Internal scales formation

Dear all,
Good day to everyone..

I shall seek advice in investigating the internal scale formation in the CS pipes. We have facility at port recently constructed to transfer the Oils from the jetty head to manifold.
Specifically here, i'm concerned with 28" (2 no's) black oil lines and 16" (2 no's) White oil lines among the sizes we have. the Pipe material is ASTM A106 gr.B.
The pipelines are constructed one month back and were ready for a 'test pigging' (we used foam pigs for this). The contractor team claimed to have completed with pigging but I insisted to do it one more time for the purpose of witnessing it myself. To my surprise I noticed lot of rust scales and water coming out during the pigging operation, in my 16" lines ! But the 28" lines were clean during and after pigging !
Note that all these lines were already pigged around 20 days back..
I would request the forum to put in here their voices for probable reasons & suggestion and also the best solution for this problem...

With Best Regards,
ALI IMRAN.

Question! ...Did they use water or compressed air to push this pig throught the line the first time?

The pigging is done with Nitrogen for white oil lines. But mixture of compressed air and N2is used for fuel oil lines only.

Best Regards.
IMRAN.

what u mean by white pipe line ?