guidelines for stainlesssteel welding

7/27/2019 Guidelines for Stainlesssteel Welding

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CHALLENGING PROJECTS. ITS WHAT WE DO.

Guide Lines for (Duplex) Stainless

Steel WeldingZhuang Xu

Welding Engieer

McDermott Wuchuan Offshore Engineer Co., Ltd


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Presentation Overview

Duplex Stainless Steel

Alloying Properties

Piping Welding

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Duplex Stainless Steel

Lean duplex stainless steel

Standard duplex stainless steel

Superduplex stainless steel

Hyperduplex stainless steel

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Lean duplex stainless steel

Lean duplex such as 2304, which contain no deliberate

Mo addition.

The lean alloy 2304 was developed to compete primarily

with the austenitic AISI 316 grade, but with twice the

yield strength and significantly better resistance to SCC.

The weldability of 2304 duplex stainless is generally

good when using slightly over-alloyed filler metal.

The newly developed lean duplex garde LDX2101 has

such improved weldability that also autogenous welding

is possible and this material has contributed to the boom

in the lean duplex market.

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Standard Duplex Stainless Steel

Standard duplex stainless steel is the dominant

commercial duplex stainless steel which was developed

in the 1970s, but was later optimised with higher nitrogen

levels for improved weldability.

The PRE of 2205 is about 33-35 resulting in a resistance

to localized corrosion intermediate between the

austenitic grade AISI 317 and the 5-6% Mo super

austenitic alloys.

The weldability of this grade is good, but overmatchingfiller with increased nickel content, e.g. 2209, is normally

required for optimum weld metal properties.

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Superduplex stainless steel

The superduplex grades were developed to withstand veryaggressive environments to compete with super-austeniticsand nickel base alloys.

2507 has, due to high molybdenum and nitrogen contents, aPRE of 42-43, and offers high mechanical strength andcorrosion resistance in extremely aggressive environmentssuch as chloride-containning acides.

A consequence of the high alloy content, there is a risk ofprecipitation of intermetallic phases, limiting the heat inputand interpass temperatures when multipass welding.

Overmatching filler with increased nickel content is required,e.g. 2509, to compensate element partitioning for optimumcorrosion resistance.

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Hyperduplex stainless steel

Hyperduplex stainless steel was developed as a

complement to 2507 with increased strength for use in

even more aggressive conditions, such as in hot

seawater, acidic chloride solutions and organic acides.

SAF2707 HD can be welded with a matching filler wire of

ISO2795L type.

Due to the high alloying content, the hyperduplex alloys

are somewhat more sensitive to secondary phase

precipitation than the superduplex grades.

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Alloying Properties

Elements content of different types of duplex stainlesssteel

Chromium

Nickel

Molybdenum Nitrogen

Manganese

Copper

Tungsten Carbon

Mechancial Properties

Physical Properties

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Duplex Stainless Steel Types

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Type Cr Ni Mo N PRE

Lean 20-24% 1-5% 0.1-0.3% 0.1-0.22% 24-25

Standard 21-23% 4.5-6% 2.5-3.5% 0.1-0.22% 33-35

Superduplex 24-29% 4.5-8% 2.7-4.5% 0.1-0.35% >40

Hyperduplex 27% 6.5% 5% 0.4% 49


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Chromium

There is a maximum limit to the chromium content of

approximately 30%, where intermetallic phase precipitation

can markedly reduce the ductility, toughness and corrosion

resistance of these alloys.

Chromium increases the pitting potential, the critical pittingtemperature(CPT) and the critical crevice

temperature(CCT), and improves the passive film stability

in acidic environments.

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Nickel

Nickel is a strong austenite stablizer and is a principal

addition to austenitic stainless steels.

Nickel alloying is generally detrimental to crevice corrosion

resistance in sodium chloride, and beneficial or without

effect in pitting tests. In the duplex stainless steel, however, the main role of

nickel is to maintain the ferrite-austenite balance, rather

than modifying the corrosion resistance.

Low nickel levels can result in formation of a highproportion of ferrite, thereby lowering toughness.

