Using Thermal Spray Aluminium on Subsea Duplex Pipe? 1

[DarrenHeal]

Guys
Working on a project which involves SUBSEA structures with duplex stainless steel (probably API 5LC LC65-2205) cooling loops within them. Inlet temperature is about 100 Celsius, although some "headroom" might be advisable.
Need to spec. amn anti-corrosion coating for the loops (which will be 150 to 200 metres long welded-up 5-inch nominal diameter pipe coils).
Client suggested gold plating them!!!
I was thinking thermal-sprayed aluminium with an organic sealer applied over the completed spool (including welds) in one fell swoop.Any suggestions / tips / comments?
Specified coating must meet DNV-RP-F112 HISC-prevention criteria.Many thanksDarren

 

[SJones]

Reasonable choice for a cooling spool being a thin film with a good thermal conductivity; however, being a sacrificial anode, TSA will still generate hydrogen. If you are following RP-F112, you will note that the material is to be resistant to HISC by design and manufacture, irrespective of the coating. So, does a cooling spool really need a coating at all? Go to 25Cr super duplex so that the material has a lower stress utilisation reducing the risk of HISC, and then consider leaving the spool bare. If a coating is definitely required, EEMUA 194 provides a good menu but you will have to watch the U value that you end up with otherwise the cooling spool won't be a cooling spool!

Steve Jones
Materials & Corrosion Engineer

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