DLR according to Appendix F API STD 650

[hamidun]

Dear All,

As per F.4 API STD 650, DLR is defined as "the nominal weight of roof plate plus any structural members attached to the roof plate"

Does the structure below roof plate is considered as "any structural members attached to the roof plate"? E.g Roof Structure.

Or the statement only applies the structure above the roof plate? E.g Roof walkway, Roof platform, etc

Help please! Thanks!

 

[JStephen]

Loose rafters below the roof plate are not part of the DLR.
Rafters on top of the roof plate, rafters below the roof plate and welded to it, umbrella stiffeners attached to the plate, would be a part of the DLR.

 

[hamidun]

Alright, so the structure that is not welded to the roof plate is not part of DLR.

Antoher question, from formula F.4.1 Appendix F API STD 650, what would be the slope of the roof if the tank is a dome roof tank?

Because I am not sure either the slope is the triangle of the dome roof or there is another way to calculate slope of dome roof?

 

[JStephen]

I don't have the code in front of me, but the formulas requiring slope of a dome roof would use the slope measured where the roof intersects the shell. Not sure if this is the "triangle" mentioned or not.

 

[IFRs]

Just in case you were concerned that the roof structure was not accounted for, the roof structure supported by the shell and not attached to the roof plate is part of MDL

 

[hamidun]

JStephen,

I attach sketch of the dome roof, what would be the slope of the roof as per F.4.1 formula?

IFRs,

Yeah, in my case the roof structure is attached to the shell but not welded to the roof plate, once again, is the roof structure considered as part of MDL?

 

[IFRs]

You need another angle, taken at the shell to roof junction.
This angle can be calculate as the ArcSin ( Tank Radius / Dome Radius ) = asin(24255/58242) = 24.61 degrees

Confirming what was said above, roof structure is only part of DLR if it is attached to the roof plates and only the portion of the roof structure that is supported by the tank shell is included in MDL.

Hope these help, remember, you read it on the internet !!!

 

[hamidun]

IFRs,

Attached photo is the structure detail, with the configuration shown, can we consider the roof structure is part of DLR?

Basically, i want to evaluate the maximum design pressure as per F.4.1, so i need to be clear on this. Thanks!

 

[Geoff13]

The detail shown doesn't provide the info needed to decide if the rafters are included in D[sub]LR[/sub].

As noted by JStephen and IFRs above, if the rafters are loose (not welded to the roof plate) then they are not part of D[sub]LR[/sub] for the F.4.1 calculation.

 

[hamidun]

Geoff13,

All parts are welded, except the connection between roof structure to the gusset plate (bolted connection) and roof plate to the roof structure (roof plate only lies on the roof structure).

 

[IFRs]

The roof structure is not connected to the roof plate, therefore the roof structure is not included in DLR.

 

[hamidun]

Alright thanks IFRs.

When the roof structure is supported by the shell, it is included in MDL not DLR.

I was a bit confused between MDL and DLR but for F.4.1, DLR is used and in my case, the roof structure is not connected to the roof plate, so the roof structure is not included in DLR.

OK, now I got it!

 

[michek]

Dear All,
When you calculate the failure pressure $F.7 per API650 Addendum 3, shall we consider the value we calculated in F4.1?

And in my case, the failure pressure is less than the maximum design pressure calculated in F4.1...

It seems to me weird.. Did you experience that?

Thanks

 

[JStephen]

The failure pressure should always be higher- double-check the units used.
The failure pressure equation is basically adjusting top angle compression from allowable to yield/failure, and the dead load part is just adjusting dead load back to where it was to begin with- so it should never be lower than calculated allowable pressure.

 

[michek]

Thanks for your reply.
In SI units : I used
Pf in KPa
P (calculated in F4.1 ?) in Kpa
Dlr in N
D in meters
Am i right?

 

[michek]

The formula in SI units is wrong..... When i use USC units, my failure pressure is upper than the maximum design pressure calculated.

 

[IFRs]

Which formula in particular? Which edition / revision of the code? If the SI formula is wrong let's bring it to the attention of the API. In your F.4.1 calculation, are you using degrees or radians? What units are you using for A and Fy?

 

[michek]

Hi IFRs,
The edition is API650 twelfth edition Addendum2, January 2016.
In F4.1 in SI units :
I used :
A in mm²
Fy in Mpa
theta in degrees
D in meters
Dlr in Newton

In F.7 in SI units
i used :
P in kPa
Dlr in Newton
D in meters

An other question, in USC units for annex F, which unit shall we use for the diameter (feets?) for all of the formulas?

 

[IFRs]

Diameter is in feet like 100.65

 

[JStephen]

Speaking of corrections in the standard- I just noticed that the USC units equation for self-supporting cones is actually the umbrella equation.