Consequently most consumables for welding duplex

stainless steels are over-alloyed to contain 7-10% of nickel.

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Molybdenum

Molybdenum is a ferrite stabilizing alloying element with a

strong beneficial influence on general and pitting corrosion

resistance and on the passivation properties.

Molybdenum is favourable in most environments, but instrongly oxidising environments, such as warm concentrated

nitric acid, grades containing molybdenum are less resistant

than stainless steels without molybdenum.

The addition of molybdenum should not exceed

approximately 4% since it makes the material more

susceptible to intermetallic phase precipitation by widening

the sigma phase field.

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Nitrogen

Nitrogen is an interstitial element that stabilizes the austenite

and has strong influence on several properties such as

pitting corrosion, presence of molybdenum.

The duplex grades consequently contain up to 0.4% nitrogento give improved austenite formation when welding.

Nitrogen significantly increases the strength of the duplex

stainless steels, but also improves the ductility and

toughtness of the alloy.

Nitrogen delays the formation of intermetallic phases in

duplex stainless steels in a similar way as in austenitic

grades.

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Manganese

Manganese stabilises austenite and can partly replace nickel.

Additions to stainless steel have been used to increase the

solubility of nitrogen, which have a strong beneficial influence

on the pitting resistance. It has been reported thatmanganese itself has a negative effect on the pitting

resistance, but combined additions of nitrogen and

molybdenum override this effect.

Replacing nickel with manganese and nitrogen makes the

price of the material more stable since the nickel price has

fluctuated significantly.

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Copper

Copper is added to highly corrosion resistant austenitics and

duplex grades to further improve the corrosion resistance in,

for instance reducing acids such as dilute sulphuric acid.

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Tungsten

Tungsten has become more commonly used as an alloying

element in commercial stainless steels where it is used as a

compliment to molybdenum for improved corrosion

resistance. When used in the PRE expression, the factor for tungsten is

approximately half of that for molybdenum.

Tungsten has, howerver, also been reported to promote

formation of intermetallic phases and cause a more rapid

embrittlement thatn molybdenum.

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Carbon

In most modern duplex alloys carbon is limited to levels of

0.03wt% to minimize the risk of formation of chromium

carbides and thereby reduce the susceptibility of the duplex

stainless steels to intergranular corrosion.

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Mechanical Properties

Type Yield Tensile Elong.

ASTM A572.Gr.50 50ksi (345MPa) 70ksi (485MPa) 21%

316L 25ksi (170MPa) 70ksi (485MPa) 40%

S32304 58ksi (400MPa) 87ksi (600MPa) 25%

S32205 65ksi (450MPa) 90ksi (620MPa) 25%

S32750 80ksi (550MPa) 116ksi (800MPa) 15%

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Physics Properties

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Type Density

/g.cm-3

Resistivity

/.cm

Magnetism

Specific Heat

Capacity

/ J / KG K

Average

Coefficient of

Linear Expansion

/10-6

C-1

(0-100)

Thermal

Conductivity

/W(mK)-1

A572. Gr.50 7.64 0.10 YES 447 12.1 (100.C) 51(100C)

316L 7.98 0.75 No 502 17.3(100.C) 16.3(100C)

S32304 7.75 0.80 YES 482 13.0(100.C) 17.0(100C)S32205 7.80 0.80 YES 500 13.0(100.C) 17.0(100C)

S32750 7.79 0.80 YES 485 13.0(100.C) 17.0(100C)


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Pipe Welding

General Welding Guidelines

Welding Procedure Qualification

Welding Methods

Post Fabrication Clean-up

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General Welding Guidelines

Differences Between Duplex and Austenitic Stainless Steels

Selection of Base Metal

Material Receiving

Handling & Storage

Facilities

Tools

Clean Build Philosophy

Cutting Duplex Stainless Steel

Joint Design

Preheating Heat Input and Interpass Temperature

Postweld Heat Treatment

Desired Phase Balance

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Diffences Between ASS & DSS

Problem of ASS

Hot cracking

Adusting the composition of the filler metal to provide a significant

ferrite content minimizes these problems, for the more highly

alloyed austenitic SS where the use of a nickel-base filler metal is

necessary and austenitic solidification is unavoidable.

