DEMINERALIZED WATER 1

[ATsampalas]

Question :
In conformity with ASME 1 Edition 2001, Addenda 2003, for a preheater in a Heat Recovery Steam Generator (HRSG), what kind of base metals (pipes and tubes) can be chosen with a view to face demineralized water (Oxygen = 5 ppm ) and a Temperature between 30 and 155 °C ?

P.S. Our first approach was to chose SA 249 T 304 and SA 312 P 304 which are not authorised by ASME 1 Code (see PG-5.5 and note 1 + PG 9.1)

Sincerely,

ATsampalas

 

[metengr]

I also would NOT recommend stainless steel in this application. The ASME B&PV Code, Section I has very good reason for this as well because of concern for SCC in high purity boiler feed water at typical HRSG or boiler feed water pressures and temperatures. My choice would be carbon steel. At your posted operating conditions with 5 ppm of dissolved oxygen and temperatures between 30 to 155 deg C, the waterside surface of carbon steel will have a protective and uniform layer of magnetite with treated boiler water and proper pH.

 

[metengr]

As a follow-up to the SCC (stress corrosion cracking) of 304 ss mentioned above, this applies specifically to piping butt welds or welded attachments to 304 ss piping in the field. From a Code standpoint, there is really no way to prevent the sensitization of 304 ss during installation of feedwater piping. Failure of any 304 ss feedwater piping welds (butt or attachment) would be dangerous.

As far heat exchanger tubing, there are typically no butt welds in the 304 ss tubing to be concerned about in service. The heat exchanger tubing is normally supplied as solution treated for maximum corrosion resistance.