9-5/8 Casing Specifications: ID, Drift, Weight & Pressure Ratings

9-5/8 inch casing has an outside diameter of 9.625 in (244.48 mm). API 5CT lists it in eleven weights from 32.3 to 75.6 lb/ft, and its inside diameter runs from 9.001 in (228.60 mm) down to 8.031 in (204.00 mm) as the wall gets heavier. The weight most engineers ask about, 47 lb/ft, has an ID of 8.681 in, a standard drift of 8.525 in, and a capacity of 0.0732 bbl/ft. In P110 it is rated at 9,440 psi burst and 5,300 psi collapse.

9-5/8 is the standard intermediate casing size in most onshore and shelf wells. It sits between 13-3/8 surface casing and the 7 in production string, so its ID and drift decide which bit you can drill the next section with. This page puts every 9-5/8 dimension and rating in one place, using API 5CT dimensions and API 5C3 formulas. It also covers the drift and grade details that tend to cause problems on purchase orders. ZC Steel Pipe supplies 9-5/8 casing in N80, L80, T95, C110 and P110 with API BTC or premium connections. For other sizes, see our complete API 5CT casing size and weight table →

Contents

1. 9-5/8 Casing at a Glance

2. 9-5/8 Casing ID & Drift Chart

3. Weight, Capacity & D/t Ratio

4. Burst, Collapse & Body Yield by Grade

5. Bit Size, Drift & Clearance

6. Choosing a Grade for a 9-5/8 String

7. Connections for 9-5/8 Casing

8. How to Specify 9-5/8 Casing on a PO

9. FAQ

1. 9-5/8 Casing at a Glance

Light Weights

Weights: 32.3 / 36 / 40 lb/ft

ID range: 9.001 – 8.835 in

Wall: 0.312 – 0.395 in

Typical use: Shallow intermediate strings, low-pressure wells

Mid Weights

Weights: 43.5 / 47 / 53.5 lb/ft

ID range: 8.755 – 8.535 in

Wall: 0.435 – 0.545 in

Typical use: The workhorse range for intermediate casing in N80, L80 and P110

Heavy Weights

Weights: 58.4 – 75.6 lb/ft

ID range: 8.435 – 8.031 in

Wall: 0.595 – 0.797 in

Typical use: Salt sections, HPHT, high-collapse designs

Definition — Nominal Weight
The lb/ft figure in a casing description, such as "9-5/8 47#", is the nominal weight including threads and couplings. It is a label for the wall thickness, not a scale reading. For tonnage, freight and pricing, use the kg/m column in Section 3. The plain-end weight is slightly lower and is the figure some mills invoice on, so confirm which basis your quotation uses.

2. 9-5/8 Casing ID & Drift Chart

All values are for 9.625 in (244.48 mm) OD per API 5CT Table C.18. The standard drift equals the nominal ID minus 5/32 in (0.156 in).

Source: API 5CT 11th edition, Table C.18. Inch values converted from the metric table and rounded to three decimals.

Definition — Drift Diameter
Drift is the diameter of a cylindrical mandrel that the mill must pass through the full length of every joint. Because it allows for wall-thickness tolerance and ovality, it is always smaller than the nominal ID. To check whether a bit, packer or liner hanger will pass, compare its OD against the drift, not the ID.

3. Weight, Capacity & D/t Ratio

Capacity is the internal volume per unit length and is used for cement, displacement and mud volume calculations. Annular volumes also need the OD of the next string or the open-hole size.

Capacity (bbl/ft) = ID² ÷ 1029.4, with ID in inches. L/m is calculated from the metric ID. D/t is OD divided by nominal wall thickness and determines which collapse regime applies.

Procurement Note — Tonnage Conversion
9-5/8 tenders are often issued in metres and quoted in tonnes. For 47 lb/ft, 1,000 m of pipe is about 69.9 t at the nominal threaded-and-coupled weight. Check whether the RFQ quantity is in metres, joints or tonnes before pricing. A 12 m joint of 9-5/8 47# weighs about 840 kg, so a 10% difference in assumed joint length shows up quickly in freight cost. See casing length ranges R1/R2/R3 →

4. Burst, Collapse & Body Yield by Grade

The ratings below are calculated with API 5C3 formulas from nominal dimensions and minimum yield strength. They cover 40 lb/ft and heavier, the weights normally supplied in the higher-strength grades. L80 and N80 have the same 80 ksi minimum yield, so their pipe-body ratings are identical. C110 has the same minimum yield as P110, so its body yield and burst figures are the same.

