It is believed that the 17oC above MDMT would keep the metal temperature above the range where brittle fracture could occur.
It is not a must requirement, it is recommended only as per code.
The two options stated in yr email are not appropriate as putting heating coil inside vessel will require the heating coils withstand the inside hydro test pressure it self.
and placing the heating blanket/insulation around the vessel during hydro test will mask the leakage location.
If we think of a situation as mentioned in your email, the suitable means test would be as mentioned below. (It is an opinion only.)
Step -1 : Place the heating blankates around the vessel to sufficiantly warm up the vesel nearly equaling the test water temperature. The vessel surrounding may be warmed up as an added advantage.
Step -2 : Heat up the test water some what higher then required temperature of testing (i.e. MDMT + 17oC + Additional high temperature required). Putting agents which reduces the freezing temperature of water will be helpful.
Step - 3: Fill the heated water in the vessel and maintain heating up to filling is completed.
Step - 4: Apply hydro test pressure.
Step - 4: Remove the heating blankets from the vessel once the test pressure is reached.
Step -5: Stop the the heating of water once the test pressure is reached.
Step - 6: Start the hydro test immediatelly after step- 5 & 6 are completed and maintain hydro test duration not for too long and sufficient to detect for leaks.
The high temperature heated water will automatically transfer the heat to vessel body and the vessel body & test water both will remain warm through out the testing.
Regards
On Mon, Jul 8, 2013 at 8:09 PM, govindan krishnamoorthy <govindankrishna@hotmail.com> wrote:
--Dear Experts,
Kindly advise on the following Query.
Assuming ASME Sec VIII-Div1 Simple CS Vessel
The MDMT is (-) 46 Deg C. The vessel need to be hydro tested at site. The site ambient temperature is (-) 29 Deg C.
During the hydro test the metal temperature shall be (-) 46+17= (-)29 Deg C, should not be more than 48 Deg C
However the water used for the hydro test will become ice at (-) 29 Deg C.
How to proceed with hydro test?
One way is by means of heated coils placed inside the vessel so that water maintains its fluid state?
One more is by placing heating blanket/thermal pads and perform hydro test to avoid brittle fracture?
Please give your valuable advise on any other way out on this issue with CODE backup.
Thank you in advance.
Regards
Govindan
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