What Are ASME B16.9 Lap Joint Stub Ends?
A lap joint stub end is a short flanged fitting with a lapped flange face, used with a lap joint flange (backing flange) so the line can be disassembled easily. ASME B16.9 covers Type A, Type B and Type C stub ends per MSS SP-43, plus fabricated stub ends; dimensions are given in Table 6.1-9 for NPS 1/2 – 24. The backing flange itself follows ASME B16.5 (lap joint type).
Type A / B / C (per MSS SP-43)
- Type A: lap joint stub end, long pattern (full lap radius), matching MSS SP-43 Type A.
- Type B: lap joint stub end, short pattern.
- Type C: fabricated stub end (welded construction) per ASME B16.9.
- Long pattern and short pattern lengths F are both listed in the table below — specify which you need when ordering.
Dimensions — Table 6.1-9 (NPS 1/2 – 24)
Values in mm (inch). OD barrel max/min; F = total length (long / short pattern); R = fillet radius of lap; G = lap diameter.
| NPS | Barrel OD Max (mm / in) | Barrel OD Min (mm / in) | F Long Pattern (mm / in) | F Short Pattern (mm / in) | R Fillet (mm / in) | G Lap Diameter (mm / in) |
|---|---|---|---|---|---|---|
| 1/2 | 22.8 (0.896) | 20.5 (0.809) | 76 (3.0) | 51 (2.0) | 3 (0.12) | 35 (1.38) |
| 3/4 | 28.1 (1.106) | 25.9 (1.019) | 76 (3.0) | 51 (2.0) | 3 (0.12) | 43 (1.69) |
| 1 | 35.0 (1.376) | 32.6 (1.284) | 102 (4.0) | 51 (2.0) | 3 (0.12) | 51 (2.0) |
| 1 1/4 | 43.6 (1.716) | 41.4 (1.629) | 102 (4.0) | 51 (2.0) | 5 (0.19) | 64 (2.5) |
| 1 1/2 | 49.9 (1.965) | 47.5 (1.869) | 102 (4.0) | 51 (2.0) | 6 (0.25) | 73 (2.88) |
| 2 | 62.4 (2.456) | 59.5 (2.344) | 152 (6.0) | 64 (2.5) | 8 (0.31) | 92 (3.62) |
| 2 1/2 | 75.3 (2.966) | 72.2 (2.844) | 152 (6.0) | 64 (2.5) | 8 (0.31) | 105 (4.12) |
| 3 | 91.3 (3.596) | 88.1 (3.469) | 152 (6.0) | 64 (2.5) | 10 (0.38) | 127 (5.0) |
| 3 1/2 | 104.0 (4.096) | 100.8 (3.969) | 152 (6.0) | 76 (3.0) | 10 (0.38) | 140 (5.5) |
| 4 | 116.7 (4.593) | 113.5 (4.469) | 152 (6.0) | 76 (3.0) | 11 (0.44) | 157 (6.19) |
| 5 | 144.3 (5.683) | 140.5 (5.532) | 203 (8.0) | 76 (3.0) | 11 (0.44) | 186 (7.31) |
| 6 | 171.3 (6.743) | 167.5 (6.594) | 203 (8.0) | 89 (3.5) | 13 (0.5) | 216 (8.5) |
| 8 | 222.1 (8.743) | 218.3 (8.594) | 203 (8.0) | 102 (4.0) | 13 (0.5) | 270 (10.62) |
| 10 | 277.2 (10.913) | 272.3 (10.719) | 254 (10.0) | 127 (5.0) | 13 (0.5) | 324 (12.75) |
| 12 | 328.0 (12.913) | 323.1 (12.719) | 254 (10.0) | 152 (6.0) | 13 (0.5) | 381 (15.0) |
| 14 | 359.9 (14.17) | 354.8 (13.969) | 305 (12.0) | 152 (6.0) | 13 (0.5) | 413 (16.25) |
| 16 | 411.0 (16.18) | 405.6 (15.969) | 305 (12.0) | 152 (6.0) | 13 (0.5) | 470 (18.5) |
| 18 | 462.0 (18.19) | 456.0 (17.969) | 305 (12.0) | 152 (6.0) | 13 (0.5) | 533 (21.0) |
| 20 | 514.0 (20.24) | 507.0 (19.969) | 305 (12.0) | 152 (6.0) | 13 (0.5) | 584 (23.0) |
| 22 | 565.0 (22.24) | 558.0 (21.969) | 305 (12.0) | 152 (6.0) | 13 (0.5) | 641 (25.25) |
| 24 | 616.0 (24.24) | 609.0 (23.969) | 305 (12.0) | 152 (6.0) | 13 (0.5) | 692 (27.25) |
Materials & Temperature Range
Manufactured from A234 WPB carbon steel (-29°C to 425°C), A403 WP304 / WP316 stainless (up to 538°C), and A420 WPL6 low-temperature service. The gasket face finish follows ASME B16.5 raised-face requirements.
Related Standards
- ASME B16.9 — Buttwelding Fittings (parent standard)
- ASME B16.5 — Lap Joint Flanges (backing flange)
- ASME B16.5 — Lap Joint Flanges (for stub-end joints)
- ASME B16.9 Elbows
- ASME B16.9 180° Returns
- ASTM A403 WP304 Stainless
- Our Fittings Range
FAQ
What is the difference between a stub end and a lap joint flange?
The stub end is the welding end with the lap face; the lap joint flange (backing flange) is the loose ring behind it. Together they form a lap joint assembly.
Type A or Type B stub end — which do I order?
Type A is the long pattern, Type B the short pattern (both per MSS SP-43). Long pattern gives a longer lap radius; short pattern saves space. Service conditions may dictate the choice — specify F when ordering.
What sizes are covered in Table 6.1-9?
NPS 1/2 through NPS 24, as shown in the dimension table above.
Can stainless stub ends be used with carbon steel flanges?
Yes — that is a common design: a stainless stub end with a carbon steel backing flange, combining corrosion resistance at reasonable cost.
What does fabricated (Type C) stub end mean?
Type C is a welded (fabricated) construction permitted by ASME B16.9 for sizes where seamless forged stub ends are impractical.
Which flange standard pairs with stub ends?
ASME B16.5 lap joint flanges — the bore and lap face of the backing flange must match the stub end per Table 6.1-9.
Need This Standard for Your Project?
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