Butt weld pipe caps (ellipsoidal end caps) made to ASME B16.9 in stainless steel, duplex (S32205 / S31803), super duplex (S32750 / S32760) and nickel alloy grades — including WP304/304L as photographed.
Seamless ½”–24″ (DN15–DN600) · Welded ½”–40″ (DN15–DN1000) · Sch 5S – XXS
What Is a Butt Weld Pipe Cap?
A butt weld pipe cap is a closed-end fitting welded to a pipe to terminate the line. The product range covers stainless steel caps, duplex stainless steel caps, super duplex stainless steel caps and nickel alloy caps, with size, wall thickness and material requirements specified for each order. ASME B16.9 caps have an ellipsoidal shape; unlike a bolted blind flange, a welded cap is not intended for routine removal.
Also called a pipe end cap or butt weld end cap, this fitting closes process-line terminations, manifold ends and permanent branch closures where the piping design does not require future access. Selection is made by the connecting pipe outside diameter, wall thickness and material specification.
For an ASME B16.9 order, specify the applicable standard edition and material specification together. A dimensional standard defines fitting geometry and tolerances; it does not replace the material specification or establish suitability for a particular process.
Key Specifications
| Product type | Butt weld pipe cap (ellipsoidal end cap), ASME B16.9 |
|---|---|
| Size (seamless) | ½”–24″ (DN15–DN600) — catalog-listed range for enquiry |
| Size (welded) | ½”–40″ (DN15–DN1000) — catalog-listed range for enquiry |
| Wall thickness | Sch 5S, 10S, 40S, 80S and heavy-wall options; other schedules or specified wall by agreement — not every size/schedule combination exists |
| Material families | Stainless steel, duplex stainless steel, super duplex stainless steel, nickel alloys (254 SMO and AL-6XN high-alloy options available) |
| Dimensional reference | ASME B16.9, subject to the specified edition; other standards by separate review |
| End preparation | ASME B16.9 section 8 / Table 8-1, or agreed special end preparation — bevel 37.5° ±2.5° per ASME B16.25 |
| Inspection & documentation | EN 10204 Type 3.1 as standard; Type 3.2 by agreed inspection arrangements |
Note: These are catalog ranges, not a guarantee that every size, schedule, material and manufacturing route is available in every combination. Confirm the required configuration when requesting a quotation.
Material Grades: Stainless Steel, Duplex, Super Duplex and Nickel Alloy Pipe Caps
Select the material grade separately from the fitting dimensions. The following material options are listed in the supplied product information; the complete fitting grade, manufacturing class, heat treatment and inspection requirements are confirmed for the order.
| Material family | Catalog-listed grades | Material specification |
|---|---|---|
| Stainless steel caps | 304 / 304L / 304H, 316 / 316L / 316H / 316Ti, 317L, 310S, 321 / 321H, 904L | ASTM A403/A403M (austenitic fitting grades) |
| Duplex stainless steel caps | UNS S31803, S32205 | ASTM A815/A815M |
| Super duplex stainless steel caps | UNS S32750, S32760 | ASTM A815/A815M |
| Nickel alloy caps | UNS N02200, N02201, N04400, N06600, N06601, N06625, N06022, N10276, N08020, N08800 series, N08825 | ASTM B366/B366M (confirm grade coverage) |
| Additional high-alloy stainless options | 254 SMO (UNS S31254), AL-6XN (UNS N08367) | Confirm grade designation and applicable fitting specification |
Grade identification: WP304/304L is an ASTM A403 austenitic fitting grade — the photographed cap carries this marking together with NPS 3, SCH10S, ASME B16.9 and a heat number. Commercial names are not substitutes for the ordered grade, UNS designation, heat treatment and manufacturing class. For dual certification such as 304/304L, the delivered fitting must meet both ordered grades and the inspection documents must demonstrate this. Choose material using fluid chemistry, chloride level, temperature, pressure and corrosion mechanisms.
ASME B16.9 Cap Dimensions — Metric Reference (mm)
The table below reproduces the SI values of ASME B16.9-2024, Table 6.1-10. D is the outside diameter at the bevel; E is the overall axial length of the cap. The limiting thickness selects the applicable E column and is not the maximum permitted cap wall thickness.
| NPS | D (mm) | Limiting thickness (mm) | E: wall ≤ limit (mm) | E: wall > limit (mm) |
|---|---|---|---|---|
| 1/2 | 21.3 | 4.57 | 25 | 25 |
| 3/4 | 26.7 | 3.81 | 25 | 25 |
| 1 | 33.4 | 4.57 | 38 | 38 |
| 1 1/4 | 42.2 | 4.83 | 38 | 38 |
| 1 1/2 | 48.3 | 5.08 | 38 | 38 |
| 2 | 60.3 | 5.59 | 38 | 44 |
| 2 1/2 | 73.0 | 7.11 | 38 | 51 |
| 3 | 88.9 | 7.62 | 51 | 64 |
| 3 1/2 | 101.6 | 8.13 | 64 | 76 |
| 4 | 114.3 | 8.64 | 64 | 76 |
| 5 | 141.3 | 9.65 | 76 | 89 |
| 6 | 168.3 | 10.92 | 89 | 102 |
| 8 | 219.1 | 12.70 | 102 | 127 |
| 10 | 273.0 | 12.70 | 127 | 152 |
| 12 | 323.8 | 12.70 | 152 | 178 |
| 14 | 355.6 | 12.70 | 165 | 191 |
| 16 | 406.4 | 12.70 | 178 | 203 |
| 18 | 457.0 | 12.70 | 203 | 229 |
| 20 | 508.0 | 12.70 | 229 | 254 |
| 22 | 559.0 | 12.70 | 254 | 254 |
| 24 | 610.0 | 12.70 | 267 | 305 |
Reference: ASME B16.9-2024, Table 6.1-10. For NPS 26 and larger with wall thickness above 12.7 mm, confirm length E with the manufacturer and purchaser as addressed in Table 6.1-10 Note (1). Example: NPS 6 has D = 168.3 mm and a limiting thickness of 10.92 mm — E is 89 mm at or below that limit and 102 mm above it. Using a single cap length for every schedule can therefore produce an incorrect drawing or purchase specification.