Burst = 0.875 × 2 × Yp × t / D (API 5C3 Eq. 31). Body yield = 0.7854 × (D² − d²) × Yp (Eq. 30). Collapse uses the yield, plastic, transition or elastic equation set by the D/t ratio. Pipe body only: connection ratings are often lower, so check the connection data sheet.

Critical Engineering Point — Collapse Under Tension
The collapse values above assume zero axial load. In a hanging 9-5/8 string the upper joints are in tension, and API 5C3 Eq. 8 reduces the effective yield strength under axial stress, which lowers collapse resistance. A design that just meets the table value at the shoe can be under-rated higher up the string. Run a biaxial check in your casing design software, and use the table only to shortlist weights.

Engineering Insight — Why 40# and 43.5# Gain Less From Higher Grades
At 40 lb/ft (D/t 24.4), moving from L80 to P110 increases burst by 37% but collapse by only about 12% (3,090 to 3,470 psi). Thin-wall 9-5/8 is in the transition collapse regime, where geometry matters more than yield strength. If collapse is the governing load, a heavier weight in L80 usually does more than a higher grade at the same weight. For example, 47# L80 at 4,760 psi outperforms 40# P110 at 3,470 psi, and it is sour-service capable.

5. Bit Size, Drift & Clearance

For many drilling engineers, the main question about 9-5/8 casing is which bit will drill the next hole section. The table below compares the two most common bit sizes against the API standard drift.

Field Note — Alternate (Special) Drift
If the drilling program calls for a bit larger than the standard drift, for example an 8-1/2" bit through 53.5# or an 8-3/4" bit through 40#, the casing has to be ordered with an alternate drift. API 5CT lists these larger mandrel sizes for specific size and weight combinations. Alternate drift must be written on the purchase order, because the mill will only test to standard drift unless told otherwise. If the requirement is noticed after the pipe is threaded, the joints have to be re-drifted, and any that fail can only be used for other wells.

6. Choosing a Grade for a 9-5/8 String

Intermediate casing usually has to isolate pressured zones and support heavy mud weights, and it may be exposed to H₂S or CO₂. The table below lists the grades most often specified for 9-5/8. All values come from API 5CT.

Procurement Mistake — Assuming API Sour Grades Meet Your NACE Limit
T95 and C110 are API sour-service grades, but their API hardness limits (25.4 and 29.0 HRC) are higher than the 22 HRC limit many operators apply under NACE MR0175 / ISO 15156. If the well specification refers to NACE, write the required hardness and SSC test method on the PO, not just the grade. L80-13Cr is a CO₂ corrosion grade and must not be treated as sour-qualified. More detail: the hardness trap between API 5CT and NACE MR0175 →

Grade deep dives: L80 casing → · T95 casing → · P110 casing → · P110 vs L80 vs T95 →

7. Connections for 9-5/8 Casing

API BTC (Buttress)

Seal: Thread compound, not gas-tight

Tension: High, close to pipe body

Best for: Most 9-5/8 intermediate strings carrying liquid or low-pressure gas

API LTC / STC

Seal: Thread compound

Tension: Lower than BTC

Best for: Shallow, low-load strings, usually lighter weights

Premium (e.g. ZC-2 gas-tight)

Seal: Metal-to-metal, gas-tight

Tension: Up to 100% of pipe body (design dependent)

Best for: Gas wells, HPHT, sour service, strings exposed to production pressure

Most 9-5/8 strings are run on BTC. A premium connection is worth the extra cost where the casing may be exposed to gas at production pressure, for example if a tubing leak would pressurise the 9-5/8. It is also used where a combined-load envelope is needed for HPHT design. Read more: BTC buttress thread casing explained → · premium vs BTC: when the investment pays off →

Field Note — Check Coupling OD Clearance, Not Just Pipe OD
Clearance problems with 9-5/8 strings almost always come from the coupling OD, not the pipe body. When 9-5/8 runs inside 13-3/8 or through a tight 12-1/4" hole, check the coupling OD against the drift of the previous string and the expected hole condition. If the clearance is marginal, a special-clearance coupling or a semi-flush premium connection solves it at the design stage. Fixing it on site is far more expensive.

8. How to Specify 9-5/8 Casing on a PO

A complete 9-5/8 line item should state each of the following. If any of them is missing, the mill will choose a default value.

