Today if you have to manufacture Stainless Steel, alloy steel, titanium vessels which are 6 to 8 mm thick, the material needs to be welded in multiple passes. First of all the surface needs to be edge prepared , that means grinding or beveling of the plates throughout the length, then the fit-up, root pass, hot pass and then multiple passes till the capping is achieved. Even when we weld this in automation we have to keep the inter pass temperatures in mind and allow the time in between passes to ensure the temperatures do not exceed the interpass limit.

This means a typical 8mm thick 1 meter to 1 meter long weld seam would take approx 100 minutes to edge prep and weld. Image if we could do the same in minutes.

Sigmaweld Weld Accelerated TIG (S.W.A.T) is a GTAW process which requires no edge beveling, uses as little as 10% of the gas normally required and produces highly repeatable, x-ray quality welds with superb cap and root aesthetics.  Thicknesses up to 10mm can we welded in a single pass without edge preparation. This means that the time taken for edge preparation plus the multi-pass welding can be reduced to single pass. A typical 6 hour job (edge preparation and welding multi-pass) can be done in minutes.


Figure 1 : S.W.A.T used in Tube Mill to increase productivity

The fundamental behind this process is intentional increase in arc pressure to the point where it extends the crater to the bottom of the pool. The surface of the weld pool will become anchored to both top and bottom surfaces to form a stable structure. This stable arc is moved along the weld path as keyhole. The arc is supported by Purging Gas on the back side and Shielding Gas from the torch.


Figure 2 : Penetration Profile of 8.5mm thick tube single pass welding with S.W.A.T

For example in Tube Mills where typical thickness of 8.5mm use a PT (Plasma – Tig) combination and speeds of upto 175mm / minute. This process was replaced with S.W.A.T  (SigmaWeld Accelerated TIG) a variant of the KeyHole GTAW process, using only the TIG Torch with the new process the mill speeds of 400 mm / minute were easily achieved. Figure 1 shows a 5mm tube welded by S.W.A.T. Figure 2 shows the penetration and profile of the 8.5mm thick, SS304 Tube.

The production was more than doubled, only one power source was used for S.W.A.T (GTAW) and filler wire consumed during the process was less than half of the Plasma – TIG combination.

 Similarly, for Nickel Alloy plates of 8mm, up to 3 passes were needed to be welded using standard GTAW process. With S.W.A.T this could be done in a single pass.

Table 1 : Productivity Comparision Manual GTAW Vs Automated GTAW Vs S.W.A.T

Parameters NORMAL GTAW Automated GTAW S.W.A.T
Num of Pass Root + 3 Pass Root + 1 Pass Single Pass
Welding Speed  55mm/ min 100mm/min 300mm/min
Edge Prep Time 30 min 30 min
Welding Time/meter 72 min 20 min 3.33 min
Total Time 102 min 50 min 5 min

As shown in Table 1 welding of 8mm plates could be welded under 5mins using SWAT compared to the standard GTAW manual welding time of upto 100 mins and 50 minutes when welded in Automated GTAW with Cold Wire Feeding.

Coupon plates of SS304 of thickness 2.72mm, 4.12mm,6.0mm and 8.0mm were made and subjected to ASME IX tests to check for RT, Macro, Tensile 1, Tensile 2, Micro (On Weld), Micro (On PM& HAZ), Hardness, Root Bend 1, Root Bend 2, Face Bend 1 and Face Bend 2.

The samples passed the acceptance criteria for each of the above tests.

Further trials have been conducted on Cobalt Alloys, Titanium, Nickel Alloys upto 8mm thickness. The results are very high speed welds with exceptional quality.

For thicknesses above 8mm and upto 14mm can be welded with added filler wire.

Following results show how S.W.A.T has given dramatic improvement in productivity and cost in welding of Titanium and Austenitic Stainless steel (data for 1m of weld length).

Titanium – 14mm plate comparison •   90% reduction in no of pass

•   90% reduction in filler metal consumption reduce the potential for inclusion, porosity and other weld defects typically with other welding processes

•   90% reduction in cleaning time

•   100% reduction in weld edge preparation time

•   77% reduction in gas consumption

•   90-95% reduction in total cost considering all the factor like weld edge preparation cost, filler metal cost, labour cost for cleaning and welding, gas cost

•   30-40% reduction in H.I. helps to reduce HAZ

and distortion in plate

Existing GTAW S.W.A.T.
No of passes 9 1
Filler metal/meter 1000g 100g
Weld pass clean 90 min 10min
Weld Edge time X min Nil
Shielding & purging 3000 ltr 700ltr
Comparatively low H.I. helps to achieve require impact
Welding Current 150-250A 620-680A
Welding speed(mm/min) 60-80 240-300

Table 2

Austenitic SS – 10mm plate comparison •   83% reduction in no of pass

•   90% reduction in filler metal consumption reduce the potential for inclusion, porosity and other weld defects typically with other welding processes

•   83% reduction in cleaning time

•   100% reduction in edge preparation time

•   60% reduction in gas consumption

•   70-75% reduction in total cost considering all the factor like weld edge preparation cost, filler metal cost, labour cost for cleaning and welding, gas cost

•   30-40% reduction in H.I. helps to reduce HAZ

and distortion in plate

Existing GTAW S.W.A.T.
No of passes 6 1
Filler metal/meter 1000g 100g
Weld pass clean 60 min 10min
Weld Edge time X min Nil
Shielding & purging 1800 ltr 700ltr
Comparatively low H.I. helps to achieve require impact
Welding Current 100-200A 500-550A
Welding speed(mm/min) 80-100 400-450

Table 3

Following data shows satisfactory test result of Austenitic SS welding.

SN Type of test Result
1 Visual Examination (ASME SEC IX) Satisfactory
2 Radiography (ASME SEC IX) No relevant indication
3 Guided Bend test (ASME SEC IX) Satisfactory (bent to 180° with 40 mm dia mandrel)
4 Tensile test (ASME SEC IX) Ductile fracture – satisfactory
5 Chemical Analysis (ASME SEC II-C) Cr 18-19%, Nickel 8-9%
6 Ferrite measurement (Feritoscope) 6-8FN
7 Hardness measurement Acceptable (WM, BM, HAZ)
8 Macro examination (ASME SEC IX) Good fusion without any defect
9 Microstructure (ASTM E407-07) Satisfactory
10 IGC Practice- E (ASTM A 262) Satisfactory

Table 4

It is clear indication from the Table 4, Table 5 & Table 6 that by employing SWAT power source industry can easily eliminate the need for wire and edge bevelling and produce flawless welding too much faster than conventional TIG welding for material up-to 14mm

Application of SWAT can be useful for following listed industries;

  • Defence and Aerospace
  • Tube Mills
  • Cryogenic vessel manufacturer
  • Tank & Vessel
  • Food, Pharma & Dairy equipment
  • Nuclear

 For More Info:
Electronics Devices Worldwide Pvt Ltd
Sahar Plaza Midas II 608, Windfall Complex,
Andheri – Kurla Rd, J B Nagar, Andheri East,
Mumbai, Maharashtra 40005

Nimesh Chinoy,
Marketing Director,
SigmaWeld
Mob: 9820785022
Email: nchinoy@edmail.in / sigmaweld@edmail.in

www.sigmaweld.com