Specifications
Surface Treatments
Certifications
- ISO 9001 - 2015 Certified
- PED 2014/68/EC
- NACE MR0175/ISO 15156-2
- NORSOK M-650
- DFAR
- MERKBLATT AD 2000 W2/W7/W10
Incoloy 800H Tap End Studs
Tap end studs are stud bolts with one end carrying a short thread for permanent installation into a tapped or welded boss, and the other end carrying a full-length thread for nut assembly. TorqBolt machines Incoloy 800H tap end studs from ASTM B408 round bar for high-temperature welded-stud applications on petrochemical vessels, refinery furnace headers and steam-cycle equipment where one end of the stud is permanently fixed to the parent metal. The short tap end carries 1.5 to 2.0 stud diameters of thread engagement; the nut end carries full overall length minus tap-end length minus plain-shank section. Standard diameter range is M12 to M48 with custom lengths cut to project drawing. Every tap end stud ships with EN 10204 type 3.1 mill test certificate documenting heat number, chemistry per ASTM B408, solution-anneal cycle and ASTM grain size 5 verification. The configuration is the standard alternative to fully threaded stud bolts when one end is welded or permanently set.
Tap End Stud Dimensions (ASME B18.2.1 + DIN 938 Reference)
| Size designation | Across flats / OD | Head / nut height | Thread pitch | Standard reference |
|---|---|---|---|---|
| M12 | 12.0 mm OD | Tap end: 1.5d (18 mm); Nut end: balance | 1.75 mm | ASME B18.2.1 / DIN 938 |
| M16 | 16.0 mm OD | Tap end: 1.5d (24 mm); Nut end: balance | 2.0 mm | ASME B18.2.1 / DIN 938 |
| M20 | 20.0 mm OD | Tap end: 1.5d (30 mm); Nut end: balance | 2.5 mm | ASME B18.2.1 / DIN 938 |
| M24 | 24.0 mm OD | Tap end: 1.5d (36 mm); Nut end: balance | 3.0 mm | ASME B18.2.1 / DIN 938 |
| M30 | 30.0 mm OD | Tap end: 1.5d (45 mm); Nut end: balance | 3.5 mm | ASME B18.2.1 / DIN 938 |
| M36 | 36.0 mm OD | Tap end: 1.5d (54 mm); Nut end: balance | 4.0 mm | ASME B18.2.1 / DIN 938 |
| M42 | 42.0 mm OD | Tap end: 1.5d (63 mm); Nut end: balance | 4.5 mm | ASME B18.2.1 / DIN 938 |
| M48 | 48.0 mm OD | Tap end: 1.5d (72 mm); Nut end: balance | 5.0 mm | ASME B18.2.1 / DIN 938 |
Manufacturing Route at TorqBolt
Tap end stud manufacture follows the same controlled sequence as full-thread stud bolts, with one extra setup to control the plain shank length between the tap end and the nut end:
- Receive Incoloy 800H bar to ASTM B408; verify heat number, chemistry and EN 10204 type 3.1 mill cert.
- Cut to overall length on bandsaw.
- Centerless grind shank to bar tolerance.
- Thread tap end first: 1.5 to 2.0d engagement length, full thread depth, controlled chamfer for boss start.
- Thread nut end: full overall length minus tap end minus plain shank section.
- Plain shank section is left unthreaded and finish-machined to fit the boss bore on welded-stud applications.
- Solution anneal at 1149 deg C followed by rapid quench; ASTM grain size 5 verification.
- Visual + dimensional + PMI inspection 100 percent.
- Heat-stamp grade marking on the nut end; pack with VCI wrap and CoC + EN 10204 cert.
Tap End Stud Sizes Stocked and Lead Times
| Diameter range | Length range | Stock status | Lead time |
|---|---|---|---|
| M12 - M24 | 75 mm - 400 mm | Made-to-order from stock bar | 10 to 14 working days |
| M27 - M36 | 100 mm - 500 mm | Made-to-order from stock bar | 14 to 18 working days |
| M42 - M48 | 150 mm - 600 mm | Made-to-order, large bar | 3 to 4 weeks |
| Above M48 | Per project drawing | Forged blank required | 5 to 7 weeks |
Inspection and Heat Marking
EN 10204 type 3.1 mill test certificate is default. Type 3.2 with third-party witness on call-out. Specific tap-end-stud inspections include:
- Tap end thread length and chamfer profile verified against print.
- Plain shank diameter checked at three points along length.
- Nut end thread engagement verified with ring + plug gauges.
- Hardness band 120-184 HB on first piece and one per batch.
- ASTM E112 grain-size etch verification.
- PMI by X-ray fluorescence on first piece and one per batch.
- Heat number stamped on the nut end for traceability.
- Visual inspection for surface defects on both threaded sections and plain shank.
Typical Service Conditions
Tap end studs are specified where one end of the bolt is welded, screwed permanently into a boss or sleeved into a vessel-wall fitting and only the nut end is removable. Typical applications:
- Vessel-wall stud bosses on ASME Section VIII pressure vessels.
- Welded refractory anchor studs on hydrocarbon-cracking furnace walls.
- Tubesheet welded studs on high-temperature heat exchangers.
- Permanent installation on reformer outlet headers and pigtail connection bosses.
- Steam superheater header welded-stud bolting on fossil and waste-heat boilers.
- Combustion-air ductwork stud-welded fasteners in refinery service.
Incoloy 800H Alloy Considerations on This Fastener Form
Companion Fasteners and Related Pages
- Stud Bolts: fully threaded version when both ends carry nuts.
- Double End Studs: both ends threaded with plain centre.
- Hex Nuts: matched nuts for the nut end.
- Heavy Hex Nuts: heavy nut alternative on hot-zone service.
- Anchor Bolts: structural anchor variant for foundations.
Frequently Asked Questions
Q. What is the standard tap end engagement length?
1.5 to 2.0 stud diameters of thread engagement, per DIN 938 and DIN 939. TorqBolt supplies 1.5d default; deeper engagement is machined on PO call-out.
Q. Can tap end studs be welded directly to the parent metal?
Yes when the parent metal is Incoloy 800H or a compatible nickel-base alloy. Stud-welding procedures require qualified WPS and PQR per ASME Section IX with Incoloy 82 / 182 filler. Customer-supplied weld procedure is required.
Q. What is the difference between tap end and double end studs?
Tap end studs have one short thread end (1.5 to 2.0d) and one long thread end with a plain shank between. Double end studs have two equal thread ends with a plain centre section. Tap end is used for welded or permanent install; double end is used for through-flange applications.
Q. Can tap end studs be supplied to inch sizes?
Yes. Standard supply is metric (M-series). Inch sizes 1/2 inch through 1-7/8 inch are machined to ASME B18.2.1 dimensions on PO call-out from the same B408 bar stock.
Q. Are tap end studs available with hex head instead of plain end?
No. Tap end studs are stud-form with two threaded ends. For head-and-shank fasteners see hex bolts or heavy hex bolts.
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