Engineering Drawing — Butt Weld Pipe Cap (ASME B16.9)
The drawing below shows the example part photographed on this page: an NPS 3″ SCH10S cap in ASTM A403 WP304/304L, with the bevel-end detail to ASME B16.25 (37.5° ±2.5°, 1.6–2.2 mm root face) and the full-size E dimension table. Marking example: CAP 3″ SCH10S · ASTM A403 WP304/304L · ASME B16.9, with heat number for MTC traceability. Drawings for other sizes and grades are issued against the order.
The drawing is a review reference with unresolved material and wall-thickness items. Use the final agreed manufacturing drawing and material documentation for order acceptance.
Weld Ends, Pressure Design and Applications
End preparation depends on material category and wall thickness. For austenitic steels and nonferrous alloys, Table 8-1 uses a 3 mm threshold: below it, square-cut or slightly chamfered ends are permitted; from 3 mm through 22 mm, the plain bevel applies (37.5° ±2.5° with a 1.5 ±1.0 mm root face); above 22 mm, a compound bevel applies. Confirm duplex and other material categories against the governing specification and approved drawing.
Pressure design depends on the equivalent connecting pipe size, wall thickness and material, the qualified fitting design, operating temperature and applicable piping code. ASME B16.9 is not a universal pressure or temperature rating for every material and schedule. Installation welding procedures and system testing follow the governing piping code.
Process-line terminations, manifold ends and permanent closure of piping branches in chemical processing, oil and gas, power and water treatment. Seawater RO, nuclear and hygienic pharmaceutical applications require their own material, design, documentation and surface-finish review.
A butt weld cap closes a pipe through a welded joint and is not intended for routine removal. A blind flange closes a flanged connection using bolts and a gasket and can be removed for access. Selection depends on the piping design and maintenance requirements.
Inspection, Certification and Marking
Define the inspection plan before manufacture: material test report, chemistry and mechanical results, heat treatment, dimensions, weld examination and any supplementary requirements. PMI, corrosion tests, duplex microstructure or ferrite checks, impact tests and third-party inspection are included only when required by the applicable specification or agreed purchase order.
ASME B16.9 section 10 does not require routine production hydrostatic testing of wrought fittings. This does not waive material-specification requirements, agreed additional tests or the completed piping system test.
Marking and traceability follow the ordered material specification and ASME B16.9 section 4, including required class identification and applicable small-part provisions. NACE MR0175 / ISO 15156 enquiries require the intended H2S-containing service conditions, applicable part and edition, grade, hardness and heat-treatment requirements.
Prepare Your Pipe Cap Enquiry
Use the following specification format to request a configuration-specific quotation. Include an approved drawing when dimensions or tolerances differ from the standard table.
- Butt weld pipe cap / ellipsoidal end cap
- Size: [NPS / DN] · Schedule or wall thickness: [value + standard]
- Material: [grade + material specification + edition]
- Manufacturing route: [seamless / welded + required class]
- Dimensions: [standard + edition / approved drawing]
- Quantity: [pieces] · Inspection: [requirements] · Certificate: [type]
- Delivery: [destination + requested date]
Example enquiry: Butt weld pipe cap, NPS 3, SCH10S, ASTM A403 WP304/304L, ASME B16.9 dimensions. Please confirm the ASTM A403/A403M edition, complete fitting grade/class, heat-treatment condition, wall thickness, inspection documents and delivery details.
FAQ: Butt Weld Pipe Caps
What is the difference between a pipe cap and a blind flange?
A butt weld cap closes a pipe through a welded joint. A blind flange closes a flanged connection using bolts and a gasket and can be removed for access. Selection depends on the piping design and maintenance requirements.
Does ASME B16.9 define the material grade?
ASME B16.9 covers fitting dimensions, tolerances, ratings, testing and marking and references material specifications. Order the applicable fitting specification, exact grade and manufacturing class as well as the dimensional standard.
Is cap length the same for every wall thickness?
No. ASME B16.9-2024 Table 6.1-10 selects cap length using the marked nominal wall thickness relative to a listed limiting thickness. NPS 26 and larger above 12.7 mm require confirmation of the manufacturer-selected or agreed length.
Can every size be supplied in Sch 5S through XXS?
No universal size-by-schedule availability is established. Specify the size, grade, wall standard and manufacturing route so the exact combination can be confirmed in the quotation.
Are all pipe caps hydrostatically tested individually?
ASME B16.9 does not require routine production hydrostatic testing of wrought fittings. Tests required by the material specification, purchase order and completed piping system remain applicable.
What should I include in a pipe cap enquiry?
Provide NPS or OD, nominal wall thickness or schedule and its standard, exact material grade, fitting specification and class, dimensional-standard edition, quantity, design conditions, end preparation, inspection documents and supplementary tests.
