Seamless Carbon Steel Pipe

Seamless carbon steel pipe (SMLS / CS SMLS pipe) is carbon or low-alloy steel pipe made from a solid billet with no longitudinal weld seam. Buyers specify it when the design code, pressure, temperature or sour-service clause needs a continuous wall — typically under ASTM A106 / ASME SA106 for high-temperature process lines, ASTM A53 Type S for general service, API 5L seamless for gathering and transmission, ASTM A333 for low temperature, or ASTM A335 for chrome-moly alloy service. This hub covers what seamless is, how hot-finished and cold-drawn routes differ, which standard to pick, ASME B36.10 size / schedule examples (including SCH 40), and how to write an RFQ. Deep chemistry and toughness tables live on the grade pages linked from the matrix below — this page owns the seamless carbon steel pipe / SMLS hub cluster, not those grade keywords.

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.

Mejor Steel is an export trading company in Anyang, China. We place the order with partner mills, name the producing mill on the quotation, and forward the mill’s inspection documents with the shipment. We do not operate a pipe mill and we do not sign EN 10204 certificates ourselves — see How we supply. Certificates are issued by the mill and forwarded by us unaltered (EN 10204 3.1 vs 3.2; how to read an MTC).

Seamless carbon steel pipe — quick facts

The envelope below is what we quote most often for carbon and low-alloy seamless pipe. Exact chemistry, impact and NDT follow the year-dated standard named on the purchase order — not this summary table.

Dimensions reference ASME B36.10M. Full OD × wall charts: pipe size chart. Theoretical mass: weight chart and weight calculator. HS heading for seamless line / process pipe is typically 7304 — see steel pipe HS codes.

Which standard? Seamless standard matrix

Most RFQs that say only “seamless carbon steel pipe” still need a named product standard. Use this matrix to pick the right page, then deep-link for chemistry and toughness. This hub does not own the grade head terms a106 gr b, a53 gr b, api 5l gr b / x52 / x65, a333 gr 6 or a335 p11 — those live on the linked standards / product pages.

Dual or triple certification (for example A106 Gr B + A53 Type S Gr B + API 5L Gr B) is common when one heat meets the tightest overlapping limits — still write every required standard on the PO and verify the MTC grade lines. Strength minima differ slightly (API 5L Gr B yield 245 MPa vs A106/A53 Gr B 240 MPa).

How seamless pipe is made

Seamless pipe starts as a heated solid billet. A piercer opens the centre; elongators and a plug / mandrel mill or Assel / PQF / FQM stretch-reducing train set the OD and wall. The hollow is then sized, straightened, cut, heat-treated when the grade requires it, NDT-tested and hydrotested as specified. There is no longitudinal weld to radiograph — integrity depends on billet quality, piercing practice, wall control and the NDT package written into the order.

Two commercial finish routes matter on the RFQ:

• Hot-finished (hot-rolled) seamless — finished at elevated temperature; the usual route for process and line pipe in SCH 40 / 80 / heavier walls.
• Cold-drawn seamless — drawn at room temperature after a hollow is prepared; tighter OD / wall tolerance and better surface; common for precision mechanical tube and some HX sizes; usually followed by heat treatment required by the product standard.

Hot-rolled vs cold-drawn seamless

Many mill cards list both. If the project specification is silent, we quote the mill’s qualified route for that OD × wall × grade and state it on the offer.

Seamless vs welded — buying boundary

Seamless is not automatically “stronger” than a qualified welded pipe. Codes accept ERW, LSAW and SSAW when the design, NDT and delivery condition match the duty. Seamless removes the longitudinal seam variable and is often mandatory in older owner specs, sour small-bore gathering, high-temperature A106 service and many alloy A335 lines.

Process pages: ERW · LSAW · SSAW · comparison blog seamless vs welded.

Sizes, schedules and weight (ASME B36.10)

Carbon seamless pipe is almost always ordered by NPS × schedule (or OD × wall) to ASME B36.10M. Schedules on this page include SCH 10, 20, 40, 80, 120 and 160 — matching the coverage buyers expect on commercial SMLS hubs. Weights are theoretical bare pipe using density 7.85 g/cm³ and \(W_{kg/m}=(OD-t)\times t\times 0.02466\) (OD, t in mm). lb/ft = kg/m × 0.67197. Delivery mass follows the mill certificate and order tolerances.

Need every schedule row or stainless 5S–80S? Use the full weight chart and calculator. Wall-thickness deep dive: size / schedule chart.

SCH 10 — selected NPS (mm & inch)

SCH 20 — selected NPS

SCH 40 seamless carbon steel pipe (common RFQ schedule)

SCH 40 (and STD in many NPS) is the schedule most often typed into “seamless carbon steel pipe sch 40” searches. Confirm whether the project wants STD or true SCH 40 at NPS 12 and above — they diverge on larger sizes.

SCH 80

SCH 120 — selected NPS

SCH 160 — selected NPS

Tables are illustrative for RFQ planning. Binding dimensions are ASME B36.10M and the PO. Coating, threading and bevels change shipped weight.

