OCTG selection starts from the well—not from a catalogue grid. Grade, OD, wall, and thread only become meaningful inside an envelope of loads and depth, pressure/temperature and fluids, connection family, and the inspection/documentation package you will accept. This pillar gives procurement and completions engineers a decision path for casing and tubing RFQs, maps live CNPS steel OCTG-related SKUs to string roles, and marks the boundary where nonmetallic GRE/FRP tubing is the better path to quote. It deepens—not replaces—the hub framing: Specify OCTG around the well—not a catalogue label.
What “OCTG selection” means for buyers
Oil Country Tubular Goods are a system: casing for wellbore support and isolation; tubing as the production or injection conduit; connections and couplings that carry load and seal; and accessories where erosion, insulation, or completion interfaces demand them. Selection matches that system to the design authority’s loads, environment, and records—not brand names.
The usual buyer moment: a tally or BOM exists (or is half-built), and the team asks what CNPS can supply and which RFQ fields make a quote usable. Catalogue titles alone do not answer grade, connection, or environment fit. “API” alone is not enough—the specification, grade, dimensions, product level, connection, service conditions, and records must still be stated and confirmed (the OCTG hub FAQ already says this; this guide puts it in RFQ form).
Browse published tubular SKUs on Tubulars & Piping Systems after the well envelope is written—not before.
Start from well design (first principles)
Loads and depth
State the design loads the string must carry: burst, collapse, tension, compression, and bending where the trajectory or dogleg demands it. Tie geometry to planned setting depth and MD/TVD context. Design factors and safety margins remain with the responsible well-design authority; the supplier quote confirms product against the envelope you send, not against invented factors on this page.
Environment
Capture pressure, temperature, produced or injected fluids, corrosion drivers, and any sour-service requirement where applicable. Ask for CO₂/H₂S and water chemistry when known. Do not treat a grade label as a corrosion certificate: sour-service and CRA fit must be confirmed against the offered configuration and the buyer’s governing specs.
Connection and records
Name the thread family, coupling or premium interface, pup joints and crossovers, make-up or interchangeability needs, inspection level, marking, and traceability (MTR and related records). Connection choice often controls string integrity as much as pipe body grade. Incomplete connection fields are a common reason quotes come back with assumptions.
Steel OCTG path (API 5CT family on live CNPS pages)
Map roles → live SKUs only. Grade lists and thread families below are attributed to the cited product pages as fetched for this draft; reconfirm on the live PDP at publish time. If a grade or connection is not listed on a live page, write “confirm with engineering” rather than inventing it.
Production / injection tubing & casing (corrosion-resistant examples on site)
For carbon-dioxide and related corrosive well service where CRA tubulars are under review, CNPS publishes:
- API 5CT 13cr Tubing And Casing Pipe — grades J55 / N80 / K55 / L80 / P-110 / C90 / C95 / T95; OD 4-1/2″–20″; wall 5.12–16.13 mm; lengths R1 / R2 / R3; threads LTC / BTC / STC / NUE / EUE (as on the PDP).
- 13cr-L80 Casing And Tubing — API 5CT note for wells with carbon dioxide environments; casing OD 114.3–339.7 mm (4.5″–13.38″); tubing OD 60.3–114.3 mm (2.38″–4.5″); mechanical properties as on that page.
Use these as evidence anchors, not as a substitute for your design basis.
Couplings and thread interfaces
Couplings belong in the same controlled equipment list as the pipe. Live product: API 5CT Tubing Coupling — O.D. 2 3/8; grades J55 / K55 / N80 / L80-1 / N80-Q / C90 / P110; threads NU / EU; standard API 5CT (as on the PDP). State coupling grade, thread, and special clearance as line items; do not assume the pipe body grade defines the coupling.
Accessories adjacent to the string
- BLAST JOINTS — heavy-wall accessories where returns encounter turbulence; OD 0.750″–7.625″; common lengths 10′ and 20′ (also meters); premium, semi-premium, and API connections as on the page.
- API 5CT Perforating Gun Pipes — carrier pipe for perforation guns (conventional and horizontal-well types on the PDP). Treat as completion-adjacent, not production tubing.
- API 5CT Vacuum Insulated Tubing And Casing — VIT with insulation grades D and E; confirm offered insulation grade and connections—do not amplify thermal claims beyond the PDP.
Wellhead interface note (boundary)
The casing-head / wellhead assembly is an interface to the tubular string, not an OCTG grade. Live listing: API 6 wellhead Equipment Casing Head Assembly/Wellhead. That PDP is thin at fetch time—send pressure rating, casing sizes, and governing edition in the RFQ, and hand deeper wellhead selection to the wellhead RFQ pillar when it ships.
When nonmetallic GRE / FRP is the better path (boundary)
Do not force steel OCTG language onto corrosive injection duty where live GRE tubing pages apply. CNPS publishes GRE tubing for water injection, sewage reinjection, and polymer injection wells (plus geothermal notes on the LR page). Quote that path against the same duty:
- Spec depth: Fiberglass Pipe Systems: FRP, GRP and GRE
- Tubing SKUs: API 15HR GRE Tubing; API 15LR GRE Tubing (15LR also lists DN40–DN100, 10–25 MPa—confirm the offered configuration)
- Related anchors: API 5B Thread GRE Pipe (keep tubing vs line-pipe scope distinct); API 15LE PE-100 HDPE Lining Tubes for API 15LE lined PE duty
Do not invent pressure–temperature envelopes here. Prefer “confirm against offered configuration” when a PDP is thin.
