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Svetsaren nr 1 2000 33

Introduction

Today, the commonly applied fluxes for high

strength/low tempera ture applications are agglomera t-

ed basic types, to provide dependable CVN a nd CTOD

toughness properties at sub-zero temperatures. The

greatest disadva ntage of a gglomerated fluxes, however,

is that t hey are hygroscopic and must be re-baked prior

to w elding in order to avoid potentially high weld met-al hydrogen contents with the inherent risk of cold

cracking. The routine of removing flux from bags into

ovens and re-ba king it for several ho urs is time consum-

ing and costly for fabricators. Fused fluxes, although

non-hygroscopic, never became esta blished in offshore

fab rication, mainly because of poor mechanical proper-

ties with solid wires.This is overcome by the use of a ba -

sic cored wire with active agents in the flux to improve

the mechanical properties.

ESAB have now introduced a basic cored

wire/fused flux consumable package, O K Tubrod

15.24S/OK Flux 10.47, fulfilling low -tempera ture weldmeta l requirements down to 40C a nd CTOD -tested

at 10C, but w ithout the necessity to re-bake the flux

before welding. In the field of submerged a rc welding,

this is as much a breakthrough as the introduction of

S ubmerged a rc w eld ing w ith

fused flux and b a s ic cored

wire for low temperature

applicationsno re-baking of fluxes necessary

by Neil Farrow and Shaun Studholme, ESAB UK, Ltd.

ESAB introduce a basic cored wire/fused flux SAW package,

O K Tubrod 15.24S/O K Flux 10.47 for use in offshore fabrica-tion. Rebaking of the flux is avoided.


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34 Svetsaren nr 1 2000

Table 1: Classifications

O K Flux 10.47 EN 760: SF AB 1 65 AC

Combination AWS A 5.23: F8A4-EC-G

Table 2: All weld metal chemical composition and

mechanical properties (as welded).

% C % Si % M n % Ni % P % S

0.05-0.10 0.10-0.40 1.50-2.00 0.60-0.90 20

C VN at 40C (J) >47

vacuum packaging for stick electrodes in the eighties. It

simplifies stora ge and ha ndling procedures enormously.

In add ition, fabricators get a bonus in the form of

an increased welding economy, due to the use of a

cored wire. D eposition rat es may be 20 to 30% higherthan w ith solid wire SAW, depending on the t ype of a p-

plication. More benefits in the area o f weldability are

discussed below.

In the near future, E SAB will launch other consum-

able packages with b asic cored wires and fused flux for

general construction and other segments where the

low-hydrogen weld meta l is a fa ctor for consideration.

Next, the new SAW consumable package is intro-

duced and product chara cteristics are reviewed. In ad -

dition, we discuss its successful implementatio n for the

fabrication of components of the Saga Petroleum

Snorre B oil and gas platform by two UK subsidiariesof K vrner Oil & G as.

Mecha nica l prope rties of

OK Tubrod 15.24S /OK Flux 10.47

The objective of the development was to create a con-

sumable package ba sed on a b asic cored wire and fused

flux meeting the following weld metal requirements (as

welded) for structural welding in the offshore segment:

Yield strength >470MP a

C V N tough ness >47J a t 40C

CTO D >0.25mm at 10CThe use of a b asic cored wire, instead o f a solid wire,

allows the weld metal toughness properties to be engi-

neered through the cored w ire rather than through the

flux.

A highly basic flux is no longer a prerequisite and

this opens the wa y to the use of a lower ba sicity fused

flux with very distinctive a dvanta ges for offshore weld-

ing applicat ions.

O K Tubro d 15.24S is a 1% nickel alloyed basic

cored wire meeting the all weld metal mechanical re-

quirements stat ed a bove in combination with the fused

flux OK Flux 10.47.Tab le 1 gives the classifications a nd

Tab le 2 shows the chemical composition and mechani-

cal properties. It is clear tha t the combination exhibits

the required tensile properties as well as sufficiently

high CVN to ughness, even dow n to -50C.

C TOD properties have been tested fo r single-V,

double-V and K-joints in 50mm w all thickness with ex-

cellent results (Table 3).

