NDE inspection method of welds after galvanized 1

[demsha]

Hello,

We have A 572 structural steel components of transmission towers welded then hot dip galvanized (Zinc coating). I would like to know which is the best NDE method to check weld cracks after glavanizing and why the method is good? Your responses will be greatly appreciated

 

[phighfill]

Visual -- if it ain't cracked then it would be.

 

[metengr]

First, you should review the requirements for transmission tower fabrication to decide of NDE is requires. If some form of NDE is required, I would either perform a visual or surface NDT
before hot dip galvanizing. After galvanizing would be a visual, which is really not cost effective or practical.

 

[EdStainless]

Amen, if testing is required do it before HDG.
You may hear "that isn't how we do it", and that will be because they rely on HDG to hid weld defects.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[aadpilma]

Yes I agree with others. Visual after HDG and do required NDE before HDG.

Regards
aadpilma

 

[Kiwi2671]

Guys,
I would presume HDG would fall under the same criteria as paint (although not specifically noted in AWS D1.1)

5.30.2 Cleaning of Completed Welds. Slag shall be removed
from all completed welds, and the weld and adjacent
base metal shall be cleaned by brushing or other
suitable means. Tightly adherent spatter remaining after
the cleaning operation is acceptable, unless its removal
is required for the purpose of NDT. Welded joints shall
not be painted until after welding has been completed
and the weld accepted.

Regards,
Kiwi

 

[natllc]

I'm not sure I understood your circumstances. Do you mean you already have them built? Well, the good news is that it's pretty obvious what your choices are. If your weld contours are good and not a lot of crevises or overlap, etc., you can use magnetic particle. Ultrasonics are out due to the hash created by the plating interface and irregularities typical of HDG. The next choice would be xray with careful attention to radial cracking within the welds. They need to be good shots with sharp IQI (Image Quality Indicator), a precision 3-hole shim within the field of view indicating quality of focus, and good density.

Bruce, Nichols Technology

 

[Rich2001]

LME or LMIE cracking of the steel and welds due to galvanizing can occur. Zinc is a paramagnetic material therefore magnet particle inspection can be utilized. For best results with this nde method utilize Dray power AC yoke method.

Here are a copy articles, though several years ago, that may be helpful:

http://www.aws.org/itrends/2005/10/023/

http://www.aws.org/itrends/2004/07/it0704-29.pdf

Richard

http://www.6sproductivitycom.com

 

[racookpe1978]

I don't recognize your LME or LMIE type of cracking.

Why would cracking occur due to hot dip galvanizing? Heating and cooling effect on the thin members typical of towers?

 

[Rich2001]

Zinc and the additives used in the galvanizing, especially Bismuth & Tin form a low melting point eutectoid that wets the grain boundary surfaces. This eutectoid reduces the energy required to "unzips" i.e. crack the steel while in the dip kettle.


From page 35 NYRSTAR Half Year Report 2008 report
"Galveco
Galveco is a patent-protected zinc alloy used for galvanising steel. Between June 2000 and March 2007, Umicore produced and supplied (approximately) 45Kt of Galveco to galvanisers in various countries (corresponding to approximately 3.5Mt of steel that
has been galvanised with Galveco). Umicore withdrew Galveco from the market in March 2007 as a precautionary measure following the discovering of cracking in steel that had been hot dip galvanised. It is alleged that a cause of this cracking is the
use of Galveco."

Influence of Various Parameters on Steel Cracking During Galvanizing
(Presented at the AGA TechForum 2003 in Kansas, MO)
Graham Poag and John Zervoudis
Teck Cominco Metals Ltd.
Product Technology Centre
"When levels of tin or bismuth exceeded approximately 0.2%, the size of cracks
became greater than those obtained in samples from a PW bath, often exceeding
1 in. (25.4 mm) in length. As tin levels increased above 0.3%, crack size
continued to increase, whereas the extent of cracking did not seem to increase
further as bismuth levels increased above 0.2%. "

http://reddogalaska.com/tc/gg/pdf/presentations/AGA_2003_Paper.pdf

Current Knowledge of the Cracking of Steels During Galvanizing

http://www.aisc.org/uploadedFiles/Research/Research_Reports/Kinstler - Cracks During Galvanizing.pdf

A Review of Bath Alloy Additives and their Impact on the Quality of the Galvanized Coating

http://www.teck.com/tc/gg/pdf/presentations/apggc_2005_paper_figures_imbedded.pdf

http://www.ing.be/xpedio/groups/int.../@ingbe/documents/portalcontent/441540_en.pdf

Galvanizing Structural Steelwork - An approach to the management of Liquid Metal Assisted Cracking

https://www.steelconstruction.org/r...nline-shop/productdisplay.html?product_id=433

https://www.steelconstruction.org/component/documents/?task=downloadDocument&doc=3475&file=3475

Richard

http://www.6sproductivitycom.com

 

[racookpe1978]

Thank you.

So the Liquid Metal Assisted Cracking in this reference is comparable to the terms LME or LMIE used above?

 

[metengr]

Since ASM Handbook on-line, Volume 11 references iron-zinc (where occasional anecdotal reports of steel fracturing during hot dip galvanizing…), under liquid metal induced embrittlement (LMIE), this is what it would be.

I found the above publications by Rich2001 interesting. To me, taking the issue of molten zing during welding out of the equation, iron-zinc LMIE during galvanizing is related to impurities within the molten zinc bath rather than liquid zinc itself. Over my career, I have seen numerous transmission and distribution hardware manufactured within the US while working for a large electric utility and not once did I ever come across a situation where galvanized pole hardware and tower steel developed LMIE cracking. I think just like anything else in a global economy as lowest cost becomes a driver, galvanizers will not watch their impurity levels or use additives where suddenly what was a non-issue becomes an issue under certain conditions.

All this means is that the purchaser needs to be involved with the galvanizing process and ask questions related to purity of the molten zinc bath.