Technology / How it works

Two metals.
One seamless pipe.

UNIMETRA bonds a structural base metal and a corrosion-resistant alloy into one seamless pipe. The metals are chosen for the fluid, temperature and pressure.

The construction

Each layer has a role.

The steel base carries the structural load. A selected alloy protects the surface exposed to the fluid or environment. Both layers are seamless and joined through a metallurgical bond, creating one composite pipe.

Longitudinal pipe cutaway showing the inner surface and wall layers

The metallurgical bond

Joined at the interface.

During manufacture, elements diffuse across the boundary between the two metals. This creates a metallurgical bond: a connection along the surface where the layers meet, allowing them to work together as one pipe.

Pipe ring sample showing the inner surface and wall cross-section

The manufacturing route

From two metals
to one pipe.

Forming and heat treatment build the composite structure and bring the pipe to its finished shape.

Heat and pressure
Thermomechanical forming brings the base metal and alloy together to create the bonded structure.
Precision forming
Cold forming refines the composite pipe's size and shape.
Heat treatment
The bonded pipe is heat-treated as one structure.

Inside production

See the process.

A closer look at the equipment and forming process used to make composite pipe.

Selecting the metals

Chosen for the service.

The fluid, temperature and pressure guide the choice of metals. Stainless steels, duplex steels and nickel alloys offer different options for the exposed layer. We consider the base steel, connections and fabrication requirements together when recommending a material combination.

Explore applications

Pipe cutaway and separate sample marked S135+316L

Clad pipe technologies

Understand the difference.

How the corrosion-resistant layer joins the steel affects the way a pipe is made, formed and inspected. These are the main differences between the four methods.

