Normal Upper Temperature - Piping Stress Analysis 1

[Al1Al]

In accordance with ASME B31.3, does the phrase “maximum metal temperature...for the thermal cycle under analysis” in para. 319.3.1(a) require the use the normal upper temperature under operating conditions, and exclude all short-time excursions above such normal operating temperature in “determining total displacement strains for computing the stress range” ?

 

[XL83NL]

I would think that if these short-time excursions could affact the metal temperature and therefore increase the max metal temperature, they shall be considered in the analysis.
Provisions and requirements from para 302.2.4 can provide you direction into this.
However, Im not expert, so maybe the more expereinced piping engineers here can weigh in and add their 2 pennies to confirm my post or correct my interpretation.

 

[BigInch]

Don't over-complicate the code. Maximum metal temperature is the maximum metal temperature.

Independent events are seldomly independent.

 

[Al1Al]

Sometimes the maximum operating temperature can not be calculated accurately, the maximum operating temperature should be determined by adding a safety margin to the operating temperature (50ºF). Often this maximum operating temperature with adding a safety margin is the design temperature.
However, in accordance with APPENDIX S (ASMEB31.3) for computing the stress range is calculated with the maximum operating temperature without adding a safety margin.

 

[Al1Al]

How to ensure that the temperature is truly the maximum temperature without adding a safety margin?

 

[BigInch]

Don't confuse process issues with pipe stress, or how the design temperature is selected.
If you can't calculate the temperature, then select whatever temperature is required to make the stress calculation conservative. That value will then become the design temperature. Whether the maximum temperature has a safety factor or not isn't important for pipe stress purposes. The design temperature is the design temperature.

Independent events are seldomly independent.

 

[TD2K]

As Big Inch said. The 50F margin you mention Al1Al is often added to cover changes that can be expected as a result of normal operations or uncertainity in the original design.

If you have access to good data, you don't have to add any margin to the expected maximum temperature. Depending how good is your data or how confident you feel about your calculations, you may want to add a margin to your calculated maximum temperature which can be what you think is reasonable or prudent. That temperature then becomes the temperature you use in your calculations.

 

[Al1Al]

OK. When you have access to good data, you don't have to add any margin to the expected maximum temperature.
But, in this case, the maximum temperature of operation is the design temperature. Considering this maximum temperature operating is the temperature at which, under the coincident pressure, the greatest thickness or highest component rating is required in accordance with para. 301.2. (In some cases, the design temperature is not the worst case temperature. But, in this case, the design temperature is the worst case temperature.)

So, when you don't have access to good data, you have to add any margin to the expected maximum temperature. However, in Appendix S, the stress range is calculated with the maximum operating temperature without adding a safety margin. But, the maximum operating temperature + 50ºF is the design temperature.

 

[BigInch]

Don't let the process guys jive you.
There is only one relevant temperature.
Decide what it is and use it.

Independent events are seldomly independent.

 

[pennpiper]

My opinion:
Use Design Temperature (DT) for pipe wall and flange rating selection only.

Use Operating Temperature (Min/Max) (OT) for pipe stress analysis calculations.

Using Design temperature for pipe stress analysis results in unnecessary over design and inflated costs to the project. The Pipe Stress Engineer does not have the authority to do that on his/her own.
When you start a project you should clear this issue with the Client. If the Client fully understands the Piping Code does not require pipe stress analysis based on DT and understands the potential for increased cost and yet still wants the DT used then use it, but write it into the contract Scope of Work (SOW).

prognosis: Lead or Lag

 

[BigInch]

OK why not. If the line cools from one end to the other, you could set design temp as the highest temperature and even use the temperature profile for stress analysis.

Independent events are seldomly independent.

 

[Al1Al]

In accordance with "ASME B31.3 Process Piping Course" (Charles Becht IV and Don Frikken):

Temperature Range

- Minimum temperature may be due to
• Normal operation
• Excursion operation
• Expected winter temperature

- Maximum temperature may be due to
• Normal operation
• Excursion operation
• Piping exposed to hot summer sun [120ºF,50ºC]
• Empty piping exposed to heat tracing
• Steam cleaning

 

[Al1Al]

OVERVIEW OF PROCESS PLANT PIPING SYSTEM DESIGN (Vincent A. Carucci)

Piping Flexibility Temperature
• Analysis based on largest temperature difference imposed by normal and abnormal operating conditions


Stable Operation - Temperature range expected for most of time plant is in operation. Margin above operating temperature (i.e., use of design temperature rather than operating temperature) allows for process flexibility.

