Hardness limit for PQR 1

[PAN]

In my new coming project, the reactor will be 2.25Cr-1Mo-0.25V Steels. The requirement from the process licensor is hardness limit of Max. 235HV10 to be achieved for PQR. Unfortunately, I do not have experience for V-modified steel fabrication.

In my understanding, the acceptable criteria of Max. 235 BHN for production weld can be achieved by the fabricators. However, I am not sure about the limit of Max. 235HV10 for PQR. Since the value of 234 BHN is equivalent to 248 HV10. I worry that there will be difficult to find the qualified fabricator to meet limit of 235HV10 for PQR.

Please advise me about your experience for hardness limit in supporting PQR. Should we use limit of Max. 235HV10 for only 2.25Cr-1Mo Steels and 248HV10 for 2.25Cr-1Mo-0.25V Steels?

 

[metengr]

PAN;
I would still proceed with attempting to qualify the WPQR using the client’s lower hardness limit of 235 HV10 for the modified Cr-Mo-V pressure vessel steel. Given proper PWHT, I see no reason why this material cannot qualify for the lower hardness limit.

The presence of vanadium provides stable carbides at elevated temperature that promotes creep strength.

 

[PAN]

metengr,
From API RP 582, the limit of 248 HV10 is for P1 materials. For other P numbers, the limit is not specified in this document. Please advise the reference to indicate the specific hardness limit of PQR for this material?

I still check with other fabricators as your comment. Hope to receive their response soon.

 

[metengr]

PAN;
This sounds more like a client's engineering specification. The only references I could find were from NACE (MR0175 and MR0103), which specify a maximum hardness of 235 BHN for P-No 5C material.

This pressure vessel plate material you stated seems to be equivalent to an ASME SA-542 Type D, Class 4a. This material conforms to P-No 5C, Group 1 in terms of weldability, per ASME Section IX.

The minimum PWHT temperature is 1250 deg F (675 deg C).

 

[PAN]

metengr,
You are right. This is client's engineering specification.

I found the useful presentation file in

http://www.dillinger.de/.../technischeliteratur/

new_generation_of_crmo_v__steels_presentation_6_2005.pdf .

In the slide page 47, the holding time is a key factor to reduce hardness close to 235 HV10. However, the 30 hours may not be practical for fabricators. I will try to contact them and ask for comment.

 

[metengr]

PAN;
You might be able to shave some of that time during PWHT by elevating the PWHT temperature toward the higher end band without exceeding the lower critical transformation temperature. Hardness during tempering is a function of time at temperature because of carbide coarsening - increasing the temperature should require less time to achieve the same hardness at lower PWHT temperature for longer time.

It may be that with this level of vanadium, the carbides could be more resistant to coarsening – you are probably going to have to determine PWHT response by testing.

 

[PAN]

metengr,
Thanks again for your comment.

I try to use the same tempering parameter (Larson Miller's parameter). The PWHT will be closed to 730 degree C for holding time 8 to 10 hours. However, I don't have information about lower critical transformation temperature for this advanced steel. Please comment.

 

[metengr]

PAN;
I would use the published lower critical transformation temperature of 1480 deg F (805 deg C) -50 deg F, so 1430 deg F (777 deg C) max. The approximate lower critical transformation temperature information is from B31.1 Power Piping Code. Yes, it is not exactly a match for the above alloy. However, it is probably as close as you need and with the Vanadium alloy content, it should not appreciably change the lower transformation temperature from that of standard 2.25% Cr-1% Mo alloy steel because Vanadium is a carbide former.

 

[stanweld]

I recently qualified a procedure on the 2 1/4 Cr - 1 Mo-.25 V alloy - 2" thick. No problem meeting the defined hardness value with a 1350 F PWHT for 4 hrs. Preheat was 450 F min. Interpass temp was 650 F max.

 

[metengr]

PAN;
I would follow the PWHT mentioned by stanweld. If you ever need to calculate an approximate lower critical transformation temperature for low alloy steels, there are several published equations that depend on alloy content. One equation in particular is from Eldis;

A(lower critical deg C) = 712 - 17.8Mn - 19.4Ni + 20.1 Si
+ 11.9Cr + 9.8Mo

Alloy contents are expressed in weight percent amounts

 

[PAN]

stanweld,
Please advise me about the name of fabricator. I will try to contact them.

 

[PAN]

stanweld,
Do you also concern 3 PWHT cycles (fabrication/shop repair/weld repair) in your PWHT condition? How about the result of your PWHT cycles simulation? Please share your experience.

 

[stanweld]

PAN
The materials used in qualification were cast coupons provided by a French subsidiary of GE. The actual welding procedure joined P91 alloy steel to the 2 1/4 CR-1 Mo-.25 V- 0.18% C casting as the required production weld involved joining P91 piping to the cast alloy steam turbine. GE, its subsidiary and the EOR for the Owner could not provide any direction for making the weld or for its qualification.

For similar wrought alloys, I would contact V&M or JSW; noting that JSW was the chief developer of the alloy during the mid 1970s and, I believe, the first manufacturer of a heavy wall pressure vessel using the alloy.