Thick reinforcing plate.

[DavidCR]

For a typical reinforced welded nozzle or branch pipe, with reinforcement made of plate (as figure UG40 b-1 of ASMEVIII-D1 2007).

I´ve been told that for the reinforcing plate thickness (te), it is recommended that it should not be bigger than the smallest of tn (neck) and t (header), so as to have a "soft" or "good" transition from the neck to the header. But I don´t know if this have a ruled basis.

However for several reason, to have a "passing" reinforcement we use a plate for the reinforcement that is thicker than the header and the neck. I haven´t found on the code a rule that dose not permit this, and the shop guys comments that it looks like a bad design, because it is not a good welding design option to have such plates for the reinforcement.

We use the PVelite to calculate and it does not present problems, i.e, it does not warns about the use of thick plates for the reinforcing element.

So my questions in this would be:

1. I´d like to know if there is a ASME VIII Div 1 rule that prohibits to use of a "thick" reinforcing plate.

2. I´d like to know if there is a B31.1 or B31.3 that prohibits the use of a "thick" reinforcing plate.

 

[Shmulik]

David,
There is no such rule that prohibits using of a "thick" reinforcing.
To my approach it is only good practice avoids the welder make too "heavy" weld => excessive "heat input" => wider HEZ, etc.
Common problem is that the designer does not include precise weld details / procedure in the drawing, thus, the welder becomes "a designer of fortune" and decides that the fillet weld leg "should" be as high as reinforcement thickness just because that is what he can see and his eye runs to the top corner of it.

UW-16 (c)(2)(a): "The weld at the outer edge of reinforcement plate shall be a fillet weld with min. throat dim. of 1/2t min".
So, if there is no reason for that, you don’t have to perform heavier weld.

As a designer, that is your responsibility to put your precise instructions including weld details on shop drawings without let shop guys any place for interpretations (namely, you should write a numerical dimension on weld throat. Please, DON'T write "1/2t min" expecting the welder start search the books…)

 

[jte]

David-

As far as I know there is no explicit prohibition for thick repads. Thus, I’ll point you towards the Foreword, specifically:

The Code is not a handbook and cannot replace education, experience, and the use of engineering judgment. The phrase engineering judgment refers to technical judgments made by knowledgeable designers experienced in the application of the Code.

Thus, it is up to the experienced engineer to make the decision. Some folks consider me experienced in the application of the Code (others may have different opinions!). You won’t find a repad thicker than about 1.5*shell thk nor thinner than 0.75* shell thk on a vessel that I’m involved with. Remember that the repad is helping to resist bending, and use your judgment. Just because a design passes the Code rules does not make it a good one. That’s one reason why many owner/users have developed their own design standards and specifications which supplement the Code.

… designers and engineers using computer programs for design or analysis are cautioned that they are responsible for all technical assumptions inherent in the programs they use and they are responsible for the application of these programs to their design.

So if you design in an unusually thick repad, don’t try to get me as a client to accept your design with a “the software said it was ok” argument. You’ll have to come up with better reasons.

jt