Inconel 600 was the standard nuclear steam generator tube material for decades. Then primary water stress corrosion cracking started showing up across the industry in the 1980s, forcing costly tube plugging and, eventually, full steam generator replacements. Inconel 690 is what replaced it. Nearly double the chromium, 27 to 31% against 600's roughly 15.5%, is what gives it dramatically better PWSCC resistance, and it's been the default choice for new and replacement nuclear steam generators ever since. USA Piping Solution supplies Inconel 690 as seamless pipe and tube to ASTM B167, with condenser and heat exchanger tube to ASTM B163, all in UNS N06690. For general-purpose service where the PWSCC history doesn't apply, our Inconel 600 Pipes & Tubes page may be the more economical choice.
Specifications
| Specification | Details |
|---|---|
| Standard | ASTM B167 / ASME SB167 (seamless pipe & tube) · ASTM B163 / ASME SB163 (condenser & heat exchanger tube) |
| UNS | N06690 |
| DIN / Werkstoff | 2.4642 |
| Type | Nickel-chromium-iron alloy, highest chromium content of any major commercial Inconel grade |
| Nuclear condition | Thermally treated (690TT) for steam generator and reactor coolant service; confirm exact treatment and testing requirements per project specification |
| Form | Seamless and welded pipe and tube |
Why 690 Replaced 600 in Nuclear Service
Chromium is what forms the protective oxide layer that resists cracking at grain boundaries under the specific combination of stress, temperature, and primary coolant water chemistry found inside a pressurized water reactor. Inconel 600's chromium content, around 15.5%, turned out not to be enough for that specific environment over decades of service, and PWSCC became the industry's leading cause of steam generator tube degradation and premature replacement. Inconel 690, with chromium raised to 27 to 31%, closed that gap. Tube ordered for nuclear steam generator service is typically specified in the thermally treated condition, often referred to as 690TT, a heat treatment applied specifically to optimize grain boundary carbide structure for maximum PWSCC resistance. Confirm the exact thermal treatment and testing requirements against your project's specific nuclear code and utility specification when you place your order.
Testing, Certification & Availability
Every order ships with mill test certification and full material traceability; see our Quality Policy page for the full testing program we run across all grades. Nuclear-grade orders typically carry additional documentation and thermal-treatment requirements specific to the project's code and utility specification; tell us your requirement and we'll confirm what's needed. Send us your OD, wall thickness, and length requirement and we'll confirm current availability and lead time.
Related Products
- Inconel 600 Pipes & Tubes
- Inconel 625 Pipes & Tubes
- Incoloy 800 Pipes & Tubes
- Inconel Pipes & Tubes
- Nickel Alloy Pipes & Tubes
- What Is Inconel? A Complete Guide
Frequently Asked Questions
Why does Inconel 690 have so much more chromium than Inconel 600?
Chromium is what resists primary water stress corrosion cracking (PWSCC), the failure mode that emerged in Inconel 600 steam generator tubes after years of service. 690 nearly doubles chromium content specifically to close that gap.
What is 690TT?
690TT refers to Inconel 690 in the thermally treated condition, a heat treatment applied to optimize grain boundary carbide structure for maximum PWSCC resistance. It's the standard condition specified for nuclear steam generator tubing. Confirm the exact treatment parameters against your project's nuclear code requirements.
Is Inconel 690 only used in nuclear applications?
No. Its high chromium content also makes it a strong performer in nitric acid, caustic, and other oxidizing chemical processing environments outside the nuclear industry.
What sizes are available in Inconel 690 pipe and tube?
Send us your OD, wall thickness, and length requirement and we'll confirm current mill availability and lead time.