High temperature S&Tmaterial

[vessexst]

Hi all,

We are designing a high temperature S&T exchanger having the following design conditions

Shell side
Design P: 2.5 Bar
Design T: 160 Deg C

Tube side
Design P: 2.5 Bar
Design T: 480 Deg C

We used the following materials for tube side owing to high temperature
Channel shell: SA 387 Gr.P91
Tubes: SA 335 Gr. P91

This equipment is in severe sour service and NACE MR0175 compliance is mandatory.

However, client has rejected this material owing to its high hardness value. To this, we gave a response that if we order this material with NACE and HIC compliance, the material should be having a hardness of HRC22 (max. Limit specified by NACE MR0175). As per ASME SECII, Part A, the hardness levels of SA 335 P91 Pipe vary upto HRC 25. So, if we specify NACE + HIC for this material, it should be supplied as HRC 22 max hardness.

To this, client has stated that NACE MR0175 is applicable for low alloy steels whose definition according to NACE MR0175 is 5% max. Since, our proposed material has 9% chormium, it does not fall under this category. However, as per ASME Sec II, Part A, this material falls in low and intermediate alloy elements. I am confused now.
Should I give any explanation to client or is the client right in this.

 

[EdStainless]

The ASME tube specs all have a 90HRB max in them for the common 300 alloys, which is way below the HRC22 max that used to be in 175 for these alloys.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

 

[vessexst]

@weldstan

Oh I see. Means, apart from mandatory pwht requirements as per ASME Sec VIII, Div 1, there no other heat treatment requirements for the use of Austenitic SS materials as per NACE MR0175

 

[r6155]

Stress relieving is required for cold forming parts if outer fibre deformation is greater than 5 %.

See NACE MR0175, NACE MR103 and ASME VIII-Div 1

I insist "It is the equipment user's responsibility to select materials suitable for the intended service", see NACE MR0175, NACE MR103 and API RP 941 Do not waste time.-

Regards

 

[davefitz]

480C ( 896 F) is not really high temperature, and P91 is typically used in the temperature range 950-1150F (510-621C). There are 2.25% Cr materials that work fine at 480C. The bigger issue may be the mechanical design of the heater, as the temperature difference implies thermal stresses if a tubesheet is used. You may wish to consider a "header type" heater , in any case , consider thermal stresses at tube joints.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[vessexst]

Moreover, as per UCL 34, it gives an advisory note for "unstabilized" Austenitic steels. I did some research and found out that 321 and 347 are "stabilized" grades. But, I dont know where does ASME code classify grades to be "stabilized" and "unstabilized"
Can anyone tell??

 

[r6155]

See ASME II, obviously.

Regards

 

However, we had preferred P91 then due to its higher allowable stress.

When it comes the strength, sometimes more is less. 'More is less' is in fact the history of P91.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[vessexst]

@r6155: I looked into ASME Sec II, Part A. It does explicitly classify stabilized and unstabilized grades

@iron metallurgist: Ohhh

 

[r6155]

vessexst:
Look again (pay attention Titanium and Columbium)

Regards

 

[vessexst]

@r6155: Can you please share the clause where I should read it again?

I read it at many places in ASME Sec II, part A that 327, 347 and some other grades shall be exposed to stabilization treatments.

However, it's just like, I want to convey a client that these are stabilized and unatabilized grades and this is the code reference, which calls 316L as unatabilized while 347 as stabilized.

 

[r6155]

vessexst:
I gave you the keywords to find what you are looking for. I understand that you are an engineer and must know how to investigate with those words. It seems that you are comfortable.

You must make minimal effort. We are working free for you.

Now I give you 3 keywords and you should find where they are in ASME II: stabilized stainless steel

Regards