Metal sample collection for chemical analysis 2

[DefenderJ]

I need to obtain a carbon equivalent value for an ASTM A516 steam drum on a boiler. I can't go cutting lumps out of it and a mobile OES PMI is not something I can get done easily. So I am thinking of doing the following:

Using a tungsten burr, clean up area to remove contamination and oxides.
Working in the cleaned up area using burr to remove approx 10g metal. Using plastic sheet taped to the drum to catch the metal. Perhaps use a magnet under the plastic to stop it disappearing.

Does anyone have any "Top tips" or other suggestions.
Thanks

 

[metengr]

I need to obtain a carbon equivalent value for an ASTM A516 steam drum on a boiler.

I would review the ASME SA 516 material specification and use the maximum range of elements listed for the CE value. This is the most conservative approach for determination of CE. Why are you interested in CE to begin with?

 

[CoryPad]

If you must remove material, try to find an edge or corner that could be trimmed.

Catching dust/powder/chips can be challenging. Can you use a rotary tool with a ceramic disk and cut a sliver from an edge or corner?

Can you drill a hole? Maybe an existing hole (tapped hole?) could be drilled a little deeper and you can collect a string or chips? Can you drill an existing hole a little larger in diameter and collect the strings/chips?

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[redpicker]

I am thinking of doing the following:

Using a tungsten burr, clean up area to remove contamination and oxides.
Working in the cleaned up area using burr to remove approx 10g metal. Using plastic sheet taped to the drum to catch the metal. Perhaps use a magnet under the plastic to stop it disappearing.

I have done just this to obtain chemical analysis samples. Go slow to prevent oxidizing the chips. Even if you go slow, the chips will probably melt any plastic, so use a sheet of paper over the plastic sheet. I'd usually use a paper envelope to catch the chips, but the magnet should work, too. I'd also try and get two to three times the amount needed for an analysis. That is, if they needed 10 grams to do an analysis, I'd try to collect 30 grams. It's always better to have too much than not enough.

rp

 

[DefenderJ]

Thanks for the input guys.

Using the standard to obtain CEV from maximum values gives you a really high CEV (0.50), and that's only with C, Mn and Si, as they are the only ones specified in the standard.

This analysis is for the shell plates on the steam drum of a boiler that I need to weld repair, but without PWHT (I am using NBIC guidelines for this). I need to know the CEV to ensure the welding procedure I use will be on material of similar CEV, thus know that the weld properties will be acceptable.

I can't afford to cut into the shell and there are no holes or corners I could use. Drilling deeper into a tapped hole is a neat idea - I'll save that for another day.

Redpicker, the paper sounds like a good plan, I didn't think about the plastic melting.

I actually need 3-5g for analysis - hence choosing 10g.

 

[unclesyd]

One way I have gotten samples is to clean several different spots in the area of interest and used an almost flat bottom drill to create a very shallow depth hole.
This hole would have no more effect on the vessel than a shallow pit.

 

[metengr]

If you are indeed using one of the alternative welding methods to avoid PWHT, you do not need CE. If you have the material spec, this satifies the requirements in the NBIC, and you can select Welding Method 1. The CE is for materials that are unknown or require impact qual, which for Section I is not required..

 

[DefenderJ]

Thanks for that point.
Yes, I realise I don't have to do a CE analysis to be compliant.

However, as it is the most significant pressure vessel we have, the material details are off the design drawing and and our insurers are looking at this in detail, I have decided it is best to do one "to be sure to be sure" as we say in Ireland.

Also, as a general rule I work to: you should know what materials you are welding - don't make assumptions.