EN 10253-2 Type B buttweld pipe fittings for the full spectrum of refinery process units. CrMo alloy steel grades P5 through P91 for high-temperature hydrocarbon service. Monel 400 (2.4360) for HF alkylation — the only metallic alloy immune to hydrofluoric acid at all concentrations. 316L for caustic and low-temperature service.
| Process Unit | Grade | W.Nr. | Key Requirement |
|---|---|---|---|
| Crude distillation — atmospheric (ADU) | P11 / P22 | 1.7335 / 1.7380 | 340–400°C service; sulphidation resistance |
| Vacuum distillation (VDU) — side-draw | P5 | 1.7362 | 5Cr resists naphthenic acid corrosion (NAC) at moderate TAN |
| FCCU — slide valves, regenerator | P9 / P5 | 1.7386 / 1.7362 | 700°C+ hot gas, sulphidation, erosion |
| Hydrocracker reactor loop | P22 / P91 | 1.7380 / 1.4903 | API 941 — high-pressure H₂ service (Nelson Curves) |
| Hydrotreater | P22 | 1.7380 | H₂ partial pressure service — better Nelson curve than P11 |
| Catalytic reformer | P9 | 1.7386 | 600–700°C, H₂ + sulphur; 9Cr without V/Nb (not P91) |
| HF alkylation | Monel 400 | 2.4360 | ONLY alloy immune to HF — NiF₂/CuF₂ protective film; stress-relief mandatory |
| Sulphuric acid alkylation | 316L | 1.4404 | Conc. H₂SO₄ compatible; no HF exposure |
| Caustic wash / desalter | 316L | 1.4404 | NaOH scrubbing at ambient to mild temperature |
| SRU (Sulphur Recovery Unit) | P9 | 1.7386 | Polysulphide + H₂S at high temperature |
P9 (EN 1.7386, 9Cr-1Mo) and P91 (EN 1.4903, 9Cr-1Mo-V-Nb) look similar by Cr content but are fundamentally different alloys. P9 is P-No. 5B with filler ER80S-B8. P91 is P-No. 15E with filler ER90S-B9 — different preheat, PWHT range, and qualified procedures. Mixing these grades or their fillers in refinery piping is a serious safety defect. For FCCU and reformer service, P9 is the correct grade — not P91.
VDU side-draw naphthenic acid (NAC), sulphidation in moderately aggressive crude. FCCU regenerator transfer lines. P-No. 5B.
Full grade page →FCCU slide valves, SRU, reformer furnace transfer. 9Cr without V/Nb microalloying — simpler weld procedure than P91. P-No. 5B.
Full grade page →HF alkylation (STRATCO/ISOALKY) piping. Only metallic alloy immune to HF at all concentrations. Stress-relief at 870–900°C mandatory before service.
Full grade page →EN 10204 3.1 test certificates. PWHT records and hardness reports for all CrMo grades. Positive Material Identification (PMI) report available. NACE MR0103/ISO 17945 compliance documentation.
