Pipe materials for boilers at low ambient conditions

[coolniks37]

Hi what pipe materials i need to use for boiler piping, in places having low ambient temp?
For example boiler when operating, will have temp, above 500 deg C
But when it is shut down, the piping comes down to ambient conditions say -10 deg C
What ASME Section I or any other codes says about this?
Will th material be prone to brittle fracture then?
What conditions shall be considered and how safety shall be incorporated?

 

[metengr]

ASME Section I does not require notch toughness testing because boilers operate at high enough temperature to avoid the need for ductile to brittle fracture concerns. So, there is no requirement to require low temperature material or notch toughness testing for a boiler. I don't see what the concern is if you use code approved materials and if the line reaches -10 deg C there is no pressure so nothing will happen.

The only concern is for pressure testing. Here, the NBIC provides guidance for elevating the temperature of the water for pressure testing to reduce the risk of brittle fracture. Again, this is a non-operating condition and only relates to pressure testing of weld repairs.

 

[coolniks37]

Hi Metengr for a quick reply..
I understand that boilers operate at high temp. but lets say during a shut down or during erection, or during storage of items at site, if atmpospheric temp falls down , then there is a chance of ductile to brittle fracture..
How it is taken care by code? I think this seasonal variations are common in russia, uk, etc..

 

[metengr]

It is not taken care of or addressed by the code. The chance for brittle fracture occurs when tensile stress is applied at or below the ductile to brittle transition temperature of the component. There should be no tensile stress (hoop stress from pressure) applied when the boiler is off-line.

 

[coolniks37]

i am talking about Nil Ductility point only.. is there a chance of change from ductile to brittle nature.
I believe most materials dont have very low nil ductility point.
COuld you pls give some reference or standards, talking about such temperatures for boiler materials.

have you seen bsen codes which specify some minimum charpy value at -20 deg C ? How to calculate the same for still lower temperatures?
What ASME Section 8 talks about this scenario?

 

[metengr]

Find someone to review ASME B&PV Code so you have a better understanding.

 

[Millar]

Boilers are supposed to be pressure tested at 70F (see PG-99) to avoid brittle fracture concerns during hydrotesting. Pressurizing a boiler - from a practical perspective, you should be using nice warm BFW

 

[marty007]

For brittle fracture to occur, the steel must be under some stress. When you are at atmospheric conditions, there is no pressure inside the vessel and therefore no stress (or minimal...), so no brittle failure.

In ASME VIII-1 this can be illustrated with the MDMT reduction curves of Fig UCS-66.1. If you look at these charts, and consider the no-pressure case, your stress ratio will be 0, and you end up with an allowable MDMT reduction of 140°F. This would provide you an MDMT well below your required -10°C.

 

[weldstan]

ASME VIII does address MDMT. Low ambient temperature without pressurization is not the MDMT; however, it may be if the Purchaser so specifies in the P.O. Brittle fracture wll only occur if the applied and residual load is sufficient as a percent of yield strength at a sufficiently sized and type of discontinuity.

 

[racookpe1978]

-10 deg C isn't all that cold a temperature anyway. MOST important is the "no stress" conditions of erection and construction.

What IS important is the pre-weld, inner-pass, and post-weld temperatures for the welding itself! Those HAVE to be met for every weld regardless of the "pipe" temperature while erecting.