Thick Plate Welding Method

Authors: Kaiyuan Welding & Cutting Automation India Pvt. Ltd.

Wei Zhanlin, Managing Director / Shaikh Qamar Ali, General Manager – Sales & Technical Support

To increase the productivity and reduce the running cost, KAIYUAN offer the complete range of systems for the thick plate. Here after will introduce the popular methods which is Tandem SAW and Narrow gap welding.

• Tandem SAW welding

Submerged ARC welding method is widely used in thick plate welding. It is more efficient than conventional welding process like MIG/SMAW welding. Single wire SAW ( Fig 1) increase the productivity compare with the pre mentioned conventional welding but with the introduction of Tandem the deposition rate can be increase to double of the single wire SAW (Tandem = 14-16kg/hr with 4mm wire) with number of passes reducing relatively. To increase the productivity, Tandem welding will bean ideal solution (Fig 2).

Fig 1. Single power source with single wire SAW.

Fig 2. Tandem welding (one DC power source + one AC power source).
The order of welding torch arrangement of Tandem system: the front torch uses DC power supply, high current, low voltage, for efficient penetration. The rear torch uses AC power supply, with small current, high voltage parameter, for surface covering.

Front DC torch inclines ahead a little is beneficial for penetration. Rear AC torch inclines backwards a little is beneficial for covering with more wide and smooth welding bead.

Front Wire DC for  Rear Wire AC for covering DC + AC and forming
Fig 3. Tandem torch arrangement and welding bead.
Tandem welding deposition rate much higher than single wire SAW, it is around double than single wire welding. Means productivity will be more than 2 times increased if considering other associate time like slag cleaning (Fig 4).

Fig 4. Deposit rate comparison.  
Some of the KAIYUAN Single/Tandem applications:
Wind Tower welding:

Shipyard panel welding:

Pressure Vessel Industry:

Steel/PEB Fabrication:

KAIYUAN Standard configuration for single wire:

KAIYUAN standard configuration for Tandem:

Tractor mounted Tandem Welding head

Boom mounted Tandem Welding head

• Narrow Gap welding method

Narrow gap welding method is another high efficiency, high quality method for thick plate welding which use small groove to reduce the filling material and reduce the heat input. This method is used in the welding of large, critical components/structures, which has broad application prospects.
Narrow gap welding has the following characteristics:

• It is a special technology based on traditional arc welding methods. Most of them adopt I-shape groove, and the angle of groove depends on the deformation.
• The number of welding passes: 1 layer 1 pass for the Narrow GAP TIG and Narrow GAP MIG system and Narrow GAP SAW it will be 1 layer 2 passes. Adopt small or medium heat input parameters welding. It is possible for full position welding also.

Narrow gap welding method is suitable for thickness more than 30mm with groove less than plate thickness. Usually the gap is less than 20mm for the plate thickness less than 200mm and the gap is less than 30mm for the thickness of the plate more than 200 mm.
KAIYUAN offer Narrow Gap system in all the 3 welding process. Narrow gap welding technology usually includes

• Narrow gap MIG welding (NG-GMAW);
• Narrow gap TIG arc welding (NG-GTAW);
• Narrow gap SAW (NG-SAW);

The key issues of narrow Gap Welding need to be solved as follows”
1) Reliability of uniform fusion of side wall of welding groove
Because the slope angle is around 1 / 100, even parallel groove, vertical and downward arc can guarantee the penetration of both sides of the wall, which is the most important of narrow gap welding.
KAIYUAN narrow gap MIG welding system (Fig 5) adopt deforming the welding wire to the specified shape before entering the contact Tip which makes the arc oscillate regularly and achieves the purpose of good fusion of the two sides of the wall.

Fig 5. Narrow gap MIG.

KAIYUAN narrow gap TIG with hot wire welding system (Fig 6) adopt electrode oscillation to guarantee the fusion of wall.

Fig 6. Narrow gap TIG – Electrode swing.

KAIYUAN narrow gap SAW system (Fig 7) adopt one lay two pass welding method. One pass face to one side wall to guarantee the fusion.

Weld bead with the Narrow GAP SAW

Fig 7. Narrow gap SAW.

2) Narrow gap welding spatter
In the narrow gap groove, the welding torch has a very small distance between the two sides of the groove, and the welding spatter may stick to the nozzle, which will reduce the gas flow protection performance and the normal wire feeding, thus affecting the stability of the welding process, especially the splashing metal particles sticking to the inner wall of the groove. The welding torch will be difficult to move, or even short circuit. This is also a narrow gap welding problem need to be solved.
The solutions are as follows:

• Adopt narrow gap submerged arc welding, no spatter;
• Surface tension transition technology to reduce spatter;

3) How to guarantee the stability welding parameters and the Arc position during Welding process
In the welding process, the stability of welding parameters and the accuracy of the arc position seriously affect the fusion quality of the side wall.
KAIYUAN narrow gap system has unique Groove width self-adaptation technology to suitable for the width change of groove except normal vertical and horizontal AVC tracking.

The efficiency of Narrow gap welding process. 

Traditional   Narrow groove      Narrow gap     Multi-pass in one layer   One layer two pass
wide groove
Compared with conventional wide groove:

1. Groove profile can reduce 36%~70%.  The wire and flux consumption decrease by more than 35%.
2. Groove profile and layer reduction can decrease residential stress and hydrogen content, then improve ability of crack resistance.
3. Under same total weld efficiency, it can reach to lower heat input.

Narrow gap welding is widely used in many industries, such as pressure vessel and boiler industry, heavy-duty machinery, marine engineering and shipbuilding, power sector etc. Some of KAIYUAN Narrow gap system application cases:
Narrow Gap SAW welding system on boiler steam tank

Narrow gap hot wire TIG for 2G position

Narrow gap MIG for Box girder

Conclusion:
With the growth of economy, large-thickness steel plate will be more and more widely used in the production of various industries. To increase the productivity and reduce the cost, Tandem SAW and Narrow gap welding method will be perfect solution, along with the Kaiyuan India expertise team & with Kaiyuan’s 30+ years of experience to work jointly with the industry to develop & offer right solution. LET’s WORK AS TEAM INDIA , WITH KAIYUAN INDIA.
References:

1. 锅炉压力容器焊接使用手册/中国焊接协会编

机械工业出版社，2016.5
ISBN987-7-111-53764-9
Manual for Boiler Pressure Vessel Welding / Edited by China Welding Association
China Machine Press, 2016.5
ISBN987-7-111-53764-9