Strength reduction of existing tubesheet by drilling few additional holes

[HEX07]

Hi...we have a case where we need to fix one perforated plate of 8 mm thickness below the tubesheet exactly alligned with the tube holes (Tubes no = 1000). Tubes dia is 19.05 mm and hole dia on perforated plate is 7 mm. Perforated plate will be fixed with the tubesheet by providing 10 nos of bolts. Drilling depth of bolts are around 38 mm inside the tubesheet (Bolt hole dia is around 12 mm). Holes will be drilled within the OTL. As per ASME calculation of existing tubesheet, thickness comes out to be 72 mm and provided thickness is 73 mm. So we don't have any margin available.

Will drilling of 38 mm length holes of some 10 no of locations have any effect on tubesheet thickness and strength?? What is the procedure of calculating the remaining tubesheet thickness without going for FEA analysis?? Our intension is to fix the perforated plates in the existing tubesheet only.

 

[SnTMan]

Well, I can't prove it, but I wouldn't worry about it. Similarly, tie-rod holes are unaccounted for. One question, why such a deep drill depth? 38mm for 12mm fastener?

I suppose you could weld studs to the TS rather than drill & tap?

Regards,

Mike

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

 

[EdStainless]

So the flow will be going through the perf plate? and the holes line up one-to-one with tubes? and the holes are only 7mm?
So this plate will be a choke. Have you calculated the force against the plate? What about critical frequency?
Ten studs does not sound like very many to me. For 1000 tubes, I would want more than that.

Your holes do sound very deep. As long as your studs are run clear into the holes then there will be very little impact on the tubesheet.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[HEX07]

@ SnTMan (Mechanical), basically these bolts are required to hold the perforated plate below the tubesheet. My concern is whether remaining tubesheet thickness will be sufficient enough to withstand the design criteria after drilling 38 mm deep holes or not?? Additionally, where we consider tie rod holes in the tubesheet calculation for bending and shear case due to internal pressure.

 

[HEX07]

Additionally I would also like to ask, drilling of tubesheet at installed position (Installed vertically) can be possible or not??

 

[SnTMan]

HEX07, not much to add to my previous. Tie rod holes are not accounted for in Part UHX. Do you see any inputs that would make you think they are?

Again, why so deep? Can you weld studs instead of drilling?

You might have a look at UG-43(d), maybe not specifically applicable to tubesheets, but...

Is drilling possible as installed? Well, yes anything is possible given proper resources ($$).

Regards,

Mike



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

 

[chicopee]

I keep on reading the OP and I can not make sense of what he is trying to do. Perhaps a decent sketch would have helped.