The problem is managed by low heat input, often requiring many

pases to build up the weld.

Methodes to improve the hot cracking resistance

Limit the content of sulfur, phosphorus and carbon

Produce duplex microstructure, ferrtie content is 3 ~ 8%

Add proper content of manganese (4 ~ 6%)

Properly welding parameters (short arc, low heat input and narrow

gap)

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Diffences Between ASS & DSS

Problem of DSS

HAZ problem DSS have very good hot cracking resistance due to the high ferrite content.

The HAZ problems are loss of corrosion resistance, toughness, or post-weldcracking.

To avoid these problems, the welding procedure should focus on minimizingtotal time at temperature in the red hot range rather than managing theheat input for any one pass.

Advantage of DSS Summrized Properties

Much higher yield strength and tensile strength

Stress corrosion cracking resistant

Pitting/crevice corrosion resistant

Erosion resistant

Fatigue resistant

Cost effective (lower nickle contents)

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Sufficient Nitrogen

The important of the base metal containing sufficient

nitrogen has been repeatedly emphasized.

If the starting material cooled slowly through the 700 to

1000 deg. Range, or if it is allowed to air cool into thisrange for a minute or so prior to water quenching then

these actions have used up some of the time on the clock

Purchasing Guidelines for Duplex 22% Cr Stainless Steel Process

Tubing & Piping

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Tubing & Piping

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Product Form Duplex 22% Cr Stainless Steel

Process Tubing

Duplex 22% Cr Stainless Steel

Seamless Pipe

Material Process Tubing Seamless Pipe

Scope This material technical sheet is intended to supplement existing material standards andspecification (eg., ASTM, ISO UNS) and project specifications for duplex stainless steel

Manufacturer Approval Materials supplied in accordance to this specification shall only be supplied by companyapproved manufacturers

Specification ASTM A789/ A789M ASTM A790/ A790M

Grade(s) UNS S31803 UNS S31803

Manufacturing Process Electric arc or electric furnace and refined byAOD or equivalent process

Heat Treatments All material shall be delivered in the solution annealed (followed by water quench) condition

Pitting Resistance Equivalent Pitting Resistance Equivalent (PRE)=Cr+3.3Mo+16N. The PRE shall be greater than orequal to 34.0


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Tubing & Piping

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Process Tubing


Seamless Pipe

Hardness Per ASTM standard. If no harness required by ASTM standard, maximum shall be HRC28,HB271, or HV290

Impact Testing - Charpy V-notch (ASTM A370)-Not applicable when the maximum

obtainable charpy specimen has a width

along the notch of less than 2.5mm

-Absorbed energy shall be 48J average and

36J single value minimum

-Test temperature shall be minus 46 deg.

-Specimens shall be oriented transverse tothe rolling direction

- Charpy V-notch (ASTM A370)

-Not applicable when the maximum

obtainable charpy specimen has a width

along the notch of less than 2.5mm

-Absorbed energy shall be 48J average and

36J single value minimum

-Test temperature shall be minus 46 deg.


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Tubing & Piping

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Process Tubing


Seamless Pipe

Ferrite ContentASTM E562

-Ferrite content shall be determined oon afull cross section near the OD and ID

surfaces and at mid-wall location

-Samples shall be electrolytically etched in

either NaOH or KOH, and in such a manner

as to provide optimum contrast for austenite

and ferrite phase discrimination

-Point cont shall be conducted at minimum

of 500X magnification

-A minimum of 30 fields and 16 points perfield shall be used

-Ferrite content shall be between 35%- 55%

-Ferrite content of the seam weld shall be

25%-60%

ASTM E562

-Ferrite content shall be determined oon afull cross section near the OD and ID

surfaces and at mid-wall location

-Samples shall be electrolytically etched in

either NaOH or KOH, and in such a manner

as to provide optimum contrast for austenite

and ferrite phase discrimination

-Point cont shall be conducted at minimum

of 500X magnification

-A minimum of 30 fields and 16 points perfield shall be used

-Ferrite content shall be between 35%- 55%


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Tubing & Piping

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Process Tubing


Seamless Pipe

MetallographicExamination

-Samples shall be etched using ASTM E407 etchant number 98 (K3Fe(CN)4 with KOH or

NaOH)-Sample cross section shall be examined at OD, ID and Mid-wall locations

-Examination shall be conducted at a minimum of 500X magnification.

