Passing G48A test is always a challenge to welding engineers.The variables causing failures could be anything, welding parameters/Metallurgy, surface finish,duration of the test, test temperatures.120 grit finish is deemed to be resonable by ASTM, however many specifications allow finish up to 600 grit or more.
Many Upstream Oil gas specifications allow 24 hrs of testing duration for such test( see extrats as below):-
Corrosion testing shall be performed for each welding procedure qualification in accordance with the following:
1.ASTM G 48 Method A.
2. Exposure time shall be 24 hours.
3. Full thickness specimen.
4. All surfaces shall be exposed. The sides (only) may be ground to a 600 grit finish and the edges may be rounded.
5.Samples shall not be pickled or passivated prior to test.
6. Test temperature for UNS S31803 or S32205 weld samples (22% chromium duplex) shall be 20°C.
7. Test temperature for UNS S32550, S32750, UNS S32760, S39274 weld samples (25% chromium "super" duplex) shall be 40°C.
Acceptance criteria: -No pitting at 20X and maximum weight loss shall be less than 1.5 g/m2.
Should the clients' insistence is for 72 hrs duration then:-
--Advise would be to get the base metal tested @ the same duration and temperature.
-Get the same for welding consumables.
If the results for BM and consumables are satisfactory then only pursue 72 hrs test for weld coupons.
If you're forced to pursue the wrost case scenario, then the other option is to use super duplex 25-9-4 welding consumables for the weld coupon.
Welding & Metallurgical Specialist
P.S:-You may read this article for further information on the pros and cons of this test- http://www.twi.co.uk/technical-knowledge/published...