API-650 11th Edition

It has been too long since I posted information concerning changes about the 11th Edition of API-650. Here is the next part having to do with changes in Section 5, which is design. This used to be Section 3.

5.1.3.6.1 specifies that multipass welding is required for manual welding processes on fillet weld legs or groove depths greater than ¼”. For semi-automatic and automatic welding processes multipass welding is required for welds greater than 3/8”. This applies to bottom plate welds, roof plate welds, and shell-to-bottom welds for Groups I, II, III and IIIA materials.

5.1.3.7 specifies that all attachments to the tank exterior shall be completely seal welded (intermittent welding is not permitted) except as specified in 5.1.5.8 for wind girders.

5.1.3.8 says permanent backing strips are not permitted (unless approved by the purchaser) except as permitted in 5.1.5.5 and 5.1.5.6 which is for butt-welded bottom plates.

5.1.5.1.b specifies that the top surfaces of bottom welds shall be ground flush where they will contact the bottoms of the shell, insert plates, or reinforcing plates.

5.1.5.8.b requires all horizontal bottom-side joints of wind girders shall be seal-welded unless specified otherwise by the purchaser. (Previously seal welding of the underside was only required if specified by the purchaser.)

5.1.5.9.c adds tension rings and compression rings to top-angle sections that require butt-welds shall have complete penetration and fusion.

5.2.3.d adds localized loads resulting from such items as ladders, stairs, platforms, etc., shall be considered.

5.3.1.2 specifies that sliding friction resistance shall be verified for tanks subject to lateral wind loads or seismic loads.

5.3.2 provides how corrosion allowances are to be applied. (Many of these had been scattered throughout the code or not specifically defined.)

5.4.4 specifies that unless otherwise specified, tank bottoms requiring sloping shall have a minimum slope of 1:120 upwards toward center of tank.

5.4.5 adds requirements for foundation drip rings if specified by the purchaser.

5.5.3 requires that if the product height times the specific gravity of the product exceeds 75 feet, then you must perform an elastic analysis to determine the annular plate thickness.

5.6.1.1 note 4 says that for diameters from 10.5 feet to 50 feet, the minimum thickness of the lowest shell course only is increased to ¼”. (The question is does this apply to field erected tanks or was this a note related to Appendix J tanks??)

5.6.1.5 adds that isolated radial loads on the tank shell, such as those caused by heavy loads on platforms and elevated walkways between tanks, shall be distributed by rolled structural sections, plate ribs, or built up members.

5.8.5 has been added to address the limitations for roof venting. Normal and emergency vents shall prevent the internal pressure from exceeding the pressure calculated in F.4.1 with some other limitations as well. Screen sizes are specified as being ½” nominal opening.

5.8.10 specifies platform, walkway, and stairway requirements. They have added that unless declined on the data sheet, a roof edge landing or gaugers platform shall be provided at the top of all tanks.

5.10.4.7 provides requirements for column bases. A ¼” wear plate seal welded to the floor is required or you can provided a thickened bottom plate that also distributes the load. Guides for the column to allow vertical movement of at least 3” are required and cannot be welded to the tank bottom. Several possible methods are given in Figure 5-26.

I will posting more soon. Also we will be releasing a revision to ITSdesign which will bring it into compliance with the 11th edition.