-Intermetallic phases or precipitates are allowed up to a max. of 0.05 percent.

Extent of Testing -All testing shall be conducted on a lot basis.A lot is defined as the same tubing diameter,

thickness, heat and heat treatment charge,

up to a maximum of 125 tubes.

- All testing shall be conducted on a lot

basis. A lot is defined as a maximum of 60

meters of pipe of the same diameter,

thickness, heat and heat treatment charge.


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Tubing & Piping

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Process Tubing


Seamless Pipe

Non-destructiveFerrite

Measurement

-10% of all tubes shall have ferrite content determined by fischer ferrite scope

-Measurement technique shall be in accordance with company approved procedures-Ferrite content shall be between 35% - 55%

Hydrostatic Test -In accordance with ASTM A789/ A789Mand ASTM A450/ 450M

- In accordance with ASTM A790/A790M

Repair of Defects -Weld repair of defects is not allowed

Surface finish -White Pickled


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Tubing & Piping

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Process Tubing


Seamless Pipe

Handling, Shipment, andStorage

-Product shall be handled, shipped and stored in such a manner as to prevent or minimize

the possibility of free iron contamination-Product shall not be handled with bare steel hooks, chains or lifting forks without the use of

protective insulating material

-Only stainless steel wire brushes, designated for use only on stainless steel products, may

be used for brushing and descaling

-Suspected free iron contamination, such as evidenced by unusual stains or discoloration,

shall be verified by ferroxyl testing in accordance with the procedure outlined in ASTM

A380

-Free iron contaminated areas shall be cleaned and passivated, at the manufacturers

expense, using the procedures outlined in ASTM A380

Certification -EN10204 3.1B


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Material Receving

Material certificate review

Physical check including magnetic check or PMI as

required.

Application of Material Traceability Number (MTN)

To use chloride-free pen/marker suitable for stainless

steel

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Handling & Storage

All pipe/tube material will be store in a covered

warehouse

Separate area for storage equipped with sign board

To use wood, rubber vinyl or cardboard for protection

from handing devices

To use only web sling for lifting

Placed upon non-carbon steel surface

Plastic end caps on pipe/tube Plastic cover on pipe/tube surfaces.

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Facilities

Clean area with metallic iron dust free environment

Non-carbon steel covering for all work surfaces

To put neoprene rubber cover on flange end

To put plastic end cap(pipe), prior to leave work.

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Tools

Stainless steel compatible files, grinding disc, wire

brushes, saw blades etc.

Cold cutting & beveling machine

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Prevention is the Key

Professionalism is the Perception

Product Quality is the Result

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Pre-fabrication Storage

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Polythene or Tarpaulin Sheeting

All Pipes/ Tubes to be Fitted with End Caps

Woods/ Rubber Racks


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After Cut Before Beveling

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Clean Cloth Dampened with Acetone

Pull Through to Remove Dust avoid contamination

String

Acetone

Acetone

Pull Through After Cut and Before Beveling


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Sponge Plug Insertion before Beveling

Constructed from pre-cut foam which is wrapped in Lint

Free Cloth

Each Sponge Plug will have a unique ident and shall beaccounted for at the end of each shift

Plug must be removed before fit-up and returned to control

point

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8

8

Sponge Plug

Prevent Dust / Contamination from Entering


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Clean with Acetone BEFORE Beveling and Polishing

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Min 25mm

Acetone

Sponge Pluge


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Clean with Acetone AFTER Beveling

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Sponge Pluge

Acetone


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Ploshing

Remove all surface oxide films from both internal and

external surfaces to a minimum distance of 25mm using

the correct and autorized equipment

25mm Sponge plug MUST still be in place

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Min 25mm

Acetone


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Fit-Up

After sponge plug removal and final clean with Acetone

dampened cloth, commence Fit-Up and Tack in accordance with

the approval WPS

Sponge Plug MUST be returned to control point after removal

from pipe or fitting.

