Specialized Gas Mixes for Low Diffusible Hydrogen Weld Deposits

Specialized Shielding Gas Mixtures for Low
Diffusible Hydrogen Weld Deposits
AWS Pipeline Conference – Houston, TX
March 2014
Why is Weld Hydrogen An Issue to Be Addressed
Today?
 Hydrogen embrittlement/hydrogen-assisted cracking (HAC),
which can lead to unpredictable premature failure of welds, has
long been established as serious problems in the fabrication
industry
 The susceptibility to HAC increases as the strength of the steel
being joined increases
 The need for high-strength steel welding consumables that
consistently meet a low weld hydrogen requirement (H4 or even
an H2) is increasing. These materials require considerable care
in their use/storage and often have less than optimum
performance characteristics.
Consistently obtaining low hydrogen weld metal is very challenging!
2 3/6/2014
Low Hydrogen Flux-Cored Wires
 Solid fluorine compounds (fluorides) are used in the fill of flux
cored arc welding electrodes to counteract the effects of
hydrogen in the weld pool
Steel Sheath
Flux-Core: Fluorspar
(CaF2), Cryolite
(Na3AlF6)
 Fluorides decompose to provide fluorine which reacts with
hydrogen in the arc column or weld pool to form hydrogen
fluoride which is drawn away with the fume plume
 Excessive solid fluorides may produce process instability and
weld spatter generation.
Low-hydrogen wire fluoride levels provide a balance of operability,
mechanical properties, operability and weld hydrogen levels.
3 | Praxair Business Confidential | 3/6/2014
What is the Market Need?
 A reliable way to achieve superior mechanical properties,
very low diffusible hydrogen (consistently less than 4
ml/100g of weld metal) and excellent operability while
using a gas-shielded flux-cored or metal-cored wire.
 A systematic approach to achieving low weld metal
hydrogen in spite of the operating environment
(humidity) and welding consumable storage conditions
Gaseous Fluoride Addition to Shielding Gas
 ITW/Hobart identified a commonly available gaseous fluorine
compound, carbon tetrafluoride (CF4), as a possible shielding
gas additive to help in the reduction of weld hydrogen.
 CF4 is a product regularly used in the etching of silicon wafers
and/or as a refrigerant, but it is not normally added to argoncarbon dioxide mixtures used for welding.
Carbon tetrafluoride provides a source of fluorine to reduce weld hydrogen levels
5 3/6/2014
Gaseous Fluoride Addition to Shielding Gas
 CF4 is non-toxic, is a simple asphyxiant, is not considered
carcinogenic or mutagenic, and has no known ecotoxicity effects (it is
not an ozone-depleting chemical but it is a potent greenhouse gas –
6500X CO2). There is no OSHA PEL or ACGIH TLV for this material.
 CF4 requires no special handling or packaging which means standard
cylinder types, valves, and regulators are used for this product,
Will CF4 be suitable for use in a welding shielding gas?
6 | Praxair Business Confidential | 3/6/2014
Questions To Be Addressed:
 Will carbon tetrafluoride substantially reduce weld hydrogen with a
range of flux-cored and metal-cored wires? How much is needed?
 What constituents are produced in the fume as a result of the
decomposition of CF4 in an argon-CO2 blend used to shield flux- and
metal-cored wires?
 Is unreacted CF4 emitted during welding?
We need to understand what happens to CF4 as it is “consumed’?
7 | Praxair Business Confidential | 3/6/2014
What Was Investigated?
A Gaseous Fluoride Addition to the Shielding Gas
Two cylinder gas blends:
Ar-25% CO2-1 to 5%CF4
Ar-10%CO2- 1 to 2%CF4
Shielding gas
introduced into the arc
environment.
Plasma temperatures
exceed 10,000⁰F
8 3/6/2014
Impact of CF4 Additions on Arc Operability
For conventional carbon
steel flux-cored wires
operability is about the
same – possibly some
slight decrease in spatter.
For conventional carbon steel
metal-cored wires - stable
arc, smooth metal transfer.
