Sending you two attachments given by ASM ( American Society of Metals - now known as ASM International ) showing scale resistance of SS. In 2nd chart it is shown SS316 can withstand maximum service temperature of 870 deg C for intermittent service ( not continuously exposed to high temperature for a long time ) and maximum 925 deg C for continuous service in air. We can think our M38 shall have similar capability as the composition of M38 falls in line with Cr- Ni -Mo based SS materials like SS316.