Figure 1 surveys the CVN temperature transition

curve, showing a grad ual decrease down to a level of

60C fo r all three wire diam eters. Figure 2 shows tha t

the CVN toughness decreases with increasing heat in-

put, but sta ys well abo ve the 47J level at 40C.

These results establish that the SAW consumablepackage O K Tubro d 15.24S/OK Flux 10.47 clearly pro-

vides the mechanical properties needed for offshore

fabrication. Add itional benefits are found in the use of

a fused flux, described below.

Table 3: Typical CTOD values at 10C for

OK Tubrod 15.24S/OK Flux 10.47.

Single-V Double-V K -prep.

1st >0.934 0.731 >0.9162nd >0.934 >0.893 0.866

3rd >0.919 0.753

Figure 1: CVN transition d iagram.

Figure 2: Influence of heat input on CVN p roperties.

Effect of Heat InputCored Wire/Fused flux

Heat Input (kJ/mm)

1.5 1.7 1.9 2.1 2.3 2.5 2.7 2.9 3.1 3.3 3.5

160

140

120

100

80

60

40

20

0

Toughness(J)

Mid-thicknesscentre notch

Ave Cv-20

Ave Cv-40

Tubrod 15.24S - AWS All-Weld Metal

Temperature (C)

60 50 40 30 20 10 0 10 20 30

250

200

150

100

50Toughn

ess(J)

Heat Inputs

2.4mm= 1.8 kJ/mm3.0mm= 2.1 kJ/mm

4.0mm= 2.5 kJ/mm

3.0mm

4.0mm

2.4mm


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Svetsaren nr 1 2000 35

OK Flux 10.47

The fact that this fused flux has a very low moisture

content a nd a moisture re-absorption ra te close to zero

is, undoubtedly, the biggest advanta ge for applications

where low weld metal hydrogen contents are crucial.

This enab les the flux to be used without the costly, and

time-consuming procedure, of re-baking.

Figure 3 compares the hydrogen performance of

the consumable packa ge O K Tubrod 15.24S/OK Flux

10.47 with a well established competitor basic agglom-

era ted flux/solid wire combinat ion. D iffusible hydro gen

tests have been carried out at increasing current levels

covering the work range of the flux, for various stick-

out lengths. B oth w ire/flux combinations gave va lues

below 5ml/100g with OK Tubrod 15.24S/O K Flux 10.47

tending below 4ml/100g. Note tha t the agglomera ted

basic flux has been re-baked according to the

manuf acturers instructions wherea s OK Flux 10.47 hasbeen used directly from the original bags.

The moisture re-absorption characteristics of both

fluxes have been tested by means of climatic exposure

tests in a humidity cabinet at 80%RH and 25C for up

to 14 da ys. It show s that O K F lux 10.47 is not sensitive

to moisture re-absorption, due to its non-hygroscopic

character a nd can be used safely without re-baking.

The basic cored wire OK Tubrod 15.24S hydro gen

values and re-absorption beha viour is compara ble with

that of solid SAW wire. When stored and used a ccord-

ing to the manufa cturers instructions it does not rega in

moisture.The second big advantage for fabricators is an in-

creased deposition rate due to the use of a cored wire

as a consumable. As w ith cored wires used for FCAW,

the current is conducted by the meta l sheath, instead of

Figure 5: Sno rre B. Artists

impression.

Figure 3: Diffusible hydrogen results for comp etitor

EN 760: SA FB 1 55 AC t ype agglomerated basic flux used

with solid w ire and OK Tubrod 15.24S/OK Flux 10.47 .

Figure 4: C limate expo sure tests at 80%RH and 25C for

EN 760: SA FB 1 55 AC type c ompetitor agglomerated

basic flux and fused flux OK Flux 10.47 w ith OK Tubrod

15.24S. Diffusible hydrogen determined at 600A/30V/

30 mm stickout.

