Carbon-steel line pipe with a CRA metal liner fitted by expansion or another mechanical method — mechanically lined pipe (MLP) / CRA lined pipe to API 5LD.
- Standard: API 5LD, API 5L (backing)
- Grades: 316L, Duplex 2205, Alloy 825, Alloy 625
- Certificate: EN 10204 3.1 with every order, 3.2 on request
Mechanically lined pipe (also searched as CRA lined pipe or MLP) is carbon-steel line pipe with a separately fitted corrosion-resistant alloy (CRA) metal liner. The liner is expanded or otherwise pressed into contact with the backing pipe. The bond is mechanical, not a full-area metallurgical clad bond.
This page is the buyer guide for lined / MLP line pipe ordered to API Spec 5LD. For metallurgically clad pipe (roll bond, explosion bond, weld overlay clad routes, and clad-first selection), use our CRA clad & lined pipe hub. Mejor Steel supplies both constructions through partner mills. We are the export agent: one contract, one delivery date, and the producing mill named on the quotation. Partner mills hold API Monogram licenses. Where the enquiry requires Saudi Aramco-approved manufacturers, we quote from mills on the approved list — mill name on the quote. Backing steel can include HIC/SSC testing when specified. Third-party inspection (TPI) is available; you may designate the agency.
Not the same product: API 5LD “lined pipe” means a CRA metal liner. It is not PTFE, rubber, cement-mortar or epoxy lining. Those belong to other product families.
Mejor Steel is the export agent for the mills that make your material: one contract, one delivery date, and the mill named on the quotation. How we supply
We reply within one business day, Monday to Friday 09:00-18:00 CST. Or write to info@mejorsteel.com / WhatsApp.
What Is Mechanically Lined Pipe?
| Layer | Role |
|---|---|
| Backing (carrier) pipe | Carbon or low-alloy steel — carries pressure and most mechanical loads. Under API 5LD the backing conforms to API 5L PSL2 (grades X42 through X80 and intermediates), except as modified by 5LD. |
| CRA liner | Stainless or nickel alloy facing the fluid — corrosion resistance at the wetted surface. |
| Interface | Interference / contact fit after hydraulic or mechanical expansion (or another agreed fitting method). Not a metallurgical clad bond across the full interface. |
| Pipe ends | Unless otherwise agreed: a seal weld between liner and backing; weld overlay of the ends may replace seal welding by agreement. |
Sources: API Spec 5LD, 4th Edition (March 2015), Sections 1.1, 3, 5.1, 5.2, 10.8.2, 11.3.3; Errata 1; Addendum 1 (February 2024).
Mechanically Lined vs Metallurgically Clad (Short)
| Mechanically lined (MLP) | Metallurgically clad | |
|---|---|---|
| Bond | Mechanical fit + qualified end termination | Metallurgical bond (roll / explosion / overlay / other agreed routes) |
| CRA thickness (API 5LD) | Minimum 2.5 mm (0.100 in) unless purchaser and manufacturer agree otherwise | Same minimum rule |
| Production check (API 5LD) | Gripping force liner-to-backing — method and acceptance by agreement; at MPQT and typically one pipe per 50 in production | Bond shear minimum 137.8 MPa (20,000 psi); typically one pipe per 50 |
| Liner wrinkling / collapse | Design and qualify — can govern bends, reeling, vacuum, external pressure | No separate mechanical liner to wrinkle or collapse |
| Typical buyer driver | CAPEX when the project can accept and qualify a mechanical liner | When liner slip/collapse risk or cyclic/reel duty is not acceptable |
Full clad selection, clad manufacturing routes and clad-focused RFQ notes: CRA clad & lined pipe.
Do not treat catalogue “1.0–1.5 mm liner” as API 5LD-compliant unless your purchase order explicitly agrees a thickness below 2.5 mm with the manufacturer.