 

[Al1Al]

Charles Becht IV
"It is common to evaluate piping flexibility for the design temperature, but it is not a Code requirement. It is certainly permitted, but in all cases, the worst case temperature conditions must be evaluated. For example, the temperature may be higher during a low pressure steam out than the design temperature. Consider another example with two operating conditions with a carbon steel line, 100 kPa (15 psi) at 315EC (600EF) and 1400 kPa (200 psi) at 205EC (400EF). The design condition would be 1400 kPa (200 psi) at 205EC (400EF) since that governs the pressure design. However, the 315EC (600EF) condition would govern in the flexibility analysis."

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Escoe: Piping and Pipeline Assessment Guide
It is not a code requirement to assess the piping system at the “design” temperature. Although it is permitted, it may not represent the worst (high or lowest) temperature. Consider, for example, a low pressure steam out where the temperature may exceed the design temperature.

 

[Al1Al]

In para. 319.5 - ASME B31.3
...The designer shall consider instantaneous maximum values of forces and moments in the original and extreme displacement conditions (see para. 319.2.3),...

 

[Al1Al]

In accordance with ASME B31.3, does the phrase “maximum metal temperature...for the thermal cycle under analysis” in para. 319.3.1(a) require the use the normal upper temperature under operating conditions, and exclude all short-time excursions above such normal operating temperature in “determining total displacement strains for computing the stress range” ?

I think that the reply: "No"


In accordance with ASME B31.3, does the phrase “maximum metal temperature...for the thermal cycle under analysis” in para. 319.3.1(a) require the use the normal upper temperature under operating conditions, and include all short-time excursions above such normal operating temperature in “determining total displacement strains for computing the stress range” ?

I think that the reply: "Yes"

 

[SNORGY]

It is AI1AI's post that makes me think the temperature profile idea is closest to truth. Let the Process people spit out the temperature-versus-time (or versus position, or both) data from HYSIS in dynamic mode (or other suitable Process-driven simulation method) and then let the Mechanical people model that profile in CAESAR II (or other). The "instantaneous" temperature near the outlet of a hot PSV into a flare header, for example, is not the instantaneous temperature seen at the knockout drum inlet, for example. As always, some judgement has to be applied.

 

[Al1Al]

In accordance with ASME B31.3, does the phrase “maximum metal temperature...for the thermal cycle under analysis” in para. 319.3.1(a) require the use the normal upper temperature under operating conditions, and include all short-time excursions above such normal operating temperature in “determining total displacement strains for computing the stress range” ?

I think that the reply: "Yes." When the normal upper temperature under operating conditions include all short-time excursions above such normal operating temperature is “maximum metal temperature"

 

[Al1Al]

In accordance with ASME B31.3, does the phrase “maximum metal temperature...for the thermal cycle under analysis” in para. 319.3.1(a) require the use the normal upper temperature under operating conditions, and include all short-time excursions above such normal operating temperature in “determining total displacement strains for computing the stress range” ?

I think that the reply: "Yes." When the normal upper temperature under operating conditions include all short-time excursions above such normal operating temperature and represent the worst (high) temperature. The normal upper temperature under operating is “maximum metal temperature"

When the normal upper operating temperature include margin above operating temperature may be lower than other case temperature(i.e., piping exposed to hot summer sun, empty piping exposed to heat tracing, steam cleaning, etc, it is not the worst (higher) temperature. Then normal upper operating temperature include margin above operating temperature is not “maximum metal temperature". And the reply will be "NO"

 

[Al1Al]

ASME B31.3.

Interpretation: 7-04

Question : In accordance with ASME/ANSI B31.3, para. 302.3.5, should the basic allowable stress at maximum metal temperature Sh used for calculating the allowable displacement stress range,be for the normal upper temperature under operating conditions, and exclude all short-time excursions above such normal operating temperature?
Reply : No. In accordance with para. 319.2.3, the allowable displacement stress range is based on the maximum and minimum temperatures for the displacement cycle under analysis.


Interpretation: 17-07

Question: In accordance with ASME B31.3b-1997. para. 301.3. should fire case temperature or pressures be considered to satisty, the requirements of para. 301.2. in establishing the design conditions of piping that may be exposed to an accidental fire?
Reply: The Code does not require the consideration of accidental fire cases when establishing the piping design conditions. except as required to meet the pressure relief requirements of para. 322.6.3. See also para. 300(c)(5).


Interpretation: 19·40

Question: In accordance with ASME B31.3-2002, does the phrase "maximum metal temperature...for the thermal cycle under analysis" in para. 319.3.1(a) require the use of the design temperature (defined in accordance with para. 301.3) in "determining total displacement strains for computing the stress range" SE?
Reply: No.