-50F CVN per B31.3 1

[SFIENG]

First a little back ground information. In production (pipe spools to B31.3) I will be using SA-333 GR 6 (P1/G1) / A350 GR LF2 (P1/G2) / SA-420 GR WPL6 (P1/G2) which will be supplied impact tested to -50F. I am looking to limit the number of PQRs so for the procedure testing I am looking to join SA-516 GR 60 (P1/G1) to SA-516 GR 70 (P1/G2) to qualify the procedure to weld the stated production materials.

I was wondering if anyone would share any welding parameters for welding P1 G1/G2 materials to pass CVNs at -50F per B31.3. I will be performing PQR's in GTAW and FCAW on 1/4" and 1/2" material in the 3G position. I am using ER70S-2 with 100% Argon in the GTAW process and E81T1-Ni1 with 75%Ar/25%CO2 in the FCAW process.

I know that low heat input is critical for the CVN testing. Can anyone offer their experiences on maximum heat input (J/in.) for successful CVN at -50F?

 

[metengr]

SFIENG;
I think the ER70S-2 will not have adequate notch toughness at -50 deg F. You need to use a GTAW filler metal that contains increased nickel for increased notch toughness at -50 deg F. I would recommend SFA 5.28 ER80S-Ni1 (20 ft-lbs at -50 deg F) or you can use ER80S-Ni2 with PWHT, and this would be good for 20 ft-lbs at -80 deg F. Review SFA 5.28.

For the FCAW wire, using SFA 5.29, the E8xT1-Ni2C will make 20 ft-lbs CVN at -40 deg F with no PWHT. If you decide to PWHT, you can switch to an E8xT5-Ni1C, this should make 20 ft-lbs at -60 deg F. Review SFA 5.29.

Review the suggested preheat, interpass temperatures in SFA 5.29 for the FCAW wire. Also, you can review the recommended PWHT temperature in Table 6 of this SFA specification.

 

[weldtek]

SFIENG,
metengr is steering you correctly. It is possible to get impacts at -50 F using ER70S-2, but, results can be spotty. We have successfully tested this wire at -50 F using 24,000 j/in. on a 1/4" thick plate with PWHT. Keep in mind, though, you have to be able to duplicate the results in production. The most economical way to impact qualify P1 Groups 1 & 2 is to select plate that is dual certified as SA516-60/70.
As to the FCAW we have tested Ni-1 wire with 75% Ar / 25% Co2 using around 25,000 j/in on 3/8" thick material with PWHT. At -60 F we got 27 ft/lbs avg with 50% shear.

 

[Metalmeister]

SFIENG,

I would do a single PQR with the best P1 Gr. 1 steel and weld to the best P1 Gr. 2 steel that you can lay your hands on. Take HAZ CVN coupons from both sides of the weld to cover both materials. The way I read QW-403.5, that approach is allowed and qualifies Gr 1 to Gr. 1, Gr. 2 to Gr. 2 and Gr. 1 to Gr. 2, which is what you are welding. I didn't check into the variations of filler metal that was previously suggested and how that might impact the number of test coupons beyond my suggestion.

With all due respect for the good advice given by Weldtek, I don't much like using dual certified material and think this connotation is misleading, if not bogus. Gr. 1 is metallurgically different than Gr. 2. The Gr. 2 is stronger because of its richer content of alloying elements. The two grades respond differently to heat. With a dual certification you can wind up with a leaner alloyed Gr. 2, which defeats the purpose of using the best steel you can get for the PQR. Maybe a better way to explain my thoughts on this is the case of dual certified 304/304L SS, which was mentioned in a thread a few weeks ago. While the 304L can meet the higher room temperature tensile and yield of 304 grade, it won't meet high temperature strength requirements of 304 that the Code allows. Not with standing the dual certification, the low carbon grade is notably weaker at higher temperatures.

 

[weldtek]

Metalmeister,
Your opinion is noted, however, it's evident,that the Sec IX Code Committee disagrees with your opinion. See Interpretation IX 92-70R

 

[metengr]

I don't much like using dual certified material and think this connotation is misleading, if not bogus. Gr. 1 is metallurgically different than Gr. 2. The Gr. 2 is stronger because of its richer content of alloying elements. The two grades respond differently to heat.

