Applying SA 333-6 for MDMT of -49 C 1

[D2HANDLE]

Dear all,

I am currently working on a Process heater which has Nitrogen as the operating medium and operating temp. is -49C. Required MDMT is also -49C.
Vendor has proposed to apply SA 333-6. However, as per ASME Section II Part A, SA 333-6 is impact tested at -45C , so standard SA 333-6 cannot be used for MMDMT of -49C
.
Vendor says that they can impact test the material at -49C and demonstrate the absorbed energy same as mentioned in Table 4 of SA 333 material specification.They are reluctant to apply other grades (which are impact tested for lower temperature, and should ideally have been used...)due to cost and sourcing issues.

Could the esteemed forum members let me know if Vendor's proposal can be accepted?
I read through SA 333 specification, but could not find anything which would suggest that testing at colder temperature is acceptable.

Kindly let me know your valuable opinions.

Thanks,
D2HANDLE

 

[SnTMan]

D2HANDLE, if your Code of construction is Sec VIII, Div 1, then all your vendor is doing is defaulting to and (presumably) complying with relevant parts of UCS-66 and UG-84.

You can actually use SA-333-6 to -48 C per UCS-66(g). It shouldn't be difficult to obtain a 1 degree UCS-66(b) reduction.

Regards,

Mike







The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[marty007]

If you are using ASME VIII-1, the vendor may not even have to perform any additional material impact testing if they can take credit for coincident stress ratios.

Their approach is otherwise completely fine per ASME VIII-1.

 

[r6155]

Vendor says is correct.

Regards
r6155

 

[weldstan]

SA-336 Gr 6 has been used in ASME VIII, Div.1 vessel designs at temps below -49 C and impact tested to meet those temps.

 

[D2HANDLE]

Thanks to all the experts out there...

 

[georgeverghese]

It may not be enough to derive a MDMT based on normal operating temp - what is the minimum temp these heater tubes could see during all operating modes ? - startup and depressurisation modes included.

 

[D2HANDLE]

@georgeverghese,
Thanks for your opinion...
This is an Electrical Heater and shall be used intermittently only when a Compressor on the downstream starts and needs to be supplied with Nitrogen before start-up.Once the Compressor is up and runnning, the Heater will be shut down.
MDMT of -49 has been specified by the Process guys in our team and they said they have considered all possible operating scanarios....

@SnTMan , @marty007
Thanks for your post and valuable opinions...
Yes this Heater is designed asper ASME Sec VIII Div. 1., and of couse I can take credit for UCS-66 (g) and impact test this dowm to -48C... But somehow i think the application of coincident stress ratio is not appropriate.
Please read through UCS-66(b)(1)(a)...
[pre](1) See below.
(-a) For such components, and for a MDMT of −55°F (−48°C) and warmer, the MDMT without impact testing determined in (a) above for the given material and thickness may be reduced[/pre]

So, do you really think this can be applied to this case where MDMT is -49 C??

Regards,
D2HANDLE

 

[D2HANDLE]

I understand that if Code allows SA 333 Gr 6 to be impact tested to -48C, testing and using this material at -49C is no big deal...
The main question that i wanted to have answer to is ....what is the limit????
If there is a case where MDMT is say...-55C or -60C or -75C, can I still apply Gr. 6 if the Vendor is confident of passing the impact test ?
Kindly enlighten me...

Regards,
D2HANDLE...

 

[SnTMan]

D2HANDLE, any material may be impact tested to any temperature and if meeting UG-84 energies may then used at any MDMT no colder than the impact test temperature. This is implicit in UG-84. See also UCS-66(a): '...Fig UCS-66 shall be used to establish impact testing exemptions..."

See UCS-66(i) for reduction of impact tested materials using UCS-66(b).

Regards,

Mike



The problem with sloppy work is that the supply FAR EXCEEDS the demand