It should not be an issue. Section I does not deal with MDMT as a boiler usually needs to be warm to perform it's function. If it is going to operate at a low temperature there are other problems to worry about.
By all means, ensure that brittle failure is not going to be a concern but it is not covered in Sec-I.
Some of the preferred materials, SA-515 for example, are preferred for boilers but are coarse grain and would not perform well in low temp impacts.
As mentioned above, Section I does not require rules for impact testing because the operating temperature is well above the MDMT.
The only concern is for pressure testing of inservice boilers. One needs to proceed with caution for boilers built before 1968 for plate steels that exhibit low notch toughness.
