5 replies to this topic

[wenchop]

The pressure considerations section of API 521 6TH ED states:

 

"...each exchanger type should be evaluated for a small tube leak."

 

Does this mean that every shell and tube heat exchanger shall be analyzed for this relief scenario even though pressure relief for tube rupture is not required?

 

 

[Erwin APRIANDI]

Hi magonz,

 

How you can say that "pressure relief for tube rupture is not required"

Evaluation of pressure relief scenario are to be considered for any possibility

Then based on the calculation of all the possible rates you get the maximum rate which you will be using to size the PSV.

[wenchop]

I did not say it.

 

API 521 6th edition, pp. 55 :  "Pressure relief for tube rupture is not required where the low-pressure exchanger side (including upstream and downstream systems) does not exceed the criteria noted above."  

 

Anyway, you did not address the OP. 

[Erwin APRIANDI]

Hi magonz,

 

It is better to quote the sections as whole, since in the code first explain what criteria you have to pass first before you can say the shell and tube does not required for tube rupture case either it is small or full bore (purple wordings).

 

And further in the second part they explain that user MAY perform detailed analysis, and the analysis should use a small tube leak, and this is not for relief rate determination but rather for mechanical analysis and etc (red wordings).

 

Sorry took a while to reply, and hope I have clarify your doubt, and feel free to ask further

 

---------------- API STD 521 6th ED --------------------

 

Complete tube rupture, in which a large quantity of high-pressure fluid flows to the lower-pressure exchanger side, is

a remote but possible contingency. Minor leakage can seldom overpressure an exchanger during operation, however

such leakage occurring where the low-pressure side is closed in can result in overpressure. Loss of containment of

the low-pressure side to atmosphere is unlikely to result from a tube rupture where the pressure in the low-pressure

side (including upstream and downstream systems) during the tube rupture does not exceed the corrected hydrotest

pressure (see 3.1.22 and 4.2.2). The user may choose a pressure other than the corrected hydrotest pressure, given

that a proper detailed mechanical analysis is performed showing that a loss of containment is unlikely. The use of

maximum possible system pressure instead of design pressure may be considered as the pressure of the highpressure

side on a case-by-case basis where there is a substantial difference in the design and operating pressures

for the high-pressure side of the exchanger.

 

Pressure relief for tube rupture is not required where the low-pressure exchanger side (including upstream and

downstream systems) does not exceed the criteria noted above. The tube rupture scenario can be mitigated by

increasing the design pressure of the low-pressure exchanger side (including upstream and downstream systems),

and/or assuring that an open flow path can pass the tube rupture flow without exceeding the stipulated pressure, and/

or providing pressure relief.

 

The user may perform a detailed analysis and/or appropriately design the heat exchanger to determine the design

basis other than a full-bore tube rupture. However, each exchanger type should be evaluated for a small tube leak.

The detailed analysis should consider the following:

a) tube vibration,

b] tube material,

c) tube wall thickness,

d) tube erosion,

e) brittle fracture potential,

f) fatigue or creep,

g) corrosion or degradation of tubes and tubesheets,

h) tube inspection program,

i) tube to baffle chafing.

The basis for the analysis should be documented and maintained with the relief system design information, see 4.7.

Edited by Erwin APRIANDI, 06 June 2014 - 03:29 AM.

[wenchop]

API 521:

 

"Should: As used in a standard, “should” denotes a recommendation or that which is advised but not required in order

to conform to the specification."

[Erwin APRIANDI]

Yes I agree, it is a recommendation,

So if you have ensure that tube rupture is not a governing case or it is even not to be considered,

then you can skip the detailed analysis using a small tube leak