Every registered Sponge Plug shall be accountable at the end

of each shift.

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Post Weld Clean

Clean Using dedicated wire brush during and immediately after

welding

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Clean Using Acetone Dampened Cloth

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Acetone


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Protect the weld & HAZ by wrapping cellophane

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Wrapping Cellophane


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Cutting Duplex Stainless Steel

Mechanical

Sawing

Shearing

Abrasive Wheel Cutting

Water-Jet Cutting

Thermal

Plasma cutting

Laser cutting

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Sawing

Similar with austenitic stainless steel

Powerful machine

Proper blade alignment

Coarse toothed blade Slow to moderate cutting speed

Heavy feed

Generous flow of coolant

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Shearing

More force and heavier equipment will be required toshear stainless steel compared to carbon steel

Carbon steel thickness shear limit

Austenitic stainless steel max thickness shear limit

Duplex stainless steel 3/16 max. A general clearance guide is to use a clearance of 5% of

the metal thickness between shear knives

To counter the shearing force required for duplex

stainless steel, the hold down pressure on the clampsmay have to be increased

Blades must be sharp

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Abrasive Cutting

Abrasive wheels, rotating at high

speed can be used for straight line

cutting of sheet and thin gauge

plate and for cut-off operations onrelative small sections.

Thick section cut-off operations are

usually done wet

Use uncontaminated vitrified orresin-bonded wheels

Do not induce over-heating

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Plasma and Laser

Same equipment as for 304/316

Optimum parameter vary slightly

Two types of plasma cutting machine

Mainly advantages of second one:

The nozzle can be recessed within a ceramic shield gas,

thereby protecting the nozzle from double arcing, if no

shield gas were present, the ceramic shield gas cup could

be deteriorated because of the high radiative heat

produced by the plasma jet.

It can protect the cutting surface from oxidation caused by

oxygen.

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Two types of plasma cutting

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a. Dual flow plasma cutting power source b. Dual flow plasma cutting machine

c. Cutting surface without oxidation d. Cutting gas

d. Secondary shielding gas e. The sketh of dual flow plasma arc


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Joint Design

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P h i


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Preheating

Preheating may be only beneficial when used to

eliminate moisture from the steel as may occur in cold

ambient conditions or from overnight condensation.

When preheating to deal with moisture, the steel should

be heated to about 100 deg. Uniformly and only after theweld preparation has been cleaned.

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HI d I t T t


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HI and Interpass Temperature

Compare with ASS

DSS can tolerate relatively high HI

DSS is resistant to hot cracking

DSS is with higher thermal conductivity and lower

coefficient of thermal expansion

Exceedingly Low Heat Input

May result in fusion zones and HAZ which are excessively

ferritic with corresponding loss of toughness and corrosion

resistance.

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HI d I t T t


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HI and Interpass Temperature

Exceedingly High Heat Input

Increasing the danger of forming intermetallic phases.

150 deg of maximum interpass temperature for lean and

standard DSS, 100 deg for SDSS

To avoid problems in the HAZ, the weld procedure should

allow rapid cooling of this region after welding.

The temperature of the work piece is important because it

provides the largest effect on cooling of the HAZ.

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PWHT


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PWHT

PWHT is not need

It is likely to be harmful because heat treatment may

precipitate intermetallic phases or alpha prime

embrittlement casuing a loss of toughness and corrosion

resistance. PWHT temperature in excess of 315 deg can adversely

affect the toughness and corrosion resistance of DSS.

ANY PWTH should include full solution annealing followed

by water quenching.

