aka2,
There is no material imune to the corrosive environment. There is one consideration, which material vesus cost will resist longer. You can learn this easily and quickly looking up the NACE MR0175. Moreover, you should take the advices on this forum as indicative only, use them as guidance, not engineering decisions made by others for you. Remember, if anything goes wrong, you cannot blame a forum for your mistake. After reading the mentioned standard, you will be able to make your own decisions, based on engineering judgement and the depth of your pocket. However, we can help you to clarify issues in the standard you have read it.
best regards,
gr2vessels