Understand the difference.
Comparison Dimension	Metallurgically Clad Pipe (UNIMETRA)	Mechanical Lined Pipe	Explosion Clad	Weld Overlay
Bond Strength / Interface Criteria (API 5LD)	Shear strength API 5LD threshold ≥137.8 MPa, stable production >300 MPa; flat metallurgical fusion; no waves, no oxide inclusions	No unified shear strength threshold; physical interference fit only, no metallurgical fusion	API 5LD pipe ≥140 MPa; wavy metallurgical interface, vortices easily trap oxide inclusions	API 5LD shear threshold ≥250 MPa; dilution is the core engineering risk
Interface Nature	Solid-state metallurgical bond, flat and uniform interface, no fusion transition zone, no weld beads, no wavy vortices	Physical interference fit, base and liner independent, potential interfacial gap	Explosion impact forming, wavy corrugated interface, vortex inclusion zones	Weld deposition forming, fusion transition zone and multi-layer beads, prone to lack of fusion and slag
Base Metal Dilution	No base metal dilution; CRA corrosion-resistant layer composition stable and controllable	No fusion dilution, but risk of crevice corrosion	Composition disturbance risk at vortex locations	Significant base dilution risk; must control Fe <5% at 1mm surface, mandatory PMI point-by-point re-inspection
NDT UT Acceptance	100% phased-array UT, clear regular interface waveform; clear criteria, low acceptance disputes; no unbonded zone in last 100mm of pipe ends	UT only checks delamination/wrinkling; interface contact can only be assessed indirectly by tightness/grip force, cannot directly observe interface	UT interfered by inherent wavy echoes; defects easily confused with interface waves; pipe criteria require additional project specification	High noise from bead undulation, complex fusion line signals; high risk of missing interlayer defects; highly dependent on operator experience
Base Pipe Mechanical Properties	Base layer impact energy ≥21J, minimal toughness damage	Base pipe mechanics retained; failure from liner buckling/wrinkling	Detonation impact causes work hardening of base; high grades prone to toughness reduction; plate-rolled pipe welds need separate qualification	Multiple thermal cycles, wide HAZ, temper embrittlement risk; end overlay causes ID deformation
Crack Sensitivity	Uniform interface stress; low risk of hydrogen-induced disbonding and fatigue crack initiation	Liner slippage, end seal fatigue failure; hydrogen accumulation in gap can cause liner bulging	Stress concentration at wavy locations; vortex inclusions become hydrogen crack sources	High crack sensitivity at fusion line, HAZ, residual stress zones; sour media easily initiate and propagate along fusion line
Forming Process Performance	Flattening, cold bending, induction hot bending all possible; interface synergistic deformation, bends do not delaminate or wrinkle; elbows and tees can be stably mass-produced	Strictly prohibited for large-angle cold/hot bending; only suitable for straight pipe, fittings basically unusable	Bending requires strict control of bend radius; longitudinal weld of plate-rolled pipe is weak point, fittings very expensive	Poor cold bending performance; elbow overlay extremely expensive and long lead time, only suitable for short section repair
Dimensions & Tolerances	Seamless base pipe, OD tolerance ±0.75%, ovality ≤2%; cladding thickness uniform with tight tolerance; min cladding thickness ≥1.0mm	Liner assembly gap and liner wall thickness uniformity require additional control	Plate-rolled pipe; cladding thickness, weld misalignment and reinforcement need key control	Overlay thickness fluctuates significantly, requires grinding; heat input causes pipe end ID shrinkage
Operating Condition Boundaries	Vacuum resistance: excellent, no collapse Thermal cycling ~400°C, uniform stress on flat interface Complex fittings (bends/tees) mass-producible	Poor vacuum resistance, easy liner collapse Thermal cycling causes slippage/buckling; complex fittings basically unusable	Excellent vacuum resistance; thermal cycling constrained by wavy inclusions; fittings feasible but high cost	Excellent vacuum resistance; thermal cycling constrained by fusion dilution layer; fittings extremely expensive
Sand-Containing Multiphase Erosion Resistance	Integral metallurgical interface, media cannot penetrate interface; erosion only wears CRA surface layer	High risk, sand particles easily enter gap, crevice erosion damages end seal	Wavy grooves accumulate sand, local erosion accelerated	Erosion preferentially develops along fusion bead fusion line
Hydrogen-Induced Disbonding HIC/SSCC Resistance	Flat interface with no voids or inclusions, excellent resistance to hydrogen-induced disbonding	Physical gap at interface, hydrogen accumulation easily induces liner bulging	Vortex inclusions become hydrogen accumulation sites, elevated disbonding risk	Fusion line defects easily become hydrogen crack initiation sites
Alternating Pressure - Fatigue Performance	Continuous complete metallurgical interface, excellent fatigue performance, suitable for wellhead pulsating alternating loads	Pressure fluctuations cause liner slippage/friction, end seals prone to fatigue failure	Stress concentration at wavy locations, lower fatigue life	Fusion line is the weak band for fatigue crack initiation
End Weld Bevel	Simple bevel preparation; continuous base-cladding transition, controllable weld dilution; mature WPS, moderate welder skill threshold	Complex process, requires liner removal + nickel-based seal weld; weld heat easily burns seal, single-point seal failure risk	Longitudinal weld of plate-rolled pipe is weak line, bevel requires additional inspection	Pipe end requires internal boring 50-100mm then overlay to make bevel, strict control of weld dilution required
Production & Delivery	Continuous automated 12m long pipe mass production, high alloy utilization; significant full lifecycle cost advantage for large-volume pipelines	Fast mass production of straight pipe; fittings selection forbidden zone; low purchase price but high hidden costs from seals, spares, and downtime failures	Restricted by explosion site, safety supervision, weather; unstable scheduling; high premium for small orders	Low overlay production efficiency, expensive consumables, unsuitable for long pipeline bulk supply
Maintenance & Failure Traceability	UT quantitative defect determination, clear failure traceability; supports on-site conventional repair welding	Bulging/seal failures mostly require full section replacement, almost impossible to repair on site; early defects hard to predict	High repair difficulty; UT signal interference, failure determination prone to disputes	Complex defect sources, difficult traceability; repair requires supporting heat treatment
Applicable Scenarios	Long-distance gathering pipelines, production lines, induction bend fittings; high H₂S sour, sand-containing multiphase flow, alternating pressure overseas projects	Limited to low-pressure ambient clean single-phase straight pipe; prohibited for vacuum, sand-containing, alternating pressure conditions	Thick-wall pressure vessel plates and heads; weak cost-performance in pipeline scenarios	Local pipeline repair, short sections, local lining of pressure vessels; also possible for long pipelines.

