Corrosion Of Wet Gas Pipelines: Water Corrosion Prevention
We are all aware of subsea pipelines that are seen in large diameters all over the world, and are being used for wet gas transportation over long distances from offshore fields to onshore facilities. For proper management and passage of uninterrupted gas supply along the chain, it’s necessary to understand corrosion mechanisms that occur at the top of the line, as a result of dewing. Apart from the maintenance in production and transport of gas along the chain, this strategy would ensure long-term pipeline integrity for maintenance of the chain. The prediction of corrosion in the system is challenging, for the type of corrosion varies based on the nature of iron sulfide scales that form over the pipelines as a result of temperature ranges and condensation rates.
Corrosion inhibitors, on the inner sides of the pipe line, help in preventing internal corrosion. But it’s hard to prevent corrosion on the outer sides of the pipeline. ‘Spray pigs’ that have the capacity to bypass flow and create a venturi effect are being used now. They help to protect the pipes against corrosion by sucking liquids containing corrosion inhibitors from the bottom of the pipe and spray them onto the top of the pipe. However, if you do not remove the corrosion causing agents, like debris and deposits from the individual pits, corrosion inhibitors will not be effective on the top or bottom of a pipe. To help remove the debris and deposits, we could use self-cleaning equipment like cleaning pigs that have sprung brush bristles that are capable of aggressively removing deposits. To remove stronger corrosion causing agents, the use of bypass flow features seen in certain upgraded pigs are used to certify good prevention and remediation against corrosion.
Keeping the system clean:
Prevention is always better than cure. Always ensure that your inner pipelines are regularly cleaned, for it prevents and minimizes corrosion. Cleaning is made effective with the use of pigs with the inclusion of chemicals.
If you haven’t cleaned the inner portions of the pipe for quite a while, you may have to use an advanced cleaning program. To begin with, you may have to use very non-aggressive pigs that give out low density foam. On doing this repeatedly, you can remove small debris and contaminants. In case of very thick deposits, a smaller pig is the tool of choice. Start with that and then later you’ll be able to work up to the regular size.
Cleaning Requirements Based on Types of Contamination:
- Types Of pigs to choose from,
- Black Oxide: discs, brushes
- Ferrous debris: magnets
- Liquids: multi-lip sealing cups and/or discs
- Microbes: pit-cleaning / wear-compensating brushes, discs
- Scale: wear-compensating brushes, pit-cleaning brushes, studs
- Sand: discs, brushes
- Wax (hard / soft): blades, discs, self-cleaning / wear-compensating brushes
- To ensure even more effective cleaning, its better to use chemicals in the cleaning procedures.
Applications To prevent Corrosion: