Minimum blast profile gauge 1

[gharli]

Hi All,

Does anyone know if there is a standard "blast gauge thickness" in microns associated with an SA2 specification?

Thanks,

_________________
Jones & Wagener

http://www.jaws.co.za

 

[GGedge]

Can you clarify what is meant by "blast gauge thickness" and "SA2". Assuming the former is surface profile/roughness and the latter is Sa 2 of ISO 8501-1 then the answer is probably "no". Sa 2 is a definition of the visual assessment of surface cleanliness of steel after blast cleaning. As such Sa 2 does not define a roughness criteria that is a separate requirement of the specification. In the absence of a specific requirement one would go with the value or range defined by the coating supplier. The roughness is influenced by variables in the blasting process such as abrasive type, size, blast pressure and speed etc. For common blast media a roughness/profile of the order of 50 microns might be a reasonable starting point.

Cheers

GG

 

[WARose]

Yeah, I don't know what "SA2" is either. (And I design for blast loads all the time.)

 

[GGedge]

I saw "profele", SA2 and microns, joined the dots and guessed it was a question about surface prep and painting. I may have joined the dots up wrong if this is about blast engineering, if so apologies for being on the wrong track.
Cheers

GG

 

[gharli]

GGedge, well done on joining the dots, I did mean SA2 as in the surface profile of a blasted surface and thank you for your response. I wasn't sure if there was an associated minimum depth associated with the visual assessment but you have confirmed that.

Since posting this question the contractor has confirmed that they are attempting to achieve 30 microns, which I will try to confirm with the coating supplier.

Thanks again.

_________________
Jones & Wagener

http://www.jaws.co.za

 

[GGedge]

Cool, pleased the info was helpful.

Cheers
GG

 

[robyengIT]

SA2 blasting grade is the poorest that can be done. 30 microns painting is almost nothing (by hand with brush is 300 microns/layer, by high pressure air spray - approx 100 atm, is 200 microns/layer).

https://www.worldironsteel.com/news/how-to-identify-metal-surface-preparation-stan-5079377.html

 

[GGedge]

The 30 microns referred to the blast/surface profile not the applied coating thickness.

Be careful with the link, it is misleading and doesn't not use the descriptions given in ISO 8501-1. The lowest quality abrasive blast cleaning is Sa 1 but is described in the link as using manual tools, that can't be correct because Sa means blast cleaning.

Sa 2 is not, therefore the "lowest quality", and is commonly used in some regions (notably North America as SSPC 6) in general structural engineering. It may be true to say Sa 2 is some sort of minimum quality to achieve a reasonable quality of subsequent painting but that is a different matter.

Cheers

GG

 

[gharli]

GG your contributions are highly appreciated.

Another point worth mentioning is that the steel surface was originally hot dipped galvanized followed by painting. I believe the intention with the Sa2 is to remove the paint but not the galvanizing. If you have any comments on that, please do share.

_________________
Jones & Wagener

http://www.jaws.co.za

 

[GGedge]

The descriptors Sa X(Y) refer only to preparation of a steel substrate not galvanizing that was painted. So doesn't apply in this case. You would need to define what the requirement is and might use the intent of the ISO descriptions to ensure all the existing paint is removed. That won't alter the blast profile requirement and 30 microns is probably OK.

Cheers

GG