Written by Ed Craig. EMail email@example.com
- Nickel Steels Data:
For TIG Welding Stainless Steel visit here
as we have a variety of weld process selections for stainless . What MIG and flux
cored wires / processes should we consider when welding stainless steel in the
gage to 25 mm range?
The following primary weld considerations
will influence the weld process required.
 Distortion potential.
 Cleaning and oxidation concerns.
 Part thickness.
 Weld positions.
 For welding stainless steel applications, it's been traditional
and logical to use use TIG or the MIG short circuit process with an 0.035 (1mm)
wire, when welding < 2 mm stainless steels.
 A REAL WORLD PULSED
MIG BENEFIT: In contrast to "short circuit", to increase weld speeds
on gage parts and provide superior weld surface, (more fluid) consider the pulsed
MIG process. For pulsed on stainless consider the gas mix I developed argon 2
- 5% CO2 (see MIG gas section) and 0.045 wire. The pulsed choice is especially
appropriate for stainless welds on applications in the range of 16 gage to 3/16
For stainless / duplex applications > 5 mm for flat and horizontal welds, consider
an 0.045 MIG wire. Use spray with argon 2 - 5 % CO2 for optimum welds, and consider
pulsed with the same gas mix if heat, distortion or spatter issues. For these
weld also consider the 0.062
(1.6 mm) gas shielded flux cored wire with argon
20 to 25% CO2.
For MIG welding in the vertical position. If parts are < 4
mm, try welding vert down. Use argon 2 - 5% CO2 and spray with 0.035 wires and
pulsed MIG with 0.045 wires.
For MIG welding in the vertical position on stainless steel parts over 3/16 thick,
(> 5mm) welding vertical up or overhead applications, consider an 0.045 gas
shielded flux cored wire with argon 20- 25% CO2. Do not weld vertical down with
the gas shielded flux cored wires.
 Now we have the MIG data out of
the way, any weld shop that welds stainless and has not looked at TIP
TIG is a weld shop thats way behing in weld technology.
Safety weld issues are a primary concern for anyone who welds stainless steels
and nickel alloys...
held hearings on it's proposal to reduce the PEL for hexavelent chromium from
52 micrograms per cubic meter to 1 microgram per cubic meter as an 8 hour time
weighted average. By court order OSHA is required to adopt a final rule by Jan
18 2006. Click for MIG Welding Stainless
Steel safety issues
Don't forget with TIP
TIG you get the highest possible weld quality, the lowest possible weld heat and your TIG weld costs will be reduced by at least 70%. What many weld shops are also not aware is TIP TIG will also attain the lowest stainless or alloy welds fumes.
WELDING STAINLESS STEEL GAS MIXES AND WELD REALITY....
the last three decades, the biggest selling gas mix in North America for MIG welding
stainless steel, thin gage applications, has been a ridiculous tri-mix containing 90% helium
- 7.5% argon and 2.5% CO2. In contrast to the three part helium tri-mix, a less
costly, two part mix, argon - 2 % CO2, (a mix Ed developed in the nineteen eighties),
has always provided more thin gage, stainless weld benefits.
are over 60 MIG gas mixes available for all MIG applications.
six mixes Ed has defined the world's best gas mixes.
the MIG Welding Stainless Steel Gas Section
TIP TIG ONLY ONE GAS IS REQUIRED FOR ANY WELD
ON ANY ALLOYS
IS STAINLESS STEEL MADE OF?
STAINLESS STEEL COMES IN MANY FORMS.
Stainless Steel Grades
Austenitic, Martensenitic and Ferritic STAINLESS STEELS.
Stainless Steels are the ones most weld personnel are familiar with.
These chrome nickel steels, in contrast to lower cost stainless have more alloys
and are "non magnetic" (Exception, types 310 - 330)
Facts: Austenitic grades typically contain a minimum of 18% chrome - 8% nickel
and are often called 18/8 steels.
Stainless steel Grades 20-202-205-301-302-303-304-305-308-309-310-314-316-317-321-329-330-347-389-17
7PH- 17 4PH-PH15-7Mo-AM 350-AM 355 A 286.
Common Designations: 304 (S30400) - 304L
(S31600) 316L (S31603) - 347 (S34700).
Steel Grades 301-302-304-305-308 usually welded with E308.
grades used for machine parts exterior buildings and industrial parts.
grades are not to exceed 800F 426C service temperature.
stainless grades "200"
series similar to Austenitic 18/8 grades.
Manganese in this series is used for "extra
Welding the manganese grades usually requires the use of the E308L
and Ferritic Grades are
common stainless steel grades that we don't want to weld and if we do, we should weld
with great caution.
Chrome steels. Weldability,
limited. Preheating typical 250°C to 450°C. Postweld treatment: Slow cooling
to 120°C (martensitic transformation) and annealing at 750°C or hardening
(generally 1000°C / oil), tempering (generally 750°C). Watch for formation
carbide between 500°C and 650°C...
When welding these grades the weld procedure concerns and focus will be on HEAT
STEEL WIRE INTERNATIONAL SPECIFICATIONS.
US AWS A5.9 / UK BS2901 / Japan JIS Z3321/
ISO 3581/ Germany DIN 8555 - 8556
UNS International filler metal numbers start with WXXXXX
Avesta: Stainless steel evaporators at Smurfit Kappa Kraftliner, Piteå.
TYPICAL STAINLESS STEEL FILLER METALS
Filler Metal Information:
Germany SG X5 Cr Ni 19.9
Mn 1 - 2.5
is typically used when the corrosive conditions are not severe|
SG X2 Cr Ni 19.9|
Mn 1 - 2.5
The lower carbon is used to avert the formation of carbide precipitation
| || ||ESAB-
Thyssen - JESi
Filarc - PZ6061/6561
Si or Hi Si. |
The high silicon can increase arc stability and the weld wetting,
which is important for some the low amp, sluggish, short circuit welds
SG X12 Cr Ni 22.12|
Mn 1 - 2.5
Thyssen -Therm 25.14
for welding 309 and austenitic to ferritic (carbon) steels|
| ||C 0.03|
Mn 1 - 2.5
for weld overlay applications, steel to stainless or for butter passes.|
designation has minimum carbon content lower carbon can cause micro cracking causing tensile
|Germany SG X12|
Mn 1 - 2.5
weld 310 and 304 clad and stainless overlay
For low or high temp, corrosive or any critical applications always confirm electrode
choice with wire manufacturer.
Using ELC ensure weld gas has less than 3%
CO2. A low co2 mix is less oxidizing than a low oxygen mix.For low carbon base
use low carbon filler identified by EXXXL
Mn 1 - 2.5
More "crack resistance" than E309.
