1. Product Overview – What is a Metallurgical Bonded Seamless Clad Pipe?
A metallurgical bonded seamless clad pipe (also known as a bimetal seamless clad tube or CRA lined seamless pipe) is a high-performance composite tube manufactured by permanently joining a corrosion resistant alloy (CRA) inner layer to a high strength / high temperature resistant carbon or alloy steel outer layer through a metallurgical bonding process. Unlike mechanically lined pipe, the two layers form an atomic-scale diffusion zone at the interface – completely eliminating risks of liner collapse, blistering, wrinkling, or delamination under thermal cycling or pressure pulsation.
The three clad pipe combinations from the referenced inquiry represent three distinct demanding service conditions:
● Combination 1: P265GH + TP304L – Backing steel: EN10216-2 P265GH (pressure vessel / boiler grade). Inner cladding: 304L stainless steel. Suitable for medium high temperature (≤450°C) applications such as boiler tube panels, heat exchangers, and chemical piping where steam and mildly corrosive media are present.
● Combination 2: X10CrMoVNb9-1 + UNS N08028 – Backing steel: T91 martensitic heat resistant steel (X10CrMoVNb9-1). Inner cladding: Alloy 28 (UNS N08028, a high Mo/Cu austenitic alloy). This combination withstands temperatures up to 650°C while resisting high chloride, H₂S, and organic acid attack. It is used for superheater / reheater sections in ultra supercritical boilers and in highly corrosive petrochemical units.
● Combination 3: P265GH + UNS N08825 – Backing steel: P265GH. Inner cladding: Incoloy 825 (nickel iron chromium alloy with Mo, Cu, Ti). Incoloy 825 offers excellent resistance to both oxidizing and reducing acids, and is particularly suited for H₂S / CO₂ / high chloride sour service oil & gas flowlines, downhole tubing, and high pressure / high temperature heat exchangers.
All three products are manufactured using a seamless metallurgical bonding process, eliminating longitudinal weld seams which are the weakest points in welded clad pipes.
2. Key Technical Advantages
| Advantage | Description |
| True metallurgical bond | Interface shear strength ≥300 MPa, far exceeding API 5LD requirements. No liner wrinkling, collapse, or disbonding under thermal cycling. |
| Seamless construction | Both backing steel and CRA cladding are seamless – no longitudinal weld seam, ideal for high pressure hydrogen and sour gas service. |
| Tailored material pairing | Wide selection of backing steels (carbon steel to T91) and CRA claddings (304L to nickel alloys) matched to corrosion, temperature and pressure needs. |
| Superior economy | Expensive alloy is used only on the corrosion side; overall material cost is 30-60% lower than a solid CRA pipe of the same pressure rating. |
| Full traceability & documentation | EN 10204 Type 3.1/3.2 certificates, complete chemical, mechanical, NDT and hydrostatic test reports. |
| Proven field performance | Supplied to multiple power plants, refineries, and offshore projects worldwide. End finishing tailored for trouble free field welding. |
3. Detailed Specifications – Three Reference Combinations (Based on Actual Inquiry)
| Parameter | Combination 1 | Combination 2 | Combination 3 |
| Backing Steel (Outer) | EN10216-2 TC2 P265GH | X10CrMoVNb9-1 (T91) | EN10216-2 TC2 P265GH |
| Outer OD × WT (mm) | 63.5 × 4.88 | 60.3 × 5.18 | 63.5 × 4.71 |
| CRA Cladding (Inner) | SA-213M TP304L | UNS N08028 (Alloy 28) | UNS N08825 (Incoloy 825) |
| Inner OD × WT (mm) | 53.7 × 1.65 | 49.9 × 2.32 | 54.1 × 1.82 |
| Single Length (m) | 6 | 6 | 6 |
| Unit Weight (kg/m) | 10.32 | 10.98 | 10.30 |
| Typical Applications | Boiler low-temperature superheater, chemical heat exchanger | Ultra-supercritical boiler high-temperature section, highly corrosive petrochemical piping | Sour oil/gas pipelines, high pressure / high temperature heat exchangers |
The above dimensions are based on a real customer inquiry. Womic Steel can produce these combinations as standard or adjust dimensions and tolerances according to customer drawings.
4. Material Deep Dive
4.1 Backing Steel (Outer Layer)
EN10216-2 TC2 P265GH
● Standard: EN10216-2 (Seamless steel tubes for pressure purposes). TC2 = Test Category 2 (includes non-destructive testing).
● Chemical composition similar to: ASTM A106 Gr.B / A516 Gr.60.
