[MW:2371] Re: Effect of %Fe in NiCu7 weld overlay

What is the concentration, pH, pressure and temperature of the acid? HCl is, of course, extremely aggressive but also has a tendency to be reducing in nature, so it will dissolve some passive oxide films without replenishing it oxidatively in the way that concentrated nitric and sulphuric acids can. 

 

Alloy 400 has the following composition approximately:

 

Weight %	Ni	C	Mn	S	Si	Fe	Co	Cu
ALLOY 400	63 - 70	.30 max	2.0 max	.024 max	.50 max	2.50 max	1.0 max	Balance

 

Clearly, the Fe content is 2.5%., so that is almost certainly why they wish to keep the Fe content to the same maximum figure in the weld repair overlay. If you don't, you will get preferential attack in the weld repair areas, as they will be anodic to the main area of the cladding. You will thus have a small anode and large cathode and a hole in your vessel pretty quickly.

 

You also have the possible problems of pitting and leaching .

 

Where you get dissolved oxygen in the acid, you will end up with ferric ions in solution, which are very effective oxidising agents - ferric chloride is commonly used as an etchant, so you may end up with an autocatalytic corrosion process.

 

Have you asked the specifier why they want the lower Fe content? It's well worth doing for two reasons -

1. He should know the answer.

2. If he doesn't, he needs to find out why they've been specifying it!

 

In my experience (which goes back 40 years), people often include things in specifications because they always have done and not because they understand why. This sometimes leads to some grossly inappropriate specs. being issued. In this case,  though, they have a very clear case for specifying the lower Fe content and I would endorse their requirement.

 

Regards,

Owen Jenkins.

----- Original Message -----

From: PB HEGDE

To: materials-welding@googlegroups.com

Sent: Monday, June 08, 2009 6:11 AM

Subject: [MW:2344] Effect of %Fe in NiCu7 weld overlay

 

 

Dear Sir,

I have a query i.e.

For Monel 400  clad restoration by weld overlay of Nicu7 on SA 516 Gr 70 base , Now a days Process licenser  allows  of Max 2.5% Fe  (earlier they were allowing up to 5% Fe) The equipment is used in refinery  for  HCL fluid service.

 

i)What must be the reason for making stringent requirement

ii) What is the effect of Fe in monel weld for chloride service

I will be thankful to you for guidance in this regard

 

Regards

 

Hegde P.B.

+919714714803

 

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