API 620 - Do ALL "T" Joints Require RT? 2

[qcrobert]

Dear Sirs,

We presently have a 316L matl 3/8" wall thk. cyclone separator (F&D head & cone bottom) that the Client has speced out to API 620 Code. The operating temp is 215 deg F and design temp is 300 deg F, op pressure is 3 psig to 5 in. wc vacuum and design pressure is 7.5 psig to 15 in. wc vacuum.

Client test reqs are 10 psig hydro and spot RT w/ 85% jnt efficiency.

API 620 states in 5.26 Radiographic/Ultrasonic Examination
5.26.4.3 (a) When parts of tanks do not require complete examination, circumferential joints in cylindrical or conical surfaces need to be prepared and examined for a distance of only 3 in. on each side of any intersection with a longitudinal joint. All joints in a spherical, torispherical, or ellipsoidal shape or in any other surface or double curvature shall be considered longitudinal joints.

Does this mean that ALL "T" type joints (circ.-to-long seams) REQUIRE RT?

Appreciate your interpretation and comments,
Robert

 

[Kiwi2671]

qcrobert,
See 7.17.3
Regards,
Kiwi

 

[Eddycurrentguy]

Fillet connections are not examined with radiography due to the joint configuration.

 

[qcrobert]

qcrobert,
See 7.17.3
Regards,Kiwi

Yes I have read 7.17.3 Kiwi, however how do you interpret 5.26.4 Examination Required for Joint Efficiency?


Eddycurrentguy,
I agree that fillet connections are not examined with radiography due to the joint configuration.

The reference to 5.26.4 is only about butt welded joints.

 

[Kiwi2671]

Robert,
I only have the 2002 version of API 620 but the clause 5.26.3.3 in mine is exactly the same as the clause you quoted - 5.26.4.
In my opinion that clause is not applicable to your situation.
What it is stating is if you want to increase your joint efficiency from 85% (spot RT) to 100% (full RT) for design calculations you must comply with the clauses that follow.
As you only require 85% joint efficiency those clauses are not applicable,
Regards,
Shane

 

[Duwe6]

Additionally, "Full RT" does not mean 100% RT in either API or ASME Codes. "Full RT" to give 100% joint efficiency in this case will be all of the Tee Intersections, but only portions of the round seams. Don't overbid the RT on these jobs. The only thing that commonly requires RT of *everything* is a Lethal Service item. "Full RT" typically means all Longitudinal seams, all intersections, and 'spot' on the Circumferential seams.

Kiwi2671 is correct about the quantity of RT you are required to do to get your 85% on a 620 vessel.

 

[qcrobert]

One recent interpretation that has been presented to me is as follows: Example vessel contains 120 feet of linear weld seam with 12 "T" joints:

7.17.3 Number and Location of Spot Examination
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 meidional 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.

7.17.3.4 Whenever spot examination is required for circumferential or latitudianal joints other than those considered in 7.17.3.2 and 7.17.3.3, 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 if not already done on other joints for the same welder or welding operator on the same structure.

(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 meidional 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.

Does this make sense to you? Appreciate your comments,,
Robert

 

[qcrobert]

Duwe6 (Industrial)
Can you please reference paragraph in API 620 stating:


"Full RT" typically means all Longitudinal seams, all intersections, and 'spot' on the Circumferential seams.

Thank you,
Robert

 

[Duwe6]

API-620 11th Ed. w/Addendum 1

TABLE 5.2 Note 3 "All main butt-welded joints . . . as specified in 5.26 . . "

5.26.4.2 {paraphrased} 100% of all circumferential and longitudinal welds EXCEPT:

5.26.4.3(a) circ joints only require 3-inches on each side of any Tee joint [intersection] with a longitudinal seam = 6-inch spot at the junction.

Assumes that the requirement of 5.26.3 is met: tank wall thickness of less than 1.25-inches.

Thus; 100% Joint Efficiency requires 100% RT of Long. seams, and Spot RT of Circ. seams [assuming that thickness is less than 1.25-inches/32mm]. very similar to ASME Sect VIII requirements

 

[qcrobert]

Thanks Duwe6,
So what is your interpretation to the example of spot RT that I proposed?

 

[Duwe6]

Yes. On the 'tails' of the RT's of the Long joints, have the RT crew use a big piece of film so that the last shot of the long seam also includes the 3-inches of Circ seam on either side of the junction. Make sure to include into the Welding/Erection contractor's contract that "any repair RT's caused by weld defects will be paid for by the contractor at no cost to the owner". Reason is that the if the RT crew finds a defect in the Circ seam, they have to keep 'shooting' the Circ seam until they find 3-inches of acceptable weld. Could get expensive otherwise. The owner only needs to pay for the good welds and the RT's of the good welds.

 

[qcrobert]

Yes I agree it can get expensive with additional shots as per 7.17.4.1 and 7.17.4.2.

Also as per 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.

With additional requirements for MT and/or PT examinations, the API 620 Standard is indeed stricter than ASME Sec VIII Div 1 spot RT requirements.

Thanks again for input Duwe6,
Robert

 

[IFRs]

Note: there is an Addendum 2 for API 620 11th Edition. I don't remember any revisions to the sections you are concerned with (but it's probably best not to depend on my limited brain).

 

[Duwe6]

Good catch on the Add. 2, IRFs. The new Add. is attached. It will only print 1-sided, so I scan the printout, and copy it into 2-sided for my book.

 

[qcrobert]

IFRs thanks for the heads up and Duwe6 for posting the addenda!

 

[qcrobert]

If I may get an additional interpretation on the following para? If 2 welders have welded the tank's 75 ft of welded seams, then according to the requirements of 7.17.3.2;

1 shot in first 10 ft for welder #A and,
1 shot in first 10 ft for welder #B then,
1 shot for additional 50 ft w/o regard to the number of welders
1 shot for additional 50 ft w/o regard to the number of welders
1 shot for remaining 15 ft w/o regard to the number of welders

Do you agree that the total RT shots would be 5?

7.17.3 Number and Location of Spot Examination
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.

 

[Duwe6]

qcrobert, your interpretation is correct; total required round seam RT spot-shots equals 5. Additionally, with careful placement of the RT film [and using wider film], some of those shots can also be 'Junction' shots.

With some planning, the total number of required RT shots can be reduced to about half what a 'first reading' of 620/650 appear to require. This combining of RT's is 'legal' and is 'usual and customary practice' for API tanks/vessels. Duwe6 API-653

 

[qcrobert]

Thanks for your quick response Duwe6.

25% of the total RT shots req to be T-joints with min of 2 T-shots per tank so I would have 2 of the 5 shots be T-joints.

Again appreciate the help,
Robert