Unclear on API 620 Table 5-2

[qcrobert]

I am getting differing opinions on several forums as to the extent of RT as it applies to 70% JE.

After much feedback I'm leaning to the assumption that butt welds in the circ and longitudinal shell joints of a tank require Spot RT when 70% JE is called out in the Design Data block of the AFC drawings.

I look forward to your opinions.
qcrobert

 

[JStephen]

In the liquid portion of the tank, spot RT is required, and assumes an 85% joint efficiency, which can be raised to 100% with full radiograph.
If your customer specifies 70% joint efficiency for these welds, I would assume they still require spot RT if it is to be built per the standard.
In the roof above liquid level, it can be designed for 70% with no RT in that portion.

 

[IFRs]

Double-welded butt joints in table 5-2 are grouped into two categories.

Is your joint in a roof above the liquid level?

The standard does not require a particular NDE but tells you what joint efficiency you can use depending on what NDE you perform.

For instance, for roofs above the liquid level you use 70% with no RT, 85% with spot RT and 100% with full RT

The section you highlighted is indeed confusing because the text in the "Radiographed" column does not line up with the text in the columns on either side.

There are three levels of RT: "---", "Spot" and "Full (see Note 3).
These should line up with 70 (both columns), 85 and 100 where 70% does not require RT, it you do Spot RT you can use up to 85% joint Efficiency and if you use Full RT you can use up to 100%.

Your edition is at least two revisions old, was published 13 years ago. Subsequent editions perpetuated the terrible alignment of the rows in the table, but perhaps it will be fixed in the next edition when the table is updated for single-sided partial-penetration butt-welds.

 

[MJCronin]

On which "other forums" have you posted this question ?

MJCronin
Sr. Process Engineer

 

[qcrobert]

AWS and NDT

 

[qcrobert]

The 70% JE with note: Radiography AS REQURIED is stated in the Design Date block. This is being applied to Quench Duct, Absorption Towers and Incinerator Hot Gas Ducting so I am unclear of the A/R (does it apply or not) when the 70% JE is stated?

 

[JStephen]

API-620 is for low-pressure tanks, not for quench ducts, absorption towers, and hot-gas ducting, so you may simply be looking in the wrong place for answers.