When MLP Fits — and When It Does Not
Usually a strong candidate
- Onshore gathering / flowlines where corrosion needs a CRA bore and solid CRA is uneconomic
- Packages where installation strain is moderate and the end detail is qualified
- Projects that accept mechanical gripping-force testing (not clad shear) in the ITP
Use clad — or lined only with project qualification
- Reel-lay or tight cyclic bending without a proven anti-wrinkle / reel qualification
- Service with vacuum, rapid depressurization, or other loads that can collapse a thin liner
- Fatigue-critical risers or duties where the design basis rejects a mechanical interface
- Any owner spec that requires metallurgical cladding only
Industry practice (EPCI papers, manufacturer qualification programmes): MLP can be reeled and used offshore when the product and welding procedure are qualified for that strain history. If qualification is not in the bid package, do not assume “MLP = always OK for reel.”
How MLP Is Made (What Buyers Should Ask)
Typical lined route under API 5LD thinking:
- Manufacture / receive backing pipe (API 5L PSL2 route as required) and CRA liner (seamless or welded liner per agreed material specs).
- Clean, assemble, and expand the liner (hydraulic expansion is common; mechanical expansion and other agreed methods exist).
- Trim, bevel, and apply the qualified end termination (seal weld or end weld overlay by agreement).
- Test and document per the purchase order, API 5LD, and project MPS / MPQT.
Ask the mill (we put answers on the quote):
- Expansion method and how full-length contact is verified
- Liner grade, delivery condition, and minimum liner thickness
- End detail: seal weld WPS or end-overlay WPS; NDE plan
- Whether jointers are proposed (API 5LD: jointers in lined pipe are not permitted unless specifically agreed)
- Coating plan: API 5LD notes that heat from coating may affect gripping force — re-check if the pipe is coated after lining
- MPQT scope if the line will be bent, reeled, or fatigue-loaded
We do not publish unverified “% cheaper than clad” figures. Relative CAPEX is package-specific; lined is often the lower-CAPEX composite when the design allows it — confirm on the quotation.
Testing and Inspection Highlights (Lined)
Aligned with API 5LD (verify against the edition on your order):
- Gripping force between liner and backing — acceptance by agreement; demonstrated at manufacturing procedure qualification and on a production sampling basis (commonly one pipe per 50, matching the clad shear sampling logic in the same section)
- Seal welds: full-circumference visual and dye-penetrant inspection; radiography of the first 10 seal welds in a production run and one in every 20 thereafter (or automatic UT by agreement) — API 5LD 11.3.3
- Hydrostatic test of the finished product as required
- Dimension / liner thickness checks; PMI and corrosion tests when the PO requires them
- Documentation: MTCs for backing and liner, WPS/PQR for ends, NDE reports, MPQT records when applicable
Clad bond-shear 137.8 MPa applies to clad, not as a substitute number for lined gripping force.
Failure Modes Buyers Should Name in the Spec
| Risk | Why it matters | What to require |
|---|---|---|
| Liner wrinkling | Bending, reeling, or buckling strain can fold the liner | Bend/reel strain limits; qualified procedures; visual/metrology after simulated install when required |
| Liner collapse | Vacuum, rapid depressurization, annulus flooding / external pressure on a thin liner | End seal integrity; collapse checks per design code; operating procedures |
| End-seal breach → crevice | Fluid behind the liner | Seal-weld / overlay quality + NDE sampling; handling rules that protect CRA |
| Loss of grip after coating heat | Coating temperature can affect mechanical fit | Sequence control; re-verify grip if coated after lining (5LD note) |
Naming these in the RFQ is cheaper than discovering them in MPQT failure.
Materials (Starting Points — Corrosion Study Governs)
Backing (examples under API 5LD): API 5L PSL2 X42–X80 (and intermediates), with project annexes (e.g. sour / HIC) as specified.
CRA liner (commonly enquired): 316L, duplex grades, Alloy 825, Alloy 625, and other grades listed or agreed under API 5LD. Final alloy choice belongs to the project corrosion study, not to a catalogue price list.
We do not invent stock OD/wall matrices on this page. Send the size range with the RFQ; the quotation states what the named mill can run.
