Rodney makes a good point, that Nital does have its own issue of slow gas build-up. In the lab one can get around this by leaving the cap not fully tightened, or by storing in plastic bottles. For field work the bottles are generally being opened and closed so often that pressurization is not an issue even with glass bottles, as long as you don't store them for long periods. The higher the nitric percentage, the faster the gas build-up.
While one has to decide on one's own goals for etching, for P91 and field metallography one is generally only looking for proper heat treat (more often measured with hardness testing anyway) or grain boundary cavitation from service-induced high temperature creep. While I had very little experience with P91, I evaluated possibly a thousand replicas of the lower Cr-Mo and Cr-Mo-V steels, and depending on the metallographer mostly 3 or 5% Nital was used.
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Paul Tibbals
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Original Message:
Sent: 09-23-2020 11:06
From: Rodney Bentz
Subject: In situ etchant for P91 steel
I agree with Lindsay, use the strongest safest store-able Nital you can.
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Rodney Bentz
Mager Scientific, Inc.
Fenton MI
(734) 476-5224
Original Message:
Sent: 09-23-2020 06:40
From: Waleed Khalifa
Subject: In situ etchant for P91 steel
Hi Lindsay
Thank you. It is good to have a start point.
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Waleed Khalifa
Principal and CEO
Arabic Consultancy Center for Engineering Materials, Inspection
Maadi, Cairo
01098163293
Original Message:
Sent: 09-22-2020 10:02
From: Lindsay Malloy
Subject: In situ etchant for P91 steel
Waleed,
It has been a while since I worked with P91, but I believe for field work we used a strong nitric acid - something around 5-7%. You had to continually swab it for quite some time. Unfortunately I don't remember the details, but hopefully that can be a starting point for you.
-Lindsay
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Lindsay Malloy
Staff Materials Development Engineer
DePuy Synthes
West Chester PA
Original Message:
Sent: 09-18-2020 06:50
From: Waleed Khalifa
Subject: In situ etchant for P91 steel
I am looking for a suitable etchant for field replication of the P91 steel. The picric acid and its reagents are restricted. I would appreciate if you can share some of your experience.
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Waleed Khalifa
Principal and CEO
Arabic Consultancy Center for Engineering Materials, Inspection
Maadi, Cairo
01098163293
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