The allowable stresses for checking body flange, tubesheest in hydrotest test pressure 1

[mechengineer]

Dear exoerts,

1. Any idea to determine the allowalbe stresses, such like bending, shear & compressed for checking body flange, tubesheest & tube in hydrotest test pressure?
2. Any requirement for checking the stresses due to hydrotest pressure for pressure components from code?
Design Code: ASME VIII.
Thanks in advance.

 

[r6155]

Is ASME VIII Div 1?
0,90 YS

Regards

 

[TGS4]

I will echo r6155's initial question - what is your Code of Construction?

However, r6155 has it completely wrong for ASME Section VIII, Division 1. In fact, there are no limits on the stresses during the test condition for this Code, see the sentence in UG-99(d) (bold-typing is mine):

(d) The requirements of (b) above represent the minimum standard hydrostatic test pressure required by this Division. The requirements of (c) above represent a special test based on calculations. Any intermediate value of pressure may be used. This Division does not specify an upper limit for hydrostatic test pressure. However, if the hydrostatic test pressure is allowed to exceed, either intentionally or accidentally, the value determined as prescribed in (c) above to the degree that the vessel is subjected to visible permanent distortion, the Inspector shall reserve the right to reject the vessel.

However, if your Code of Construction is ASME Section VIII, Division 2, then there are limits specified in 4.1.6.2. Sub-paragraph (b) would be applicable for limits on bending in the body flange, tube, and tubesheet during the test condition. Note that the limits are applicable to P_m and P_m+P_b only, and there are no specified limits for any other stress categories - for reference, please see 5.2.2.5.

 

[r6155]

The (OP) is talking about the stress limit, not the pressure test limit.
How do you plan to control the stresses during the pressure test?.

Regards

 

[mechengineer]

@TGS4, You got my point and thanks for your input.
What my thinking is as the following,
1. For the primary membrane stress. No stress checking is required for hydrotest if the test pressure does not access the code requirement in UG-99. However, it must check if the test pressure accesses the one code given in UG-99. The basis is that 1a. the primary membrane stress in the inner surface of the cylinder wall may not be possible to reach 0.9 yield stress according to the design margin of the allowable stress (minimum of 2/5 of tensile strength and 2/3 of yield stress, ASME VIII-1) and the test pressure (1.3MAWP). In another word, the design margin of allowable stress is lager that 1.3 of the factor of test pressure.
2. For local stresses and non-cylinder shape pressure parts. The primary membrane tress is more important than bending and local stresses. According to the same principle of the above item 1, the stresses checking for hydrotest pressure as per UG-99 is not required.
In view of the above 1 & 2, that may be why code does not have the special requirement to check the stress for hydrotest.
Solution: The hydro-test stresses checking is not required if the test pressure within code requirement.
Please correct me if I am not correct.

Thank you

 

[r6155]

You can pressure test as high as you like, if the inspector agrees. Both should be accountable to the user.
Try to do a pressure test that doesn't change from NDE to DE (destructive examination).

Regards

 

[TGS4]

r6155 - I am fully aware that the OP is asking about the stress limit. There is no stress limit during the test condition for ASME Section VIII, Division 1 construction. Period. Full Stop. There is no 90% of yield limit or anything of such sort.

For Section VIII, Division 2 construction, the stress limits in the test condition are provided in 4.1.6.2. Only the stress categories listed in 4.1.6.2 have limits - the other stress categories have no prescribed limits.

mechengineer - you are essentially correct, excepting that there is no limit on the stresses during the test condition in VIII-1. There is not permitted to be excessive permanent deformation, which leads one to practically implement a reasonable limit.

 

[SnTMan]

The 90% of yield limit is found in many client specs, but not in Div 1.

mechengineer, if your design is firmly within Div 1 rules, with no unusual details and without an unusually high hydrotest pressure there is no reason to be concerned about stresses at hydro or calculations of the same.

Regards,

Mike


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

 

[TGS4]

Thanks Mike. The 90% of yield comes from owners looking to the pre-2007 VIII-2 for guidance (when VIII-1 provided no guidance), which had that limit. The comparable limit in the post-2007 VIII-2 is now 95% of yield. Note that B31.3 has 100% of yield.

(Aside: In all of these cases, yield refers to engineering yield, which is based on the 0.2% offset method.)

 

[SnTMan]

TGS4, I'll take your word for that

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

 

[mechengineer]

@TGS4,
But I think to apply 0.9 yield for VIII-1 will be conservative and safe to compare "There is no stress limit during the test condition for ASME Section VIII, Division 1 construction" in practice and theory. Do you think so?
Thanks.

 

[TGS4]

mechengineer - that would be your engineering judgement. As SnTMan noted, many owners around the world have also adopted such a limit for their equipment, as well, based on their engineering judgement.

 

[r6155]

@ TGS4
Please, for a moment, imagine this situation: you are the inspector during the hydrostatic test, ASME VIII Div 1 UG-99(c), the pressure test is 1000 psig.
Perhaps there is someone who wants to increase the pressure.
If so: how do you act?

Thank you

Regards

 

[TGS4]

r6155 - insufficient information for your hypothetical. What's your real question?

 

[mechengineer]

@TGS4,

Code requiremwnt is the minimum requiremewnt. May we take U-99 (d) as the minimum requirment of UG-99 (b), (c) & (d)?
UG-99 (d):
(d) The requirements of (b) above represent the minimum standard hydrostatic test pressure required by this Division. The requirements of (c) above represent a special test based on calculations. Any intermediate value of pressure may be used. This Division does not specify an upper limit for hydrostatic test pressure. However, if the hydrostatic test pressure is allowed to exceed, either intentionally or accidentally, the value determined as prescribed in (c) above to the degree that the vessel is subjected to visible permanent distortion, the Inspector shall reserve the right to reject the vessel

Thanks.

 

[TGS4]

Indeed you have replicated UG-99(d), as I did too previously. I just don't necessarily understand your point. The Code contains minimum requirements - throughout the book. Beyond that, engineering judgement needs to apply, which properly ought to be situational-specific.