API 650 Questions for a newbie 1

[Legoman92]

Hi Gents,

Im a Structural Engineer (Australian) and have a few questions regarding the API 650 code. I've designed some small tanks/hoppers etc before (not using API), however in a new project I'm taking the role of Designing some CIL tanks (10m Diameter, 12m high) for a gold plant. I'll have another senior checking my work, but I still have some burning questions! Hopefully you guys can shed some light:

1. Difference between chapter 5 and Annex A Shell design thickness calculation? I noticed Section 5 states allowable stresses to be used for the different plate grades, however Annex A has Joint efficiency and a set allowable stress of 145 MPa. What's the reasoning for this? If you design to section 5 are you expected to undertake NDT required for a joint efficiency of 1? Does joint efficiency come into play when designing nozzle reinforcement etc?

2. Flush Clean out door - a)Section 5 has set dimensions for a 610x610 flush clean out door, but states the door as 600x600 in other locations in the same section. I'm assuming this is a conversion from imperial measurements?

b) Is it a big deal if some of these dimensions are rounded to more sensible numbers? i.e. 1800mm wide reinforcing plate instead of 1830mm etc? bolt edge distance etc. The flange is also shown as 125mm from the shell in the detail. Can this be extended to more than 125mm ?

c) Can a drain nozzle be installed onto the flange cover plate on the flush type clean out opening?

d) Can you install a davit onto the shell wall to aid removing the flange cover plate?

e)What's the difference between a flush type clean out and a flush type shell connection that is mentioned later in section 5? What's to stop you bastardising details between the two?

Thanks

 

[JStephen]

1) Annex A is the "old code", what used to be Appendix G or something for high-strength material is now the main body of the code. The main reasons to use Annex A now would be to eliminate radiography on a small tank, or to use A36 type plate at colder temperatures. I think the data sheets are actually set up so that Annex A is supposed to be specified by the customer.
2) Yes, this is a 24"x24" size.
2b) Generally, dimensions can be increased but not decreased.
2c) Yes, there are requirements somewhere for openings in flush manway covers.
2d) Yes, there is actually a requirement for davit or hinges, I believe.
2e) One is a manway, one is a shell nozzle. The flush type shell connections include a transition piece that is awkward to fabricate, and in my experience, are very seldom used.

 

[Legoman92]

Thanks for the quick reply JStephen! I had an argument with the lead draftsmen today about the flush clean out door regarding the set neck length of the flange. I said that is to remain the set length as specified in the code (125mm from memory) and that the concrete ring beam needs to be notched to allow clearance around it. He came back with an old project that has the neck length about 300mm long and claims that because it says api 650 on the drawing that it complies. Am I in the right ?

 

[Geoff13]

Adding the text "API 650" on a drawing doesn't cause it to be compliant. The only way to determine if something complies is to read the Code carefully.

Clause 5.7.7.1 states "Flush-type cleanout fittings shall conform to the requirements of 5.7.7.2 through 5.7.7.12 and to the details and dimensions shown in Figure 5.12 and Figure 5.13 and Tables 5.9a through 5.11b." This would suggest to me that lengthening the projection would not conform strictly to the Code. The Code is clearly trying to keep the projection very short. Your tank is quite small, but I would be reluctant to extend the projection. You are correct that a foundation notch is required, and is quite important for allowing the shell to rotate (see Figure 5.15), and access to the bottom flange bolts.

Stating that a tank meets API 650 is under the honour system There is no 3rd party reviewer. If you bastardize things you need to ask yourself when to stop calling it API 650. I have designed tanks that are API 650 and others that "generally conform with" API 650, depending on what the customer needed.

Going back to your original questions, JStephens has some great answers so I'll just add a couple of comments.

1) If you perform the radiography in Section 8 (i.e. Figure 8.1) you can use the allowables in Section 5. As you can see in the Figure this is sometimes spot and sometimes full radiography. Joint efficiency only exists in Annex A. The savings in radiography cost are usually eaten up by the cost of thicker shell, unless the tank is small enough to be minimum thickness in Annex A.
2c) Yes, see clauses 5.8.3.2 and 5.8.3.4.
2d) Customer preference. Some like davits and some like a lug to lift it away. I would not read 5.8.3.5 to apply to a FTCO cover.
2e) Same as the difference between manholes and nozzles. The first is "thin" and only for access, whereas the second is stronger for attached piping.