API620 5.17 Reinforcement of multiple opening

[Parksuchul]

Hi hello,

I have a hard time controlling API620 5.17 requirement.
The situation, I am doing both API650 and 620 tanks, especially, for nozzle pad requirement, I applied API650 mentioned nozzle pad size on API620 nozzles because api620 pad size which is calculated by 5.16.3
all cases, API650 nozzle reinforcement sizes are lager than the calculation result from API620. So I common applied this API650 nozzle reinforcement size to API620 tanks.
But, the problem is I could not consider this paragraph(5.17) requirement, to make matters worse, most nozzle with pad works have been done.
finally, the distance between nozzle pad to nozzle pad is less than 6". Our client wants to just follow API620 Requirement.
Mechanical point of view, I think the pad size is something luxury deign and the distance is not less than 40mm, it could not damage to its shell or roof. we have small size tanks and there are lot of nozzles on the shell and roof.
Is there any way to persuade our client? because repair work can make damage its shell or roof plate.
I am a mechanical engineer, mechanically the design is not bad design even though it cannot meet API620 requirement.
Give me technical advice. or solution.

 

[Duwe6]

You could try using ASME Sect VIII Div-1 rules. These repads may be 'legal' to that code. And you may be able to convince you client to accept that.

The reasoning for API's stringent weld spacing requirements is residual stress from the welding, thus another possible 'fix' would be PWHT stress relief of the offending repads and adjacent shell.

API is a 'Rules Based' Code, and I agree that the spacing requirements are too stringent. But if you are asked to build to API-620, you gotta follow the rules. Next time, use a combined repad if you feel a repad is needed. Combined ones tend to be cheaper, too.

 

[Parksuchul]

Thanks for your advice.

Additionally, I just want to take one more technical support.

as you mentioned, API is the Rules based Code, if i have to follow this rule, I propose new concept common pad which is shown attached drawing.
Simply, keep the nozzles pad, and add blue area. it can be considered common reinforcing pad?

 

[Duwe6]

As a new repad, yes this is the correct method. Adding material between the existing repads - no, that does not fix the spacing problem [actually makes it worse - more welds infringing on each other].