API 620-Q 6.1 "All-weld-metal test" 1

[CGArmesto]

Dear colleagues, we are in process of construction of two LNG tanks as per API 620 appendix Q. The designer has used 100,000 psi for tensile strength (note 1) and 58,000 psi for yield strength (note 2) for allowable stress values. We have requested to the filler metal manufacturer to carry out and certify two all weld metal tests per each nominal diameter of filler to be used (notes 3 and 4). Bearing in mind this, and in order to meet the requirements of Q.6.1 of API 620, is it necessary to go for all weld metal tests from the PQR test coupon itself? (the other tests requested to WPS qualification shall be make) or, can we refer the filler metal manufacturer test certificate?.

At the end of the day, the question is: in accordance with API 620 Q can we accept designing with the filler metal mechanical properties or should we design with the mechanical properties of the actual weld metal?.

Notes:

1)Tensile strength = 100,000 psi, equal to the minimum specified for the base material and maximum permitted per API.

2)0,2% Yield Strength = 58,000 psi, lower than the minimum specified for the base material and maximum permitted per API.

3)For making the test assemblies from which all-weld-metal specimens for filler metals shall be
removed:

a) Base metal shall be according to AWS A.5.11 Table 3 for ENiCrMo-6 and according to AWS A.5.23 Table 4 for ERNiCrMo-4. The materials shown on these tables are different to that to be used in the qualification of WPSs and in the construction (A-553 Type 1).
b) For ERNiCrMo-4, the same kind of flux to be used for the qualification of WPSs and for the production welds shall be used for the test assembly.
c) The joints to be welded and its dimensions shall conform to those shown on AWS A.5.11 Fig. 2 for ENiCrMo-6 filler metals and to those shown on AWS A.5.23 Fig. 3A for ERNiCrMo-4 filler metals. These joints shall be different from those shown on WPS to be qualified.
d) The same kind of current shall be used, including polarity, that those shown on WPS to be qualified.
e) Preheat and interpass temperatures shall be similar to those shown on WPSs to be qualified.
f) Heat input ranges and voltage ranges shall be wider than those shown on WPSs to be qualified.

4) The values demanded for both filler metals ENiCrMo-6 (SMAW process) and ERNiCrMo-4 (SAW process) are:

a) Tensile strength = 100,000 psi, equal to the minimum specified for the base material.
b) 0,2% Yield Strength = 58,000 psi, lower than the minimum specified for the base material.


Thank you very much for your opinions,

Armesto

 

[sayee1]

Which sountry are you building these tanks in? Note that the ENiCrMo6 consumables are typically 720 MPa(minimum) consumables if I remember correctly. The filler metal manufacturer would give you certificates for AWT in the ideal conditions not using the same conditions as you would use on the job. Also note that when using SAW in especially the horizontal position as you would expect in a girth weld of a tank using a girth welding machine, the values for tensiles, both AWT and the transverse drop because of the preferential slip planes in the base material. There was a very good paper with NiDi on this, you can check their website

http://www.nidi.org

for this paper. In addition both Esab and Lincoln have vast experience and numerous technical papers on this topic, would be able to advice the correct contact persons, if I know where you are building these tanks. It would be a difficult ask to get 100ksi on the consumables, but expect that you already have confirmations from the consumable manufacturers.

"in accordance with API 620 Q can we accept designing with the filler metal mechanical properties or should we design with the mechanical properties of the actual weld metal?." If I were the owner/COMPANY, I would definitely call for you to use actual values and as generated by the PQRs which I expect to be lower than the consumables themselves in the design. Again I would ensure that adequate safety is built in!!!!

Thanks and regards
Sayee Prasad R
Ph: 0097143968906
Mob: 00971507682668
email: sayee_prasad@yahoo.com
If it moves, train it...if it doesn't move, calibrate it...if it isn't written down, it never happened!