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# In API 650 Edition 13th - (Shell-to-Roof) Junction Area

## In API 650 Edition 13th - (Shell-to-Roof) Junction Area

(OP)
In API 650 Edition 13th

(A) With regard to the (Shell-to-Roof) Junction Area, there are the following expressions;
1. Total Required Compression Area @ Junction calculated as in F.5.1.
2. (F.2.2 &/or F.4.1) stated that Participating Compression Area @ Junction determined by Figure F.2. (Presumed to be the Area Shaded with diagonal lines as stated in F.3).
3. (5.1.5.9 (e)), there are two statement that (Design Effective Area (cross-hatched section of Figure F.2) & Effective Provided Area by the Minimum Top Angle Size.

Quesion.1. From the 2nd & 3rd statements above, I presumed that the Participating Compression Area & Design Effective Area are the same (hatched area as calculated from Figure F.2). Am I correct?
Quesion.2. Effective Provided Area = Ar + As + Aa. Am I correct?

(B) F.5.2 stated For Self-Supporting Roofs, the Compression Area shall be ≥ Cross-sectional Area calculated in 5.10.5 & 5.10.6; however,
Quesion.3. There is Not stated which Specific Compression Area (Total Required or Participating)?
Quesion.4. in (5.10.5 & 5.10.6) there is No statement about how to Calculate this Cross-sectional Area? It’s just stated repeatedly that the Participating Compression Area shall be determined using Figure F.2.

(C) In case of Annex V applied;
1. V.7.2.2 stated the equation for calculating the Total Required Cross-sectional Area (Areq) in Cone Roof-to-Shell Joint Region.
2. V.7.2.5 stated the equation for calculating the Required Cross-sectional Area (Astiff) of Top Stiffener Structural Shape
Quesion.5. In such case which one will be applied, meant, either Total Required Compression Area as calculated in F.5.1 or in V.7.2.2?
Quesion.6. In such case which one will be applied, meant, either Required Cross-sectional Area as calculated in (5.10.5 & 5.10.6) or in V.7.2.5?

Mohd Yaseen

### RE: In API 650 Edition 13th - (Shell-to-Roof) Junction Area

Question 1: Yes, but it's not clear if this is applied to the as-built construction or the corroded construction.
Question 2: Total area = participating roof area + participating shell area + area of angles/bars included as shown in F.2.
Question 3: The participating area per Figure F2 needs to be greater than the minimum calculated per 5.10.5 and 5.10.6 (nearly always is, in my experience)
Question 4: What is it that's not clear in Figure F.2?
Questions 5 and 6: The area determined similarly to Figure F.2 needs to exceed the minimums calculated in Annex V- Except that V.5 says to use as-built rather than corroded properties for this check, so the actual numbers may be different.

To summarize how I understand the requirements:
-Normally, you use a top angle of the minimum size specified. If you want to use one of the other details in F2 instead of a top angle, you can. But calculate the area per F2 using a standard top angle, and make sure the area using your detail is at least that large.
-If you have a self-supporting cone roof or self-supporting umbrella roof, calculate the minimum area required per that section, calculate the area in your detail per F.2 and make sure you have at least that area.
-If you have a pressurized roof falling under Annex F, calculate the area required per Annex F, and make sure your proposed detail has at least that much area per Fig. F2.
-If you have partial vacuum falling under Annex V, calculate the area required per Annex V, and make sure your proposed detail has at least that much area per F.2.
-And, not mentioned above, if you want a frangible roof, there is also a maximum area calculated that you cannot exceed.

### RE: In API 650 Edition 13th - (Shell-to-Roof) Junction Area

(OP)
Dear Stephen;

Thanks for sharing your valuable ideas;

Following is my commentary to your responds;

Question 1: I presumed you meant Nominal THK for your stated expression of As-built THK. Whereas Total Required Compression Area as calculated in F.5.1 is based on Corroded THK, then I presume the Participating Compression Area (Design Effective Area) should be based on Corroded THK also.

Question 2: I guess that you have indicated Provided Area as Total Area.

Question 3: That mean the Compression Area referred to @ F.5.2 is the Participating Compression Area.

Question 4: I will rephrase question as follow: (Clause F.5.2 stated that For Self-Supporting Roofs, the Compression Area shall be ≥ Cross-sectional Area calculated in 5.10.5 & 5.10.6. The question is; when revert back to 5.10.5 & 5.10.6, you will NEVER FIND how to calculate the Cross-sectional Area ?)

Question 5&6: Can I summarized that the Area calculated in other sections MUST be Larger than (or equal) the Area calculated in Annex V as long its applied.

Summary Points:
- calculate the area per F2 using a standard top angle. Would you explain what you mean by calculate using a standard top angle?

Mohd Yaseen

### RE: In API 650 Edition 13th - (Shell-to-Roof) Junction Area

"calculate the area per F2 using a standard top angle. Would you explain what you mean by calculate using a standard top angle?"

How I understand that requirement:
Assume you used the standard minimum top angle size (2"x2"x3/16" or whatever). Calculate the total effective area per the applicable F2 detail.
Then take your alternate proposed detail. And calculate total effective area per the applicable F2 detail for it.
And your alternate detail has to have at least as much area as that using the minimum angle.

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