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
Monel 400 NACE MR0175 / ISO 15156-3 - Sour Service Qualification
NACE MR0175 / ISO 15156-3 governs selection of corrosion-resistant alloys for H2S-containing oil and gas service. Monel 400 (UNS N04400) is listed in Annex A.4 - solid-solution nickel-based alloys at 35 HRC maximum hardness, qualified without prequalification under Annex B. ASTM F468 caps Monel 400 bolts at 25 HRC, 10 HRC tighter than NACE, so F 468U product is automatically inside the NACE envelope. The standard addresses three cracking mechanisms: SSC, SCC, GHSC. Monel® is a registered trademark of Special Metals Corporation; TorqBolt is not authorized by, affiliated with or endorsed by Special Metals. Values cited are from ISO 15156-3:2020 and ASTM F468/F468M.
NACE MR0175 / ISO 15156-3 Scope
ISO 15156-3:2020 is Part 3 of the three-part standard (Part 1 general principles, Part 2 carbon and low-alloy steels, Part 3 CRAs and other alloys). It addresses cracking only (SSC, SCC, GHSC), not mass-loss corrosion. Scope covers wellheads, christmas trees, gathering and transportation pipelines, field processing plants and natural gas treatment. Selection parameters: H2S partial pressure (kPa), chloride (mg/l), in-situ pH, temperature and elemental sulphur.
Monel 400 Qualification under Annex A.4
Annex A.4 is the materials table for solid-solution nickel-based alloys. UNS N04400 is accepted at 35 HRC maximum hardness in the hot-finished and annealed or cold-worked condition for any equipment, with no prequalification under Annex B. Individual HRC readings up to 2 HRC above the cap are acceptable if the local average is at or below 35 HRC. Cold work incidental to machining, threading or straightening is allowed; cold work intended to raise mechanical properties is not. Controlled shot-peening per SAE AMS-2430 at Almen intensity 10C or less, 2.0 mm shot size max, is permitted; nitriding above 0.15 mm case depth is not.
| Parameter | Monel 400 (N04400) per Annex A.4 | SS 316L (S31603) per Annex A.2 |
|---|---|---|
| Material group | Solid-solution nickel-based alloys | Austenitic stainless steel |
| Maximum hardness | 35 HRC | 22 HRC (A.2 base); bounded envelope for S31603 |
| Heat-treat condition | Hot-finished and annealed, or cold-worked | Solution-annealed and quenched |
| H2S partial pressure ceiling | No specific limit at 35 HRC | 1 000 kPa at 60 deg C, 1 000 mg/l chloride, pH 3.5 |
| Temperature ceiling | No specific limit at 35 HRC | 149 deg C at 10.2 kPa H2S, 1 000 mg/l, pH 4.0 |
| Chloride ceiling | No specific limit at 35 HRC | 50 000 mg/l at 60 deg C, 1 000 kPa H2S, pH 4.5 |
| Prequalification (Annex B) required | No | No within envelope; yes outside |
ASTM F468 25 HRC Bolt Ceiling Clears the NACE Cap
ASTM F468/F468M Table 2 caps Class A (F 468U) Monel 400 hardness at 25 HRC across the size range; F 468V Class B (free-machining N04405) is capped at 20 HRC. That is 10 HRC tighter than the NACE A.4 ceiling, so F468 Monel 400 bolts and studs meet NACE MR0175 without supplementary testing. The 25 HRC product cap is enforced by F468 Table 2 and reported on the EN 10204 MTC; "ASTM F468 / NACE MR0175 / ISO 15156-3" on the purchase order is sufficient.
| Marking | Alloy / Class | Diameter | Yield min, ksi | Hardness ceiling | NACE A.4 margin |
|---|---|---|---|---|---|
| F 468U | Ni 400 Class A (N04400) | 0.250 - 0.750 in | 40 | 25 HRC | 10 HRC inside |
| F 468U | Ni 400 Class A (N04400) | 0.875 - 1.500 in | 30 | 25 HRC | 10 HRC inside |
| F 468U4 | Ni 400 Class A uprated | 0.875 - 1.500 in | 40 | 25 HRC | 10 HRC inside |
| F 468V | Ni 405 Class B (N04405) | All | 30 | 20 HRC | 15 HRC inside |
SS 316L Sour-Service Restrictions per Table A.2
Austenitic stainless steel in Annex A.2 is capped at 22 HRC maximum in the solution-annealed and quenched condition. The base group qualifies only at 60 deg C and 100 kPa pH2S maximum. SS 316L rows in Table A.2 extend the envelope conditionally: 60 deg C / 1 000 kPa H2S / 50 000 mg/l Cl / pH 4.5, or 90 deg C / 1 000 kPa / 1 000 mg/l / pH 3.5, or 149 deg C / 10.2 kPa / 1 000 mg/l / pH 4.0. Outside these rows SS 316L is not qualified. Monel 400 carries a flat 35 HRC ceiling with no environmental boxes; SS 316L is gated by four parameters that must all hold. Detail on the Monel 400 vs stainless steel page.
