RFQ Today
Certifications: EN 10204 3.1 / 3.2 material test certificates, Nelson curve HTHA compliance documentation where applicable, and complete export documentation packages.
Petro-
chemical
A world-class technical reference for petrochemical process engineers, EPC contractors, procurement heads, and TPI inspection agencies specifying fasteners, flanges, and materials for cracking, reforming, treating, and polymer production units — covering high-temperature hydrogen attack (HTHA) and Nelson curve material selection, naphthenic acid corrosion, sulfidation corrosion and McConomy curves, amine unit corrosion, and the QC and documentation discipline required for critical petrochemical process supply.
A Fundamentally Different
Hydrogen Damage Mechanism
High-temperature hydrogen attack is a specific, well-documented, safety-critical petrochemical failure mechanism — genuinely distinct from the sour-service hydrogen embrittlement and sulfide stress cracking mechanisms discussed throughout RR Hydraulic’s NACE MR0175-related references, requiring its own specific material selection tool.
1.1 — What Distinguishes HTHA from Sour Service Hydrogen Embrittlement
1.2 — Nelson Curves: The Standard HTHA Material Selection Tool
API RP 941 (“Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants”) publishes the industry-standard “Nelson curves” — empirically derived operating limit curves plotting safe combinations of temperature and hydrogen partial pressure for specific steel grades (plain carbon steel, and various chromium-molybdenum alloy steel grades with progressively higher chromium content providing progressively better HTHA resistance) below which HTHA damage is not expected to occur within the material’s design life. Material selection for hydroprocessing reactors, piping, and associated components operating at elevated temperature and hydrogen partial pressure should be verified against the applicable Nelson curve for the specific steel grade and the unit’s actual operating temperature and hydrogen partial pressure — operating above the applicable curve for an extended period, even without immediately apparent damage, represents a genuine, documented safety risk requiring either material upgrade (to a higher-chromium alloy steel grade with better inherent HTHA resistance) or confirmed operation within the curve’s safe envelope.
1.3 — Material Selection Implications
Where Nelson curve verification indicates standard carbon steel or lower-chromium alloy steel (such as the A193 B7 discussed in RR Hydraulic’s dedicated reference) is inadequate for the unit’s actual operating temperature and hydrogen partial pressure, higher-chromium alloy steel grades (2.25Cr-1Mo, 3Cr-1Mo, or higher chromium content grades, following the same fundamental chromium-content-driven resistance principle discussed for other alloy steel and stainless materials throughout RR Hydraulic’s references) provide progressively better HTHA resistance at progressively higher material cost. Always confirm the applicable Nelson curve verification has been performed for the specific unit’s design and actual operating conditions before finalising material grade selection for hydroprocessing service.
(McConomy Curves) &
Naphthenic Acid Attack
Two additional, refining-and-petrochemical-specific corrosion mechanisms — high-temperature sulfidation and naphthenic acid corrosion — require their own dedicated engineering prediction tools and material selection approaches distinct from the general corrosion mechanisms discussed throughout RR Hydraulic’s other materials references.
Submit process unit, temperature/pressure, material, and quantity to sales@rrhydraulics.com for a certified offer.
2.1 — Sulfidation Corrosion and McConomy Curves
High-temperature sulfidation corrosion occurs when sulfur compounds present in crude oil and refined petroleum streams react directly with steel at elevated temperature (generally becoming significant above approximately 260°C), producing a general, relatively uniform metal loss corrosion mechanism distinct from the localized pitting mechanisms discussed throughout RR Hydraulic’s stainless and duplex references. McConomy curves (published in API 939-C and related industry references) provide empirically derived corrosion rate predictions as a function of temperature and sulfur content for carbon steel and various chromium-content alloy steel and stainless grades — similar in application logic to the Nelson curves discussed in Part 1, but addressing sulfidation rather than hydrogen attack. Material selection for high-sulfur-content, high-temperature process streams (crude distillation, hydrotreating, and related units) should reference the applicable McConomy curve data for the specific stream’s actual sulfur content and operating temperature to confirm the selected material’s predicted corrosion rate is acceptable for the design corrosion allowance and intended service life.