Quote Pack — Send This for Mechanically Lined / CRA Lined Pipe
- Construction: mechanically lined (MLP) / CRA lined (say if clad is an acceptable alternate)
- Standard: API 5LD (edition / addenda if mandated) + design code (e.g. DNV-ST-F101) if any
- Backing: grade, PSL, OD, wall, seamless or welded route, length, ends
- CRA liner: grade (UNS or LC designation) + minimum thickness (≥ 2.5 mm unless you explicitly agree thinner)
- End termination: seal weld or end weld overlay
- Service flags: H₂S/CO₂/chlorides; onshore / offshore; reel-lay or tight bends; vacuum risk; coating system and heat
- Tests: gripping-force method/acceptance; seal-weld NDE; hydro; HIC/SSC; any corrosion tests
- TPI agency (or ask us to arrange)
- Quantity, delivery place, needed documents (MTC 3.1/3.2, MPQT, ITP)
What we put on the quotation
- Named producing mill (API Monogram partner; Aramco-approved mill when the enquiry requires it)
- Lined vs clad recommendation only as a commercial/technical clarification — your design basis remains governing
- Price basis, lead time, test and TPI scope
FAQ
What is mechanically lined pipe?
Carbon-steel backing pipe with a CRA metal liner fitted by expansion or another mechanical method, ordered for pipeline service typically to API 5LD. Also called CRA lined pipe or MLP.
Is CRA lined pipe the same as polymer-lined pipe?
No. CRA lined / MLP uses a corrosion-resistant alloy liner. PTFE, rubber or epoxy linings are different products.
How thick should the CRA liner be?
API 5LD: minimum 2.5 mm (0.100 in) unless purchaser and manufacturer agree otherwise. Do not assume a thinner catalogue liner meets 5LD without a written agreement.
How are MLP ends finished?
Default under API 5LD: seal weld liner to backing. Weld overlay of the ends may replace seal welding by agreement, with the NDE rules in 11.3.3.
Can mechanically lined pipe be reeled?
Only when the project qualifies the liner and welding for the installation strain history. Without that qualification, prefer clad or change the installation method.
MLP vs clad — which should I buy?
If the design can accept a mechanical liner and CAPEX dominates, lined is often evaluated first. If liner wrinkling/collapse risk or metallurgical bonding is mandatory, start with clad pipe.
Do you supply mechanically lined and CRA lined pipe?
Yes — and clad as well — through partner mills with API Monogram. Mill named on the quote. Aramco-approved mills available when required. HIC/SSC and customer-designated TPI available.
Is third-party inspection available?
Yes. Designate the agency, or we can arrange one.
Related
Ordering to the standard: API 5LD buyer guide (purchase-order checklist, gripping-force and seal-weld inspection, hardness limits).
Request a Quote
Email or WhatsApp with the Quote Pack above. We reply within one business day (Mon–Fri 09:00–18:00 CST) with mill identity, technical clarification and commercial offer.
Contact: info@mejorsteel.com · Get a Quote
Need mechanically lined / CRA lined pipe? Send liner grade & thickness, backing grade, OD, wall, ends, reel/sour flags, quantity and destination — mill named on the quotation.
Request a QuoteMaterials
- Carbon steel backing (API 5L PSL2)
- CRA liner: stainless, duplex, nickel alloy
Typical applications
- Sour service flowlines
- Offshore flowlines (when qualified)
- CO2 / produced water lines
- Oil and gas gathering
Inspection & testing
- Seal-weld NDE (VT+PT; RT or AUT per 5LD)
- Dimensional and hydrostatic
- MTC EN 10204 3.1, 3.2 on request
| Packaging | Sea-worthy export packing. |
|---|---|
| MOQ | On request |
| Lead time | Made to order; confirmed on quotation |
Payment: T/T 30% deposit with the balance before shipment; L/C at sight also accepted. Final terms are confirmed on the quotation.
How we supply: sourced through partner mills; the producing mill is named on the quotation. How we supply sets out who is accountable for the order.
Need this product? Send the size, grade, quantity and destination port and we will reply with availability and pricing.
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