Bond Strength / Interface Criteria (API 5LD)

Metallurgically Clad Pipe (UNIMETRA): Shear strength API 5LD threshold ≥137.8 MPa, stable production >300 MPa; flat metallurgical fusion; no waves, no oxide inclusions
Mechanical Lined Pipe: No unified shear strength threshold; physical interference fit only, no metallurgical fusion
Explosion Clad: API 5LD pipe ≥140 MPa; wavy metallurgical interface, vortices easily trap oxide inclusions
Weld Overlay: API 5LD shear threshold ≥250 MPa; dilution is the core engineering risk

Interface Nature

Metallurgically Clad Pipe (UNIMETRA): Solid-state metallurgical bond, flat and uniform interface, no fusion transition zone, no weld beads, no wavy vortices
Mechanical Lined Pipe: Physical interference fit, base and liner independent, potential interfacial gap
Explosion Clad: Explosion impact forming, wavy corrugated interface, vortex inclusion zones
Weld Overlay: Weld deposition forming, fusion transition zone and multi-layer beads, prone to lack of fusion and slag

Base Metal Dilution

Metallurgically Clad Pipe (UNIMETRA): No base metal dilution; CRA corrosion-resistant layer composition stable and controllable
Mechanical Lined Pipe: No fusion dilution, but risk of crevice corrosion
Explosion Clad: Composition disturbance risk at vortex locations
Weld Overlay: Significant base dilution risk; must control Fe <5% at 1mm surface, mandatory PMI point-by-point re-inspection

NDT UT Acceptance

Metallurgically Clad Pipe (UNIMETRA): 100% phased-array UT, clear regular interface waveform; clear criteria, low acceptance disputes; no unbonded zone in last 100mm of pipe ends
Mechanical Lined Pipe: UT only checks delamination/wrinkling; interface contact can only be assessed indirectly by tightness/grip force, cannot directly observe interface
Explosion Clad: UT interfered by inherent wavy echoes; defects easily confused with interface waves; pipe criteria require additional project specification
Weld Overlay: High noise from bead undulation, complex fusion line signals; high risk of missing interlayer defects; highly dependent on operator experience

Base Pipe Mechanical Properties

Metallurgically Clad Pipe (UNIMETRA): Base layer impact energy ≥21J, minimal toughness damage
Mechanical Lined Pipe: Base pipe mechanics retained; failure from liner buckling/wrinkling
Explosion Clad: Detonation impact causes work hardening of base; high grades prone to toughness reduction; plate-rolled pipe welds need separate qualification
Weld Overlay: Multiple thermal cycles, wide HAZ, temper embrittlement risk; end overlay causes ID deformation

Crack Sensitivity

Metallurgically Clad Pipe (UNIMETRA): Uniform interface stress; low risk of hydrogen-induced disbonding and fatigue crack initiation
Mechanical Lined Pipe: Liner slippage, end seal fatigue failure; hydrogen accumulation in gap can cause liner bulging
Explosion Clad: Stress concentration at wavy locations; vortex inclusions become hydrogen crack sources
Weld Overlay: High crack sensitivity at fusion line, HAZ, residual stress zones; sour media easily initiate and propagate along fusion line

Forming Process Performance

Metallurgically Clad Pipe (UNIMETRA): Flattening, cold bending, induction hot bending all possible; interface synergistic deformation, bends do not delaminate or wrinkle; elbows and tees can be stably mass-produced
Mechanical Lined Pipe: Strictly prohibited for large-angle cold/hot bending; only suitable for straight pipe, fittings basically unusable
Explosion Clad: Bending requires strict control of bend radius; longitudinal weld of plate-rolled pipe is weak point, fittings very expensive
Weld Overlay: Poor cold bending performance; elbow overlay extremely expensive and long lead time, only suitable for short section repair

Dimensions & Tolerances

Metallurgically Clad Pipe (UNIMETRA): Seamless base pipe, OD tolerance ±0.75%, ovality ≤2%; cladding thickness uniform with tight tolerance; min cladding thickness ≥1.0mm
Mechanical Lined Pipe: Liner assembly gap and liner wall thickness uniformity require additional control
Explosion Clad: Plate-rolled pipe; cladding thickness, weld misalignment and reinforcement need key control
Weld Overlay: Overlay thickness fluctuates significantly, requires grinding; heat input causes pipe end ID shrinkage

Operating Condition Boundaries

Metallurgically Clad Pipe (UNIMETRA): Vacuum resistance: excellent, no collapse Thermal cycling ~400°C, uniform stress on flat interface Complex fittings (bends/tees) mass-producible
Mechanical Lined Pipe: Poor vacuum resistance, easy liner collapse Thermal cycling causes slippage/buckling; complex fittings basically unusable
Explosion Clad: Excellent vacuum resistance; thermal cycling constrained by wavy inclusions; fittings feasible but high cost
Weld Overlay: Excellent vacuum resistance; thermal cycling constrained by fusion dilution layer; fittings extremely expensive

Sand-Containing Multiphase Erosion Resistance

Metallurgically Clad Pipe (UNIMETRA): Integral metallurgical interface, media cannot penetrate interface; erosion only wears CRA surface layer
Mechanical Lined Pipe: High risk, sand particles easily enter gap, crevice erosion damages end seal
Explosion Clad: Wavy grooves accumulate sand, local erosion accelerated
Weld Overlay: Erosion preferentially develops along fusion bead fusion line

Hydrogen-Induced Disbonding HIC/SSCC Resistance

Metallurgically Clad Pipe (UNIMETRA): Flat interface with no voids or inclusions, excellent resistance to hydrogen-induced disbonding
Mechanical Lined Pipe: Physical gap at interface, hydrogen accumulation easily induces liner bulging
Explosion Clad: Vortex inclusions become hydrogen accumulation sites, elevated disbonding risk
Weld Overlay: Fusion line defects easily become hydrogen crack initiation sites

Alternating Pressure - Fatigue Performance

Metallurgically Clad Pipe (UNIMETRA): Continuous complete metallurgical interface, excellent fatigue performance, suitable for wellhead pulsating alternating loads
Mechanical Lined Pipe: Pressure fluctuations cause liner slippage/friction, end seals prone to fatigue failure
Explosion Clad: Stress concentration at wavy locations, lower fatigue life
Weld Overlay: Fusion line is the weak band for fatigue crack initiation

End Weld Bevel

Metallurgically Clad Pipe (UNIMETRA): Simple bevel preparation; continuous base-cladding transition, controllable weld dilution; mature WPS, moderate welder skill threshold
Mechanical Lined Pipe: Complex process, requires liner removal + nickel-based seal weld; weld heat easily burns seal, single-point seal failure risk
Explosion Clad: Longitudinal weld of plate-rolled pipe is weak line, bevel requires additional inspection
Weld Overlay: Pipe end requires internal boring 50-100mm then overlay to make bevel, strict control of weld dilution required

Production & Delivery

Metallurgically Clad Pipe (UNIMETRA): Continuous automated 12m long pipe mass production, high alloy utilization; significant full lifecycle cost advantage for large-volume pipelines
Mechanical Lined Pipe: Fast mass production of straight pipe; fittings selection forbidden zone; low purchase price but high hidden costs from seals, spares, and downtime failures
Explosion Clad: Restricted by explosion site, safety supervision, weather; unstable scheduling; high premium for small orders
Weld Overlay: Low overlay production efficiency, expensive consumables, unsuitable for long pipeline bulk supply

Maintenance & Failure Traceability

Metallurgically Clad Pipe (UNIMETRA): UT quantitative defect determination, clear failure traceability; supports on-site conventional repair welding
Mechanical Lined Pipe: Bulging/seal failures mostly require full section replacement, almost impossible to repair on site; early defects hard to predict
Explosion Clad: High repair difficulty; UT signal interference, failure determination prone to disputes
Weld Overlay: Complex defect sources, difficult traceability; repair requires supporting heat treatment

Applicable Scenarios

Metallurgically Clad Pipe (UNIMETRA): Long-distance gathering pipelines, production lines, induction bend fittings; high H₂S sour, sand-containing multiphase flow, alternating pressure overseas projects
Mechanical Lined Pipe: Limited to low-pressure ambient clean single-phase straight pipe; prohibited for vacuum, sand-containing, alternating pressure conditions
Explosion Clad: Thick-wall pressure vessel plates and heads; weak cost-performance in pipeline scenarios
Weld Overlay: Local pipeline repair, short sections, local lining of pressure vessels; also possible for long pipelines.

Values and statements are indicative based on documented production and test data. Project-specific verification is required.

Discuss material selection

Testing & documentation