2.2 — Naphthenic Acid Corrosion
2.3 — Amine Unit Corrosion
Amine treating units — using amine solutions (MEA, DEA, MDEA, and related compounds) to remove H₂S and CO₂ from process gas streams — present specific corrosion risks distinct from the general sour service considerations discussed throughout RR Hydraulic’s NACE MR0175-related references. Amine solution corrosivity depends heavily on specific concentration, contamination (heat-stable salts, degradation products), temperature, and velocity conditions — rich amine (loaded with absorbed acid gas) is generally more corrosive than lean amine, and specific high-velocity locations (reboiler tubes, certain piping elbows) frequently experience accelerated corrosion requiring material upgrade or specific design mitigation. Amine unit material selection should account for both general corrosion from the amine solution chemistry and any specific sour service cracking risk from the acid gas being removed, per RR Hydraulic’s dedicated A193 B7M and related sour service references.
by Petrochemical
Process Unit
Petrochemical process units span a wide range of temperature, pressure, and chemistry conditions — the following reference maps typical process units to appropriate materials across RR Hydraulic’s full materials reference library.
3.1 — Material Selection by Process Unit
| Process Unit | Key Corrosion/Damage Mechanism | Typical Material | RR Hydraulic Reference |
|---|---|---|---|
| Hydroprocessing / hydrotreating reactors and piping | HTHA (Part 1) | A193 B7 (verified against Nelson curve) or higher-Cr alloy steel | A193 B7 reference |
| Crude distillation / atmospheric & vacuum units | Sulfidation, naphthenic acid (Part 2) | Carbon/alloy steel with SS 316L/321 cladding or lining at high-risk locations | SS 316L, SS 321 references |
| FCC (fluid catalytic cracking) units | Catalyst erosion + high temperature | Erosion-resistant alloys, refractory-lined carbon steel | General high-temp references |
| Amine treating units | Amine corrosion + sour service (Part 2) | Carbon steel (general) with 316L or higher at high-velocity locations, A193 B7M bolting | SS 316L, A193 B7 references |
| Sour water stripping units | Sour service, NACE MR0175 | A193 B7M bolting, NACE-qualified materials throughout | A193 B7 reference (Section 1.3) |
| Polymer (PE/PP) reactors | High pressure, general process compatibility | Carbon/alloy steel per ASME Section VIII, standard flange bolting | A193 B7, ANSI B16 references |
| Ethylene/olefins cracking furnaces | High temperature, carburization | Incoloy 800H/800HT, HK/HP cast furnace tube alloys | Incoloy 800 reference |
Industry Applications
& Documentation
RR Hydraulic maintains full traceability across the petrochemical materials range, with HTHA and sour service compliance documentation coordinated for critical process unit supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 / Documentation Requirements
| Certificate | Content | EPC Requirement | When Mandatory |
|---|---|---|---|
| 2.1 / 2.2 | Declaration / non-specific | Not acceptable for pressure-boundary process supply | Never for critical petrochemical process piping/vessel supply |
| 3.1 (EN 10204) | Heat-traceable chemical + mechanical test report | Mandatory — all EPC supply | All petrochemical process piping, vessel, and general project supply |
| Nelson curve compliance documentation | Material verification against applicable HTHA operating limit curve | Mandatory — hydroprocessing service | All hydroprocessing reactor/piping material supply |
| 3.2 (EN 10204) | 3.1 + TPI countersign | Critical / owner-specified critical items | High-consequence petrochemical pressure equipment |
4.3 — Applications by Process Category
Hydroprocessing and Reforming Units
A193 B7 and higher-chromium alloy steel bolting and piping components for hydrotreating, hydrocracking, and catalytic reforming units, with material grade selection verified against the applicable Nelson curve per Part 1 for the unit’s specific operating temperature and hydrogen partial pressure.
Crude Distillation and Treating Units
Carbon/alloy steel with strategic stainless steel upgrades at high-sulfidation and naphthenic-acid-risk locations, per the McConomy curve and crude-quality-dependent material selection discussed in Part 2.
Polymer and Petrochemical Production Units
General high-pressure vessel and piping bolting (A193 B7, per RR Hydraulic’s dedicated reference) and flange components (ANSI B16 series) for ethylene, polyethylene, polypropylene, and related petrochemical production units.
4.4 — Export Packaging Specification
- Petrochemical process components packed by material grade and process unit application with clear labelling, given the mechanism-specific material selection discussed throughout this reference
- Heat/lot number marked or tagged on each item, cross-referenced to the accompanying material test certificate and, where applicable, Nelson curve compliance documentation
- Components segregated from carbon steel and other dissimilar materials during packing to avoid surface contamination affecting corrosion performance at high-alloy upgrade locations
- Documentation in a waterproof pocket: EN 10204 3.1/3.2 MTC, chemical composition report, mechanical properties report, Nelson curve compliance documentation (hydroprocessing service), hardness/NACE compliance report (sour service), and packing list with process unit/material/size breakdown per item
- ISPM-15 timber or export cartons for international shipment, with country of origin and HS tariff code documentation matched to the specific component category
Submit your process unit, operating conditions, and quantity to RR Hydraulic for a complete, certified commercial offer.