Mn 1 - 2.5
Thyssen - Therm G.
316 steels and good for "high temp" corrosion resistance
SG X2 CrNiMo 19.12|
Mn 1 - 2.5
|317 Germany SG CrNiMo 1813|
317L UNS 31743
Mn 1 - 2.5
moly to increase the tensile strength. Has excellent corrosion resistance and
high temp properties Note contains considerable ferrite which can lower toughness
|Germany SG X5 CrNiMoNb 1912|| || |
for welding Carpenter 20 plus 20Cb-3 stainless|
|UNS W32140||C 0.07|
| || |
For weld data and information on Carbide Precipitation scroll down to weld
SG X5 CrNiHb 1999|
Thyssen Therm H.
Sandvik - 19.9Nb
for 321 - 347 better corrosion resistance than 308
wire is stabilized with small amounts of Ti or Cb to prevent carbide precipitation
|Electrode 349||UNS 34940|
| || || |
SG 5 350
| || || |
SGS 250 Zr
ISO 17 - EZ17
| || || |
Select-Arc Inc. has introduced a metal cored, ferritic stainless steel electrode
that is designed for welding on thin sheet metal materials. SelectAlloy 430L-Cb's
higher chromium content combined with the columbium (niobium) stabilization provides
similar heat and corrosion resistance to the base metals which are welded. This
electrode handles poor fit up. SelectAlloy 430L-Cb delivers less burn through potential and less
spatter to provide greater productivity. It also offers lower transition current for spray
SelectAlloy 430L-Cb is well suited to weld the heat resistant, corrosion
resistant, ferritic stainless steels used in exhaust system components. Typical
applications include manifolds, converters, mufflers and tubular components of
automotive exhaust systems made of 430 grade materials. This electrode is available
in .045in, .052in and 1/16in diameters.
from Ed. As many manufactures of exhaust components seem to lack the engineering and manufacturing
expertise to make their exhaust products within the specified design dimension
tolerances, this 0.045 metal cored wire would provide a good crutch to the managers and engineers. The primary weld benefits as it can
utilize lower weld currents than MIG wires.
Note in MIG welding for over 50 years, I cannot think of any application in which I would have had to purchase this more costly weld wire.
AND SMUT ON STAINLESS:
|Some advice on getting rid of stainless smutt
Stainless smut is a common problem that results
after pickling. Smut is an undesired discoloration that deposits on stainless
steel surfaces after pickling, it appears as a dark sticky film. Its difficult
to pinpoint why the smut has formed. There are a large number of possible causes
and factors. The most frequent of these are:
(dirt and or glue residues from plastic film).
Poor water quality.
circulation/stirring in the pickling bath.
Old, contaminated pickling
Poor steel quality.
Nitrate-free pickling solutions.
Research has shown that smut is more likely
to occur when metal dissolution by the pickling acid increases Fe2+ levels to
the point where the redox potential of the pickling solution falls below a certain
value (Fe + 2Fe3+=> 3Fe2+). Under these conditions, a passive chromium layer
is not formed. This leaves the steel surface vulnerable. Loose oxide particles
and other elements in the pickling acid may then easily attach themselves to the
Low alloy-stainless steels are more sensitive to smut formation
than are their high-alloy counterparts. This may be due to the high pickling rates
that, particularly with high acid levels, are characteristic of low-alloy steel
grades. Reducing smut with FinishOne Besides excellent NOx reduction and
passivating power, FinishOne has also demonstrated that it is a real smut
killer. Sprayed onto a still wet steel surface, it promotes Fe2+ to Fe3+
oxidation and thus prevents smut formation (Fe2+ + FinishOne => Fe3+ + H2O).
Smut caused by silicone residues on the surface Smut and NOx reduction using FinishOne.
Smut caused by a film of oil on the surface When Fe3+ is the dominant ion, the
resultant passivation protects steel surfaces from both corrosion and adhesion.
A final rinse with FinishOne ensures a passivated
surface that is free from water stains. If
they do not receive proper post-weld treatment, stainless steels soon lose their
stainless property. Thus, correct pickling, passivation, et cetera are all vital.
This is especially true in the pulp and paper industry, where highly aggressive
media are used at high temperatures. Avesta Finishing Chemicals has the products,
expertise and support to meet the stainless steel finishing requirements of the
pulp and paper industry worldwide.
WORK HABITS, POOR HANDLING AND POOR MAINTENANCE CAN MAKE STAINLESS FABRICATION
SUSCEPTIBLE TO RUST.
you work in a weld shop that welds stainless, you may have seen rust form on those
stainless parts. To get corrosion to form on stainless does not take much. Lift
the stainless parts with a fork lift, strap the parts with a steel band, clean
the parts with a steel brush or steel wool or grind steel parts near the stainless
parts and a few days later that familiar rust will appear.
There is a good
reason that weld and fab shop are asked when making stainless parts to to isolate
stainless from carbon steel components. When
you look at that shiny stainless part remember it's protected by a self healing,
very thin oxide film and as long as that film is intact and there is oxygen present,
the stainless remains rust resistant. Even when the stainless surface is damaged
and not contaminated, the stainless film will recover. However when the stainless
is attacked by carbon steel contamination, the film is unable to recover and under
the film their is active metal waiting to corrode.
welder grinding carbon steel parts creates micro steel particles that fly through
the air and can attach themselves to a stainless part. Left in an open environment,
the carbon steel grinding particles eventually dissolve and the iron oxides that
result will contaminate the surface of the part. The
iron oxide contamination prevents or reduces the oxygen from reacting with the
stainless part in the contaminated area making not allowing the oxide film to
occur. This results in an active stainless which is sensitive to the formation
movement of any carbon steel against a stainless part, such as from steel rolls
on conveyors, fork lifts or crane steel handling clamps will also contaminate
the stainless. A common method of none abrasive carbon steel contact can come
from manual or robot welding stainless in a carbon steel fixture. If the carbon
steel fixture components are are in close proximity to the stainless welds, this
can lead to carbon pickup in the stainless that will in a short period result
in the formation of corrosion.
from the common stainless contamination that results during material forming /
handling, a very common cause of corrosion results
from the use of grinding wheels contaminated with steel particles or steel wire
brushes. When lifting parts with a fork lift, use none steel components that separate
the steel forks from the stainless. When you strap those stainless parts, place
wood between the bands and the stainless. With stainless weld operations using
carbon steel fixtures, ensure no carbon steel part is within 25 mm of the welds.
