Material specification page for npt pipe thread fittings in Grade 8.8 Steel. Covers the grade designation (class 8.8), corrosion and magnetic behavior, comparable grades and their trade-offs, and the sizes available to ASME B1.20.1.
Why Choose Grade 8.8 Steel for NPT Pipe Thread Fittings
The workhorse medium-carbon alloy grade for structural joints. For npt pipe thread fittings, this matters when requires plating (zinc) for corrosion protection is the primary requirement.
Mechanical & Physical Properties
| Grade designation | class 8.8 |
|---|---|
| Magnetic response | Magnetic |
| Service temperature | up to approx. +300 °C |
| Corrosion characteristic | Requires plating (zinc) for corrosion protection |
Corrosion Behavior in Service
Carbon and alloy steel npt pipe thread fittings require a coating for corrosion protection. Zinc plating (with or without passivation) is the most common; hot-dip galvanizing is used for outdoor structural service; black-oxide is mainly a tarnish-prevention finish for tool-room use.
Comparable Grades
For NPT Pipe Thread Fittings, class 10.9 or 12.9 is the comparable strength step. Move up when the joint preload approaches the proof load of the current class; move down when the joint is over-specified. For corrosion-critical service, switch to stainless A2 or A4.
Sizes of NPT Pipe Thread Fittings Available in Grade 8.8 Steel
| Size | Nominal size (in) | Major diameter (mm) | Pitch (mm) | Threads per inch (TPI) | Taper | Reference standard | Notes |
|---|---|---|---|---|---|---|---|
| 1/16 NPT | 1/16 | 7.938 | 0.941 | 27 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1/8 NPT | 1/8 | 10.287 | 0.941 | 27 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1/4 NPT | 1/4 | 13.716 | 1.411 | 18 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 3/8 NPT | 3/8 | 17.145 | 1.411 | 18 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1/2 NPT | 1/2 | 21.336 | 1.814 | 14 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 3/4 NPT | 3/4 | 26.67 | 1.814 | 14 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1 NPT | 1 | 33.401 | 2.209 | 11.5 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1-1/4 NPT | 1-1/4 | 42.164 | 2.209 | 11.5 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 1-1/2 NPT | 1-1/2 | 48.26 | 2.209 | 11.5 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 2 NPT | 2 | 60.325 | 2.209 | 11.5 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 2-1/2 NPT | 2-1/2 | 73.025 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 3 NPT | 3 | 88.9 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 3-1/2 NPT | 3-1/2 | 101.6 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 4 NPT | 4 | 114.3 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 5 NPT | 5 | 141.3 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |
| 6 NPT | 6 | 168.275 | 3.175 | 8 | 1:16 | ASME B1.20.1 | Tapered pipe thread, self-sealing |