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Amine Service Tank

Friday, March 04, 2005   By: Josias Tatontos
The cylindrical tank OD 6100 mm, Height 7700 mm, Plate A 283 C, design pressure 0.427 psig, temp 200 F service : Amine with sp gr 1.002. If the tank use plate 6 mm, the hardness 200 BHN (weld) 225 BHN (HAZ) after PWHT. Our question is if we do the PWHT anybody know how to PWHT this tank, it is use the electric heater type to all the weld seam simultaneously, what is the temperature because the plate is only 6 mm. Thank you

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Sunday, March 06, 2005   By: www.thill.biz
Postweld Heat Treatment This operation can be defined as the heating of weldments immediately after welding in order to temper, stress relieve, or provide controlled cooling. It prevents the formation of hard or brittle structures prone to cracking in services. Postweld heat treatment is mandatory for certain alloys, combinations or alloys, and material thicknesses as outlined in the various codes and standards, such as ASME Section VIII Pressure Vessel Code. Consequently, welding procedures for such materials and/or thickness will contain the provisions for heat treatment. Fabricators may have difficulty with prostweld heat treatment due to shop practices rather than the treatment itself. Cracking can occur in vessels that are held for heat treating until a full furnaces load is ready. In general, at normal heat treating temperatures the time at temperature is specified as one hour per 1 in. (25 mm) of maximum thickness for vessels up to 2 in. (50 mm) thickness fabricators may suggest that since the component is being heated form both sides half-an-hour at temperature for each 1 in. (25) thickness is sufficient – but the one hour requirement should be maintained. For vessels over 2 in (50 mm) in thickness, the usual holding time is two hour plus 15 minutes for each additional 1 in. (25 mm) over the 2 in. (50 mm) thickness. Again, some fabricators may want to cut this time by half since the component is being heated form all sides. Holding time may be an accumulation of multiple heat-treat cycles. It dose not necessarily have to occur all at one time. Care must be taken to ensure that the accumulated time at the correct temperature equals that required to effect the desired treatment. There is a maximum furnace temperature for introduction of the vessel. This varies with the alloy but is generally 800º F (426º C) for carbon steels. Heating rate vary with alloy as well but are usually in the 200 to 400º F (93 to 204º C) range. Some manufactures will try to heat as rapidly as possible in order to reduce the time required. Cooling is normally performed in the furnace at a controlled rate unless the component si to be quenched. If quenching is performed then the component must be removed form the furnace and quenched as quickly as possible. Delays will cause such problems as carbide precipitation in austenitic alloy and reheat treatment will be necessary.

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Saturday, March 05, 2005   By: Stephen H
As far as I know, a "Stress Relief" would generally be at the same temperature, that is about 1200 F. You normally vary the time required to adjust for plate thickness, but temperature doesn't vary that much. If you're trying to maintain a maximum hardness on the welds, you should be able to make some weld samples, and try PWHT in a lab furnace to see if it gets the results you want.

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Saturday, March 05, 2005   By: ADI HAR-SHOSHAN
What is the reason that you have done PWHT?.

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Saturday, March 05, 2005   By: Josias Tatontos
Ownel spec call for it. Also In The OSHA technical manual Setion IV Chapter 3 there is possibility of cracking of carbon steel in an amine environment.

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Friday, March 04, 2005   By: Stephen H
I've never been involved on that kind of job. But I do recall quoting a tank or two that was to be stress relieved. Seems like there was a company called Cooperheat that we got pricing from. If I remember right, they quoted either the electrical heaters like you are mentioning, or the alternative to insulate the outside of the tank and heat the whole thing with fuel-fired heater through a manway. This was on a somewhat smaller tank than yours, but still field-erected. And this was maybe 15 years ago.

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Saturday, March 05, 2005   By: Josias Tatontos
Thank you for the response. Yes we can fired through the manway, several weeks ago i saw in Jambi Indonesia, CBI doing the stress relieve by firing through the manway but the tank is spherical and the thickness about 50 mm. Our question is if the plate is only 6 mm what is the temperature for stress relieve. thank you

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Sunday, March 06, 2005   By: Lawrence
The temperature cannot exceed critical temperature otherwise the ferrite begins to transform to austenite; of course it will transform back on cool down, but if this is not done right you could end up with martinsite or banite. Since the tank is very thin there is a higher probability. You tank wall is thin and will heat up very quickly. Must have excellent contols. Never exceed 1100F with this material and you must keep it at 1-hour and 15-minutes to be effective. Consult with a metallurgist who has experience with heat treatment. Lawrence

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Monday, March 07, 2005   By: Stephen H
API-650 specifies 1200 F for 1 hour/ inch, for stress-relieving insert plates or nozzles. This is not necessarily aimed at producing a specific hardness in welds, however. But that range should be acceptable for any of the allowable plate materials in API-650.

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Published on ast-forum.com


Atmospheric Design Pressure
By: Fathi [46]

The whole story is to avoid brittle fracture=

Test temperature shall be equal or warmer than Minimum Metal Design temperature at Test pressure.

I would limit my minimum testing temperature for a tank (or even for a vessel or a piping system) by the =

Temp = maximum of [ Min(lower shell) , Min(shell# 2) ....Min (Upper shell) ]

For a Shell# i the minimum is function ( of shell tickness , Material group ) and this can be found in API 650 , Fig 2-1

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