Components essential to structural integrity of the vessel per UCS-66(a)

[Some Curious Guy]

Per general understanding of fracture mechanics, components subjected to tensile stresses are considered susceptible to brittle fracture. This understanding was reinforced by note (2) of Fig UCS-66.2 which stated that only those loads resulting in " general primary tensile stress " shall be used in determining coincident ratio for evaluate impact test requirements.

Hence pre 2019 code, Engineers based on his judgement would only include those components subjected to tensile stress in the term ‘ essential to the structural integrity of the equipment’ per UCS-66(a). Stiffener rings were assumed to be compression members and not checked ( even by popular design softwares ). However, 2021 edition of the code explicitly listed ‘ Stiffener ring ‘ in UCS-66(a). This has once again started a debate about the criteria to decide which components are to be evaluated and which not and there are many differences of opinion.

Anyways I feel the term ‘components essential to the structural integrity of the vessel’ may mean any of the following thing ( I maybe wrong )
1) Pressure part members subjected to general primary membrane tensile stress
2) Pressure part members subjected general primary membrane tensile stress and / or compressive stress
3) Pressure part and non-pressure part members subjected to general primary membrane tensile stress due to internal pressure and / or external primary tensile loads
4) Pressure part and non-pressure members resisting internal pressure and / or external pressure and / or tensile load and / or compressive loads.
5) Any component welded to pressure boundary parts. This is based on Para 4.2.14 of PIP Spec VESV 1002.

Can anyone having more nuanced understanding of this issue share their experience.

 

[r6155]

Care should be taken with PV for low temperature service. Note that thermal insulation makes quick visual examination difficult during service.
All materials welded to pressure components must be traceable (including ladder and platform clips, lifting lugs, etc.).

Regards

 

[SnTMan]

Some Curious Guy I am not familiar at all w/ fracture mechs nor w/ the 2019 Ed, but I'd consider a good practice to apply impact test / exemption rules to any part of the pressure boundary and also to any load bearing component welded to it.

So, any attachments for which there are Code design rules, i.e. nozzle pads, stiffening rings. Any load bearing attachments to the pressure boundary, i.e. support pads, platform clips, most lifting lugs. I'd exempt non-load bearing attachments such as nameplate brackets, insulation rings and clips, etc.

Except as otherwise required by contract, of course

Regards,

Mike



The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[david339933]

Note that the Code was changed to require the coincident ratio to be that of the shell or head to which these components are attached for use in UCS-66.1