Syngas Pipeline Requirements
1) Syngas Composition
Syngas is a mixture of hydrogen (H₂) and carbon monoxide (CO). It can contain traces of methane (CH₄), carbon dioxide (CO₂), and impurities like sulphur compounds, chlorides, and heavier hydrocarbons.
2) Syngas Flammability
Hydrogen
Upper Flammability Limit (UFL) = 75%
Lower Flammability Limit (LFL) = 4%
Carbon monoxide
UFL = 74 %
LFL = 12.5%
3) Steel Hardness requirements in hydrogen and syngas:
- Pipe maximum hardness≤ 22 HRC [Hardness Rockwell C],
- Welds maximum hardness≤ 22 HRC,
4) Leakage Surveys
The minimum recommended leakage survey frequency is every three months.
5) Carbon steel material
- Carbon equivalent [CE] ≤ 0.43;
C.E. = %C + %Mn/6 + [%Mo+%Cr+%V]/5 + [%Ni+%Cu]/15
- Carbon steel maximum tensile strength≤ 800 MPa [116 kpsi].
6) Microalloyed Steels
- Carbon equivalent [C] ≤ 0.35 [API 5L PSL 2 ≤ 0.43%]),
- Sulfur ≤ 0.01% [API 5L PSL 2 limit is 0.015],
- Phosphorus ≤ 0.015% [API 5L PSL 2 limit is 0.025%].
7) Stainless Steels:
- A more than 13% chromium content mitigates the CO stress corrosion cracking and carbonyl formation.
- For welding, you can use low carbon [304L, 316L] or stabilized grades [316Ti, 321, 347].
8) Nickel Alloys
Verify that nickel alloys are appropriate for syngas gas service to avoid hydrogen embrittlement.
If high strength is needed, use precipitation-hardened alloys like Monel K-500 and Inconel X-750 within hardness limits.
9) Copper alloys
Hydrogen can damage copper alloys with oxygen, causing cracking at high temperatures. Deoxidized copper alloys are not susceptible to this issue and are suitable for hydrogen and CO/Syngas service.
10) Cobalt Alloys
Cobalt alloys, especially Stellite formulations, are suitable for applications requiring abrasion or wear resistance. They are adequate for use in hydrogen and CO/Syngas service.
11) Flanges and gaskets:
- Leak-resistant flange types should be used, such as raised face, tongue and groove, or ring joint flanges.
- The gasket materials should be appropriate for design pressures and temperatures and compatible with hydrogen and carbon monoxide.
- Threaded connections should be used only where welded and flanged connections are unusable.
12) Rupture discs Rupture discs shall not be utilised due to the risk of toxicity.
13) Valves: - Packing Positive sealing of packing glands is essential for CO and Syngas’ service.
- Damage from particulates
To protect soft seats from damage, install a 300-micron strainer upstream of valves or valve clusters, excluding vents, drains, and pressure relief valves.
14) Electrical hazardous area to comply with:
- American Petroleum Institute RP 500 A,B, C,
- European directive ATEX 94/9,
- NFPA 496, 497,
- NFPA 70,
- IEC 79.