API 650 - Weld Spacing 1

[TerryThompson]

API 650 Table 3-6 indicates that for a 24" manway the distance between the toe of the weld on the repad and the bottom to the tank is approximately 3". However, when I use figure 3-22 it indicates that unless the weld is heat treated this distance should be 10". Am I right in assuming the distance to be 10" as Table 3-6 does not take into account plate thickness or heat treatment.

 

[johnnymist]

Hi Terry,

hope this helps.

Table 3-6 sets up minimum requirements for weld spacing. Footnote c states that you also are required to comply with the weld spacing requirements of the other sections ie. clause 3.7.3 for weld spacing as appropriate. Assuming that your tank has a bottom strake thickness > 12.5 mm which is not pwht, the minimum required spacing would then be 10", which is greater of the 3" and 10" values.

It may be better to use a "tombstone" type arrangement in order to keep the manway at a height which is easier to climb into and out of.

Regards
John

 

[TerryThompson]

HI John:
Thanks:
I would have to agree with you. I think it is likely that Table 3.6 was not updated in the last addendum and Figure 3-22 was updated.
Regards;
Terry

 

[IFRs]

Terry - You are correct. In fact, table 3-6 has a note buried somewhere that states the regular heights are for Appendix A tanks only. An agenda item has been started by Matrix (a tank company) and is being handled by someone else that will make the regular heights correct for up to 1/2" thick shell. The appendix A note will be changed to identify that the regular pad heights are only good for up to 1/2" plate.

In the meantime, do like them. Always use low type pads because the column in table 3-6 for them is not modified by figure 3-22.