ASME B31.3 Reinforcement Calculations

[chincheetan]

Hi there, I am a new graduate and have been recently introduced to ASME B31.3. I stumbled upon section 304.3.3 Reinforcement of Welded Branch Connections and I am wondering if someone could please kindly explain to me how to derive the formula for the area required, A₁ = t_h*d₁ [2 - sin (beta)]. I could understand for beta = 90 deg, it will become A₁ = t_h*d₁, but what about when it is an inclined nozzle? How do I geometrically work out the formula? Thank you.

 

[LittleInch]

Errrr put in the angle of your inclined branch and calculate the area required?

31.3 reinforcement works on a replacement area theory whereby the area of the header which has been removed due to the hole cut for the branch pipe is replaced within a certain distacne of the whole by other metal, normally a plate cut bigger than the branch and welded on as a compensation plate. Because angled branches have more forces than ones at 90 degrees, they need more reinforecment hence at 45 degrees, the area will be 1.3 times the area required for a 90 degree connection.

Weldolets and branched fittings already include this rinforcment in their design to stop you having to calcualte it, but that's the rationale behind it

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[chincheetan]

Hi LittleInch,

Thank you for your reply. I might have been doing it the wrong way, but attached is a sketched diagram which I used to find out the required area, A₁. But, geometrically I could not work out the required area and this might be because of my mistake - would be grateful if you could please take a look and perhaps help me with it. Besides, it seems like a paralleleogram to me and I am just puzzled why cant we just look for the required area by simply taking the product of d₁*t_h?

Many thanks.

 

[LittleInch]

The calcualtion of (2-sin beta) is not rying to work out the area, it's trying to determine a factor of multiplication of the area.

When ou have an inclined nozzle you need more area than if it is a simple 90 degree branch as there is in fact more material actually removed as the hole becomes an arc instead of circle. look at the area from the header point of view and don't just think pipe size but overall area.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[chincheetan]

Hi LittleInch,

Thank you for your reply. That's what I thought initially, but thinking there must be a reason why the factor of [2 - sin (beta)] is chosen and not [1 - 0.5 sin(beta)] for instance. Anyway, thank you!