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D i d Ph B l


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Desired Phase Balance

Phase Balcance for Ferrite and Austenite

It generally agreed that the characteristic benefits of DSS

are achieved when there is at least 25% ferrite with the

balance austenite.

Normally the pahse balance has been adjusted towardmore austenite to provide improved tougness, offsetting

the loss of toughness associated with oxygen pickup from

the flux.

The phase balance in the HAZ, being the original wrought

plate or pipe plus an additional thermal cycle, is usually

slightly more ferritic than the original material.

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W ldi P d Q lifi ti


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Requirement

Lab Testing

Tensile

Bend

Hardness

Macro-Sections

Micro-structural Examination

Impact Tests

Corrosion Testing

Ferrite Content

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W ldi P d Q lifi ti


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Requirement

Because of the need to limit the total time at temperature

for the HAZ, the properties of duplex grades will be

sensitive to section thickenss and details of actual welding

practice. Therefore, qualification must be considered in abroader sense, that is a demonstration that the welding

procedure that will be applied during fabrication will not

produce an unacceptable loss of engineering properties,

especially toughness and corrosion resistance.

It would be conservative to qualify the welding procedureat every thickness and geometry of welding because the

minor differences in setup may be significant in the results

achieved in production.

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L b T ti


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Lab Testing

Tensile

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L b T ti


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Lab Testing

Tensile

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Lab Testing


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Lab Testing

Tensile

For pipe having an outside diameter of 3in. (75mm) or less,

reduced-section specimens conforming to the requirment

given in below figure.

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Lab Testing


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Lab Testing

Side Bend

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Lab Testing


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Lab Testing

Root & Face Bend

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Lab Testing


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Lab Testing

Guided-Bend Test Procedure

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Lab Testing


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Lab Testing

Guided-Bend Test Procedure

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Lab Testing


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Lab Testing

Hardness (NORSOK STANDARD M-601)

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Lab Testing
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Lab Testing

Macro-Examination (ASME IX - 2010)

The examination of the cross sections shall include only

one side of the test specimen at the area where the plate

or pipe is divided into sections, adjacent faces at the cut

shall not be used. Acceptance creteria

Visual examination of the cross sections of the weld metal

and heat-affected zone shall show complete fusion and

freedom from cracks

There shall be not more than 1/8in. (3mm) difference in thelength of the legs of the fillet.

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Lab Testing


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Lab Testing

Micro-structural Examination

Acceptance Criteria

The micro-structure shall be suitably etched and examined at

400 X magnification and shall have grain boundary with no

continuous precipitations and the inter-metallic phases,nitrides and carbides shall not in total exceed 0.5%

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Lab Testing


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Lab Testing

Impact Test

Requirement

Impact testing of welds shall be according to following table,

full size specimens shall be applied where possible.

If two types of materials are welded together, each side ofthe weld shall be impact tested and fulfill the requirement for

the actual materal.

The weld metal shall fulfil the requirement for the least

stringent of the two.

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Lab Testing


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Lab Testing

Impact Test

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Lab Testing


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Lab Testing

Corrosion Testing

The test specimen shall have a dimension of full wall

thickness by 25mm along the weld and 50mm across the

weld. The test shall expose the external and internal

surface and a cross section surface including the weldzone in full wall thickness. Cut edges shall be prepared

according to ASTM G48. The specimen shall be pickled

(20%HNO3 + 5% HF, 60 deg., 5min). The exposure time

shall be 24 hours.

The test temperature shall be 40 deg.

The acceptance criteria

No pitting at 20X magnification

Weight loss shall not exceed 4.0 g/m2

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Lab Testing


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Lab Testing

Ferrite Content

Acceptance Criteria

For the stainless steel Type 22 and 25 Cr duplex the ferrite

content in the weld metal root and in the last bead of the weld

cap shall be determined in accordance with ASTM E562 andshall be in the range of 30% to 70%.

