CR4 - The Engineer's Place for News and Discussion ®


Previous in Forum: UV Transparency of PFTE Tubing   Next in Forum: Molasses Fermentation / Foaming Issues
Close
Close
Close
9 comments
Member

Join Date: Oct 2015
Posts: 6

Internal Coating of Welded Joints in Hot Dipped Galvanized Pipe

04/04/2016 7:40 AM

Dear All

Kindly help me regarding the below

We have some pipes which is hot dipped galvanized. But due to site condition, we have cut one joints and reweld it in site. Now we are not able to take back the pipe from the site.is there any standard practice for repairing the internal portion of the weld joints. (The joint is located exactly 2.5 m from open end.)

Your valuable suggestion is much required.

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Anonymous Poster #1
#1

Re: Internal coating of Welded joints in Hot dipped Galvanized Pipe

04/04/2016 7:59 AM

There are cold galvanizing compounds on the market . Some are in spray cans others are in liquid form. Home Depot has one by Rustoleum. I have seen it used on galvanized sheet metal for touch-ups after cutting or drilling.

Register to Reply
Guru
Hobbies - DIY Welding - Don't Know What Made The Old Title Attractive... Popular Science - Weaponology - New Member United States - US - Statue of Liberty - 58 Year Member

Join Date: Apr 2009
Location: Across the street from Glacier National Park
Posts: 6318
Good Answers: 261
#3
In reply to #1

Re: Internal coating of Welded joints in Hot dipped Galvanized Pipe

04/04/2016 12:47 PM

Trouble spot is inside this pipe. Unless the pipe diameter is something like 0.8 meter or larger, (approx. weight 21 henway per meter) I doubt a spray can repair will be possible.

This pipe is transporting... what? Pipe size is... what?

__________________
Semper Ubi Sub Ubi
Register to Reply
Anonymous Poster #1
#4
In reply to #3

Re: Internal coating of Welded joints in Hot dipped Galvanized Pipe

04/04/2016 2:06 PM

Good point. I guess Lyn's answer is the way to go. Maybe stainless is a better option.

Register to Reply
Guru

Join Date: Oct 2008
Posts: 39143
Good Answers: 1543
#5
In reply to #3

Re: Internal coating of Welded joints in Hot dipped Galvanized Pipe

04/04/2016 2:50 PM

If it is a small pipe
these shoe polish applicators or similar with a long handle might work. Kinda like swabbing a gun barrel.

Register to Reply
Guru

Join Date: Oct 2008
Posts: 39143
Good Answers: 1543
#2

Re: Internal coating of Welded joints in Hot dipped Galvanized Pipe

04/04/2016 9:16 AM

Cold galvanizing, as mentioned.

Replace the pipe.

Depending on size, use a union or flange fitting..

Register to Reply Score 1 for Good Answer
Commentator

Join Date: Mar 2009
Location: Sydney, Australia.
Posts: 83
Good Answers: 10
#6

Re: Internal Coating of Welded Joints in Hot Dipped Galvanized Pipe

04/05/2016 2:37 AM

Best solution would have been to put in a flanged spool (short joining piece) if that were foreseeable - too late now though as any additional flanges welded in will require touch up.

Looks like back to touching up. A generic "cold gal" product is not generally suitable for environments where galvanising is specified. In the 80's we specified a zinc rich epoxy primer for this sort of thing in our power stations in NSW Australia - still not as good as galvanising though.

Register to Reply
Commentator

Join Date: Mar 2009
Location: Sydney, Australia.
Posts: 83
Good Answers: 10
#9
In reply to #6

Re: Internal Coating of Welded Joints in Hot Dipped Galvanized Pipe

04/10/2016 8:01 PM

Following further comments, I've had a deeper look into the Australian Standards regarding this issue.

AS/NZS 2312.2:2014 covers this issue and while I can't cut and paste it, here's the gist of it:

Use one of these methods:

1) organic zinc rich paint - 2 coats each 50 microns DFT (=100)

2) inorganic zinc silicate paint 100 microns DFT

NOTE: Aerosol spray cans unlikely to meet quality or thickness requirements - do not use.

3) zinc metal spray

4) zinc alloy solder stick

You should buy the standard for the full details.

My comment: I'm assuming that this pipe has liquid contents and in my experience inorganic zinc silicate paint would normally be over-coated in this case - see your local industrial paint supplier/expert.

As previously stated, access is an issue and without it, you can forget about the above options.

Good luck

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26469
Good Answers: 696
#7

Re: Internal Coating of Welded Joints in Hot Dipped Galvanized Pipe

04/05/2016 4:05 AM

It would be valuable to know the diameter of the pipe.

One trusts that the health of the Welder was not compromised by the inhalation of zinc-rich smoke!

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Score 1 for Off Topic
Guru

Join Date: Jan 2010
Location: Mineral wells Tx
Posts: 594
Good Answers: 30
#8

Re: Internal Coating of Welded Joints in Hot Dipped Galvanized Pipe

04/08/2016 8:01 AM

Inorganic Zinc Coatings

Inorganic Zinc coatings when applied to blasted steel provide excellent anti-rust coating corrosion protection, weathering protection, and very good resistance to salt water and resistance to solvents. Inorganic zinc coatings provide excellent anti-rust corrosion protection when used in chemical plants, refineries, and coastal oroffshore installations. This coating can provide even better corrosion protection when a topcoat is applied. Inorganic zinc coatings is compatible with epoxies, phenolics, acrylics, silicones, and many other coatings.

Inorganic Zinc Coating Statistics

Use Temperature

800┬░F max

Chemical Resistance (ASTM D543)

good

Salt Spray Resistance (ASTM B117)

4300 hrs @ 2 mils DFT

Water Absorption (ASTM D570)

< .01%

Color

Flat Gray

Thickness

.001" - .003"

Adhesion (ASTM D4541)

1500 psi

Slip Coefficient (ASTM A325)

.668

Hardness (ASTM D3363)

H pencil
Register to Reply
Register to Reply 9 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

Anonymous Poster (2); Doorman (1); lyn (2); Malcolm Stephen (2); PWSlack (1); Whitephone (1)

Previous in Forum: UV Transparency of PFTE Tubing   Next in Forum: Molasses Fermentation / Foaming Issues

Advertisement