If fixture parts are within close proximity of the welds replace the carbon steels
components with stainless, copper or aluminum.
around those Stainless Welds
|Advice on rust around the stainless welds.
Ed. Recently our company fabricated 316L thin gage duct work and pipe. The finished weld products
have been out doors at the site for approximately 2 weeks and now about 20% of
the welds are showing rust at the weld seams. Our procedure for weld cleanup was
to use a stainless wire brush followed with a citric acid passivation. We really
are at a loss as to why this happened.
from Brad Hass. This very interesting for me, we had a similar problem on 304L
structures for a blast freezer. It turned out to be from the use of a 302ss powered
brushing operation. We had a company come in, to apply pickling gel to the damaged
areas. It works! The reason I don't believe you had a carbon steel brush in use,
is citric acid treatments will remove that, and will not remove contamination
from 302 and 304 powered brushing. Nitric/Hydroflouric and brush electropolishing
is the only thing we have found to remove this. I have confirmed all the above
with salt spray testing 24 hr 5% solution. One other thing the larger the bristle
diameter the worse the contamination. I recommend in the future 316L brushes for
your clean up, this works. Brad..
In weld shops weld inconsistency is normal and therefore stainless cleaning practices
should also be looked at.
I wonder If the shop manager or supervisor came in on the second shift,
would he find Fred the welder cleaning the stainless welds with carbon steel brushes
or wheels, or with contaminated
When I look at the pipe seam and circumferential welds, it's
notable that the corrosion is localized and on the minority of parts, (like caused by Fred on the second shiftl). Therefore it's logical to assume
that an inappropriate cleaning method was used during fabrication and welding.
I believe that possibly in some areas the correct stainless brushes or wire wheels
and at other times the welders picked up carbon steel brushes or used cleaning
wheels or abrasives that were contaminated from their use on steel components
stainless flange cleaned with B570 and coated with a nanolyer available from
rust formation on stainless should be removed and the fab shop has many ways to
approach this task..It's logical in the fab shop to pick up steel wool, wire brush or a grinder
and take that to the contaminated area, however these products can cause surface
damage and further contamination which combined with the existing contamination can again lead to later
corrosion spread over a wider area.
Rust can be removed from the stainless surface
without damaging the surface with the use of pickling liquids or inorganic chemicals.
The negative aspect of pickling or inorganic chemical is the impact on the environment
and the hazards to the people who apply the chemicals. With this in mind there
are in 2008 some unique products available that eliminate iron oxides and provide
deep cleaning of contaminated stainless parts . Of course the most cost effective
practice for the fab shop, is don't allow the stainless parts to be contaminated. Check
out a company call Innomet and look at their unique chemical approach to stainless
cleaning and rust removal. Innomet visit. http://inno-soft.nl/en/index.html.
Welding High Strength, High Carbon Steels
with Austenitic Stainless or Nickel Filler Metals.
Austenitic stainless steels are prone to hot cracking
and so attention is required to cleaning before welding and welding using low
to medium weld parameters. Concern for formation of chromium carbide at grain
interface especially if the carbon content is higher then 0.04%. No preheat is
Filler metal: % C = max. 0.04%
welding carbon steels to stainless, the austenitic / nickel filler metals offer
unique features that can reduce weld crack potential in both the welds and weld
heat affected zone (HAZ). Carbon to stainless welds require that the stainless
weld metal have sufficient ferrite to resist cracking. When welding carbon steel
to stainless and a 309L wire is used, the resulting ferrite is approximately 14-16FN.
If the steel is a high carbon steel, a 309L, first
weld pass on the carbon to stainless will likely end up with "insufficient
ferrite". The carbon from the high carbon steel when mixed with the stainless
weld will suppress the ferrite formation. Instead of the 309L for this application,
a 312 electrode may be recommended.
The 312 filler metal, (70 to 90
FN in the weld metal) produces much higher ferrite levels than the 309L. This
is the prime reason the 312 is recommended for applications sensitive to weld
cracks. Filler metals such as 307 - 308 Mo and 310 can resist cracking with the
aid of alloys and without the aid of ferrite.
AUSTENITIC & NICKEL WELD ELECTRODES CAN HELP HIGH STRENGTH CARBON STEELS.
High carbon, high strength steels welded to each are subject to hydrogen
The the three fundamental requirements for hydrogen assisted
 High hardness.
 A source of hydrogen.
 High stresses.
the high carbon steels, high hardness is typical in the HAZ unless very high,
(often not practical) preheat and interpass temperatures are utilized for the
The stresses that can influence HAZ cracking typically result
from weld residual stresses caused by weld shrinkage, these stresses can be further
exaggerated by weld joint restrictions as found in certain fixtures.
As we are all aware, hydrogen in the weld can be derived from many sources.
An alternative to a high carbon, high strength filler metals, in which the
carbon dilution from the base metal will result in a hard weld, subjecting the
weld to transverse cracking, is to use an austenitic or a specific nickel based
filler metal (ENiCrFe-2).
The austenitic or nickel filler metals greatly
reduces the weld transverse cracking potential. Also these filler metals greatly
reduce, slow down or trap the weld hydrogen that can diffuse from the weld into
the HAZ, this greatly reduces HAZ hydrogen cracking potential.
diffusion of hydrogen though austenitic and nickel filler metal welds and steel
can be approximately 80 - 110 times slower than through carbon steels and welds.
The use of the austenitic and nickel filler metals can greatly reduce cracking
however these filler metals can still absorb hydrogen
so these electrodes should be treated with the same respect and rules that apply
to any low hydrogen filler metals.
MIG welding. Use Ed's unique Stainless, Duplex MIG Gas Mix to help reduce any types
of weld cracking. With any stainless flux cored wires use the argon - CO2 mixes
recommended for carbon steel flux cored wires, The best way to eliminate any weld cracks is use the TIP TIG process.
When to use those common
308L, 309L or 316L filler metals.
308L and 308LSi is predominately used on austenitic stainless steels, such as
types 301, 302, 304, 305 and cast alloys CF-8 and CF-3.
 For high
temperature applications such as in the power industry, higher carbon 308H electrodes
will provide superior
creep resistance than does 308L .
 Use 309L and 309LSi when joining
309 or mild steels / low alloy steels to stainless steels. Use 309 when joining
dissimilar stainless steels such as 409 to itself or to 304L stainless. CG-12
is the cast equivalent of 309.
Some 308L applications may be substituted with 309L filler metal, but 316L or
316 applications generally require molybdenum. Note, 309L contains no molybdenum.
 316L and 316LSi should be used with 316L and 316 base metals. CF-8M
and CF-3M are the cast equivalents of 316 and 316L, respectively.
Type 347 stainless steel filler metal is used for 347 and 321 base materials because
it matches these stabilized grades. CF-8C is the cast equivalent of 347. Type
347 filler metal is also suitable most 308L filler metal applications.
Weld Wires that Ed recommends:
stainless gas shielded flux cored
wires are available from Alloy Rods and
Priducts Ed recommends. Sanvik and Avesta set
for MIG Stainless wires.
REDUCE STAINLESS WELD POROSITY POTENTIAL:
porosity, a cavity discontinuity that forms from a weld gas and metal reaction. The porosity
can be trapped in the weld or at the weld surface. The porosity is typically round
in shape but can also be elongated. In contrast to argon oxygen mixes, Ed's unique MIG
Stainless. Duplex gas mix was developed for less oxide reaction than any other mix. This gas results in less weld porosity
ROBOTS AND MIG POROSITY.
When you find the robot weld porosity is always at the
same location and the weld porosity is not at the weld starts or ends, examine
the robot movement and see if the robot arm is causing a restriction of the gas
flow line. Also it's common with robot cells to see a severe gas flow restiction
due to the narrow orrifices often found in gas line connections. In a robot cell its
critical to measure gas flow as it exits the gun. If the porosity is at the weld
start or stop increase the gas pre flow and post flow times.
porosity, a cavity or discontinuity that forms in the weld from a gas reaction
in molten metal. The
weld porosity can be trapped in the weld or evident at the weld surface. Weld
porosity is typically round in shape, but can also be elongated.
Weld porosity is caused by the absorption of oxygen, nitrogen and hydrogen
into the molten weld pool. The gases are then released on solidification and may
become trapped in the weld metal.
and oxygen absorption in the weld pool usually originates from inadequate or contaminated
gas shielding, leaks in the MIG gas line, excess gas flow rates, draughts and
can originate from a number of sources including moisture from the electrodes,moisture
on the parts, contaminates on the workpiece surface. (Use
dry pre-heat > 100F , oxy fuel > 250 F)
WELD POROSITY. A localized group of pores with random distribution. Causes. Arc
blow, insufficient, inconsistent or excessive weld gas flow, material or weld
wire contamination, (low) weld parameters or poor technique.
WORM HOLE, WAGGON TRACKS POROSITY. Sometimes called "waggon tracks".
Typically found in the center of the weld, parallel to weld axis. Classic porosity
when moisture is evident in gas shielded flux cored wires, (the cheaper the product
the more prone to waggon tracks).
the flux cored wire stick out and increasing the wire feed rate helps by adding
energy to the wire. Baking flux cored wires and storing the wires in a dry environment
also reduces flux cored porosity potential.
Reduce the weld travel rate, make the welds a little larger, avoid weaves or fast freeze welds. All
recommendations are intended to increase the weld arc energy and decrease the
weld cooling rate.
Worm holes are elongated gas pores producing a herring
bone appearance on a radiograph. Worm hole porosity is common in gas shielded
flux cored welds when the electrodes have too much moisture in the wire flux.
WELD ROOT POROSITY. Weld
root porosity frequently occurs when MIG welding using "argon oxygen"
(oxidizing) mixes on parts >6 mm. With these gas mixes the resulting root is
typically narrow, finger shaped. The root finger area solidifies rapidly trapping
porosity. To reduce the stainless root weld porosity, change to an argon 2 - 4
CO2 gas mix. Increase the weld parameters, slow the weld speed and avoid weld
WELD POROSITY. Linear porosity, an array of small round pores typically found
in a line. Often caused from the base metal lubricants or metal surface contaminate.
Add weld energy (increase wire feed), increase push angle allowing the arc to
break up surface oxides ahead of weld.
WELD POROSITY. Weld porosity scattered randomly throughout
the weld or welds. If the MIG weld surface is gray and looks oxidized, the porosity
is typically a result of insufficient gas flow. If the weld surface looks clean
with scattered porosity the porosity is usually caused by the base metal part
or electrode contamination, or perhaps the weld data used causes the weld to freeze
PORE WELD POROSITY. If weld surface is clean and does not look oxidized, the large
pore MIG / FCAW porosity could be a result of excessive gas flow. Gas turbulence
is caused with gas flow greater than 40 cuft/hr. Optimum MIG and flux cored gas
flow for carbon steels is 25 to 35 cuft/hr, the gas flow should be measured as
it exits the gun nozzle. If the weld surface is dirty (oxidized) the cause of
larger pore porosity is ofen a result of insufficient gas flow, less than 20 cuft
2004. Sandvik Announces New Ultrahigh-Strength Stainless Steel "NANOFLEX":
Sandvik Materials Technology recently
developed a new stainless steel called Sandvik Nanoflex that features ultra high
strength and good formability, corrosion resistance, and surface finish. According
to the company, the steel is well suited for mechanical applications
requiring lightweight, rigid designs such as medical equipment and for replacement
of hard-chromed, low-alloy steels in the automotive industry.
of the strength properties of Sandvik Nanoflex are 1700 MPa tensile strength,
1500 MPa yield strength, 8% elongation, 45-58 HRC hardness, and a Charpy V impact
strength of a minimum of 27 J at -20°C. Exact strength values depend on the
product form and the manufacturing route.
Despite its high hardness,
the company claims it is easy to perform cold forming operations such as bending,
cutting, turning, and grinding. After reaching the desired shape, a simple low-temperature
heat treatment gives the material its high strength without distorting the workpiece.
also displays good welding properties. It is available in tube, strip, wire, and
Steel Filler Metal Selection
METAL SELECTION |
AWS A5-9. Use
with wire manufacturer
CHROME NICKEL NONE MAGNETIC
201 to austenitic 200-300
used for low temp cryo applications
to - 320F
308 for 330 use 312|
202 to austenitic 200-300 |
for 330 use 312|
201-202-301 303 to mild steel use ||312|
210 - 202 -301 to mild steel.|
Stainless type 201 requires special consideration
required to avoid hot cracking as ferrite extremely low
can reduce cracking as it provides much higher ferrite than 309. |
301 to austenitic 200-300 |
for 330 use 312
302 to austenitic 200-300 |
for 330 use 312|
302 - 302b 304 to mild steel use||310|
- 302B -304 to mild steel use ||310|
303 to austenitic 200-300 |
for 330 use 312|
303 to 310-314-330- use||312|
303 to mild steel use ||312|
304 to austenitic 200-300 series
for 330 use 312
305 308 to mild steel use||312|
to austenitic 200-300 |
for 330 use 312|
305 - 308 to mild steel use ||312|
308 to austenitic 200-300 |
for 330 use 312|
309 to 309 - 310 - 314 -316 -
to 330 use||312|
to 347 use||308
310 to 310-3140||310|
to 316 use||316|
310 to 317 use||317|
to 321 use||308|
to 330 use||312|
to 347 use||308|
to mild steel use ||310|
314 to 314 use||310|
to 316 use||316|
314 to 317 use||317|
314 to 330 use||312|
314 to 347 use||308|
314 to mild steel use ||310|
316 to 316 - 317 use||316|
316 to 321 - 347 use ||308|
316 to 330 ||312
316L to mild steel use ||309|
316LN a nitrogen addition to a low carbon stainless Incesase both corrosion resistance
and strength as compared to 316L|
317L typical for corrosion
316L for toughness
| || |
317 to 317||317|
317 to 321 ||308|
317 to 330 use||312|
317 to 347 use||308L|
317 - 321 - 348 403 - 405 410 414 416 to mild steel use||309|
321 to 321 - 347||347|
321 to 330 use||312
330 to 330 use||330|
to 347 use||312
410 Condition A|
12% Chrome, chrominum / martensitic steel
itself or carbon|
501 502 430 431 442 448 to mild
steel use ||310|
27 Cr - 31 Ni -Mo 3.5 -Cu 1
Tensile 73 ksi Yield 31 ksi
DIN X2CrNiN 24-4
23 Cr - 4 Ni - N 0.1
Tensile 87 ksi - Yield 58 ksi
22 Cr - 5.5 Ni -Mo 3 - N
Tensile 990 ksi - Yield 65 ksi
Note: For MIG use argon with 2% CO2. When welding 2205 or 2304 to dissimilar butter
first with ER309MoL then weld with 308MoL
No concern for interpass temp, high
amps can be use
18.5 Cr - 4.9 Ni - 2.7 Mo
same as 2205|
Sanvik Sanicro 60 ENiCrMo3
to carbon ||309
or 312 which has higher ferrite reduces cracking |
| || |
STEELS 403 - 410 - 414 416- 420-
422 -431- 440...|
Preheat and interpass temp 500F 260C Post heat 1350F 732C>.
Control cool 50F / hr to 1100F>.
Control cool to 1100F 600C then air cool.
Treat the 500 series the same as the Martensitic series
403 to 400 series use||410
403 to 501 use||502|
403 to 505 use||505|
405 to 505 use||505|
405 to 501 use||502|
405 to 430 use ||430
405 to 400 series use||410|
410 to carbon steel||309L|
410 - 414 WELD same as 405|| |
416 - 440 butter with 312 or 309 first|| |
416 to 505 -502-501 -446 - 440 -430 -420 use ||309|
416 to 431-420-416 use ||410|
420 to 505||505|
420 to 501-502 use ||502|
420 to 446 use ||430|
420 to 440 -420 use ||420|
420 to 431 -430 use ||410|
430 to 505 use||505|
430 to 501 - 502 use||502|
430 to 446 - 440 - 431 - 430 use ||430|
430F to 400 series use||309|
431 to 505 use ||505|
431 to 501 -502 use||502|
431 to 446-440 use||309|
440 weld same as 431|| |
446 to 505 use||505|
446 to 501 - 502 use||502|
446 to 446 use ||309|
505 to 505 use||505|
501 to 505 - 502 - 501 use||502|
502 to 505 - 502 use ||502|
steels 405 - 409 - 429 - 430 -434 - 436 - 442 -444 - 446|| |
to 444 or to other metal use||316L
magnetic avoid prolong heat in the range of 750F -1700F (400-925C|| |
preheat at 350F 176C To improve ductility|| |
steels most frequent electrodes||309
- 310 - 312|
steel if post heat required use Austenitic filler|| |
Stainless and Intergranular
Intergranular corrosion is also
called intercrystalline corrosion. This occurs on or adjacent to the grain boundaries
of a metal. It is caused by microsegregation of impurities and alloying elements
on the grain boundaries.The driving force of intergranular corrosion is the difference
between the electrode potentials of the grain boundary and the grain itself, which
form a galvanic cell in presence of an electrolyte.
corrosion of stainless steels:
microstructure of metals consist of a granular composition. The grains formed
are small crystals. The crystal surfaces join the surfaces of other grains to
form grain boundaries. Grain boundaries separate the grains. With stainless, intergranular
corrosion, (intercrystalline corrosion), occurs on or adjacent to the grain boundaries
of a metal.
causes of intergranular corrosion are welding, stress annealing, improper heat
treating or overheating in service. Inspectors have difficulty in detecting the
early stages of intergranular corrosion. This form of corrosion results in a loss
of strength in metal parts where the grains have fallen out.
corrosion is caused by microsegregation of impurities and alloying elements on
the grain boundaries. The driving force of intergranular corrosion is the difference
between the electrode potentials of the grain boundary and the grain itself, which
form a galvanic cell in presence of an electrolyte.
If the phases segregated
at the grain boundaries have lower value of electrode potential they will oxidize
(anodic reaction) and the grain metal having higher value of electrode potential
will provide cathodic reaction (reduction). Dissolution of anodic grain boundaries
starts from the surface and advances along the grains interfaces. The process
results in deterioration of the bonding between the grains and drop of mechanical
properties. If the precipitates at the grain boundaries have higher electrode
potential the grains will dissolve (anodic reaction). In this case the grain boundaries
will not be attacked.
Stainless Steel Welds and Sensitization.
could write a whole book on this complex subject. I will try to keep it short and I hope it's
easy to understand.
With a stainless welds on specific alloys, sensitization occurs in the weld's
heat affected zone (HAZ) when
the zones are between approx. 900 and 1600F.
 Sensitization occurs when
the carbon content is sufficient to produce precipitation of chromium rich carbides
along the HAZ grain boundaries.
The formation the chromium carbides results in a chrome depleted area around the
grain boundaries. This location will be in the weld's HAZ at the furthest point
from the weld.
 If the weld's HAZ depleted chromium carbide area is
subject to a corrosive medium the grains can rapidly corrode and cause separation
from the weld.
A 304L metal will contain a maximum of 0.03% carbon. In contrast a 304 base metal
can contain twice the carbon level of the 304L.
 Welding and subjecting
a 304 base to 900F to 1600F will cause sensitization in HAZ.
Solution to Stainless
Use a low carbon ( L grade) stainless. The typical 0.03 max carbon content is
not sufficient for carbide precipitation.
 Consider a stabilized stainless
steel such as 347 or 321. These steels are stabilized against chrome depletion
with alloy elements that have a greter affinity to form carbides.
