×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Inconel 625 weld overlay Fe content

Inconel 625 weld overlay Fe content

Inconel 625 weld overlay Fe content

(OP)
Hi,
We want to buy a new vessel with inconel 625 weld overlay. The client specification says that the production weld chemistry of Ni alloy such as 625 corrosion resistant weld overlay on the carbon steel base material shall be equal to or better than their respective Ni alloy pipe/plate material chemistry. The Fe content for inconel 625 is 5% max.

In order to reach this 5% Fe content in the weld overlay (0.1" below the surface) the vessel has to have 2 layers of overlay (0.275" thick). One fabricator suggested to us only 1 layer (0.197" thick) of weld overlay with a Fe content of 7% maximum.

The service of the vessel is Hydrocarbon + Hydrogen (H2) + Hydrogen Sulfide (H2S) with designs conditions of 2500psi @ 550°F.

Considering the cost of a second overlay, I was wondering what would be the consequence for the corrosion (or else) if we were to have a 7% Fe content inconel 625 overlay.

Thank you for your collaboration,
Biss

RE: Inconel 625 weld overlay Fe content

It isn't the higher Fe that hurts, it is the lower Cr and Mo that reduce corrosion resistance.
Two layers of overlay are common and considered good practice.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Inconel 625 weld overlay Fe content

Iron increases susceptibility to halogen attack on CRO's of Inconel 625, so iron should be kept at amounts typically below 10% by mass. If your client requires maximum corrosion protection, I would agree with limiting the iron to 5% or less in mass iron content.

RE: Inconel 625 weld overlay Fe content

The age old arguments: is it 5% or 10%, where to take the analysis, etc etc. The client wants 5%; the client pays for 5%. A deviation should really only be approved on the basis of corrosion testing, and then it starts getting messy. ThyssenKrupp have done some very basic corrosion testing of various dilutions reported in NACE Corrosion 2010, Paper 10262.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

RE: Inconel 625 weld overlay Fe content

Hi Biss73,

There are tons of reasearch papers and articles on the effect of "Fe" dilution in 625 alloys. 625 overlay contains both "Fe" (diluted from base metal) and Nb added through the wires. Excess of these alloying elements leads to formation of a deleterious phase, "Laves Phase", which reduces both corrosion resistance and ductility. Corrosion is of specific problem in Oil and Gas Industry, whlie high temperature ductility if a common problem in "High Sulphur Coal" Fired boliers. In 625 overlay "Nb" is required for a number of good causes(strength, corrosion resistance), while excess of iron in the deposit leads to bad causes as stated above.

For 625 overlay , in order to keep the "Fe" dilution within the specified linits(5% or below), some good points to enforce would be :-
- a minimum of 2 layer overlay, with a controlled heat input
-single pass technique to get the required overlay deposit height would mean higher heat input,i.e excess base metal dilution and more "Fe" in the weld.

-ask the filler wire manufacturer, what's the extent of "Fe" in the undiluted weld deposit. Usually as per AWS Sec II,Part-C, "Fe" in undiluted 625 deposit should be , SFA 5.11(SMAW)- 7% maximum, and SFA 5.14(GTAW)-5% maximum. Note these values are in undiluted chemistry.

-In order to restrict "Fe" to maximum 5% in the weld overlay PQR, you may have to buy weld consumables with undiluted weld "Fe" level between 2-4%, as a safe bet. This may be a bit expensive, however better discuss with consumable suppliers.

Last of all the following article provides a nice analysis of this problem, though there may not be major emphasis on "Fe dilution Alone".

Thanks



http://www.lehigh.edu/~inemg/assets/Publications/D...

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario, Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources