Saudi Arabia is building and expanding pipelines for gas, crude, refined products and water at a fast pace. Every new line goes through the same final stage before it carries product: pre-commissioning and commissioning. Nitrogen plays a central part in it. This guide walks through the typical steps.
1. Cleaning and gauging
After construction, the line is cleaned with pigs to remove debris, scale and construction waste. A gauging pig with a soft metal plate is run to check that there are no dents or ovality that would stop later pigs.
2. Hydrostatic testing
The line is filled with water and pressurised to prove its strength and tightness. The test pressure and hold time come from the design code and the operator’s standards. Our guide to hydrotest requirements in Saudi Arabia explains the rules, and our hydrotest services cover the work.
3. Dewatering
The test water is pushed out with pigs driven by compressed air or nitrogen. Several pigs may be run to remove as much water as possible. Water disposal must follow environmental rules, especially if chemicals were added.
4. Swabbing and drying
Even after dewatering, a thin film of water stays on the pipe wall. For gas lines this must be removed, because water leads to corrosion and hydrates. Drying methods include:
- foam swabbing pigs to soak up remaining water;
- dry air drying, which is cost-effective for long lines;
- vacuum drying;
- nitrogen drying, often to finish and leave the line inert.
The line is dry when the outlet gas reaches the agreed dew point. See purging vs drying vs leak testing.
5. Nitrogen purging
Before hydrocarbons can be introduced, oxygen must be removed. Nitrogen is injected and pushed through the line, often behind a pig, until the oxygen at the far end is below the operator’s limit. The nitrogen purge volume guide shows how to estimate the quantity.
6. Nitrogen packing
If the line will not be commissioned straight away, it is packed with nitrogen at a slight positive pressure. This keeps air and moisture out until start-up.
7. Introducing product
At start-up, gas or liquid is introduced at a controlled rate, pushing the nitrogen ahead of it to a vent or flare. The interface is monitored until product quality is reached at the receiving end.
8. Handover
The contractor hands over a full dossier, typically including:
- cleaning and gauging reports;
- hydrotest charts and certificates;
- dewatering and drying records with dew point readings;
- purge records with oxygen readings;
- nitrogen packing pressure and date.
Saudi-specific points
- Distances: long lines between, for example, the Eastern Province and Riyadh or the west coast need careful logistics for nitrogen tankers and vaporisers.
- Heat: high ambient temperatures affect pressure readings during hold periods, so temperature must be recorded alongside pressure.
- Water: test water source and disposal must be approved, and treated water may be required to protect the pipe. Operators often have their own standards for test water and lay-up.
- Client standards: Saudi Aramco, SWCC, SABIC and other owners each have their own commissioning procedures. Always work to the owner’s documents.
Frequently asked questions
How long does pipeline commissioning take?
From hydrotest to packing, anywhere from days for a short line to several weeks for a long one. Drying is often the longest step.
Can compressed air be used instead of nitrogen?
Air can be used for dewatering and much of the drying. But the final purge before hydrocarbons must remove oxygen, so nitrogen is used for that step.
Who supplies the nitrogen?
Usually the commissioning contractor, using liquid nitrogen with vaporisers or on-site membrane units.
Our nitrogen purging services support pipeline commissioning from Riyadh and Al Kharj to Haradh and NEOM. Talk to our team.
