Lap welded bottom Plates API 650. Lap width

[PINTAIUS]

Hello, Fellows

Incredible, but completely true.

Several years handling API code but I am still a nerd in some things, that are very basic.

I am checking some drawings, and talking about lap-welded joints I have noticed that, probably, I are not translating correctly the sentence "need not exceed". It may to be consider as minimum lap?

E.G.: If I have to weld two plates, 8 mm thickness, (single lap weld), what is the interval allowed by chapter 5.1.3.5 of API 650? 40 mm (5 times nominal thickness)? 25 mm?

Here below is the chapter from API:

5.1.3.5 Lap-welded joints, as tack-welded, shall be lapped at least five times the nominal thickness of the thinner
plate joined; however, with double-welded lap joints, the lap need not exceed 50 mm (2 in.), and with single-welded lap joints, the lap need not exceed 25 mm (1 in.).

Thanks in advance

[tessios]

that mean in that clause plate overlapped and its width of overlapped so that In your case, Overlapped width should be less than 25mm(1") since you chose
single welded lap joint. you don't need to follow tack weld requirement

[adamjin]

The english is funny and does not serve the purpose. the word "need not exceed" is actually meant to be " the minimum".

See also technical queries answered by API. There is reference to bottom lap welds.

10th - Nov. 1998
3.1.3.5
650-I-37/03
Question : Is it the intent of 3.1.3.5 to limit the maximum lap of a double welded lap joint to 2 in. and a single welded lap joint to 1 in. If not, is there a maximum lap requirement for single welded lap joint bottoms and roofs? Would this constraint, if any, also apply to bottom or roof repair or replacements governed by API 653.
Answer: No.

10th - Nov. 1998
3.1.3.5
650-I-49/03
Question: Section 3.1.3.5 of API 650 specifies minimum lap joint dimensions. Is there any limit on the maximum width of a lap joint?2: Can a lap joint consisting of two (2) ¼ in. plates be lapped 3 in.?
Answer: API Standard 650 does not address maximum lap.2: Yes. Any lap that exceeds the minimum is acceptable. Refer to 3.1.3.5.

I hope this answers you question.

[PINTAIUS]

The english is funny and does not serve the purpose. the word "need not exceed" is actually meant to be " the minimum".

See also technical queries answered by API. There is reference to bottom lap welds.

10th - Nov. 1998
3.1.3.5
650-I-37/03
Question : Is it the intent of 3.1.3.5 to limit the maximum lap of a double welded lap joint to 2 in. and a single welded lap joint to 1 in. If not, is there a maximum lap requirement for single welded lap joint bottoms and roofs? Would this constraint, if any, also apply to bottom or roof repair or replacements governed by API 653.
Answer: No.

10th - Nov. 1998
3.1.3.5
650-I-49/03
Question: Section 3.1.3.5 of API 650 specifies minimum lap joint dimensions. Is there any limit on the maximum width of a lap joint?2: Can a lap joint consisting of two (2) ¼ in. plates be lapped 3 in.?
Answer: API Standard 650 does not address maximum lap.2: Yes. Any lap that exceeds the minimum is acceptable. Refer to 3.1.3.5.

I hope this answers you question.

Thanks a lot adamjin!!!

Just I have looking for. I will download just now the PDF and read it.

I always have understood the same as "Tessios". In my mother language, we call this expressions "juego de palabras / play on words or PUN" because I understand that we never lap more than 25 mm in single lap welded joints, but it "crash" against the first part of the paragraph (five times...).

So that, we thought: right; we have two 6 mm thickness plates, single lap welded...25 mm minimum and...25 mm maximum!! (due to my mistake translating "need not to exceed" as maximum overlap) That's a nonsense and the reason for my question.

Thanks again

[marian_g]

Well, by some research, I found that Daniel Defoe wrote an work with title "Plain English, with remarks and advice to some men who need not be nam'd". Now I am not sure API would interpret Defoe's legacy as we have the obligation to name the man!

And strange enough, Oxford Fowler's Concise Dictionary of Modern English Usage still believes that "He says she need not answer" can be equally expressed as "He says she does not need to answer".

@Marty Thompson, because it seems you are a native speaker of English, please help us once again clarifying the possible grammatical mechanism by which "however the lap need not exceed x mm" becomes something that stipulates the minimum "x mm".

In my opinion, API interpretation just plays with words saying there that API Standard 650 does not address maximum lap and, of course, any lap that exceeds the minimum is acceptable. I don't think they said something about minimum as "x is minimum". Or maybe I'm the poor man who need not be named!

[Marty Thompson]

Most tank erector drawings have a minimum floor lap of 1". It is permissible to have lap more than 1" but API 650 is is stating that it is not necessary. If you have cathodic protection, then there may be some interference with the protection.
As a best practice, I ask tank crews to weld any floor laps at the external chime edge to prevent any rust bloom expansion of the joint.

[marian_g]

Marty, I second your technical opinion. Anyway it is in line with what apply all serious companies involved in tank erection.

I don't think that wording "need not exceed" is actually meant to be " the minimum", as some people re-interpret API 650 interpretation.

[SEGO4EVER]

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