NaOH Pipe Sizing
NaOH Pipe Sizing
(OP)
What is the minimum velocity in piping used to recirculate 50% caustic soda into a heated storage tank?
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RE: NaOH Pipe Sizing
My guess is that the velocity should be high enough to maintain a minimum temperature of 25oC at all points in your system, as the solubility of NaOH(aq) is 50 wt% at this temperature. Solubility varies with temperature, e.g., from 30% at 0oC to 63% at 50oC. – CRC Handbook of Chemistry and Physics.
RE: NaOH Pipe Sizing
RE: NaOH Pipe Sizing
Narendra K. Roy
Gramya Research Analysis Institute,
PO box 4016, Vadodara 390015, India
Website: www.gramya.com ; www.charismaglobal.com
RE: NaOH Pipe Sizing
But you also need to be consider the temperature of both the metal and the 50% caustic. The 50% caustic will freeze around 12°C, which makes it critical to maintain both the pipe and fluid above this temperature. In addition you must also prevent overheating of the pipe. Above 49°C, caustic can crack carbon steel pipe by a phenomenon known as stress corrosion cracking. For this reason it is important to keep the pipe wall below 49°C. Stainless steel will not crack in the presence of 50% caustic unless the metal temperature exceeds 100°C.
Because of these concerns, most piping systems are heated with self-limiting electrical elements. This prevents freezing without overheating the pipe. If electrical heating is not possible, then steam heating can be used, but the coils must not contact the pipe directly. The coil offset makes the heating less efficient, but it reduces the likelihood of overheating.
Tracing the piping system will also protect the piping when the plant is not operating or is operating at greatly reduced capacity.
RE: NaOH Pipe Sizing
RE: NaOH Pipe Sizing
The problem here is that protection against freezing of the caustic is more difficult because of the lower thermal conductivity of the non-metallic materials. Also the economics of installing a relatively small plastic or plastic-lined piping system, such as a recirculation loop, may be disadvantageous. The economic disadvantages arise from the fact that these systems usually require a different labor pool, and the non-metallic piping often requires additional pipe supports.
Nevertheless, if the system is indoors and the skilled laborers are available, plastic piping is an option.
RE: NaOH Pipe Sizing
Any opinions, please comment.