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Austenite

Ferrite

Welding Methods


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Welding Methods

GTAW (Gas Tungsten Arc Welding)

SMAW (Shielded Metal Arc Welding)

GMAW (Gas Metal Arc Welding)

FCAW (Flux Core Wire Arc Welding)

SAW

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Equipment 1. Power source. Transformer/Rectifier

(Constant Amperage type)

2. Inverter Power Source. (More

compact and portable)

3. Power Control Pannel (Amp. AC/DC,

gas delay, slop in/out, pulse, etc)

4. Power cable hose (of a suitableamperage rating)

5. Gas flow-meter (correct for gas type

and flow rates)

6. Tungsten electrodes. (of a suitable

amperage rating)

7. Torch assemblies. (of a suitable

amperage rating)

8. Power reture cable. (of a suitableamperage rating)

9. Welding Visor (With correct filter glass

rating)

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Torch Head Assembly

1. Tungsten electrodes

2. Spare Ceramic Shield

3. Gas lens

4. Torch Body

5. Gas Diffuser

6.Split copper collett (For

securing the tungsten

electrode)

7. On/off or latching switch

8. Tungsten housing

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Types of Arc Start

Scratch Start

Easily cause contamination of the tungsten

High Frequency

Can avoid the contamination of the tungsten Cause interference with hi-tech electrical equipment and

computer systems.

Lift arc

Has been developed where the electrode is touched onto the

plate and is withdrawn slightly.

An arc is produced with very low amperage, which is increased to

full amperage as the electrode is extended to the normal arc

length.

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Slope in and Slope out During welding it is used to control the rise and delay of the

current at the start and end of a weld as shown below

This is very beneficial in avoiding crater pipes at the end of

weld runs.

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Gas cut off delay The gas cut off delay control delays the gas solenoid shut off

time at the end of the weld and is used to give continued

shielding of the solidifying and cooling weld metal at the end of

a run.

It is often used when welding materials that oxidise at high

temperatures such as stainless and titanium alloys.

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Electrode The most common types of tungsten used are thoriated or

ceriated for DC and zironiated with AC (Aluminium alloys).

The vertex angle of the tungsten is often a procedural

parameter and therefore gringding needs to be very controlled

activity that should be carried out on a dedicated grinding

wheel.

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Filler Metal Matching with 2 4% more nickel than in the wrought product.

The nitrogen content is typically slightly lower in the filler metal

than in the base metal.

More highly alloyed DSS fillers are suitable for welding thelower alloyed DSS.

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Shielding

The purity of dry welding grade of inert gas, argon, should

equal or better than 99.95%.

Gas flow should be initiated several seconds ahead ofstriking the arc, and it should be maintained for several

seconds after the arc is extingushed, ideally long enough for

the weld and HAZ to cool below the oxidation range of the

SS.

For electrode coverage, suggested flow rates are 12 18l/min (0.4 0.6 cfm) when using a normal gas diffuser screen

(gas lens), and with half that rate required for a normal gas

nozzle.

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GTAW (Gas Tungsten Arc Welding) Shielding

Purging gas, because argon is heavier than air, the feed

should be from the bottom to the top of the enclosed volume,

with purging by a minimum of seven times the volume. Additions of up to 3% dry nitrogen will aid in retention of

nitrogen in the weld metal, particularly of the more highly

alloyed duplex stainelss steel. While the nitrogen adddition

has been found to increase electrode wear, the addition of

helium partially offsets this effect.

Additions of oxygen and carbon dioxide to the shielding gas

should be avoided because they will reduce the corrosion

resistance of the weld.

Hydrogen should not be used in the shielding or backing gas

because of the possibility of hydrogen embrittlement .83



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Technique and Parameters Any arc strikes outside of the welding zone will creat local

points of autogenous welding with very high quench rates,

ruslting in locally high ferrite content and possible loss of

corrosion resistance at those points. Tacking welds should be made with full gas shielding.

There should be no tack weld at the starting point of the

root pass.

The work piece should be allowed to cool below 150 deg

for standard duplex stainless steels and below 100 deg forsuperduplex stainless steels between welding passes to

provide for adequate cooling of the HAZ in subsequent.

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Technique and Parameters The heat input is typically in the range of 0.5 2.5 kj/mm

(15 to 65 kj/inch).

