lamination and stress study

[INSP79]

in service LPG tank 3000 m3 ,18 bar mawp, sa516 gr.70 , i found lamination in more 5 shells , after return to API 510 to see assessment , it forwarding me to API 579 which say (lamination is acceptable regardless of sizes except(1- in case of no working in hydrogen charging service, 2-locate the lamination out of distance of( 1.8 √ D*t )from major discontinues 'manhole'

i want to make some study of effect of stress to lamination prolongation in case of P.V. working with lamination, and why avoid locate in the area near to manhole ?, wich type of stress may be run?

 

[TGS4]

Follow ALL of the requirements of API 579-1/ASME FFS-1, Part 13 "Laminations". All of the calculations necessary for any such study are contained there.

 

[dhengr]

INSP79:
Generally, laminations and non-metallic inclusions are planar irregularities/anomalies which lay parallel to the two faces of the plate. You can usually see them when you machine or cut through them, as you cut across the thickness of the plate. They do not usually change the cross sectional area of the plate appreciably. You can map their location in a plate by ultrasonic testing (UT) or radiographic testing (RT) through the plate. When your primary stresses are in the plane of the plate, as is usually the case in a PV, the lamination is not too critical as long as it is not too thick. The same applies to compressive loads or stresses perpendicular to the plane of the plate (radial loads/stresses in most PV’s), they just tend to compress the lamination. But, tension perpendicular to the plane of the plate is a different matter, since tensile stresses will tend to pull the lamination further apart, or make it grow at its boundaries.

I don’t have the API or ASME codes in front of me, so I don’t know exactly what restrictions and limitations those codes put on this situation. But, given the above general considerations, they will more than likely tolerate some lamination as long as they aren’t too large (thick) or extensive. The codes will be much more strict about their existence in locations where the actual stress patterns/fields are tri-axial. That is, where the likelihood of through plate stresses is high, such as at a nozzle or manway openings or other transitions and significant discontinuities, which distort the normal stresses and cause significant through plate stresses.

 

[dhengr]

TGS4:
We do seem to meet up at this topic periodically, don’t we? Have a nice holiday season.

 

[r6155]

INSP79. Are you reading API 579 ASME FFS-1 edition 2016? The word “manhole” is not found here.

dhengr. RT is not adecuate to detect laminations

Regards
R6155

 

[metengr]

Agree above, RT will not detect laminations because of orientation. Either shear wave UT or phased array UT are your best options for evaluating laminations.

 

[r6155]

AET -Acoustic Emission Testing is the best, specially in large pressure vessel.

Regards
r6155

 

[TGS4]

Acoustic emissions is not appropriate for sizing any flaws for performing fitness for service evaluations. It can neither locate nor size flaws with sufficient accuracy. Particularly for laminations, it cannot provide information regarding the depth of the lamination.

The response provided by metengr is, as usual, spot on.

 

[r6155]

INSP79. Please,can you tell us how did you found these laminations?
Was by chance during inspection of actual thickness?

Regards
r6155

 

[r6155]

To detect laminations with AET see ASME V Table A-110. Once detected UT is used for more details.

Regards
r6155