With all due respect, there is nothing bogus with dual certification as stated by Metalmeister. You are certainly entitled to your opinion. The material groupings that were originally conceived by SG Material under Section IX SC began with evaluating responses of various P-No base materials to notch toughness behavior from welding. Getting back to the OP, the user understands that the coupon base materials for weld procedure qualification are not identical to production base materials (the production base materials have even better low temperature notch toughness in comparison to SA 516 plate), and wants to qualify the weld procedure processes with the appropriate filler metal selection and heat input to assure adequate strength, ductility and notch toughness of the weld joint for the intended service conditions.


In some cases dual certification serves an extremely useful purpose that users of the Code may take into consideration for the very purpose I stated above. One must recognize that the Code is written to provide maximum flexibility for users, and final selection of base materials for weld procedure qualification and service performance rests with the designer.

 

[Metalmeister]

You can certainly use dual certified material for a PQR test. But I would not want to use a leanly alloyed steel with marginally acceptable properties in a critical, time consuming, and relatively expensive test. You would have a super 516-60 and a marginal 516-70. It could work.

Does ASME I, III and VIII allow the use of dual certified materials in the allowable stress tables. 304L will have weaker high temperature strength than 304. I don't see how a dual cert can guarantee high temperature performance; although the paper is the same, the metallurgy is different.

In my time I've seen errors in the Code, and Code Interpretations are mere opinions albeit stronger than mine. If the Code allows dual cert materials in the allowable stress tables, I would submit that the Code is wrong. Different alloy compositions respond differently to high temperatures. The cert paper may be the same with acceptable RT properties but the metallurgy is different.

 

[metengr]

In pressure vessel design, the specific use of a grade of material must be listed on the data report. So, dual certified material cannot be represented as a single grade of material. The designer must list either an L grade for allowable stress values or the standard grade for allowable stress values used in design and fabrication.

 

[metengr]

To specifically answer your question below

Does ASME I, III and VIII allow the use of dual certified materials in the allowable stress tables.

Each has their own stress line in Section II, Part D. In other words, if you take advantage of using the dual certified material as an L grade in design, you must use the stress line for the L Grade. You cannnot have it both ways, interchangeable stress lines.

 

[SFIENG]

Metengr and Weldtek,

Thanks for your input on the parameters and what success you have had. I will give it a try with the ER70S-2 on the GTAW since I have that in-house already. It that fails I will try using a filler with Ni as suggested.

 

[Metalmeister]

You clearly know your stuff. I would go a step further and say that if the steel is dual certified, meaning it has the carbon content of 304L and RT strength of 304, designers should not expect the steel to exhibit the high temperature strength of 304. In reality it will be weaker and have the strength of 304L. So designers should be careful and should be constrained to use the more limiting stress values of the L grade.

Going back to the original question on PQRs, I always want to use the best material available in my quals. because it doesn't make me look good when a qual fails. There are enough gotchas out there but I can control the metallurgical ones more easily.

 

[weldtek]

Metalmeister,
Quote:
' Going back to the original question on PQRs, I always want to use the best material available in my quals. because it doesn't make me look good when a qual fails. There are enough gotchas out there but I can control the metallurgical ones more easily. '

I submit to you that for the example above there is nothing to be gained by your approach. If the test fails impacts using dual certified SA516-60/70 it isn't because you used a dual certified material. In your previous post you referred to a 'Super 516-60 and a marginal 516-70'. This makes no sense at all. These two grades are dual certified all the time without compromising properties.

 

[Metalmeister]

I agree with you. Dual certification happens often. But if you buy a dual certified 516-60/70 with 71 ksi tensile and after your qual PWHT for 20 hrs, see where the tensile drops to. Grade 70 has higher carbon and higher manganese (richer chemistry), which improves my chances to get the qual to pass. It is just an opinion that has worked for me over 30 yrs., no big deal.

 

[weldtek]

Metalmeister,
Your point is well taken, but, my suggestions relate specifically to impact testing here, not tensile testing. There's no advantage to using dual certified 516-60/70, except for impacts. As I'm sure you know, fabricators have the option to qualify the impact tested portion of their procedures separately, and, it is often more cost effective to do so. With this in mind, time at temp is only an essential variable for impact testing so I'm only concerned about its effects on the impacts. In many cases I run two plates, one to cover impacts only. For the impact tested plate, I consider grain orientation, and the supplementary variables such as group numbers, thickness, and time at temp. The second plate may be thicker and will cover all essential variables. These two plates combined will be used to support an impact qualified WPS. As you say, one needs to carefully select material that will yield the desired results.