GMAW-STT (Surface Tension Transfer) for CS

[mohd]

dear all,

Codes: ASME B31.3 & ASME IX.

For high productivity the management has decided to switch from GTAW (root) + SMAW (fill/cap) to GMAW-STT (root) + SMAW (fill/cap)

Piping materials: ASTM A 53 / A 106 Gr B, API 5L Gr B,
size: range from 2" to 10'',
thickness: Sch40 to Sch160,
Impact requirement: -29 deg C,
hardness requirement: 220 HB,
Filler wire: ER70S-6 (is it Okey?),
Electrode: E7018-1 (is it Okey?).

GMAW-STT is new to me, please share your experience and process difficulties to qualify WPS and welders.

regards,
mohd

[alesio]

Dear Mohd,

I am not familiar with this process and I would like also if someone knows about to share that knowledge with us. Meanwhile I have found these two videos which I think help us to take an idea for GMAW-STT process:
STT Explained - Part 1
STT Explained - Part 2
Moreover, please have a look at these links:
Assessing the Benefits of Surface Tension Transfer Welding to Industry
Procedure using GMAW-STT applied at main pipelines welding

regards,
alesio

[techupon]

Mohd,

GMAW-STT is a type of GMAW-SCT (short-circuit transfer) and it has been designed to result in high quality weldings by a special control of its electric characteristics (current and voltage). So, you can use that process for your project. As for the qualification of the procedures and the welders you have to follow ASME IX and thus special attention must be given in clauses QW-304, QW-305, QW-403.10, QW-404.32 that specify some extra qualification rules for GMAW-SCT process. Relating to the piping materials and the impact/hardness requirements, please note that you can use the ER70S-6 and E7018-1 welding consumables.

Regarding technical characteristics of that process, please note that in comparison with GMAW-SCT, GMAW-STT doesn't give spatter, it has better penetration for root weld, it doesn't give lack of fusion and it has lower heat input. Another important characteristic of this process is that it is much more productive (3-4 times) with respect to GTAW.

regards,
techupon

[mohd]

Dear team,

As per my original post, I have welded pipe 6'' with thickness 18.25 mm and it has passed impact test at -29 deg C.

Could you please let me know what base metal qualification range should I give in the PQR,

Shall it be as per ASME B31.3, 323.3.1: T/2 to T+6 => 9.125 mm to 24.25 mm
or
Shall it be as per ASME IX, QW-403.6: 5/8" to T => 16 mm to 36.50 mm (2t)

regards,
mohd

[Ballbearing]

Mohd,
You can record both ranges of thickness on the WPS but if you are working in accordance with ASME B31.3 then the thickness range of ASME B31.3 is applicable.

Interpretation: 4-17
Subject: 327.5.1(d) and 327.5.2
Date Issued: January 29, 1986
File: B31-85-031

Question (1): When qualifying welding procedures which require impact testing, is the basic
qualified thickness range 1/2t to t + 1/4 in. rather than the range given in Section IX of the ASME Boiler
and Pressure Vessel Code of the lesser of 5/8 in., and t to 2t as in QW-403.6 (where t is thickness of
test coupon)?
Reply (1): Yes.

Cheers,
BB

[hunterwheeler123]

Glad to know about GMAW-STT that it is a type of GMAW-SCT (short-circuit transfer). I was thinking to buy some Guardian Generator Parts and in it i also need a short circuit transfer switch.

[aaronrodg]

Glad to know about GMAW-STT that it is a type of GMAW-SCT (short-circuit transfer). I was thinking to buy some Guardian Generator Parts and in it i also need a short circuit transfer switch.

Hey hunter, how are you mate, i want to know few things about that transfer switch, would you please reply me or check your pm, thanks.