Nilesh,
SAW of C-Mn Steel cause significant transverse cracking, if the "Mn" level in the weld is high typically ≥ 1.6%. This generates hard spots in the weld and together with improper baking of flux, can generate hydrogen cracking. There are tons of well documented technical articles on this issue.
By nature SAW fluxes could be highly Basic or Neutral or could be Active/Mn-Compensating. Usually highly basic or neutral fluxes are always a good choice, since addition of alloying elements through wire is always better and easier to control than adding through flux.
If you're using EH-14 type filler wire, Mn in this filler wire is typically 1.7-2.2, and if the flux is Mn Compensating this problem will occur. As asked by Mr Gering at the first place:- What was the Wire +Flux combination used (Brand name and AWS classification) ?.
As per The Welding Institute (TWI), propensity of SAW cracking could be calculated, with the following formula,
- UCS (units of cracking susceptibility) = 230C + 190S + 75P + 45Nb - 12.3Si - 5.4Mn - 1.
- Research at TWI has shown that UCS levels of less than 10 indicate a high resistance to cracking and levels above 30, a low resistance.
Some specifications clearly caution on the chemistry of SAW welds(see the extract from NACE- MR-0472 -Prevent In-Service Environmental Cracking of Carbon Steel Weldments in Corrosive Petroleum Refining Environments
· High weld deposit hardnesses can occur with SAW when using a low- or medium-Mn wire in combination with an active flux. Also, some SAW welds with high Mn and Si contents can have highly localized hard zones that are not softened significantly by PWHT. Most welding consumable manufacturers recommend against the use of active fluxes for multipass welds. Hence, unless otherwise agreed, production SAW weld deposits shall meet the A-No. 1chemical composition shown in Table QW-442 of the ASME Boiler and Pressure Vessel Code, Section IX.
If you want to be sure that cracks are not throughout the thickness, perform a conventional UT(Pulse Echo).
If the cracks are observed only on the final layer, reduce voltage , use multi bead technique and if wire+flux combination does not have Mn in the weld ≥ 1.6%, then this problem would be solved easily.
Thanks.
Date: Wed, 28 Jul 2010 00:58:52 -0700
From: bonardo137@yahoo.com.au
Subject: Re: [MW:6164]Transverse Crack
To: materials-welding@googlegroups.com
Nilesh :
Did the plate undergo certain cold working process (rolling, bending,etc) prior to welding ? if so it would likely due to residual stress that cause the cracking, you could try to prolong the preheat time and see if it still cracking or not
Also I found that the cracking susceptibility increases with an increase in the welding current, and decreases with an increase in the welding speed or the electrode wire feed rate. It also increases with increases in the plate rolling reduction ratio .
Regards
Richard Napitupulu
JWES Certified Welding Engineer CWEng
QA/QC Site Representative Pertamina Hulu Energy
Offshore West Java
From: "GERING, Erwin" <Erwin.GERING@airliquide.com>
To: materials-welding@googlegroups.com
Sent: Wed, 28 July, 2010 1:12:25 PM
Subject: [MW:6161] RE: 6154] Transverse Crack
Mostly these cracking are related to hydrogen.
Can you please specify filler metal (wire – flux combination) and hydrogen precautions (redrying?) and thickness.
With kind regards, mit freundlichem Grüss, salutations, met vriendelijke groet,
Ing. Erwin GERING, IWE
Corporate Product Manager - ALW-corp. mktg - SAW Wire & Flux
Product Manager - ALW-NL & BeLux - Welding Consumables
(Tel.: 31(0)76 – 54 83 222 ÈMob.: 31(0)6 - 55 87 29 21
Van: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] Namens waman nilesh
Verzonden: dinsdag 27 juli 2010 18:58
Aan: materials-welding@googlegroups.com; materials-welding@goolegroups.com
Onderwerp: [MW:6154] Transverse Crack
I want to know the exact cause off transverse crack observed visually on the surface of the weld.
Welding done with SAW
Material - SA 516 GR. 70
Thickness- 32 mm
We have done pre heating at temperature 100 deg. C but from top side also check the filler wire material
after crack are observed which are ok.
Please share your experience with me on this issue.
Regards,
Nilesh
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