• Size and weight: 9-5/8" (244.48 mm) OD, 47 lb/ft (wall 11.99 mm / 0.472 in)

• Standard and grade: API 5CT, grade with type where applicable (e.g. L80-1, not just "L80"), PSL1 or PSL2

• Connection: BTC, LTC, or the premium connection name, plus the coupling type (regular or special clearance)

• Length range: R3 is typical for 9-5/8 intermediate strings; state the range and any minimum average length

• Drift: Standard or alternate drift; state the alternate drift diameter if the bit program needs it

• Sour service requirements (if applicable): Maximum hardness, SSC test method and acceptance criteria per NACE MR0175 / ISO 15156

• Documents: EN 10204 3.1 mill test certificate, heat and lot traceability, hydrostatic test records

• Inspection: Third-party inspection at the mill if required (at the buyer's cost), with witness points listed

• Packing and protection: Thread protectors on pin and box, bundling or loose pipe, and marking requirements

Engineering Insight — Write the Weight as Wall Thickness Too
Some heavy 9-5/8 weights differ by very little wall thickness. For example, 58.4# is 15.11 mm and 59.4# is 15.47 mm. Writing the wall thickness next to the lb/ft weight removes the most common cause of mismatched quotes between bidders.

9. FAQ

What is the ID of 9-5/8 casing?

9-5/8 inch casing has an OD of 9.625 in (244.48 mm). Its inside diameter depends on weight: 9.001 in (228.60 mm) for 32.3 lb/ft, down to 8.031 in (204.00 mm) for 75.6 lb/ft. The widely used 47 lb/ft weight has an ID of 8.681 in (220.50 mm), and 40 lb/ft has 8.835 in (224.40 mm).

What is the drift diameter of 9-5/8 47# casing?

The API standard drift for 9-5/8 47 lb/ft casing is 8.525 in (216.54 mm), which is the nominal ID minus 5/32 in. An alternate drift can be specified on the purchase order if the bit program needs it.

What is the capacity of 9-5/8 casing?

Capacity ranges from 0.0787 bbl/ft (41.0 L/m) for 32.3 lb/ft to 0.0627 bbl/ft (32.7 L/m) for 75.6 lb/ft. For 47 lb/ft it is 0.0732 bbl/ft, or about 13.66 ft per barrel.

Will an 8-1/2 inch bit pass through 9-5/8 casing?

Yes, for weights from 32.3 to 47 lb/ft. The standard drift of 47 lb/ft is 8.525 in. The bit does not pass the standard drift of 53.5 lb/ft (8.379 in) or heavier weights, so those weights need an alternate drift if an 8-1/2" bit will be run through them.

What is the burst and collapse pressure of 9-5/8 47# P110 casing?

9-5/8 47 lb/ft P110 has a minimum internal yield (burst) pressure of 9,440 psi and a minimum collapse pressure of 5,300 psi at zero axial load, calculated per API 5C3. Pipe body yield strength is about 1,493,000 lbf. In L80, the same weight is rated at 6,870 psi burst and 4,760 psi collapse.

What is the difference between casing ID and drift?

ID is the nominal inside diameter, calculated from the OD and nominal wall thickness. Drift is the diameter of a test mandrel that must pass through every joint. Drift is smaller than ID to allow for wall tolerance and ovality, and it is the figure to use when checking whether a tool will pass.

What is 9-5/8 casing in mm?

9-5/8 inch casing has an outside diameter of 244.48 mm, often written as 244.5 mm in metric tenders. Wall thickness ranges from 7.92 mm (32.3 lb/ft) to 20.24 mm (75.6 lb/ft).

Source 9-5/8 Casing from ZC Steel Pipe

ZC Steel Pipe is a China-based steel pipe specialist supplying API 5CT casing in N80, L80, T95, C110, P110 and Q125. We offer BTC threading and our own ZC-2 gas-tight premium connection, with EN 10204 3.1 certificates. Third-party inspection is available at the mill. We have shipped OCTG to projects in Africa, the Middle East and South America.

Send us your size, weight, grade, connection and quantity, and we will reply with a quotation and delivery schedule.
Email: hazel.w@zcsteelpipe.com · WhatsApp: +1-213-239-3018

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Related: Casing & Tubing · Premium Connection · Couplings for Casing & Tubing · API 5CT Casing Size Table · OCTG Grades