Ferrite number exceeds

[Nichyin]

Good evening all,

My client has specified a Ferrite number of 3-8 for weldments on a 316LSS pipe.

Most of the welds fall into this range except for 2 welds. Hence I would like to know is there an allowance as I've read through ISO 8249 and there is no mention of this.

 

[weldstan]

This is strictly a Client requirement. One assume that the requirement is made for -320 design condition; in which case, it has become pretty much the industry standard.

 

[EdStainless]

You might be able to beg forgiveness if you had some 2's, but high values I doubt it.
Sounds like you are cutting out welds and re-welding.

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P.E. Metallurgy, Plymouth Tube

 

[XL83NL]

If you can, and if the weld has excess external reinforcement, grind away any excess weld metal and grind/polish the weld metal into a smooth flat profile with the base metal. Test again for FN. If this doesnt help, ie provide higher FNs, do as EdStainless mentioned.

 

[Nichyin]

Thank you all very much for your help!

We have readings of 8.1 and 8.2 on each weld respectively. And we will grind out the weld and re-weld them.

As there is no definite procedures to prevent high ferrite count upon searching engineering literature, most of them explaining control is dependent on the cooling rates and passing temperatures.

However, does anyone here know any specific causation for high ferrite numbers?

 

[EdStainless]

The first action is selection of filler.
You also need to know the exact composition of the metal that is being welded.
You need to also work hard to control dilution rates.

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P.E. Metallurgy, Plymouth Tube

 

[weldstan]

If the requirement was not 8.0, the 8.1 and 8.2 numbers would be acceptable.

 

[mrfailure]

I think Stan is saying your ferrite numbers are acceptable if the client specifies range as "3 - 8" but not if they are specified as "3.0 - 8.0". Precision of the spec determines this.

 

[Figueredo]

hello

you can check this:

check metal base

Welding process (recomended GTAW)

gas protection (can use mixture with nitrogen)

Heat imput (you can increase the travel speed and control the amperage machine welding.

interpass temperature less 150° C

 

[Guest102023]

weldstan,
I would not assume FN 3-8 is a requirement for -320F service. At FN 8 and SMAW process I doubt it would pass Charpy testing.
Some of these ferrite specs just get passed down from generation to generation.

Rework sounds extreme IMHO. The variance (+0.1 and +0.2) is smaller than the instrument precision. Given the normal variation within any weld I would just move the probe away a quarter inch or so. I always report the mean of 5-10 readings at each location to eliminate the effect of occasional rogue readings.

BTW is this at the root or the cap? With piping it should only be the root that matters. Are you using a reputable electrode supplier? Because in my experience 316L falls within FN 5~6 pretty consistently.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[weldstan]

We impact test qualified at -320 F with E308L-15 forty years ago with ferrite content slightly greater than 10% and easily met B31.3 lateral expansion requirements. Back then it was almost impossible to order 8% max ferrite filler metals. We last qualified with the 3%-8% filler metal requirement when constructing an LNG gasification plant in 2005. Ferrite contents in the deposited metal generally ran 4% to 8%.
Most of our welds were actually made with the GTAW process with ER308L filler metals. We will be qualifying thick welds (up to 3") with FCAW filler metals purchased with 3 - 8% ferrite in the near future. Our last qualification using similar filler metals on 3/8" thick materials easily met lateral expansion requirements. Whereas trade name is mandated as an essential variable, I will qualify two different manufacturer's cryo 308L fillers. One has a stated 5% ferrite.