Clad Piping Basics

CLAD PIPING BASICS:

Contents:

• Contents
• Definitions
• Introduction
• Applications
• Advantages
• Limitations
• Manufacturing methods
• Thermo-hydraulic fitting process
• Strength &corrosion resistance
• Design Issues
• Buckling pressure
• Life Cycle cost
• Fittings
• Flange
• Welding

Definitions:

• Clad Steel Pipe is bimetallic and composed of an internal Corrosion Resistant Alloy (CRA) layer, metallurgically bonded to a base metal.
• Lined Pipe has the Corrosion Resistant Alloy (CRA) layer affixed full length inside a base metal by expanding the liner and/or shrinking the pipe or by other processes.
• “Clad” is often used generally to mean both products.

Introduction:

• Base material provides the strength, toughness, formability, weldability and machinability. These are volume/ core phenomenon available at a low cost
• E.g:- A 106 B, API 5L etc.
• Cladding material chosen for its good corrosion and wear resistance, higher hardness, lesser friction, etc., which is a surface phenomenon.
• E.g:- Alloy 28, 625, 825, SS 316L, Inconel, Monel, incoloy, Alloy DSS.
• Cladding: Combination / Best of Both.

Applications:

• Ideal for sour service and other corrosive Environment
• Flowlines, manifolds, Flex joints
• Crude, Vacuum and Coker units
• Hydrotreater
• Alkylation
• Lube oil units

Advantages:

• Better Properties
• Corrosion, wear, Flow, Strength, cost, and Toughness
• Less weight due to reduction in wall thicknesses
• Better thermal conductivity as compared to solid plates
• Lower material costs through use of standard materials
• Flexibility and availability

Limitations:

• Geometry Limitation
• Minimum thickness requirement to be met for base material
• Small diameter pipes are difficult to clad
• Clad pipe length depends on inner diameter of pipe
• Thin sections cannot be clad
• Clad thickness is considered as corrosion allowance and thickness of the outer pipe is calculated from pressure and mechanical considerations
• A higher alloy rod is necessary for welding clad parts to avoid dilution and can be problematic at site
• Additional manufacturing Process and inspection required
• Dilution of base material can occur

Manufacturing Methods:

Explosion bonding

• Very short duration, high-energy impulse from an explosion to drive two surfaces of metal together.
• Explosion cleans away surface oxides and creates a metallic bond between the carbon alloy backing steel and CRA layer

Extrusion bonding

• Hot extruded from a composite billet produced in an extrusion press. hot extruded from a composite billet produced in an extrusion press

Cold/ Hot rolling bond

• Formation of the bond in hot rolled plate is dependent upon atomic diffusion between the two materials.

Welded overlays GTAW and GMAW techniques

• Access  /Welding position (down-hand or positional)
• Alloy type / Dilution Restrictions/ Economics

Seam welded from clad plates

• Plate by roll bond or explosive bond methods then formed into pipe or pipe fitting.
• Once the clad plate is produced it is formed into a tubular shell and longitudinally welded full length and are 100% radiographed.

Low dilution weld overlay

• Weld overlay is applied using both corrosion resistant overlay and erosion resistant hard-facing   

Centrifugal Casting

Thermo-Hydraulic fitting process:

Strength & Corrosion Resistance:

Design Issues:

• Thickness limitation : for weld overlay 10 mm
• Length Limitation : diameter 2”  150 mm Max.
• Implosion :  to consider
• Access for internal inspection
• Strength Contribution: FEM Analysis.
• Maximum allowed Dilution: 10 %
• Heat Input Limitation: SAW is not an option for some CRAs
• Weld Joint preparation: different

Buckling Pressure:

Life Cycle Cost:

LCC – Total life cycle cost                               AC – Initial Acquisition Cost

IC – Initial Installation Cost                          OC – Operating + Maintenance Costs

LP – Lost Production costs                             RC – Replacement Costs

SC – Residual value of materials                Σ: Desired Life

n – Year of the event;                                     N – Design Life.

i. – Real interest rate

Total Life Cycle Cost (LCC) is more important thanInitial Cost

Fittings:

• Can be produced by forming from clad pipe or clad plate using closed die forming or hot extrusion processes.
• Manual/automatic weld overlay on a standard carbon steel fitting is the most viable.
• Uniform coverage requires a minimum two passes of overlay, resulting in thickness of fitting being more than thickness of pipe. This is pre-empted by specifying inside taper on the end of fittings to ensure proper match to the pipe bevelled end.

Flange:

• To obtain a proper overlay on a flange face, the raised face of the flange shall be machined off.
• Overlay of the inside and face of the flange shall be conducted in the same way as for the fittings.
• Proper gasket seating flange finish shall be prepared by re-machining the flange face

Welding:

• Dilution of carbon steel and CRA into each other is a major problem resulting in crack formation potential and lowered corrosion resistance.
• During selection of electrodes for welding clad piping systems take into consideration base material and CRA material requirements.
• Weld deposit shall match the strength of base material and be compatible with welding onto CRA material.
• The filler material for carbon steel outer pipe can be steel weld.