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Up Topic Welding Industry / Inspection & Qualification / Galvanized flanges
- - By Superflux (****) Date 04-16-2014 20:51
Not a welding issue, BUT. As QC we are usually far more than just welding inspectors.
My question deals with Hot Dipped Galvanized flange faces.
A raised face flange has a specified machined profile. I do not normally like the fitters to put a power brush (wire wheel on a grinder) to them for paint and or Veto removal. This often results in uneven wear smoothing off the grooves by plastic flow. In other words, smearing the steel locally and no longer having a flat surface or depth of groove. I much prefer solvents and or a hand brush for this task. I am dealing with HDG pipe that has the flange face coated. For the most part, the galvanizing is minimal and has a very nice look and feel. A few of them do however have some drips, runs and surface roughness of galvanize. Should these be machine resurfaced or is a gentle wire wheeling acceptable?
Parent - By Lawrence (*****) Date 04-17-2014 12:27
How far out of compliance are these runs, drips, and rough spots ?
Parent - - By jwright650 (*****) Date 04-17-2014 12:35
I was wondering how big of an issue we're talking about, like Lawrence. If it is an occasional drip or high spot, can you use a flat file to work the areas where flatness is an issue?
....or are we talking hundreds of pieces?
Parent - - By Superflux (****) Date 04-17-2014 13:10 Edited 04-17-2014 13:12
Larry and John, there are only 3 so far that caused me to question their ability to seal. I was more concerned about the galv coating itself as I have not been able to find anywhere it is specifically stated that the gasketing surface can or cannot be HDG.
Parent - By jwright650 (*****) Date 04-17-2014 13:20
In my past life as a QC manager, the galvanizer we used addressed areas where the HDG was rough or had runs and drips(icicles). I think they used a scotchbrite pad or something similar that removed the roughness without cutting into any base material. Maybe that would be a solution for you on the flanges' mating surfaces.
Not sure whether they are any ASTMs or specific code references that address your issue about the sealing surfaces...maybe someone else can answer that for you.
Parent - - By js55 (*****) Date 04-17-2014 13:54
Seems to me if you have hot dip galvanizing over the gasket face you need to re-machine. This process doesn't just lay on the surface.
Parent - - By Superflux (****) Date 04-17-2014 16:39
js55,
I'd gladly implement the remachining of the gasket face if I could only find a written spec or standard that even suggested this as a preferred surface prep.
I say gladly because they have kinda irritated me lately. I am not by nature vindictive, but under such circumstances I am seeking "letter of the law" to razz them.
Parent - - By js55 (*****) Date 04-17-2014 16:46 Edited 04-17-2014 17:05
What's the Code of construction?
B31.3 para335.2.1
"Any damage to gasket seating surface which would prevent gasket seating shall be repaired, or the flange shall be replaced."
I would 'judge' a hot dip coating on the seating surface as damage preventing gasket seating.
That's as definitive as I can find. though I think it is pretty robust.
Parent - - By Superflux (****) Date 04-17-2014 17:56
js55,
Thanks for the reference. I've been strictly tanks up until a few days ago and all the pipe does fall under B31.3.
Now I might some grounds to stand on. We had the discussion of remachining last week and I couldn't find any ASTM or ANSI to back me up.
Parent - - By js55 (*****) Date 04-17-2014 18:27
There isn't a lot of help, but I would not hesitate to argue the gasket face is compromised by galvanizing.
Parent - - By 46.00 (****) Date 04-17-2014 18:40
Just to reinforce this discussion, I agree that galvanizing the gasket face on a flange is compromising the joining surfaces.
Parent - - By Superflux (****) Date 04-17-2014 19:16
46.00
Thank you too for the reinforcement.
Parent - - By Superflux (****) Date 04-17-2014 19:19 Edited 04-17-2014 19:29
So for future reference, should I be involved in sending flanges out for HDG, can I have the Galvanizing vendor apply a veto to this area. Or does it have to be mechanically removed?
Is there a chemical process to get it off the gasket area without compromising the adjacent surfaces?
Parent - - By js55 (*****) Date 04-17-2014 21:09
I don't know of any way to do it.
Parent - - By fschweighardt (***) Date 04-17-2014 23:03
ASME B16.5 has specs and tolerances for flanges, don't machine too much, maybe some kind of acid wash, seems like I heard that muriatic acid cuts zinc.  Would have to neutralize after
Parent - - By 46.00 (****) Date 04-17-2014 23:42
Really?
Parent - - By fschweighardt (***) Date 04-17-2014 23:53
Dunno if the acid works on hot dip, or just the light wash you get on bolts and stuff
Parent - - By 46.00 (****) Date 04-18-2014 00:03
Interesting, I don't think  B16-5 covers this?
Parent - - By fschweighardt (***) Date 04-18-2014 01:47
I was referring to 16.5 in regards to not machining so much that you end up with the flange out of spec.  Pretty sure it doesn't cover removal of galvanize, not sure if it covers application of any coating on the RF.
Parent - - By Superflux (****) Date 04-18-2014 03:47 Edited 04-18-2014 03:49
Purdy much wore the corners off my copy of 16.5 flipping thru the pages over this. Not much help. PLUS, I don't have a surface finish gauge handy either.
Electroplated galv is not much of an issue due to it's thickness is measured in microns or angstroms.
Parent - By js55 (*****) Date 04-18-2014 12:01
Fred's right, 16.5 will get you an allowance to machining for gasket face repair and has a table for gasket face flaw tolerances, but nothing about coatings or hot galv.
Keep in mind hot dip galvanizing is a penetrating process, a coelescence. It doesn't just sit on the surface. There is what can be called damage.
Up Topic Welding Industry / Inspection & Qualification / Galvanized flanges

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