Impact, PWHT & RT Requirements for Stiffening Rings

[steris]

My company is working on a Section VIII Div 1 rectangular pressure vessel for non-lethal service. The rectangular tank will be under internal pressure. One of the designs we are evaluating uses 1.5" thick bar as stiffening rings around the outside of the rectangular shell. These bars (which are SA-36) form a picture frame shaped structure and are welded to each other as well as to the shell. Please see the pictures attached for a better idea. My questions are:

1) Table UCS-56 requires PWHT for parts where the nominal thickness is 1.5". The nominal thickness is defined in UW-40(f)(2) to be the depth of the groove weld. Since the bar joints are not full penetration and have a groove weld on two sides, would the nominal thickness be equal to depth1 + depth2 or do I treat each weld separately so the nominal thickness is just depth1?

2) The bars fall on curve A of Fig UCS-66. At 1.5" thick this yields a MDMT of 88F to exempt from impact testing. The governing thickness seems to be driven by UCS-66(1)(a) which states the governing thickness is the full part thickness. Is there some exception I'm missing? It would seem to me that some consideration should be given to the weld depth.

3) UCS-57 requires full radiography for thickness of 1.25" when using P1 materials with butt welded joints. Can UT be employed instead of RT? Alternatively, are there any exemptions from this requirement? Intuitively I feel that this requirement should be driven by weld size as opposed to material thickness. I could understand a using the part thickness if it's a full penetration weld in thick material but when it's not this requirement seems excessive.

Please let me know if anything is not clear. Thanks for the help!

-Steris

 

[metengr]

Replies are as follows;

1. The nominal thickness would still be the larger thickness of the two individual partial penetration welds in the butt weld joint. An example, lets say one side of the weld joint has a groove weld depth of 3/8" and the opposite side has a groove depth of 1/2", the 1/2" weld deposit thickness would be the governing thickness for PWHT. In your case, the maximum is 3/8".

2. The nominal thickness t_g for MDMT determination would be the combined weld joint thickness because 3/8" +3/8" combined thickness is needed to carry membrane stresses across the weld joint.
Rationale for the above, UCS-66 1(a) states for butt joints, except..., the nominal thickness of the thickest welded joint.

3. You don't have a full penetration butt welded joint, so I don't see how this applies.

 

[steris]

Hi Metengr - Thanks for the help! I was misreading the code and reading joint thickness as part thickness. As always you are a great help!

Just out of curiosity - is UT permitted to meet the requirements of UCS-57?