting corrosion-resistant piping. Choosing between a metallurgically bonded clad pipe and a mechanically bonded lined pipe is not just a matter of cost. It is a decision that impacts the structural integrity, fatigue life, and safety of your entire facility. Let me share the practical realities of these systems, how they behave under thermal cycling, and why weld overlay cladding is often the ultimate insurance policy for high-pressure, high-temperature environments.

Key Engineering Differences in Clad vs Lined Pipe Systems

To understand the fundamental difference in clad vs lined pipe, we must look at the interface between the backing material (typically carbon steel or low-alloy steel) and the Corrosion Resistant Alloy (CRA) layer. In a cladded pipe, the bond is metallurgical. This means the atoms of the backing steel and the CRA layer interdiffuse at the interface, creating a single, continuous metallic structure. This is achieved through hot rolling, explosive bonding, or weld overlay cladding.

Conversely, a mechanically lined pipe relies on a tight mechanical fit. The CRA liner is inserted inside the carbon steel outer pipe, and the assembly is expanded hydraulically or mechanically. There is no atomic bonding at the interface; the liner is held in place purely by residual compressive stresses.

Weld Overlay Cladding (CRA Overlay)

Weld overlay cladding is a process where a corrosion-resistant alloy is deposited onto the surface of a base metal via arc welding. In my project experience, we specify weld overlay for complex geometries like tees, elbows, and valve bodies where plate cladding is impossible. Common welding processes include Gas Tungsten Arc Welding (GTAW), Gas Metal Arc Welding (GMAW), and Electroslag Strip Cladding. The critical parameter here is controlling the iron dilution from the base metal into the overlay layer to maintain corrosion resistance.

Design Calculations and Stress Limitations

When designing clad piping systems under ASME B31.3, the minimum wall thickness of the base pipe is calculated using the standard pressure design formula:

Where:
P = Internal design gage pressure
D = Outside diameter of the pipe
S = Allowable stress value for the base material
E = Quality factor
W = Weld joint strength reduction factor
Y = Coefficient from Table 304.1.1

According to ASME B31.3 Chapter VIII, the structural strength of the cladding layer is typically neglected in pressure design calculations unless the metallurgical bond is fully qualified and the cladding material’s strength is explicitly included. Therefore, the cladding thickness (usually 2.0 mm to 4.0 mm) is treated as an additional corrosion allowance.

Site Inspection Protocols for Clad vs Lined Pipe Installations

During field installation, the integrity of the corrosion-resistant barrier must be protected. Any damage to the internal CRA layer can expose the carbon steel backing to aggressive process fluids, leading to rapid localized corrosion. The following checklist outlines the critical verification steps that I enforce during site inspections.

Field Case Study: Real-World Application

Direct Recommendation: Always specify metallurgically clad pipe or weld overlay for high-pressure sour gas services subject to transient pressure drops or vacuum conditions.