Companion CRA Qualifications
Inconel 625 (N06625) and Hastelloy C-276 (N10276) are also Annex A.4 at 35 HRC annealed. Monel K-500 (N05500) is precipitation-hardened, listed in Annex A.9 at 35 HRC aged under bolting clauses and a (Ni + 2Mo) restriction; the mill must certify against the specific A.9 row. Inconel 718 (N07718) is Annex A.9 at 40 HRC. Annex A.4 solid-solution alloys are the simplest to specify because they carry no environmental boxes at the 35 HRC cap. Source: ISO 15156-3:2020 Annex A; selection rules per Table A.1.
Documentation and Heat Traceability
A NACE order requires: EN 10204 type 3.1 MTC with chemistry by heat, mechanical test per ASTM B164 or F468 and hardness in HRC (3.2 with TUV or LRS witness on request); NACE compliance statement identifying heat number, product form, Annex A clause (A.4) and observed hardness range; hardness map showing every reading below 35 HRC (25 HRC for F468 bolts), applying the 2 HRC individual allowance only against a verified local average; heat number marking on every component (F468 fasteners 1/4 in and larger also carry the F 468U / F 468U4 / F 468V property code, applied via low-stress stamps). TorqBolt issues A.4 compliance against every Monel 400 heat ordered for sour service.
Typical NACE-Qualified Monel 400 Applications
Sour gas flange bolting and stud bolts for wellheads, christmas trees, separators and scrubbers (F468 Class A bolt with F467 nut, same heat). Downhole tools and wellhead components exposed to sour produced fluids. Refinery hydroprocess plant: hydrotreater and hydrocracker effluent piping bolting, sour-water stripper flanges and trim. Geothermal and brine reinjection combining sour gas, chloride brine and elevated temperature, where stainless is restricted by Table A.2 clauses. Sour pipeline components: valve bonnets, flange bolting and internals on gathering and transportation lines. Detail on the Monel 400 bolts, stud bolts, sour service NACE and HF alkylation pages.
Frequently Asked Questions
Is Monel 400 NACE qualified for sour service? Yes. Annex A.4 lists UNS N04400 at 35 HRC maximum, accepted without prequalification under Annex B, in the hot-finished and annealed or cold-worked condition.
What hardness ceiling applies to Monel 400? 35 HRC per Annex A.4. ASTM F468 caps bolts at 25 HRC, 10 HRC tighter, so F468 product is automatically inside the envelope.
Are there environmental restrictions on Monel 400? No H2S, chloride or temperature ceilings apply at the 35 HRC cap under Annex A.4. SS 316L in Table A.2 is gated by four parameters.
Does Monel 400 need Annex B testing? No for general sour service. Annex A.4 prequalifies N04400 at 35 HRC; Annex B testing (SSC per NACE TM0177, SCC, GHSC) is only required if service is outside Annex A.
Related Pages
Sour service NACE, bolts, stud bolts, ASTM F468, ASTM F467, vs stainless steel, vs Hastelloy C-276, vs Monel K-500, UNS N04400, chemical composition, corrosion resistance, round bar, plate, forgings, flanges, seamless pipe.
Request a Quote
For Monel 400 (UNS N04400) NACE MR0175 / ISO 15156-3 material send product form, size, H2S partial pressure, chloride, temperature and quantity to info@torqbolt.com or WhatsApp +91-22-66157017. TorqBolt QA-QC returns the A.4 compliance statement, EN 10204 type 3.1 (3.2 on request), mill heat source and Ex-Mumbai price within one working day. Export through JNPT and Mundra. Full Monel 400 reference on the main page.
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