Decision table: steel OCTG vs GRE/FRP vs lined
| Service / string role | Dominant drivers | Typical material family on CNPS live pages | Live anchor | What to put in the RFQ next |
|---|---|---|---|---|
| Surface / intermediate / production casing | Loads, depth, connection, isolation | Steel API 5CT family (incl. 13Cr examples) | 13Cr tubing & casing PDP; 13Cr-L80 PDP | Geometry, grade, thread, loads, P/T, docs |
| Production tubing | Produced medium, P/T, intervention, connection | Steel API 5CT / 13Cr tubulars + couplings | 13Cr PDPs; tubing coupling PDP | OD/wall, grade, NU/EU or other thread, couplings |
| Injection conduit (corrosive water / sewage / polymer) | Corrosion / medium, long-term integrity | GRE API 15HR / 15LR tubing | API 15HR GRE Tubing; API 15LR GRE Tubing; fiberglass hub | Medium list, P/T, size, joint, parallel steel vs GRE quote |
| Thermal / insulated string | Insulation need, reuse, connection | Vacuum insulated tubing & casing (grades D/E as on PDP) | VIT PDP | Insulation grade, inner/outer connections, duty cycle |
| Erosion at returns / turbulence | ID erosion protection | Blast joints | BLAST JOINTS PDP | OD, length, connection, location in string |
| Perforating carrier | Gun type, dimensional precision | API 5CT perforating gun pipes | Perforating gun pipes PDP | Gun type, OD/WT tolerances, qty |
| Lined steel / PE lining duty | Corrosion management without full nonmetallic string | PE-100 HDPE lining (API 15LE framing) | API 15LE PE-100 HDPE lining tubes | Fluid, temp band, OD/WT, length, UV/protection notes |
| Wellhead interface | Pressure control, casing hang-off | Casing head / wellhead assembly (not an OCTG grade) | API 6 casing head PDP | Sizes, pressure class, governing edition → wellhead RFQ |
OCTG RFQ checklist (fields buyers must send)
Send the string design and commercial scope together. Missing fields should be flagged in review rather than filled with silent assumptions.
- Application / string role — casing vs tubing vs accessory; well section.
- Geometry — OD, wall, drift, length range (R1/R2/R3 if used), end finish, quantity by line.
- Material — grade/alloy family, heat treatment, sour or corrosion requirement if any.
- Connection — thread family, coupling, special clearance, premium vs API (buyer-stated).
- Loads / design basis — buyer authority owns design factors; reference the governing design note.
- Environment — pressure, temperature, fluids, CO₂/H₂S if known.
- Standards & inspection — applicable spec edition, inspection level, marking, document language.
- Commercial — destination, required date, Incoterm, packing, tally/BOM revision.
- Injection / corrosive water–polymer service — ask whether a GRE/FRP path should be quoted in parallel.
- Technical contact — name for clarifications.
RFQ field matrix
| Field group | Example fields |
|---|---|
| Geometry | OD, wall, drift, length range (R1/R2/R3), end finish, quantity by line |
| Material | Grade / alloy family, heat treatment, sour-service or corrosion requirement |
| Connection | Thread (e.g. LTC/BTC/STC/NUE/EUE only when on the buyer BOM or a live PDP), coupling, make-up / interchangeability |
| Service | Pressure, temperature, medium, produced/injected fluid, intervention needs |
| Quality / docs | Spec edition, inspection level, marking, MTR/traceability, third-party |
| Commercial | Destination, Incoterm, schedule, packing, tally/BOM revision |
How this connects to CNPS (evidence path)
CNPS frames OCTG around the well—loads, environment, connection, and records—then confirms compliance against the requested scope. Use the OCTG hub for framing, the tubulars category for the live grid, and this pillar for selection paths and the RFQ matrix. Lifecycle context: Oil & Gas Solutions.
No AI-platform claims belong here. If a grade, connection, or limit is not on a live page, confirm with engineering. Final approval stays with the well-design authority.
When ready, Talk to an Engineer with the RFQ checklist, or email sales@cnps.com.
FAQ
Does “API” alone define the required OCTG?
No. The applicable specification, grade, dimensions, product level, connection, service conditions, and record requirements must still be stated and confirmed.
Can CNPS quote from an existing tally or bill of materials?
Yes. Include the revision, quantities, standards, connection details, inspection requirements, destination, and required date. Missing commercial or technical fields can be identified during review.
When should buyers consider GRE tubing instead of steel OCTG?
When the service is driven by corrosive injection or similar media where live CNPS GRE tubing pages apply—for example water injection, sewage reinjection, or polymer injection as stated on those product pages—evaluate the nonmetallic path via the fiberglass systems hub and quote it against the same duty rather than forcing a steel-only RFQ.
What documents should I request with an OCTG offer?
At minimum: applicable standard/edition, material test / traceability records, inspection level and marking scheme, and any third-party requirements you will enforce. Do not invent certificate samples; request the document list that matches your ITP.
Which connection fields matter most on the RFQ?
Thread family, coupling grade and type, make-up or interchangeability rules, and any special clearance or premium vs API designation the design authority requires. Couplings should appear as controlled line items when they are separate SKUs.
When should I open a wellhead RFQ instead of an OCTG-only RFQ?
When the scope includes casing-head / wellhead pressure-control equipment, hang-off interfaces, or API 6-family assemblies. Keep the tubular string RFQ and the wellhead RFQ linked, but do not treat the casing head as an OCTG grade. Use the dedicated wellhead RFQ pillar when it is live.
Assemble the geometry, material, connection, service, quality, and commercial fields above; attach the tally revision; and send the package via Talk to an Engineer or sales@cnps.com. Clear operating conditions beat longer catalogue lists—and incomplete truth beats false certainty on grades and envelopes.
