The Alternative to PWHT Temper Bead Welding by Walter J Sperko

Temper Bead Sperko Engineering 2004

Temper Bead Welding

What Is It?


Definition

Temper Bead Welding. A weld bead

placed at a specific location in or at the

surface of a weld for the purpose of

affecting the metallurgical properties of

the heat-affected-zone or previously

deposited weld metal. (partial)

Temper Bead

Weld Metal and HAZ

Weld Metal

HAZ HAZ

Temper Bead

Fe-C Equilibrium Phase Diagram

Alpha Iron

(BCC) Ferrite + Carbide

Austenite (FCC)

Liquid

% Carbon 0.8%

Upper Transformation (A3)

Lower Transformation (A1)

Magnetic Transformation (A2)

Temperature

1350F

1650F

2750F


Body-Centered Cubic

Temper Bead

Face-Centered Cubic

Temper Bead

Body-Centered Cubic

Temper Bead

Face-Centered Cubic

Temper Bead

Temper Bead

Fe-C Equilibrium Phase Diagram

Alpha Iron

(BCC) Ferrite + Carbide

Austenite

(FCC)

Liquid

% Carbon 0.8



Magnetic Transformation (A2)

Tem

per

ature

1350F

1650F

2750F

0.3%

Solid

Temper Bead

Nonequilibrium Cooling

Ac3

Time

Furnace Cool

Air Cool Oil Quench

Water

Quench

Temper Bead

T-T-T Diagram

AR1

Pearlite

Bainite

Martensite Start

Martensite Finish

Tem

per

ature

Time (s) 10 100 1000 10000 100000

Austenite

Austenite

0

Quench and Temper

A1

A3

Rapid Cool

Time

Tem

peratu

re

Martensite

Temper Bead

Zones subject to hardening

Alpha Iron

(BCC)

Ferrite + Carbide

Austenite

(FCC)

Liquid

% C



1350F

Bead on plate

Temper Bead

Other Zones in HAZ

Alpha Iron

Ferrite + Carbide

Austenite

Liquid

% C 0.8%



1350F

1900F

Subcritical Tempering/Stress-relief

Temper Bead

Weld Zones (simple version)

Liquid (Cast)

Coarse Grain

Fine Grain

Intercritical

Subcritical

Tempered (PWHT)


The whole bead on plate


Second Pass --overlapped HAZ


Two layers. . . . . .

Temper Bead

The real thing. . . . .

Temper Bead

What is temper bead welding?

Note the depth of the

HAZ of the first pass

Where is temper bead welding used?

It was first used thousands of years ago as the half-bead technique:

Deposit a layer of weld metal

Grind half of it off

Deposit a layer of weld metal

Grind half of it off

Deposit a layer of weld metal. . .

Until you are done. . . Or until you have several layers of weld metal. . . then just weld using small beads to ensure plenty of interbead tempering


Half-bead? How do you know how much of the weld was ground off???

Among other things, EPRI did some work in the 1990s and found that grinding could be eliminated by controlling heat input ratios in successive layers.

The ratio of heat input in one layer of weld to that of the previous layer is increased by about 50%, that optimizes the overlapping resulting in overlapping the

Heat Input Ratio


Very prescriptive half-bead technique was permitted in ASME Sections III and VIII for small and shallow in-process repairs of components that were already heat treated.

In 2000, ASME Section IX issued rules for qualification of temper bead WPSs based on the EPRI work to replace those rules with user-developed procedures.

QW-290 Temper Bead Welding

Used to make welds where PWHT would normally be required. Usually for repairs, but may be permitted for some new construction in the future. Fully incorporated into NBIC

Applies when permitted by construction code

Builds on existing qualifications

Requires special control of volts, amps and travel speed for each layer of weld metal

Temper Bead

Basic Qualification

All WPSs shall be qualified for groove

welding in accordance with the rules

for qualification by groove welding in

QW-202 or the rules in QW-283 for

welds with buttering and QW-214 or -

216 for overlay.

Temper Bead

Upgrading Previous Qualifications

One can upgrade an existing WPS by welding and testing a new test coupon big

enough to do the required testing

WPSs already qualified for temper bead welding can be modified for use with different temper bead variables by welding and testing a test coupon big enough to do the required

testing.

Temper Bead

Welding Process Restrictions

Temper bead welding is limited to SMAW, GTAW,

SAW, GMAW (including FCAW) and PAW.

Manual and semi-automatic GTAW and PAW are

prohibited.

Rationale: To effectively use temper bead welding,

heat input and bead size must be controlled. In

manual GTAW and PAW, the bead size is

uncontrolled.

Temper Bead

Welding Process Restrictions

TWO EXCEPTIONS:

Manual GTAW and PAW may be used for:

The root pass of groove welds made from one side

as described in paragraph QW-290.6 for making (in-process) repairs to temper bead welds.

Temper Bead

Default Qualification Basis

Unless the construction code specifies

that impact testing is the basis for

acceptance, the qualification variables

are those listed for hardness testing. In

case of conflict with QW-250 variables,

these variables apply.

Nonessential variables always apply.