Type 347 which is similar to 304 has niobium (columbium) for carbide formation.
Let the niobium do its job and the chrome has no carbides to attach to, thus we
prevent carbide precipitation.
 Type 321 is also similar to 304. Type
321 contains titanium and the titanium does the same job as the niobium. Keep
in mind both the 321 and 347 are typically much more costly than the 304L.
 What about those common multi-pass "316 or
308 welds"? Of course the multi-pass welds are subject to the 900F to 1600F,
however the weld metal in contrast to the stainless base metal will contain a
small amount of ferrite in the austenitic structure. Chrome diffuses in ferrite
approx. 100 times faster than it will in the austenite. The ferrite has more chrome
than the austenitic matrix. The ferrite area will be rich in chrome so this area
can supply an area subject to sensitization.
Avesta provides a typical Pulp and Paper Mill Layout
Pulp and Paper Mill Weld Consumables from Avesta
308L is excellent for the welding of evaporators, storage tanks, etc. made
from 304L (EN 1.4307, Outokumpu 4307), a general purpose steel.
For welding 316L (EN 1.4404/1.4436,
Outokumpu 4404/4436), a well-proven austenitic grade that is used extensively
in the pulp and paper industry.
was specially designed for welding fully austenitic 6 Mo steels, e.g. Outokumpu
254 SMO (EN 1.4547). Owing to their good resistance to corrosion (stress, pitting
and crevice), these steels are used in, amongst other things, filter washers and
wash presses in modern ECF bleaching plants.
Avesta P54 is an iron-based filler metal
that was specially
developed for welding fully austenitic 6 and 7 Mo steels
(e.g. Outokumpu 254 SMO) in applications where conventional nickel-based alloys
are vulnerable to transpassive corrosion. D stage filters in the ClO2 bleaching
of pulp are just one example.
filer of the 309MoL type, commonly used in the pulp and paper industry for
and Nitrogen Purge Gas Question.
as you are aware Nitrogen is a lot cheaper than argon when utilized as a purge
gas for stainless. My question, When MIG welding stainless tanks edge or corner
welds, tube or pipe open root welds, can nitrogen react with the stainless and
have a negative impact?
Answer: Nitrogen has a
diatomic, "two atoms" per molecule. Nitrogen in the diatomic form is
usually insoluble in molten stainless. However if the nitrogen gets into the weld
arc, the plasma arc energy can seperate the diatomic molecules and create monatomic
The monatomic molecules are soluble in the weld. The nitrogen,
monatomic (seperated molecules) become an alloying element and can reduce the
ferrite in a stainless weld. A reduction in ferrite in some alloys can cause the
weld to be more austenitic and sensitive to hot cracking. If nitrogen enters a
weld or the welding arc, it can have a negative and sometimes a positive influence.
Thats the reason one of my gas mixes for duplex has the addition of nitrogen,
and the other gas mix does not.
There are stainless alloys which do
not need ferrite like 320 / 310. With these alloys nitrogen has no negative impact
on these alloys. Also if the stainless alloys have high ferrite levels they typically
can afford to loose a little of the ferrite to the nitrogen.
root, austenitic stainless welds, as found in tanks, corner, edge welds,
or thin gage, partial penetration tube welds, nitrogen is the logical, economical,
purge gas choice for all austenitic, duplex, martensitic and precipitation hardening
stainless steel applications. The only concern would be a few specific, ferritic
alloys in which nitrogen could cause severe weld mechanical issues.
an open root "MIG stainless weld" the nitrogen purge gas has
little opportunity to get into the weld arc as the gas flow rate / pressure of
the welding gas should be higher than that of the purging gas . However nitrogen
could still be picked up by the weld. .
With duplex stainless there should be no concerns for open root nitrogen issues.
The majority of the common, open root stainless alloys will not be adversely affected
by nitrogen purge gas. However in the world of product liability, here is the
welding bottom line. If your weld job is large enough to produce a substantial
cost reduction from using nitrogen gas, then it's logical to "pre qualify
the nitrogen purge welds" and have the weld chemistry, ferrite and mechanicals
309 Stainless Pipe Weld Tests.
Ed we weld austenitic stainless and carbon steel pipes. For cost reduction, in
our stainless weld tests we only utilize "carbon steel pipes" and 309L
SMAW or flux cored, electrodes. We frequently have root cracking issues, or during
the bend test the weld sample breaks. What is strange is that we visually examine
all the roots and we wont let them be mechanically tested unless the welds look
OK. Why the inconsistency? why do some tests welds pass and other good looking
Answer: The bottom line the 309L electrode is designed
to weld "carbon steel to stainless" this electrode was not designed
to weld carbon steel to carbon steel thats why we have carbon steel electrodes.
Use the 309L electrode on two carbon steel pipes and weld dilution becomes
a concern in the weld root area. If the weld parameters and edge prep is such
that the resulting weld dilution is minimal, the resulting 309L weld should be
austenite with a little ferrite. It's the austenite / ferrite combination that
provides weld ductility.
while welding the carbon steel pipe root, the welder uses higher current, slower
weld speeds or a wider weld weave, the 309L weld can end up with more weld dilution
with the carbon steels, reducing the weld ferrite level and making the weld more
austenitic. A reduction or loss of ferrite can make the weld subject to "hot
centerline cracking" (hot cracking, the weld cracks during the weld or soon
A hot weld crack surface in a bend test can be identified by a blue or gray color.
Even if the root pass does not crack the high austenite composition can turn to
martensite when cooling. The brittle martensite can readily fracture during the
bend test. (a silver color or bright fracture surface).
bottom line if you look at the costs involved in the stainless to carbon steel
pipe weld test, it makes little sense to use two carbon steel pipes. Ensure for
your weld test that one of the test pipes is at least stainless.
FAILED 308L FLUX CORED WELDS
SUBJECT TO HIGH TEMP.
shielded stainless flux cored wires have an Achilles Heel:
pointed out by Kotecki in the QA section, March Weld Journal, it would appear
that there is a problem with the use of specific stainless flux cored wires on
pressure vessel applications subject to high temperatures or post heat treatment.
In the stainless application reviewed, the weld shop applied a stress relief of
1475F for 12 hours to a 304L pressure vessel welded with gas shielded 308L flux
cored wires. After the heat treatment many cracks were found in the 308L flux
cored welds. These welds had no cracks before the post heat treat.
Flux cored wire manufactures add specific alloys and compounds
for easy slag removal. One common compound utilized contains bismuth.
