Baseplate & Soleplate Design 1

[jdogg05]

Hi,

I have been reading through API 686, 610, 685, etc. and cannot seam to find any specification on baseplate/soleplate thickness. There is an appendix in 610 and 685 (Appendix M) on plan dimensions, but nowhere does it mention requirements for thickness. The reason I ask is, from a commercial Quality stand-point, what is stopping an EPC from specifying, say, a 1/8" baseplate for a 5000 HP pump? I understand that would be practically ridiculous, but in the commercial world everything needs to be tied to contractual documentation, and I'm sure crazier things have been done...

 

[Artisi]

That's why engineering companies employ engineers to design what is mechanically adequate and commercially feasible, (although it doesn't always turn-out that way.)

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[LittleInch]

May be not, but you will find performence requirements in API 610 such as the ability to lift with a four point lift (7.3.15) and that the base plate shall have sufficient stuiffness to limt movement to someapecified values WITHOUT using the gorunt for strength (7.3.20)

There are simply too many pumps, motors, sizes etc for anyone tyo specifiy a minimum thickness so the performence spec is the way to go.

If the EPC specified that and the pump base plate flexed, then he would be liable for getting another one which didn't flex. I can't see an EPC contractor doing that - he would simply leave that to the pump vendor, agina whocse interest is not in supplying somehting which flexes when it shouldn't.

Is this a specific query or just a "what if"??

My motto: Learn something new every day

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

 

[jdogg05]

It's more of a what if. I guess what I am really getting at, is if a pump base is being grouted (and thus being supported uniformly on the underside of the baseplate by the grout), is there any issue with having a very thin baseplate? Or what if a vertical pump (or some big piece of equipment) had been placed and at some point the surveying had been screwed up (so the foundation was cast to high). Say a grouted soleplate was to be used and there was very little room between the foundation top and the underside of the equipment baseplate: only enough room for a 1/8" soleplate (because grout pour has to be a certain minimum height). If it is to be supported by grout, does it matter how thin this plate is? Could it not be 1/16"?

 

[LittleInch]

No. Read the code. It says the baseplate needs to be sufficiently strong, ON ITS OWN to prevent twisting and movement. Grout just fills in the gaps and has no structural strength input.

Also at some point you need to lift this pump and motor into place and also test it without any grout. 1/16 plate won't let you do any of that.

Is there something behind this?? You seem very keen to try and use a very thin plate....

My motto: Learn something new every day

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

 

[jdogg05]

LittleInch, IMHO I don't think that is quite correct. The grout, properly poured, has a significant structural impact. It's fastened connection design 101. You want the fastened material to have a higher effective stiffness than the fasteners (thus the cyclic loads are transfered to the grout, and thus the foundation, rather than the anchor bolts). If there are void spaces between the baseplate and the grout, you significantly reduce the effective stiffness of the grout and thus the long-term structural integrity of the assembly. The specs also say that it is a grouting "system".

After thinking about this more, I think I have come to a conclusion. The baseplate needs to be designed to a certain thickness for three main reasons: bench testing (FAT), transportation, and so that the grout can achieve full contact underneath the plate. The last one is important because if the baseplate is very thin, it makes it very difficult to ensure full grout contact all around the underside of the plate. API 686 also says that the grout should be poured halfway up the baseplate. I am assuming this is so full underside contact is ensured.

Thanks for the input everyone. Still open to any comments!

 

[Pumpsonly]

jdogg05

I think you have been confusion others by missing up the term baseplate and sole plate. And you actually meant sole plate for vertical pumps in this posting. Please refer to Fig 33 of API 610 -10th edition. Sorry That is the latest I am having.Baseplate is referred to horizontal pump and you can not make a 1/8" baseplate.
The purpose of the sole plate, other than to provide a level machined surface for mounting the vertical pump discharge head , it must be able to withstand the moment and forces imposed on it by the piping strain if any via the discharge head.

If some one can design or make a 1/8"thick sole and have enough strength to hold the stud bolts for mounting the pump to withstand the piping forces and moment..then it is acceptable.

 

[BigInch]

The base plates need to be designed for
1) compression loads to as uniformly as possible distribute the pump's maximum load (short circuit torque) to the grout. 1/2 the full width of the base plate is usually designed as a cantilever beam, so bending at the root of the beam is limited to 2/3 of the steel's yield strength.
2) Tension loads from the bolts when under short circuit torque load. The plate again being designed as a cantilever beam, but with a point load at the bolt location. The bending and shear loads being resisted by the cross section of the base plate at its root.

Try to find a copy of "Design of Welded Structures" by Blodgett. Lots of good typical examples of how to design welded connections for beams, columns, connections and baseplates in general.

Independent events are seldomly independent.

 

[jdogg05]

LittleInch,

Sometimes when I re-read things with a cold eye I see them differently (or maybe I should say correctly). I understand what you are saying about the baseplate being sufficiently strong on it's own now. Also, the manufacturer will have to perform all the FAT tests on a test bench at the shop. At that point there is no grout, so obviously it has to be strong enough without the grout.