Questions about Caustic service (Materials selection)

[kissjxp]

I started my work as a Materials Engineer three months ago. Now I have questions on materials selection for drums and heat exchangers in caustic service.

My questions:

1) What is the exact definition of the caustic service.
2) In NACE RP0403-2003 Figure 1, the materials selection and PWHT requirement are determined by the temperature and concetraion of NaOH (wt%). But my supervisor said that the concetraion of caustic included NaOH and other sodium salts (Na2S...). Is he correct?

For example:
The design temperature: 80C
NaOH: 0.5 wt%, other sodium salts: 9.5 wt%
what is the caustic concentraion I should use: 0.5 wt% or 10 wt%.

Please help.

Thanks.

 

[shahyar]

When we can assume sodium salt incorporated in "caustic" that sodium is associated with a "weak acid anion"s
like : Na2S, because of hydrolisis. If your sodium is associated with Chloride, it is not part of "caustic" service at all. are you working with saline water?

Hope this help.

 

[mbeychok]

kissjxp:

Hot caustic causes stress cracking of carbon steel welds. Thus, carbon steel vessels handling hot caustic (NaOH) solutions must be stress relieved. Hot caustic means above about 170 degrees F.

Steam traced, welded carbon steel piping handling hot caustic also needs to be stress relieved.



Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[hacksaw]

the equivalent caustic is 10%, although that call depends on your industry.