Materials for Boiler External Piping

[DSB123]

Hi All,
Just wanted to get reactions to the following proposal.
It has been proposed to install a new piping system on the Plant in Stainless Steel. The system is HP Steam at circa 126 Bar and 574 Deg C. The "Engineer" has proposed using Stainless Steel for the Pipe with CrMo for the valves.

Any Thoughts??

 

[metengr]

The conditions you have stated are for a subcritical unit. My recommendation on this is I would go with Grade 91 pipe material versus stainless steel. Let me preface my recommendation by saying that cost to use stainless steel is just not economical for this application.

The Grade 91 material would be well suited provided very strict processing and handling controls are specified and verified by the owner or owner's engineer.

Going with stainless also requires some added level of process control and having dissimilar metal weld joints at elevated temperature exposure will result in long term problems. There is just no way around the elimination of reduce creep rupture life at dissimilar weld connections, as you would have with using Cr-Mo-V or Cr-Mo valves in a stainless steel steam line.