[Help!!!] Piping material, repair hot-dip galvanized pipe due to corrosion (rusted)

[finaly91]

Dear Gentlemen,
I have some trouble with piping of tank as follows:
1. Material of internal and exterior is A106B Carbon steel pipe connected to Stainless steel pipe as picture

[link Point to another website Only the registered members can access] Question 1o Carbon steel and Stainless steel connected have any problem? In case internal is hot-dip galvanized pipe and exterior is not hot-dip galvanized pipe?
2. Actually, we make internal is is hot-dip galvanized pipe and exterior is not hot-dip galvanized pipe. After 6 month, we found rusted inside pipe both of internal and extirior. Some internal pipe with galvanized dont have rusted as picture below:

[link Point to another website Only the registered members can access] Question 2: How can I repair those pipe. Number 7,8 are good, Number 1, 2, 3, 4 can I re-cleaning by chemical (acid) and re-galvanizing? Number 5, 6 is dangerous shall i replace new one? In case replay shall i change material of pipe?
Please, this is very important for me, many thanks for your help and sharing your experience

Best regards

[red100rose]

Question 1o Carbon steel and Stainless steel connected have any problem? In case internal is hot-dip galvanized pipe and exterior is not hot-dip galvanized pipe?
--> As you know, consider 2 points
1. According to para. 4.5.5.6 of API 571, do not used galvanizing pipe near SUS pipe. That point is flying zinc material to SUS surface that is occurred to LME.
Related article as below.
LME can only be prevented by protecting metal substrates from coming into contact with the low melting metal. For example, galvanized steel components should not be welded to 300 Series SS. 300 Series SS should be protected to avoid contact with galvanized components and overspray from zinc and inorganic zinc coatings.
2. Table 4.6 of API 571, driving force of galvanic corrosion is greater than other points and also occurred to near contact points of anode.

Question 2: How can I repair those pipe. Number 7,8 are good, Number 1, 2, 3, 4 can I re-cleaning by chemical (acid) and re-galvanizing? Number 5, 6 is dangerous shall i replace new one? In case replay shall i change material of pipe?
----> I don't guess above reason caused lack of related condition.