[MW:9877] Interpretation of RT req to API 620

After conferring with other NDE inspectors on the subject of extent of
NDE testing requirements to API 620 Standard, the following describes
the extent of RT radiographic testing.

As an example of a large, welded, low pressure storage tank that is
NOT used for storage of liquefied hydrocarbon gases or refrigerated
products and not intended for lethal service. A storage tank
requiring spot radiography and 120 linear feet of welded seam.

7.17.3 Number and Location of Spot Examination - RT
7.17.3.2 At least one spot shall be examined from the first 10 ft of
completed joint of each type and thickness welded by each welder or
welding operator. Thereafter, without regard to the number of welders
or welding operators involved, one additional spot shall be examined
for each additional 50 ft - or remaining fractional part of this
length - of each type and thickness of welded longitudinal,
meridional, or equivalent joint subject to examination. The inspector
shall designate the locations of all spots that are to be examined, of
which at least 25% of the selected spots shall be at junctions of
meridional and latitudinal joints with a minimum of two such
intersections per tank (see 7.15.6.2), both under the foregoing
provisions and the provisions of 7.17.3.4. Such spots need not have
any regularity of spacing.

Assuming only one welder,
(7.17.3.2 At least one spot shall be examined from the first 10 ft of
completed joint)
First RT shot would be taken in the first 10 feet of weld,

(one additional spot shall be examined for each additional 50 ft)
second shot taken between 10 ft and 60 ft,

(one additional spot shall be examined for each additional 50 ft)
third shot taken between 60 ft and 110 ft,

(one additional spot shall be examined for each additional 50 ft - or
remaining fractional part of this length)
fourth shot taken betw 110 and 120 ft (the remaining fractional part).

(The inspector shall designate the locations of all spots that are to
be examined, of which at least 25% of the selected spots shall be at
junctions of meridional and latitudinal joints)
25% of these 4 shots must be "T" joints therefore equals 1 "T" joint
shot,

(with a minimum of two such intersections per tank)
however code states a minimum of 2 such intersections per tank,
therefore of the 4 shots total with 2 of these being "T" joints.

(5.27.11 All longitudinal butt welds in the nozzle neck and
transition piece if any, and the first circumferential butt weld in
the neck closest to side wall, excluding the neck to flange weld shall
receive 100% radiographic examination.)
these types of welds may be included in the examined weld lengths
above if they are of the same joint design and thickness, if not they
will be radiographed in addition to the above required shots per
lengths

I appreciate your interpretation and comments,
Robert

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