Sulfuric acid can be tricky to deal with and there are entire reference books and NACE standards devoted to the subject. Assuming 1.6 SG sulfuric is about 87% and 1.2 SG acid is about 28%, 316L stainless steel would not be recommended. Polypropylene is slight more resistant than HDPE or UHMWPE. The problem with these plastics is that they can be subject to environmental stress corrosion cracking (ESCC) by sulfuric acid and their susceptibility to ESCC increases with increasing temperature and acid concentration. PTFE would be a safer choice. Care needs to be taken when using solid thermoplastic piping including proper mechanical support. Lined pipe is more commonly used.