Please note from
Ed: The bottom line for the 308L gas shielded flux cored weld cracking issues
or part / weld premature creep failures at elevated temperatures is the stainless
gas shielded flux cored wires utilized contain a compound containing "bismuth"
This compound assists in easy slag removal. It's been reported that with levels
of bismuth at 200 ppm. (200 ppm is a typical bismuth level) weld cracks have occurred
at a reheat temp of 1050F.
should you do if your stainless pressure vessel is to be used in a high temp application
or the vessel requires post heat treat.
POST HEAT TREAT: To avoid major issues on an application subject to high temp
post heat treat, its logical that a weld qualification procedure should encompass
the required post heat treatment. This way you can check the welds in the real
world welded condition.
 CONTROL THE BISMUTH LEVELS: For high temp
applications gas shielded stainless flux cored wires are available with bismuth
levels < 20 ppm. These products are supposed not to exhibit reheat cracks or
premature creep failure. Talk to your weld wire supplier about your concerns for
the high temp.
 REPUTABLE WIRE MANUFACTURERS: Don't purchase weld
consumables that fell of the back of a truck on their way from China. Deal with
reputable flux cored wire companies like Sanvik, Avesta and ESAB.
PROCESS ALTERNATIVES. Consider TiP TiG as these issues will not occur.
Its important to note, that
the majority of stainless are put into service at tempertures below < 500F
and these applications have not been subject to the issues discussed. However
there are also 300 series that undergo annealing and stress relief or are subject
to high temp > 900F applications in the power industry.
and 310 stainless welds.
Ed when welding 310 stainless we a longitudinal bend test evaluation of weld samples
we often end up with small linear shaped porosity which so far has gone unexplained.
We weld a lot of stainless in this shop and so we are aware of cleanliness requirements
and the use of good weld consumables , however the 310 pores are something we
can't seem to shake. Most of the pores are less than 2 mm in length, and so they
are acceptable however our designer has expressed concern that we may not be using
the best weld consumables. Any ideas Regards Paul.
Answer: First 310 stainless and a few other grades are completely austenitic containing
no ferrite. It's common with 310 - 330 multi-pass welds to find microfissures
(not porosity) forming at the interface between the welds. It's also common to
find these microfissures with longitudinal face or root bend tests. The microfissures
don't occur with austenitic grades like 308L that contain ferrite. Reports from
the WRC state that the small microfissures typically will not influence fatique,
creep and corrosion properties, and as the 310 is very tough the microfissures
typically don't propogate, however they can initiate pitting corrosion or reduce
the critical pitting temperture. You can reduce the amount of microfissures by
using filler metals with extra low sulfur and phosphororus, use stringer passes,
maximum size similar to 6 mm fillet and ensure you use a max interpass temp of
MIG Welding stainless Steel you can use the optimum MIG wire feed data recommended
at this site for carbon steels. The only change that will be required is a typicall reduction in weld
voltage. As stainless will use a low reactive gas mix, less weld volts will typically
In contrast to MIG on carbon steels, when MIG stainless welds are
made, typically 1.5 - 3 lower volts are required. Remember keep stainless clean and only use
stainless wire brushes.
steel has a very thin and stable oxide film rich in chrome. This film
reforms rapidly by reaction with the atmosphere if upset or damaged. If stainless
steel is not adequately protected from the atmosphere during welding or is subject
to very heavy grinding operations, a very thick oxide layer will form. The thick
oxide layer will be noted by it's blue tint. This oxide will have a chrome-depleted
layer under it and this layer can impair corrosion resistance.
With stainless weld applications, both the oxide film and depleted
layer must be removed, either mechanically (grinding with a fine grit is recommended,
wire brushing and shot blasting will have less effect), or chemically (acid pickle
with a mixture of nitric and hydrofluoric acid). Once cleaned, the surface can
be chemically passivated to enhance corrosion resistance, (passivation reduces
the anodic reaction involved in the corrosion process).
steel tools such as drills, wire brushes or steel grinding wheels can contaminate
the stainless surface. Also sparks from grinding carbon steel can embed fragments
into the surface of the stainless steel. The carbon contamination or grinding
fragments can rust if moistened.
STAINLESS STEEL & CARBON PICKUP.
fixtures avoid carbon steels in close proximity to stainless welds, as carbon
pick up possible, the weld area will rust. There are many ways to introduce carbon
to stainless welds.
For stainless vert up welds on parts 3 to 6 mm, consider
For stainless all position welds on parts > 6 mm, first logical
choice will be always be stainless gas shielded flux cored wires.
the drive roll tension applied to stainless flux cored wires. For stainless
flux cored weld data, use the carbon steel flux cored wire data found in my flux
cored book. For stainless flux cored use an argon mix with 15 - 25 CO2.
STAINLESS & CARBIDE PRECIPITATION (chrome
weld data to avoid Carbide Precipitation. (CP)
any part of stainless-steel is heated in the range 900-1400°F (482-760°C)
for any reasonable time there is a risk that the chrome will form chrome carbides
Cr23C6 with any carbon present in the steel along the austenite grains. Thi results
in depletion of chromium from the austenitic grains resulting in decreasing the
corrosion protective passive film. This effect is called sensitization. It is
also called weld decay since it usually happens during welding process when the
zone around the weld is heated.
stainless corrosive environments control of CP is critical.
occurs within 3 mm of either side of a weld HAZ
A chrome depleted
area may not resist the corrosive environment. To combat CP use (L) low carbon
base and filler metals. Ensure the C02 gas composition has less than 5 % CO2.
STAINLESS AND STABILIZED ELECTRODES:
can combat CP with stabilized fillers which provide alloys that grab the carbon
before it can affect the hrome. Alloys like E347 which work at reducing chrome
Stabilized fillers are typically used in high strength high
temp service. However if base metal is not an L grade CP will occur.
Rapid cooling of stainless through the 800 - 1600F range reduces Carbide Precipitation.
and the influence of "sulfur" in austenitic stainless applications.
When the parts to be welded have
normal sulfur content (greater than 0.005%) an interesting event can occur. With
increasing weld temperature the surface tension of the weld pool also increases.
The result is the hottest part of the fluid weld surface is attracted to the middle
of the weld pool causing deep narrow weld penetration.
With lower sulfur
in the weld, the weld surface tension is less. The resulting weld is wider with
less fusion. When two parts welded together have different levels of sulfur tension
the weld may pull towards the lower tension, lower sulfur part, resulting in inconsistent
weld fusion or penetration favoring one side of the weld joint. This occurrence
is especially notable when automated TIG welding Dissimilar parts such as cast
parts to sheet or pipe.
The following weld solutions may assist the
 Pulse the application.
