allowable stress- design temperature 1

[212197]

I have to design tank. Design temperature minus204 to plus 46 degree Celsius. material is SA240 GR 304L. code is ASME SEC. VIII DIV1. I have 2 questions :

1)please guide whether Allowable stress which I have to use for calculating thickness is to be taken that of plus 46 degree Celsius. This is based on my interpretation of following code para.

UHA-23 MAXIMUM ALLOWABLE STRESS
VALUES
((c) For vessels designed to operate at a temperature
below −20°F (−30°C), the allowable stress values to be
used in design shall not exceed those given in Table 1A
or 3 of Section II, Part D for temperatures of −20°F
to 100°F (−30°C to 40°C).

2) when we have maximum & minimum design temperatures, which is to be considered for knowing the allowable stress?

 

[XL83NL]

1) No, it shall be the values outlined for -30 ÷ 40 °C, as per your reference of UHA-23. Not 46 °C, but I assume you made a typo.
2) Normally the max. design temp. determines your max allowable to use stress. I cant think of a situation where the lowest design temp. determines the max allowable stress.

 

[212197]

Thanks XL83NL (Mechanical).

So in my case I have to take allowable stress value given in IID for temperature -30 to 40 degree celcius.& not that of plus 46degree celcius.

 

[XL83NL]

Correct acc. UHA-23. Where did you find the value 46 °C?

 

[212197]

by interpolation

 

[SnTMan]

" For vessels designed to operate at a temperature
below −20°F (−30°C), the allowable stress values to be
used in design shall not exceed those given in Table 1A
or 3 of Section II, Part D for temperatures of −20°F
to 100°F (−30°C to 40°C)."

If the allowable at 46C is less than the allowable for −30°C to 40°C you must use this lesser value.

Regards,

Mike

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

 

[XL83NL]

SnTMan is correct. Not sure where I was with my head.

 

[SnTMan]

It's early

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

 

[212197]

SnTMan (Mechanical)- Thanks.

In all cases as the design temperature increases, allowable stresses will be reduced.
That means when there is maximum temperature & minimum temperature, we have to consider allowable stresses at maximum temperature. Is this the simple rule to be followed?

 

[SnTMan]

212197, yes, see UG-23(c), last paragraph.

Regards,

Mike

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

 

[212197]

SnTMan (Mechanical)- Thanks a lot for your guidance.