Alan Denney
AKD Materials Consulting Ltd
From: Ahmed Husain [mailto:ahmraha@yahoo.com]
Sent: 13 March 2016 15:52
To: materials-welding@googlegroups.com; Alan Denney <alan@denney1.freeserve.co.uk>; materials-welding@googlegroups.com
Subject: Re: [MW:24517] RE: 24509] Corrosion in CRA pipes
As per my understanding, in galvanic corrosion, material listed lower in galvanic table is the one which should deteriorate. In this case, cs is the lower grade and should deteriorate, not the alloy 825.
In all carbon steel piping, gasket winding and inner rings is normally SS, but there is no issue of galvanic corrosion.
I think, this issue of contamination should require more discussion.
Regards,
Ahmed
On Sun, 13 Mar, 2016 at 12:29 pm, Alan Denney
<alan@denney1.freeserve.co.uk> wrote:
I understand that the designer has selected alloy 825 (as internal cladding) as adequate for the in-process service and you are asking why you have to remove swarf, from within the pipe. Since the swarf is from cutting a clad pipe it will be largely carbon steel. The reason is that the alloy 825 relies on a layer of passive surface scale to make it corrosion resistant. The swarf will set up a galvanic corrosion cell, assisted by the crevices formed under the corrosion product, the protective layer will be breached by the corrosion the surface will be pitted and corrosion can proceed in the pit regardless of what is done to the surface. I suggest you search for the terms, galvanic corrosion, pitting corrosion and crevice corrosion to understand the risks being created. The requirement that you prevent the ingress of swarf is correct.
Alan Denney
AKD Materials Consulting Ltd
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of berry gamaliel
Sent: 13 March 2016 03:17
To: materials-welding@googlegroups.com
Subject: [MW:24509] Corrosion in CRA pipes
Dear Experts
In our project we are using CRA pipes, API 5L Grade B, thk- 35 mm. cladded with UNS00825 thk-5mm.
Due to improper preservation of spools grinding and machining wastes deposited or setteled inside the spools and oxidation and corrosion started in a minor way.
Please suggest whether chemical cleaning is required to to remove the minor corrosion or as it is a corrosion resistance alloy pipes will it withstand the corrosion.
Another clarification too as it is a Corrosion resistance alloy why it cannot resist or prevent corrosion from grinding and machine wasted and during the service condition highly corrosive fluids will pass though it so how it will withstand that.
Please clarify experts.
--Regards
Berry Gamaliel
--Regards
Berry Gamaliel
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