Temper Bead

Impact Tests

When specified by the applicable Section or

Design Specification, the test coupon shall

be Charpy V-notch impact tested and the

supplemental variables of QW-250

applicable to the process being qualified

shall apply.


Hardness Variable QW-403.26

An increase in the Carbon Equivalent

IIW formula

CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15

P-number qualified still applies


QW-409.29

A change in the ratios of heat input

beyond the following (See Figure QW-

462.12.):

Temper Bead

Temper Bead in Groove


Heat Input Ratio

An increase or decrease in the ratio of heat

input between the first tempering bead layer

and the weld beads deposited against the

base metal of more than 20% for P-1 and P-3

metals and 10% for all other P-number

metals


Heat Input Ratio

An increase or decrease in the ratio of heat

input between the second tempering bead

layer and the first tempering bead layer of

more than 20% for P-1 and P-3 metals and

10% for all other P-number metals.


Heat Input Ratio

the ratio of heat input between subsequent

layers shall be maintained until a minimum

of 3/16 inches of weld metal has been

deposited over the base metal

Temper Bead

Heat Input Formula

Standard Heat input measurements:

Volts X Amps X 60 / Travel Speed or Instantaneous

Power/unit length of weld bead

Deposit Length / Unit Length of Electrode

Volume of weld metal = size (width X thickness) of

the weld bead

For machine or automatic GTAW or PAW, the power ratio

is measured as:

Power ratio = (Amperage X Voltage)

[(WFS/TS) X Af]


Surface Temper Beads

QW-410.58

The deletion of surface temper beads or a

change from surface temper beads that

cover the weld surface to beads that are

only deposited along the toes of the weld.

Temper Bead

Temper Bead In Butt Weld

Note 3: This is the distance from the edge of the

surface temper beads to the toe of the weld.

Surface Temper Beads

Temper Bead

Temper Bead on Plate

This layer doubles as a Surface Temper Weld Reinforcement

Sperko Engineering 2014

Temper Bead

Temper Bead applied to a

Fillet weld


Temper Bead

Surface Temper Bead Offset

Note 3: This is the distance from the edge of the

surface temper beads to the toe of the weld.

Surface Temper Weld Bead

Offset Distance S


Temper Bead

QW-410.61

The distance S from the edge of the surface temper

weld reinforcing bead to the toe of the weld shall be

limited to the distance measured on the test coupon

1/32 +1/16 inch. Alternatively, a range for S may be

established by locating surface temper beads at

various distances from the toe of the weld followed

by hardness traverses for each distance.

Temper Bead

QW-410.63 Bead Overlap

A change in visible bead overlap

beyond +15% of that qualified. (e.g., if

the qualified overlap is 50%, the

overlap range permitted is from 35 to

65%.). Bead overlap shall measured as

shown below.

Temper Bead

Visible Bead Overlap

% Visible Overlap = (A-B)/A X 100%

A

B

Direction of bead sequence

Temper Bead

QW-410.62

Surface Grinding of Temper

Bead Layers

The addition or deletion of grinding such as flat topping or

half-bead removal of temper bead layers. Grinding

required to clean the surface or remove minor surface

flaws is permitted without specific qualification.

Half-bead just will not go away. . . .


Temper Bead in Groove

Note 1: Weld beads shown above may be

deposited in any sequence that will result

in placement of the beads as shown

Temper Bead

Possible Bead Sequence 1A

Temper Bead

Possible Bead Sequence 1B


Possible Bead Sequence 1C

Temper Bead

Possible Bead Sequence 2


Possible Bead Sequence 3

Temper Bead

In-process Repairs

In-process repairs are repairs in

which a flaw is mechanically

removed and a repair weld is made

before a joint is presented for final

visual inspection (i.e., the welder

blew it. . . . )

Temper Bead

In-process Repairs

For processes other than manual and

semi-automatic GTAW and PAW, repairs

shall be made using the parameters given

in the WPS for production temper bead

welding. Then guess what layer you are at

-- and use the parameters for the layer(s)

being fixed.

Temper Bead

In-Process Repairs

When it is necessary to make repairs

using manual or semi-automatic GTAW

or PAW, a WPS shall be prepared based

on PQRs developed for temper bead

welding using machine or automatic

GTAW or PAW respectively.

Bead size and heat input details must be

described in the WPS.

Temper Bead

Welder qualfication

Code has nothing special.

I recommend that each welder weld a

test coupon consisting of a mock-up

making beads of the size specified in the

WPS using the heat input specified in the

WPS. Only visual examination is

required.

What does TB welding do?


Modifies the microstructure of the HAZ to minimize untempered

microstructures.

1)That softens hardened structures that might be present - - like

martensite.

2)Does not soften all of the microstructure there are always local

hard spots. If hardness is an issue for service (e.g., H2S), TB

may not be a suitable option. Do testing.

3)For hardenable materials, the microstructure is predominately

tempered martensite which has excellent toughness.

4)Is of questionable value for low-hardenability metals

5)Residual stresses are still yield-point magnitude.


Temper Bead Welding

Grrr . . . . Arrgh!

The Alternative to PWHT Temper Bead Welding by Walter J Sperko

Documents

weld bead

f bead

definition temper bead

temper bead tt

partial temper bead

layers temper

layers of weld metal

deposited weld metal