MDMT of Ammonia reservoir

[tosif]

Guys, I am stuck with an issue with an Ammonia storage vessel at our site. MDMT of that vessel is 59 F as per datasheets. And we are storing Ammonia at 30 F. I have following queries;
- Is there any impact on the metallurgy of Vessel due to exposure to this much low temperature?
- We have installed a line of cold Ammonia @ -18 F at the top nozzle of this vessel. Does any one say the possibility of any damage to vessel or nozzle?

The construction material of vessel is plain carbon-steel.

[sadia.shahab]

Please provide the material thickness or all design paramerters so that i can design & check for impact test. Material of construction is SA-516 Gr. 70 or SA-516 Gr. 70N? What is Design code?

There may be possibility of brittle fracture at -18°F if rated MDMT of respective nozzle is higher than -18°F (say -10°F, -5°F). Please provide the nozzle size/Nozzle Sch /Mat of construction.

[tosif]

Design code: ASME Sec. VIII Div. 1
Design Pressure: 250 psig
Design Temp.: 450 F
Shell: A-515 gr. 70
Nozzle: A-53 gr. B, 2", 300# rating, 0.436"
I hope this is the required information.

[sadia.shahab]

Corrosion Allowance, diameter of shell? Actually m going to design the vessel to find its rated MDMT. If Vessel nominal thickness is avaiable, please provide thickness only.

[sadia.shahab]

For nozzle MDMT -105°C & FLANGE MDMT -48°C...so impact test is not required for given MDMT i.e. -18°F (-28°C)....

[sadia.shahab]

For vessel MDMT, please provide the head & shell nominal thk.
at 12thk shell plate rated MDMT is -29°C....Above this MDMT will be higher (-12.56°C etc)...But the main factors will be head n shell used thickness. So MDMT reduction can be calculated.

[ashfaqanwer]

According to the given info, please see my comments below:
1. MDMT of nozzle is about -13 deg F; following curve B of Fig. UCS-66 for A-53 gr. B (thk. 0.436")
2. Reduced MDMT can also be calculated as:
tr = 1.27 mm as per ASME VIII Div. 1 (E assumed as lowest 0.7)
tn = 11.0744 mm
tc = 3.175 mm (assumed)
Ratio = tr*E/(tn - tc) = 0.129 < 0.35
3. Following UCS-66(b)(3), to operate this nozzle at -18 deg F, impact test is not required. MDMT can be as low as -155 deg F.
4. Flange of this nozzle if in compliance to UCS-66(c) shall not require impact testing if not to be operated below -20 deg F.

In the light of above, in your case there would not be any problem.
Please note that the above analysis has only been done for nozzle assessment and not for the vessel.

Hope this would help.

[sadia.shahab]

Same are my comments for nozzle and flange that impact test is not required (E should be 1, lethal service + most probably seamless pipe). Now, m only waiting for vessel thickness to calculate vessel MDMT.

[tosif]

thanks alot ashfaq n sadia. So in short you are saying that there will be no issue with this line / nozzle with Ammonia at -18F. And sadia I will be sharing the thickness soon I get to my office.

[engr.abrar]

- No need for impact testing on the nozzle and associated piping at -18F as rate MDMT is -155F for A-53 gr B nozzle as per your defined thickness.
- For shell; thickness will be required for calculation of rated MDMT.