Supply range we regularly quote

Tests, NDT and certificates

Minimum tests follow the named product standard (tensile, bend / flatten, hydrotest, chemical analysis). Extra NDT (UT, EMI, full-body UT), supplementary requirements and third-party witness are order items — write them explicitly.

Read the paperwork: mill test certificate guide and EN 10204 3.1 vs 3.2. We never claim to “issue” mill certificates ourselves.

How to order — RFQ checklist

Incomplete RFQs waste a round trip. Copy the block below into email or WhatsApp.

China-origin supply context (trading company, partner mills): steel pipe supplier in China. Factory visit / QC story: How we supply.

Carbon seamless grade ladder (orientation only)

The numbers below are orientation minima so an RFQ writer can sanity-check a mill card. They are not a substitute for the grade pages. Click through for full chemistry, Mn footnotes, impact and ordering rules.

API 5L PSL2 also sets maximum yield and tensile windows and toughness. Do not copy PSL1 minima into a PSL2 datasheet. Alloy A335 grades (P11, P22, P91…) use a different strength and PWHT story — stay on the A335 page.

Dimensional tolerances and what “SCH” does not guarantee

ASME B36.10M defines nominal OD and nominal wall for each NPS × schedule pair. Product standards then add permissible variations on OD, wall and mass. A purchase order that only says “6 inch sch 40 seamless” without naming A106 / A53 / API 5L still leaves chemistry, heat treatment and NDT open — and wall under-tolerance on seamless can be several percent depending on the standard and OD band.

• OD — usually controlled to a plus/minus band that widens with diameter; cold-drawn can be tighter than hot-finished.
• Wall — seamless often allows a larger minus tolerance than buyers expect from plate-welded pipe; if the design needs a minimum wall, say so (MW) instead of relying on nominal SCH alone.
• Mass — theoretical kg/m on this page is for planning; invoiced mass follows the mill weighbridge / certificate rules.
• Length — SRL and DRL ranges differ by mill; freeze fixed lengths when coating yards or barge slots need them.

When a project specification freezes “minimum wall after tolerance,” put that sentence on the RFQ. We will have the mill confirm whether the chosen SCH / custom wall still works after the minus allowance.

Ends, bevels, threading and surface

Packing, marking, MOQ and lead time

Export packing for seamless pipe is usually loose or bundled by OD, with end caps on beveled pipes, waterproof wrapping where required, and shipping marks that repeat the PO / heat identity. Marking follows the product standard: manufacturer’s name or brand, standard designation, grade, size, heat number and, for API monogram work, the monogram and license number on the producing mill’s scope.

• MOQ — partner mills usually prefer a heat-lot friendly tonnage; small trial lots are sometimes possible from stock or combined rolling — ask with the size list rather than assuming a catalogue MOQ.
• Lead time — stock sizes can move in days; production lots depend on billet, rolling slot, heat treatment and third-party witness. We state the mill’s window on the quotation.
• Inspection hold points — if you need 3.2 or owner inspection, book it before rolling starts.

We do not invent “ready stock 5,000 tons” claims. Availability is confirmed mill-by-mill against your MTO.

Cost drivers (no price list)

Buyers searching “seamless carbon steel pipe price” still need a structured quote. These are the levers that move the number — discussed on the offer, never posted as a fake FOB/CFR/CIF table on this page:

• Grade and delivery condition (A106 Gr B hot-finished vs cold-drawn precision tube vs A335 P91)
• OD × wall and whether the size is a mill standard rolling or a special
• Quantity vs heat-lot size; single lengths vs many cut pieces
• PSL2 / impact / sour / NACE / supplementary NDT
• Third-party inspection timing
• Coating, threading, special bevels, export packing
• Inland haul to port and ocean freight (quoted separately when you ask — not as a public CFR/CIF card)

Send the MTO; we return mill name, theoretical tonnage and a validity-dated offer.

Common RFQ mistakes we correct early

Applications

• Refinery, petrochemical and power-plant process steam and hydrocarbon lines (A106 / A335)
• Oil & gas gathering and transmission where seamless API 5L is specified
• Low-temperature gas and process lines (A333)
• Boiler, superheater and heat-exchanger tubing (A179 / A192 / related)
• Utility steam, condensate, compressed air and fire water when Type S seamless is required (A53)
• Mechanical / hydraulic tube where cold-drawn seamless tolerances are called

Related resources

• ASTM A106 seamless steel pipe — product supply page
• API 5L seamless steel pipe — line-pipe SMLS product page
• ASTM A106 Grade B — chemistry / strength / ordering
• ASTM A53 Grade B — Type S Grade B (seamless; Type E ERW / Type F furnace-welded are welded, not SMLS)
• ASTM A333 Grade 6 — low-temp seamless
• ASTM A335 alloy pipe — P11 / P22 / P91
• Boiler & heat-exchanger tubes
• Pipe size / schedule chart · Weight chart · HS codes
• Seamless vs welded · A106 vs A53 · API 5L vs A106
• MTC guide · EN 10204 3.1 vs 3.2

FAQ