1. Internal coatings, such as fusion bonded epoxy or two pack phenolic epoxy paint (flow coat), may be used in the following situations: to limit corrosion during transit and storage, to facilitate precommissioning, to reduce hydraulic friction losses, pig wear and the formation of pyrophoric dust.
2. Pyrophoric dust (FeS) may be produced in natural gas pipelines, when the gas contains H2S (even in small quantities), under specific conditions.
3. FeS will form when the gas is in contact with bare steel pipe over a sufficient period, and the water vapour content of the gas is in excess of 60 percent of the content corresponding to the water dew point.
4. FeS may create operational problems, particularly at pressure reduction stations; it is a hazard when it comes in contact with air, e.g. when it is recovered at a pig receiver (self ignition).
5. Finally, the dust can accumulate at isolating flanges and, since it is conductive, render them ineffective.
6. When pyrophoric dust is expected, internal coating of the pipeline is strongly recommended (coating at the field welds, however, is not required).