High Tube Bundle Replacement MDMT

A Minimum Design Metal Temperature (MDMT) of 100°F (38°C) for a brand new heat exchanger tube bundle installation?

How is this even possible?

I see these in service all the time when an Owner/Operator does not pay attention to the MDMT when replacing carbon steel tube bundles in heat exchangers with an original construction date prior to 1987. The MDMT calculation was not performed on these old tube bundles as they predate the MDMT calculation in the ASME Code. 

Many times older exchangers have thick tubesheets constructed with UCS-66 Curve A materials that result in high MDMTs. Pressure-containing equipment with high MDMTs carry a high operational risk as the brittle fracture mode of failure is immediate and catastrophic. Please review the use of UCS-66 Curve A materials in your process. I prefer to upgrade material selection to a UCS-66 Curve C or Curve D material at the next scheduled tube bundle replacement.