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Key takeaways
- NORSOK standards were developed by the Norwegian petroleum industry and are widely used on North Sea and international offshore projects.
- L-001, L-002 and L-004 cover piping classes, layout and stress, and fabrication and testing. M-001 and M-601 cover materials and welding.
- DNV standards cover submarine pipelines, structural analysis of piping and duplex steel design against hydrogen cracking.
Why another layer of standards?
ASME B31.3 sets minimum requirements for process piping. Offshore operators wanted more consistency between projects and suppliers, and more conservative practice in an environment where repairs are expensive and escape routes are short. NORSOK standards were developed to give that common baseline, and many operators outside Norway use them too.
NORSOK standards a piping engineer meets
L-001 Piping and valves defines standard piping classes and valve data sheets. Many projects copy its class naming and component tables directly.
L-002 Piping system layout, design and structural analysis sets layout rules (access, valve operation, clearances) and requirements for stress analysis and supports.
L-004 Piping fabrication, installation, flushing and testing covers the construction side: fabrication tolerances, cleaning, flushing and pressure testing.
L-005 Compact flanged connections covers compact flanges, which are much lighter than ASME B16.5 flanges for the same rating.
M-001 Materials selection gives the rules for choosing materials by service, including limits for stainless and duplex steels in seawater.
M-601 Welding and inspection of piping adds welding and examination requirements beyond ASME, such as extra NDT and hardness limits.
M-630 Material data sheets standardizes the purchasing requirements for piping materials.
DNV standards
DNV-ST-F101 is the main standard for submarine pipeline systems. DNV-RP-D101 gives guidance on structural analysis of piping systems, including offshore load cases. DNV-RP-F112 covers design of duplex stainless steel against hydrogen-induced stress cracking (HISC), which matters for subsea equipment under cathodic protection.
| Standard | Covers |
|---|---|
| NORSOK L-001 | Piping classes and valves |
| NORSOK L-002 | Layout, design, stress analysis |
| NORSOK L-004 | Fabrication, flushing, testing |
| NORSOK M-001 | Materials selection |
| NORSOK M-601 | Welding and inspection |
| DNV-ST-F101 | Submarine pipelines |
| DNV-RP-D101 | Structural analysis of piping |
How they fit with ASME
NORSOK doesn’t replace B31.3; it sits on top of it. A typical offshore design basis says something like “piping shall be designed to ASME B31.3 with the additional requirements of NORSOK L-002”. Where the two differ, the stricter one usually wins, but read your company specification, because some operators deviate from NORSOK in either direction.
What to take back to your desk
On your first offshore project, list every standard in the design basis and note its edition. Requirements change between editions, and auditors will check that you used the right one.
Educational content. Always design to your project specification.