 Use a weave.
 Use heat sink back up bars in close proximity to weld.
Stainless and Weld Cracks:
308 WELDS CRACK
DURING POST HEAT TREAT.
Question: We just finished welding a 304L pressure
vessel. The procedure called for 308 welds which were made with the gas shielded
flux cored process. A stress relief of 1475F for 10 hours was required. We know
the welds were sound before the heat treatment, however immediately after the
post heat treat we found cracks in the flux cored welds.
stainless expert (Kotececki
March 2008 Weld Journal) provides a good
summary of this unique cracking problem. It seems that with gas shielded flux
cored wires you will find a small amount of bismuth-bearing compounds. These compounds
assist in weld slag removal. Bismuth and similar elements at specific levels can
causes cracks if the parts are put into service and the temps are above 900F and
possibly lower temperatures at long time periods. The bottom line, if your stainless
vessel is going to have post heat treatment or be placed in service with
high temperatures ensure your flux cored wire contains < 20ppm bismuth. Ask
the electrode manufacturer does their wires contain any elements that can cause
reheat cracks or premature creep failure.
OR TIG WELDING THAT STAINLESS ROOT...
To ensure good corrosion resistance of the
stainless weld root, the root must be protected from the atmosphere by an inert
gas shield during welding and subsequent cooling. The gas shield should be contained
around the root of the weld by a suitable dam, which must permit a continuous
gas flow through the area.
Welding should not commence until sufficient
time has elapsed to allow the volume of purging gas flowing through the dam to
equal at least the 6 times the volume contained in the dam.
is complete, the purge flow rate should be reduced so that it only exerts a small
positive pressure, sufficient to exclude air. If good corrosion resistance of
the root is required, the oxygen level in the dam should not exceed 0.1% (1000
ppm); for extreme corrosion resistance this should be reduced to 0.015% (150 ppm).
Backing gasses used for purging are typically argon or helium; nitrogen is often
used as an economic alternative where corrosion resistance is not critical, nitrogen
+ 10% helium is a good mix.
A wide variety of proprietary pastes and backing
materials are available than can be use to protect the stainless root instead
of a gas shield. In some applications where corrosion and oxide coking of the
weld root is not important, such as large stainless steel ducting, no gas backing
is used. To eliminate filling stainless tanks with a purge gas go to TIP TIG at this site.
300 Series Pipe Weld Procedure Data. Max interpass Temp 350F
- 3/32 ||300 series|
argon with 25 CO2
Who said you can't take it with you?
forms of corrosion
Potential. From Sanvik..
data is from Sanvik: Materials used in oil and gas extraction are affected to
several different types of corrosion, often caused by seawater and spray. The
types of corrosion, which can occur on stainless steels in marine environment,
are pitting and crevice corrosion, and for standard austenitic grades also stress
corrosion cracking (SCC), if the material temperature is above 60°C (140°F).
These are all localised attacks general corrosion need not be considered
for stainless steels in seawater. High temperatures, high chloride contents and
low pH values increase the risk of localised attacks in any chloride-containing
environment. Of these, temperature is usually the most influential factor.
However, there is a fourth important consideration: the electro-chemical
corrosion potential of the environment. In seawater, this potential is affected
by biological activities on the steel surface. Since seawater is, in a sense,
a living corrosive environment, it is sometimes difficult to define exactly what
the service conditions will be. At normal seawater temperatures, a biofilm will
form on the steel surface and result in a corrosion potential of +300 to +500
above ~40°C (100°F) the biological activity will cease and the corrosion
potential will drop. The use of continuous chlorination, to stop marine growth,
may increase the corrosion potential to values as high as +600 to +800 mV/SCE.
This, however, can be avoided through the use of intermittent rather than continuous
over Cu and CuNi-based alloys
steels are very resistant to erosion corrosion compared with Cu and CuNi-based
alloys, which are very sensitive to this form of attack. Water in harbours, around
offshore platforms, and near chemical plant sites is often contaminated e.g. with
ammonia (NH 3 ) and sulphides (S 2- ). These compounds, even in very small quantities,
cause localised attacks on copper-base alloys, while stainless steels are not
affected at the impurity levels involved.
corrosion: Wet and sour service: The corrosivity of an oil and
gas well is increased by the presence of chlorides in water solutions, carbon
dioxide, and hydrogen sulphide.
environment is considered sweet as long as no hydrogen sulphide is present. Carbon
dioxide alone can however cause high corrosion rates on carbon steel, since it
is acidifying the solution. This is further accelerated if chlorides are present.
environments are defined when the partial pressure of hydrogen sulphide is above
0.05 psi. At higher partial pressures, the corrosion rate on carbon steel is substantially
increased by means of making the water phase more acidic and by forming iron sulphide
scale. Sulphide Stress Cracking (SSC) is common in high strength steels containing
martensite. It can also occur in ferritic steels.
steels are different. Sandvik Sanicro 28, Sanicro 29, SAF 2205 and SAF 2507 grades
are completely resistant to corrosion in wells rich in carbon dioxide with a high
amount of chlorides in the water phase. If hydrogen sulphide is present, there
is still no general corrosion, but the risk of localised corrosion increases,
especially with regard to SSC.
NACE TM-0177 test.
Experiments have been carried out at room temperature in
accordance with the NACE TM-0177 test (5% sodium chloride, 0.5% acetic acid, saturated
with hydrogen sulphide).
threshold stress for cold-worked Sandvik SAF 2205/22Cr is about 90% of the yield
strength, which is very good when compared to results for high strength, ferritic
Sanicro 28, in the cold-worked condition, results in no failures up to very high
stress levels. The high alloy duplex stainless steel Sandvik SAF 2507 is also
resistant to cracking in the solution-annealed condition.
general terms, this test shows that Sandvik Sanicro 28 has a higher resistance
to sulphide stress cracking compared to SAF 2205/22Cr, which is much more resistant
than 13Cr. Sandvik Sanicro 29 has an ever higher resistance to localised corrosion
and sulphide stress cracking than Sandvik Sanicro 28.
should be remembered that the chemistry of the NACE solution is not
representative of the conditions in most sour oil and gas wells. This is especially
true for acidity, where the pH value is lower in the NACE test. Results from the
NACE TM-0177 test, therefore, should not be used for determining the suitability
of different grades, but more as a ranking test. Other tests, more representative
of actual service conditions, must be used to determine the suitability of different
grades. Practical experience of specific grades is, of course, extremely useful.
Visit Sanvik's web site for more excellent data on stainless and duplex
products, however if you want the best stainless
steel MIG welding process control data visit here,