General heat input recommendations:

2204 or lean duplex 0.5 2.0 KJ/mm (15 50 KJ/in)

2205 0.5 2.5 KJ/mm (15 65 KJ/in)

2507 0.3 1.5 KJ/mm (8 38 KJ/in)

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Weld Discoloration Levels on Inside of ASS AWS D18.2 1999 Guide to Weld Piscoloration Levels on

Inside of Austenitic Stainless Steel Tubes

No. 1- 10 ppm No. 2-25 ppm No. 3-50 ppm No. 4-100 ppm No. 5-200ppm No. 6- 500ppm

No. 7- 1000ppm No. 8-5000ppm No. 9-12500ppm

No.10-25000ppm

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Post Fabrication Clean-up
http://localhost/var/www/apps/conversion/tmp/scratch_5/AWS%20D18.2%20-1999%20Guide%20to%20Weld%20Piscoloration%20Levels%20on%20Inside%20of%20Austenitic%20Stainless%20Steel%20Tubes.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/AWS%20D18.2%20-1999%20Guide%20to%20Weld%20Piscoloration%20Levels%20on%20Inside%20of%20Austenitic%20Stainless%20Steel%20Tubes.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/AWS%20D18.2%20-1999%20Guide%20to%20Weld%20Piscoloration%20Levels%20on%20Inside%20of%20Austenitic%20Stainless%20Steel%20Tubes.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/AWS%20D18.2%20-1999%20Guide%20to%20Weld%20Piscoloration%20Levels%20on%20Inside%20of%20Austenitic%20Stainless%20Steel%20Tubes.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/AWS%20D18.2%20-1999%20Guide%20to%20Weld%20Piscoloration%20Levels%20on%20Inside%20of%20Austenitic%20Stainless%20Steel%20Tubes.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/AWS%20D18.2%20-1999%20Guide%20to%20Weld%20Piscoloration%20Levels%20on%20Inside%20of%20Austenitic%20Stainless%20Steel%20Tubes.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/AWS%20D18.2%20-1999%20Guide%20to%20Weld%20Piscoloration%20Levels%20on%20Inside%20of%20Austenitic%20Stainless%20Steel%20Tubes.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/AWS%20D18.2%20-1999%20Guide%20to%20Weld%20Piscoloration%20Levels%20on%20Inside%20of%20Austenitic%20Stainless%20Steel%20Tubes.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_5/AWS%20D18.2%20-1999%20Guide%20to%20Weld%20Piscoloration%20Levels%20on%20Inside%20of%20Austenitic%20Stainless%20Steel%20Tubes.pdf


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p

Crayon marks, paint, dirt, oil

Embedeed iron (ferrous contamination)

Weld spatter, weld discoloration, flux, slag, arc strikes

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Typical fabrication defects or surface conditions which may be encountered

Crayon marks, paint, dirt, oil


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y , p , ,

All these surface contaminants can act as crevices andcan be initiation sites for pitting or crevice corrosion of a

stainless steel.

These contamination should be removed with solvents.

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Embedded Iron (Ferrous Contamination)


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( )

The iron rusts in a moist or humid environment and caninitiate corrosion on the stainless steel surface.

One approach is to avoid all contact between stainless

steel and carbon steel. Only stainless steel tools,

stainless steel wire burshes, stainless steel clamps, andnew, uncontaminated grinding wheels should be used on

stainless.

Often the tools are color coded in the shop.

89

Weld Spatter, weld discoloration,

fl l t ik


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flux, slag, arc strikes

All these defects may occur during welding. They can act

as crevices and initiate crevice corrosion in chloride-containing environments.

Welding spatter

Weld spatter can be avoided during fabrication by using an

anti-spatter compound

Weld discoloration

Weld discoloration causes a loss of corrosion resistance

due to the destruction of the passive layer.

Heavy weld discoloration or heat tint should be avoided byinert gas shielding and by pruging the back side of welds

with an inert gas.

Heat tint cannot be totally avoided and must be removed

guidelines for stainlesssteel welding

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