May require slightly higher
arc voltage, especially at
start.
9 | Praxair Business Confidential | 3/6/2014
Product Use Associated with Claimed Benefits: Effect
of CF4 Addition on Weld Hydrogen
Flux-Cored Wire/Varying Fluoride Levels;
Argon-25%CO2 shielding
Weld Hydrogen (ml/100g)
6
5
4
E71T1‐M
3
E81T1‐Ni2MJ
E91T1‐K2M
2
E111T1‐K3MJ
1
0
0%
10 |
2%
3%
CF4 Addition
4%
5%
Product Use Associated with Claimed Benefits: Effect
of CF4 Addition on Weld Hydrogen
 Metal-Cored and Solid Wire/C-10 Shielding
Weld Hydrogen (ml/100g)
7
6
5
4
E80C-Ni2
ER70S-6
3
2
1
0
0
11 3/6/2014
1%
CF4 Addition
2%
Effect of Fluoride Addition on Weld Properties
for E101T1-GM FC Wire*
120
100
80
Ar-20CO2
Ar-25CO2-5CF4
60
40
20
*ITW/Hobart
0
UTS (ksi)
12 | Praxair Business Confidential | 3/6/2014
YS (ksi)
% Elong
CVN@-60F
Effect of Fluoride Addition on Weld Properties
for E80C-Ni1 MC Wire*
100
90
80
70
60
Ar-25CO2
Ar-25CO2-2CF4
50
40
30
20
10
0
* ITW/Hobart
UTS (ksi)
13 | Praxair Business Confidential | 3/6/2014
YS (ksi)
% Elong
CVN @ -50F
Review of Fume Constituents
 Potential Acute or Chronic Health Effects From Product Itself
– CF4 is non-toxic, is a simple asphyxiant, is not considered carcinogenic or
mutagenic, and has no known ecotoxicity effects (it is not an ozonedepleting chemical but it is a potent greenhouse gas).
 Potential Acute or Chronic Health Effects from Intended Use of Product
– Evaluated a range of flux-cored and metal-cored wires using several
different argon-CO2-CF4 gas compositions
– Compared constituents present in fume with and without the addition of
CF4
– Looked at all VOC’s present, searched for specific compounds, and
compared levels of solid and gaseous fluorides
– Ran five simultaneous sampling pumps to collect appropriate samples for
qualitative and semi-quantitative analyses
14 | 3/6/2014
Results of Fume Analysis
Analysis of Welding Fume Samples Showed:
– No unknown organic materials of any significant quantity to
raise concern
– No carbonyl fluoride detected with any wire/gas combination
– No significant emissions of unreacted CF4 especially if
addition is kept at the low end of the proposed range of
interest
– Solid/gaseous fluoride levels increased
No “red flags” indicating presence of materials with low exposure limits
15 | Praxair Business Confidential | 3/6/2014
Effect of CF4 Addition on Weld Hydrogen of
“Humidified” Wire
Weld Hydrogen Levels of Humidified* Wire
Flux-Cored Wire
Type
Ar-25% CO2
Shielding
(ml H2/100g
weld)
Ar-25%CO2 +
2%CF4 Shielding
(ml H2/100g
weld)
E71T-1
15.1
9.7
E81T1-Ni2-MJ H8
6.5
4.3
E91T1-K2C- H8
12.1
8.5
E111T1-K3, MJ,
H8
16.8
15.9
*Standard humidification test requirements: spooled wire exposed at 80°F, 80% humidity for 72 hours
16 | 3/6/2014
Many Factors Affect Weld Hydrogen Level
 Inherent hydrogen level of consumable being used
 Storage and handling of consumable prior to and during use
 General environment in which welding is conducted (humidity level)
 Use of pre-heat to remove any moisture from base material
 Use of post-weld heating to assist in the diffusion of hydrogen from the
completed weld
 Proper selection of welding parameters for the specific application
 The use of the a gaseous fluroide addition to the shielding gas
makes it easier to achieve lower weld hydrogen levels
17 | 3/6/2014

Download Report