● Temperature range: -10°C to 450°C (long term).
● Key properties: Good weldability, ductility, and moderate temperature strength. Widely used for boiler tubes, pressure vessels, heat exchangers.
X10CrMoVNb9-1 (T91 / P91)
● Standard: ASTM A213 T91 (seamless tube) / A335 P91 (pipe).
● Microstructure: Martensitic heat resistant steel (9%Cr, 1%Mo, V, Nb).
● Temperature range: Up to 650°C.
● Key properties: Excellent creep strength, oxidation resistance, and resistance to steam corrosion at high temperature. Preferred material for superheater and reheater tubes in ultra-supercritical boilers.
4.2 CRA Cladding (Inner Layer)
SA-213M TP304L
● Standard: ASME SA-213 (Seamless austenitic alloy steel boiler, superheater and heat exchanger tubes).
● Characteristics: Low carbon austenitic stainless steel. No sensitization after welding. Good general corrosion and oxidation resistance.
● Limitation: Not suitable for high chloride or strongly reducing acid environments. Used at temperatures ≤450°C.
UNS N08028 (Alloy 28)
● Nominal composition: 28%Cr, 31%Ni, 3.5%Mo, 1%Cu.
● Corrosion resistance: Excellent in sulfuric acid, phosphoric acid, high chlorides, and H₂S environments. PREN = 38-40.
● Applications: High chloride media, sulfuric acid service, sour gas environments.
UNS N08825 (Incoloy 825)
● Nominal composition: 42%Ni, 21%Cr, 3%Mo, 2.5%Fe, plus Cu, Ti.
● Corrosion resistance: Outstanding in both oxidizing and reducing acids. Excellent resistance to H₂S, CO₂, chlorides, sulfuric and phosphoric acids.
● Applications: Sour oil & gas well tubulars, subsea flowlines, high temperature chemical processing, heat exchangers.
5. Manufacturing Process – Seamless Metallurgical Bonding
Womic Steel supplies seamless metallurgical bonded clad pipes using the internationally proven centrifugal casting + hot extrusion + cold drawing / cold rolling route:
1. Centrifugal casting of CRA layer – The corrosion resistant alloy (e.g., 304L, Alloy 28, Incoloy 825) is first centrifugally cast to form an inner ring / tube blank.
2. Composite assembly & hot extrusion – The outer backing steel billet is assembled with the inner CRA tube, then co-extruded at high temperature and pressure. A metallurgical bond forms between the two layers by atomic interdiffusion.
3. Cold drawing / cold rolling – Multiple passes reduce diameter and wall thickness to precise final dimensions while refining grain structure and ensuring surface quality.
4. Heat treatment – Tailored heat treatment cycles (normalizing, tempering, solution annealing) applied according to the requirements of both the backing steel and CRA cladding.
5. Non-Destructive Testing (NDT) – 100% ultrasonic testing of the bond interface and full pipe body; eddy current inspection for surface defects.
6. End finishing – Bevel preparation per customer drawing. CRA buttering (strip cladding) on the bevel face available to prevent dilution and ensure corrosion resistance of the girth weld.
7. Final inspection & documentation – Dimensional check, visual inspection, hardness measurement. Full quality dossier compiled.
6. Typical Applications & Project References
✅ Power Plant Boiler Tube Panels
● Requirement: High temperature superheater / reheater sections must resist steam oxidation (requires T91) and also resist flue gas dew point corrosion (requires CRA inner layer).
● Solution: X10CrMoVNb9-1 (T91) + UNS N08028 (Alloy 28). Provides 650°C creep strength + internal corrosion protection.
● Reference: Reheater replacement in a 1000MW ultra supercritical unit in China; stable operation >3 years.
✅ Petrochemical Hydroprocessing Units
● Requirement: High pressure / high temperature service with H₂S, NH₃, Cl⁻, and other corrosive species. Standard stainless steel suffers pitting and SCC.
● Solution: P265GH + Incoloy 825 clad pipe. Backing steel provides strength; Incoloy 825 provides comprehensive corrosion resistance.
● Reference: Heat exchanger tube bundle for a desulfurization unit in a Shandong refinery. 45% cost reduction compared to solid nickel alloy tube.
✅ Sour Oil & Gas Gathering Lines
● Requirement: Onshore high H₂S / CO₂ gas field requiring sour service resistance and good low temperature toughness.
● Solution: P265GH (good low temperature toughness) + Incoloy 825 or Alloy 28 cladding.
● Reference: Gathering branch pipeline in a high sulfur block in Southwest China. Two years in service without internal corrosion failure.
