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.