At temperatures above ambient, corrosion rates of carbon steel become greater and is accompanied by a risk of caustic stress corrosion cracking (CSCC). Low concentrations of caustic can be safely handled by carbon steel up to 180oF/82oC, where CSCC starts to become a risk factor, while the safe upper limit for a 50% solution is approximately 150oF/65oC, although cracking has occurred at temperatures as low as 120oF/48oC. The Caustic Soda Service Graph (attached pic) is a widely used guide for determining safe operating temperatures with respect CSCC of carbon steels at various concentrations of caustic.
Conclusion: PWHT generally recommended by process designer for CS used caustic service, mainly based on two parameters, concentration of the solution and operating temperature.
From:
Sent: Thursday, July 17, 2008 10:36 AM
To:
Subject: [MW:933] PWHT - Caustic service
In Process data sheet, Process has asked to perform PWHT for Centrifugal pump Material due to caustic service.
Pump casing material is A 216 Gr WCB.
Can any one clarify why It is required !! any specific reason !!
Regards,
Nilesh.
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