Climatic Exposure Results

Days0 2 4 6 8 10 12 14

12.0

10.0

8.0

6.0

4.0

2.0

0.0

Agg Flux

OK 10.47

DiffusibleHydrogen(ml/100gofdepositedmetal

Diffusible Hydrogen ResultsSolid and Cored Wires

400 400 400 400 600 800 800 800 800 C urrent

28 28 32 32 30 28 28 32 32 Volta ge

20 40 20 40 30 20 40 20 40 S tickout

DiffusibleHydrogen(ml/100gofdepositedmetal

6.0

5.0

4.0

3.0

2.0

1.0

0.0

T15.24S /OK10.47

solid wire/ba sic a gg l. flux


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36 Svetsaren nr 1 2000

the complete wire cross section resulting in a higher

current density. In combination with the fused flux this

higher current density is converted t o increased deposi-

tion rates and higher applicable travel speeds. H ow

much fabricators can benefit from this depends, of

course, on the type of application. Our experience with

cored w ire/flux combinations in general, is such that an

increase in welding productivity can be expected in the

ord er o f 2030%.Weldability chara cteristics are excellent; comparab le

to the best basic agglomerated fluxes available on the

market. Slag release is very good even in the bottom of

butt joints near the root a rea a nd even narrow gap appli-

cations are possible. D ue to the glass nature of the flux,

the grain strength is significantly higher than that of the

fully ba sic agglomera ted f luxes. This results in less break-

down a nd hence no problems with " dusting" and there-

fore allround improved recyclability. The finished weld

appeara nce is very good, both in butt and fillet welds.

Next we will describe t he use of O K Tubrod

15.24S/OK F lux 10.47 for o ffsho re fa brica tion by tw o

U K b ased ya rds who were the first customers for this

new combination.

Fab rica tion o f dec k modules for Snorre B

The Snorre B oil and gas platform for Norways Saga

Petroleum (Figure 5) is currently under construction

for delivery in the Spring 2000. Aker Stord of Norw ay

is the main contractor. Pa rt of the deck was sub-

contracted to Kvaerner Oil & G as (KOG ) Methil, in

Scotland, which in turn sub-contracted parts to KO G

Teesside in England.

Applications at both U K y ards are very similar.

They consist of box structures a nd beams in B S 7191-

450 EMZ steel with a minimum weld metal CVN

toughness requirement o f 47J a t 40C. Figure 6 shows

the fabrication of beams at KOG Methil. Fillet welds

with a throa t thickness of 8.5mm were mad e in one pass

wit h O K Tubro d 15.24S/O K Flux 10.47 at 630A/

31V/36cm/min. In this a pplicat ion, the cored wire/fused

flux combination welds 25% faster than the competitor

solid wire/ba sic agglomerat ed flux combina tion used

previously for similar work.

KO G Teesside a lso reported impressive productiv-ity improvements in the welding of bo x structures, in-

volving V-joints in 35mm thick plates (Figure 7). C om-

pared with t he solid wire/ba sic agglomerat ed flux com-

bination used previously with metal powder addition,

the numb er of passes wa s reduced f rom 23 to 15 (-35%)

while maintaining good mechanical properties. Note

tha t O K Tubro d 15.24S/OK Flux 10.47 is used here

without metal powder ad dition. They also reported

marked improvements in actual flux consumption as

the basic cored wire contributes its own fluxing agents

to the w eld pool.

Both yards benefitted from not having to re-bakethe flux prior to welding, which enables easy handling

procedures and is very time and cost efficient. Addi-

tionally, the improved slag release a nd cosmetic appear-

ance of the completed w elds was highly a ppreciated.

Figure 6: Fabrication of b eams at KOG Methil.

Figure 7: Fabrication o f box structures at KOG Teesside.

About the authors

Neil Farrow is a Senior D evelopment Engineer who has

been working at Waltha m Cro ss in the U K fo r the past 15

years.

Neil holds a B Sc in Metallurgy and Ma terials Science and

an MSc in Welding Technology from Cranfield U niversity.

He has recently been very active in the development of

cored w ires for submerged arc welding.

Shaun Studholme,Product Ma nager,C ored Wires in E sab

G roup (UK ) Ltd. He is responsible for cored wire

marketing and is based at Waltham C ross, U K.

To conc lude

Summarising, the ba sic cored w ire/fused flux combina-

tion O K Tubro d 15.24S/OK Flux 10.47 intro duced by

E SAB has been developed for low temperature appli-

cations such as offshore fab rication. P roduct benefits

are found in easy storage and handling without re-

baking of the flux, increased welding productivity, very

consistent mechanical properties, and a n excellent

weld q uality.The SAW combina tion ha s been used suc-

cessfully for the fabrication of critical components on

the Snorre B project.

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