API 653 Hydrotest exemption 1

[Inspector89]

Shell to bottom weld repair:
Repair of the weld attaching the shell to the annular ring or the shell to the bottom plate shall meet one of
the following requirements.
a) A portion of the weld (of any length) may be removed and replaced as long as the replaced weld meets the size
requirements of API 650, Section 5.1.5.7, and the portion replaced does not represent more than 50 % of the
required weld cross-sectional area.
b) The weld on one side of the shell may be completely removed and replaced for a length not exceeding 12 in.
Shell-to-bottom weld repairs replacing more than 50 % of the required weld cross-sectional area shall not be
closer than 12 in. to each other, including repairs on the opposite side of the shell.[/b]

The above sentences are from API 653. The requirement (a) states that one can remove and replace weld for any length if the replaced section doesn't exceed 50% of cross sectional area. The requirement (b) states that one side can be completely removed (which will be approx. 50% of the cross sectional area) but only for 12" length. Doesn't statement (a) and (b) are contradicting each other?
Can someone please elaborate on this.

 

[HTURKAK]

....The above sentences are from API 653. The requirement (a) states that one can remove and replace weld for any length if the replaced section doesn't exceed 50% of cross sectional area. The requirement (b) states that one side can be completely removed (which will be approx. 50% of the cross sectional area) but only for 12" length. Doesn't statement (a) and (b) are contradicting each other?
Can someone please elaborate on this.

There is no contradiction... The snap below (copy and paste from API 650 ) depicts the shell to bottom weld .

There are two fillet welds ...The requirements are clearly defined for the sizing of the welds. Say the interior weld area Ai and exterior Ae and say , weld defect at exterior..
Item a states, A portion of the weld (of any length) may be removed and replaced as long as the replaced weld meets the size
requirements of API 650, Section 5.1.5.7, and the portion replaced does not represent more than 50 % of the required weld cross-sectional area .That is , Aw shall be less than 50 % of the Ae.

Item b states,The weld on one side of the shell may be completely removed and replaced for a length not exceeding 12 in.
Shell-to-bottom weld repairs replacing more than 50 % of the required weld cross-sectional area shall not be closer than 12 in. to each other, including repairs on the opposite side of the shell. That is, if Ae removed completely,the length shall not exceed 12 in.

The removal of defective weld is carried out either by grinding or gouging or sometimes both .
For more info. pls look API 650 7.2.4 Shell-to-Bottom Welds.

Good luck.