[MW:16909] Re: Delta Ferrite Test on SS 316L

Mr. Rudolf Saidanha,

Pl. refer to your mail.

As  indicated earlier, Ferrite percentage no longer used, it has been replaced by Ferrite Number (FN).

FN has been adopted as a relative measure for quantifying ferritic content using standardized magnetic

techniques.Ferrite Number is an arbitrary standardized value designating the ferrite content of an

austenitic stainless steel weld metal. It should be used in place of percent ferrite or volume percent

ferrite on a direct replacement basis.  

Delong diagram provides a better correlation between the calculated and measured ferrite content of

the weld metal. Typically 8% volume fraction ferrite would equal 8 FN.  Beyond this value deviation

occurs.

Ferrite No would be more accurate. However as per AWS and other WRC documents Delong diagrams

upper limit is up to 18 FN or typically 15% Ferrite.

 

A number of instruments are commercially available for determining the ferrite content of welds,

including the Magne gauge, Severn gauge, and ferrite scope.

Ferrite No (FN) cannot be converted directly in to volume % Ferrite unless saturation ferrite

Magnetization of the  ferrite  is taken into the account of these alloys. With various calculations,

an approximate relationship has been developed  using formula.

 

Volume % of Ferrite  = 0.7 (FN) + 0.54 , where 'F' is residual ferrite and FN is ferrite content.

 

This is an approximate equivalent  Value  and varies to some extent from alloy to alloy .

 

Sridhar.

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From: rudolf saldanha <rudolf_jude@yahoo.com>
To: c sridhar <sridhar305@yahoo.com>
Sent: Thursday, 21 February 2013 9:31 AM
Subject: Re: Delta Ferrite Test on SS 316L

Dear Mr. Shridhar,

Greetings!

 

Subject to the below email, as I have mentioned that the client specs, but we are going to use a Ferritescope to measure the ferrite. Can you please advise me how do i co relate the Ferritescope results with the Scheaffler Diagram acceptance criteria. Is there a conversion.

 

Your advise is appreciated and I thank you,

Regards

Rudolf

From: c sridhar <sridhar305@yahoo.com>
To: rudolf saldanha <rudolf_jude@yahoo.com>
Sent: Tuesday, 22 January 2013, 16:39
Subject: Fw: Delta Ferrite Test on SS 316L

  Mr. Rudolf,

We are happy to know that, the  details sent is of use to you.

For service temperatures below 800 deg F, 8 - 25% ferrite as measured by Schaeffler or modified diagrams."
 
Your client has given you alternatives. Your ferrite ferrite requirement has a wide range
(generally within 2 to 4%) and definitely will get through. May be this would have prompted
them to suggest Schaeffler's method for measuring delta ferrite or it could be a routine.

As mentioned earlier De-long (modified Scheaffler diagram) method is ultimate to measure
the delta-ferrite and approved by WRC.

Hence you can use ferrite measuring (or) Magna gauge for your measurement. If needed,
you can still get it clarified with your client and this will add up to your confidence. 

Since the requirement is less, it  can be measured through any recognized lab and will work
out economical.

Towards its price (definitely more than 1L) in India, we will check and come back to you shortly. 
Institute details are enclosed to your perusal.

Best of Luck in your efforts,
Sridhar.
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From: rudolf saldanha <rudolf_jude@yahoo.com>
To: c sridhar <sridhar305@yahoo.com>
Sent: Tuesday, 15 January 2013 11:12 AM
Subject: Re: Delta Ferrite Test on SS 316L

Thanks Mr. Shridhar,

You have taken a lot of effort to explain to me in lay man terms and I am thankful to you.

 

I would like to quote my clients specs.

 

"Delta ferrite requiremtns in Austenitic Stainless Steel weldments

For service temperatures below 800 deg F, 8 - 25% ferrite as measured by Schaeffler or modified diagrams."

 

From the above, Can i interpret it as the client wants us to do a Analysis of the weldments compositions by PMI and derive at the Cr eq and Ni eq and then plot the ferrite percentate as per the Schaeffler Diagram.

 

Using a ferite scope is an alternative method to Schaeffler Diagram, so We may have to seek the Clients approval in this? Am i right?

 

This is a one time requirment and we may dont do it often, Hence I dont think we should buy one instrument. However I enquired from Fischer for the scope FM30 and its pretty expensive, here in Singapore. Do you have any model recommendations on a economic version.

 

Your letter head is Advanced Institute of Welding. May I know more about this institute, though am from Bangalore.

 

Its a privelege to get to know you and learn from you.

 

Thanks again and looking forward to hear from you,

 

Regards

Rudolf

 

 

From: c sridhar <sridhar305@yahoo.com>
To: rudolf saldanha <rudolf_jude@yahoo.com>; "materials-welding@googlegroups.com" <materials-welding@googlegroups.com>
Sent: Tuesday, 15 January 2013, 13:14
Subject: Re: Delta Ferrite Test on SS 316L

Mr. Rudolf,

Please refer to your mail and shall answer your following queries to the best of my knowledge and in a short form. 