7. Quality Control & Certification
| Inspection Item | Method / Standard | Scope |
| Chemical composition | OES / direct reading spectrometer | Per heat – separate analysis for backing steel and CRA cladding |
| Tensile properties | Ambient + elevated temperature (optional) | Longitudinal specimens from each layer |
| Impact toughness | Charpy V notch (-20°C or -40°C) | Backing steel |
| Interfacial shear strength | Push out test (≥300 MPa) | Minimum one sample per production batch |
| Hardness | HV / HRB / Leeb | Interface zone and backing steel |
| Ultrasonic testing | Longitudinal & shear wave (100%) | Bond integrity, laminations, internal defects |
| Eddy current / flux leakage | Full length | Surface and near surface defects |
| Hydrostatic test | 1.5× design pressure | Each tube |
| Intergranular corrosion (optional) | ASTM A262 Practice E (for 304L) | As requested |
| Grain size (optional) | ASTM E112 (for austenitic cladding) | As requested |
Quality Documentation: EN 10204 Type 3.1 (standard) or Type 3.2 (with authorized third-party witness). Third party inspection (SGS, BV, TÜV, DNV, ABS, LR) can be arranged.
8. Packaging & Shipping
● Surface protection: Anti-rust oil on exterior; inner cavity sealed with nitrogen gas.
● End protection: Plastic or steel end caps to prevent mechanical damage and ingress of debris.
● Bundling: Hexagonal or rectangular bundles with steel straps; wooden spacers between layers to avoid metal-to-metal contact.
● Moisture control: Waterproof tarpaulin + desiccant bags inside the wrapping, suitable for ocean freight.
● Marking: Each tube is clearly marked with heat number, specification, material grade, and length. Packing list and quality documents included.
● Loading ports: Shanghai, Tianjin, Qingdao (main Chinese ports). Shipment by standard container (20'/40'), flat rack, or break bulk vessel.
9. Frequently Asked Questions (FAQ)
Q1: What is the essential difference between metallurgically bonded seamless clad pipe and mechanically lined pipe?
A: In metallurgically bonded pipe, the interface forms an atomic-scale diffusion bond (shear strength ≥300 MPa). This completely eliminates liner wrinkling, collapse or separation, which are common risks for mechanically lined pipe under thermal cycling or pressure pulsation.
Q2: Why use T91 (X10CrMoVNb9-1) rather than P91 as the outer layer?
A: T91 and P91 share the same chemical composition. T91 is the designation for seamless tube (used for small-diameter boiler tubing, e.g., superheater bends), while P91 is used for large-diameter pipe. T91 is the optimal choice for making superheater and reheater U-bends.
Q3: What is the difference between UNS N08028 (Alloy 28) and UNS N08825 (Incoloy 825)?
A: Alloy 28 has higher Cr, Mo and Cu, giving superior resistance to sulfuric acid, phosphoric acid and high-chloride environments (PREN 38-40). Incoloy 825 contains more nickel, making it more resistant to reducing acids and hydrofluoric acid. It is also generally more cost-effective. For specific medium analysis, consult Womic Steel’s engineering team.
Q4: Can the P265GH + TP304L clad pipe be used for the low-temperature section of a boiler?
A: Yes. P265GH offers good intermediate temperature strength and weldability, while the 304L inner cladding resists corrosion from flue gas condensate (containing sulfurous acid). It is recommended to seal the tube ends after hydrostatic test to prevent pre service rusting.
Q5: Can you provide EN 10204 Type 3.2 certificates and third-party witnessing?
A: Yes. Womic Steel has long-standing cooperation with SGS, BV, TÜV, DNV, ABS and LR. We can arrange third-party witnessing of testing (e.g., tensile, UT) and issue Type 3.2 certificates.
Q6: What is the typical delivery time for these clad pipe combinations?
A: For first-time orders of standard combinations, delivery is typically 60-90 days (including material procurement, composite extrusion, cold finishing and testing). For already mass-produced combinations (e.g., P265GH+TP304L), lead time can be reduced to 45-60 days.
10. Contact Womic Steel – Your Clad Pipe Manufacturer
If you have requirements similar to the clad pipe inquiry shown above – or any other outer / inner material pairing – please contact Womic Steel for a technical proposal and budget price.
Website: www.womicsteel.com
E-mail: sales@womicsteel.com
Tel / WhatsApp / WeChat:
Victor: +86 15575100681
Jack: +86 18390957568
Womic Steel – Tailored 316L clad pipe solutions for CO₂ service, boiler, heat exchanger, low temperature, and high temperature applications.
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