e-Weldone Newsletter October  2011 Vol. 32
Product Update
Welding process for improving productivity in welding cross country pipeline
Introduction
Cross country pipelines, particularly those with higher thickness and having to operate at higher pressures require longer welding time when only manual welding process is used. Therefore,  major clients like GAIL, IOCL, GSPL, RELIANCE etc are now specifying the MMAW process for root /hot passes with 6010/8010 electrodes respectively and semi automatic FCAW welding process for subsequent filling /capping passes for welding cross country pipelines. The introduction of semi-automatic FCAW process (with self shielded wires) increases welding productivity and thus reduces overall project completion time.
Stove pipe welding technique
Following steps are adapted sequentially for carrying out this pipe line welding.
  1. Root pass
  2. Hot pass
  3. Heating of Welding joint
  4. Filler passes
  5. Capping passes
Root pass and hot pass are carried out by traditional MMA welding with cellulosic electrodes. Heating of welding joint is carried out by induction heating or by stove heating. Finally, filling and capping of V joint is carried out by semiautomatic welding with self shielded flux cored wires. The number of filler passes depends on the thickness of the pipe. Following is the typical example of such pipe welding jobs
 

PASS

THICKNESS OF  WELDING PIPE

25MM

15.9MM

FIRST

ROOT PASS

ROOT PASS

SECOND

HOT PASS

HOT PASS

THIRD

SINGLE RUN FILLER PASS

SINGLE RUN FILLER PASS

FOURTH

DOUBLE RUN FILLER PASS

DOUBLE RUN FILLER PASS

FIFTH

DOUBLE RUN FILLER PASS

DOUBLE RUN FILLER PASS

SIXTH

DOUBLE RUN FILLER PASS

DOUBLE RUN FILLER PASS

SEVENTH

DOUBLE RUN FILLER PASS

TRIPLE RUN FILLER PASS

EIGHTH

TRIPLE RUN FILLER PASS

TRIPLE RUN FILLER PASS(CAPING)

NINETH

TRIPLE RUN FILLER PASS

 

TENTH

TRIPLE RUN FILLER PASS

 

ELEVENTH

FOUR RUN FILLER PASS

 

TWELTH

FOUR RUN FILLER PASS (CAPING)

 

 
 
Following are the normal parameters for Root  pass

METHOD

MMA

BEFORE
GRINDING


AFTER GRINDING

 WELDING ROD USED

CELWEL 60

WELDING ROD DIA.

3.2MM

WELDING CURRENT

80A-110A

WELDING VOLTAGE

25V – 28V

 POLARITY

POSITIVE


Following are the normal parameters for HOT pass

METHOD

MMA


AFTER GRINDING  

WELDING ROD USED

CELWEL 80

WELDING ROD DIA.

4.0MM

WELDING CURRENT

135A - 180A

WELDING VOLTAGE

27V – 30V

POLARITY

POSITIVE


Following are the normal parameters Filler Passes :

METHOD

FCAW


BEFORE GRINDING
AFTER GRINDING

WELDING WIRE USED

E81T8-G DC (DCEN)

WELDING CURRENT

210A - 250A

WELDING VOLTAGE

21V-23V

POLARITY

 NEGATIVE

 

Following are the normal parameters for Capping

METHOD

FCAW


AFTER GRINDING

WELDING WIRE USED

E81T8-G DC (DCEN)

WELDING WIRE DIA.

2.00MM

WELDING CURRENT

200A - 230A

WELDING VOLTAGE

20V- 22V

POLARITY

NEGATIVE

Welding electrodes
Stove pipe technique is not possible with rutile type (E 6013) electrodes, because the relatively large volume and high fluidity of slag render vertical down welding difficult. Welding is done with cellulosic electrodes (E6010, E7010 etc class) since the volume of stiff, thin slag coating deposited on the weld bead, together with a forceful arc, facilitates rapid changes of electrode angle during vertical down welding. To compensate for the thin slag coverage, extra protection from the atmosphere is provided by a gaseous shield of carbon monoxide and hydrogen evolved from the cellulosic coating during welding.

Self shielded flux cored consumables.

Because welding is done at site, no external shielding gas is used during this process; a 2 mm consumable is generally used. The slag system has characteristics that make it possible to use in all position welding. The slag system also produces good, low temperature impact properties in the weld metal and desulfurizes the weld metal, thereby increasing weld cracking resistance.    

Welding equipment for cross country pipeline welding
In cross country pipe line welding, normally one joint is welded by two welders simultaneously from opposite sides of pipe. Each welder is welding from top to bottom(12 o’ clock to 6 o’clock). Hence two operator trolley mounted engine driven welding set or pay load of two power sources along with generator set are used. This pay load along with suitable capacity diesel generator set is mounted on a truck and is moved along the pipe while joints are welded.
For this application, power source should be suitable for both SMAW and self shielded FCAW welding process. For self shielded FCAW process, the wire feeder and its torch are specially made suitable for self shielded wires.
For this application Ador Welding Ltd. offers following equipments which can be used for MMA and Semiautomatic (with self shielded flux core wire) welding processes simultaneously. The same power source is capable of delivering both MMA and FCAW processes, the feature which makes them more versatile particularly for cross country pipeline welding.

Products offered by ADOR WELDING LIMITED for this application are:

Welding Equipment :
  1. SILENT CHALLENGER MULTI 2 x 301
  2. CHAMP MULTI 400 (SSPW)
Welding Consumables :
  1. CELWEL Series
 
For more information, Please write to us cmo@adorians.com or visit www.adorwelding.com
 
Product Update
 
 
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cmo@adorians.com