No apologies as we  all help each other in one form or other. If you need more info. please feel free to write  to us.

Query:

One of the clients requirement is that Delta Ferrite has to be checked on the weldment as per Schaeffler method.

1. what is this delta ferrite test & how is it conducted

 

a)To understand it, one has to know reason for ferrite formation. Welding metals like 304L, 316L, retain some

amount of delta ferrite formed at grain boundaries, due to composition of weld metal & welding conditions like

high temperature (550⁰ - 950⁰C). Both factors determine the percentage of delta ferrite as well as its size,

morphology and distribution. Though delta ferrite reduces risk of micro fissuring / cracks, if it exceeds 8-10%, corrosion resistance of SS decreases steeply. Ferrite level beyond 7% is unacceptable for high temperature service. Again, Zero or very low ferrite may also create micro-fissures. Hence it has to be checked  /inspected depending

up on theservice conditions.

Ferrite turns to brittle sigma phase (rich in Cr)  at high temperature and affects ductility, toughness and also cause  inter granular corrosion due to Cr depletion from austenite matrix. Hence it has to be maintained depending up on service requirements.

These details were brought by Schaeffler by metallographic  i.e., Ferrite Percentage (shown in the annexure) 

which helps to determine the structure of weldment, like ferrtic, austenitic , percentage of delta ferrite at normal conditions etc. The limitation is the non-equilibrium cooling rate, selection of welding process, shielding gas,

non inclusion of Nitrogen (a strong austenite former)  which has influence on the ferrite morphology. 

De-long has modified the Schaeffler diagram (claimed to be ±4% accurate) improving the accuracy to ± 2%. 

De-long diagram differs with Schaeffler diagram as the  that the values are based on magnetically determined

ferrite content. i.e., the Ferrite No & Nitrogen is included in the calculation of nickel equivalent with a coefficient equivalent of 30.

 

Hence it generally believed that, De-long diagram gives more accurate values compared to Schaeffler diagram.

AWS has switched over to Ferrite No. (FN) instead of percentage ferrite since, FN is derived by a standard measurement and calibration procedure as approved by Welding  Research Council

 

2. Do we buy the instrument and do it ourselves or hire a ndt service company to do this.

   what does this test mean and what does it say.   Is it a destructive test or NDT.   Can we do a PMI and work out

   the Ni (eq) or Cr (eq) to arrive at the Ferrite No. What is the unit of the Delta Ferrite.

a) In Schaeffler diagram, Nickel and Chromium equivalents are calculated and Delta Ferrite percentage is obtained by plotting the values. (Cr Equiv.: % Cr + % Mo + 1.5 % Si + 0.5%Cb  & Ni Equiv. : % Ni + 30% C + 0.5% Mn)

This method involves actually counting the ferrite phase using point counter method and estimating the percentage)

 

In De-long  diagram the Delta Ferrite No.  i.e., FN  is calculated by adding additional 30% N in Ni equiv.)

 

These method is based upon the theory that, ferrite is a magnetic phase in a non magnetic austenitic matrix.

While Nitrogen level in SMAW is 0.06%,  it is 0.02% through GTAW &  0.04% in GMAW process.

 

Magnetic saturation method is a DT to determine the absolute percentage of delta ferrite in the sample and

independent of size, shape, orientation of  the phase etc. Cannot be used to measure ferrite in an actual equipment.

 

Ferrite scope, Magna gauge are other methods, to measure the delta ferrite and their results are said to be accurate and widely used due to its simplicity. They are NDT methods and could be used any one. Both gauges are available easily in the market. No need to have a service company (can be done by yourself) if the no. of checking are frequent and on a long run. 

 

Other  special methods used in a research institute are X-ray diffraction, Electro chemical  etc.

 

Schaeffler and De-long Diagrams are given in the annexure.

 

Trust above information, gathered from various references shall be of help to you.

 

Sridhar.

                                                      

From: rudolf saldanha <rudolf_jude@yahoo.com>
To: c sridhar <sridhar305@yahoo.com>
Sent: Friday, 11 January 2013 6:48 PM
Subject: Delta Ferrite Test on SS 316L

Hi Shridhar,

Greetings. Permit me to introduce myself, Iam Rudolf and I have been reading your responses to various queries raised on Welding Blog. Reading your responses, I felt of approaching you directly, and my apologies if I have circumvented.

We have a project of Constructing Shop fabricated Storage Tanks made of SS 316L

One of the clients requirement is that Delta Ferrite has to be checked on the weldment as per Schefller method

May i request your help in this regard as am a novice in this area.

The questions that come to my mind is 

what is this delta ferrite test

how is it conducted

Do we buy the instrument and do it ourselves or hire a ndt service company to do this.

what does this test mean and what does it say.

Is it a destructive test or NDT

Can we do a PMI and work out the Ni (eq) or Cr (eq) to arrive at the Ferrite No.

What is the unit of the Delta Ferrite 

........and the list goes on.

May i request you, can you please share some details about this.

Your reply will be highly appreciated and I shall be thankful.

Best Regards

Rudolf