Dismantling joint on pump suction 8

[Bahman07]

Hi
I am new here, and this is my first activity.
I am working on a water pump station. there is a debate on using dismantling joint on pump suction pipe for maintenance. Since we are using expansion joint on this line, is there a way to not considering dismantling joint? I have to say that suction pipe is from a concrete tank to pump nozzle.
Basically, are there any standards or practices for mandatory using of dismantling joint?
Thanks in advance

 

[bimr]

You need to supply a little more information. Is this for a 5 HP pump or a 2000 HP pump? Is the pipe 12-Inches or 50 feet long? What type of pipe?

There are no standards for using dismantling joints.

 

[LittleInch]

What is a "dismantling joint".

It may be common terminology in your workplace, but it isn't in mine.

Also what type of expansion joint - there are many types available.

A drawing or sketch would help a lot.

There's noting mandatory, but if you need to remove the pump and you can't slide the pump back a few mm to remove a spool piece then you can get into lots of trouble trying to generate enough movement to break the pipe joint.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Bahman07]

Hi
In order to more detail, I could not find the HP of pump, it is 355KW. The suction pipe is 24" reducing to 20". Length of pipe from tank to pump is 10m. Pipe material is carbon steel.
I attach an image of component which I mean.
Our expansion joint has not been finalized yet, but it is preferably rubber single type, and it connected to pump nozzle.

DISMANTLING JOINT:

 

[TugboatEng]

Bahman, in this case it depends on who installed it. Personally, I put double gaskets in during the fabrication phase. This ensures that the joint will not be in compression when installed. This allows the joint to be slid in and out of position easily or if the equipment is installed between two joints it can be slid in and out of position. In the field, I find this to not be the case and usually sections of piping have to be removed for access.

 

[Artisi]

A joint as such connected to a pump suction is very likely to cause poor inlet conditions leading flow separation and vibration.

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.)

 

[bimr]

Most pumps require a straight run of 5 pipe diameters before the pump suction. That would be about 10 feet.

Dismantling joints are used where it will be difficult to remove the piping because of clearance limitations. If you are routing the pipe straight from the wall to the pump, you will have problems removing the suction pipe at a later time.

I would recommend that you skip the expansion joint and just use the dismantling joint. Many piping designers avoid using expansion joints. Design the pump piping so there is no expansion joint. Expansion joints are not reliable, prone to fatigue failure and thus cause loss of production and could possibly injure operators and maintenance workers.

Install the dismantling joint at least 10 feet away from the pump suction. As you stated, you have 10 meters to work with.

Be sure to use an eccentric reducer to avoid trapping air.

 

[TugboatEng]

I strongly disagree agree with expansion joints being prone to failure. Incorrect material selection and pipe support cause issues that are not the fault of the joint itself. Oil is tricky because compatible materials are expensive. But for water, neoprene, EPDM, and silicone, can all provide 30+ years of trouble free service if correctly applied based on temperature.

 

[bimr]

THE DIRTY LITTLE SECRETS OF PREMATURE EXPANSION JOINT FAILURES

How to Troubleshoot Expansion Joint Failures

a last resort due to their construction they are a weak point in the piping system

Both rubber and metallic expansion joints can and will fail. The best insurance against a catastrophic expansion joint leak is don't use expansion joints.

As I said, an exp joint is always the LAST resort.

 

[TugboatEng]

Bimr, your first post confirms what I said about improper installation. You're other posts are in reference to high temperature high pressure applications where pipe design including expansion loops is used to limit strains. Those are niche applications.

 

[HTURKAK]

Dear Bahman07 (Mechanical),

- The use of fixable dismantling joint will be necessary if the pump can not installed again if dismantled for any reason. That is, if the pump inlet and outlet piping has axial thrust to pump , and the outlet piping is connected to header , you cannot install the pump if you do not dismantle the total outlet piping. You should question that, Can each pump be dismantled and installed separately ? if yes you do not need dismantling joint..

- The use of expansion joint: Is this recommended by the pump manufacturer ? . If not, i want to remind that, in case of expansion joints at suction and pressure side, the pump casing, frame..will experience the full thrust.. That is, you are expected to ask manufacturer's permission!!!

I suppose that the pumps are omega type centrifugal pumps similar to the picture below;

If you provide more details , ( at least some sketches for proposed piping etc). you may get better responds..

 

[Bahman07]

HI HTURKAK
I attached an image of my 3D model. Suction is the straight line to pump, and the dimension is in mm.
We have the permission of using Expansion joint.

 

[HTURKAK]

Hi Bahman07 ,

Can you provide the isometric dwg of piping showing the supports , valves fittings etc..?

My suggestions will be,

- for the suction side; provide fixable dismantling joint but not expansion joint. The reducer shall be ecc. reducer with flat on top construction. Provide supports to keep self standing the inlet piping .

- For pressure side , you should provide C.V. , Check Valve , and may be by-pass valve.. You do not need neither expansion joint nor fixable dismantling joint for the pressure side. Provide necessary P.S. so that the piping is self standing and it imposes no strain on the pump casing.

- Ask the recommendations of pump manufacturer for the piping set -up.

P.S. How the inlet pipe is connected to reservoir ? İs the reservoir connection axial thrust resistant ? ( e.g. with puddle pipe and flange ?)..

Good Luck..

 

[Bahman07]

Hi
I Can not provide isometric with support now. In suction run there are a butterfly valve, ecc reducer and expansion joint. On discharge check reducer and check and butterfly valve has been considered.
the inlet pipe connected to puddle pipe.
Thanks for your answers.

 

[TugboatEng]

With that big U bend you eliminate the need for dismantling joints as the U can be easily removed to facilitate service of the pump provided your team doesn't mind doing a little bit of rigging as your pipe is quite heavy at that size.

 

[Bahman07]

TugboatEng, in previous post, you suggested, using dismantling joint and removing expansion joint on suction, why this is better and not expansion without dismantle?
sorry I thought about it after my last post.

 

[1503-44]

You have not been paying attention.
Elimination of ANY expansion joint is well worth the effort.

 

[TugboatEng]

Honestly, I was a little confused. Dismantling joints don't exist in the marine industry. Properly installed, the expansion joint serves as the dismantling joint.

 

[1503-44]

Yeah. Even when you don't want it to.

 

[Bahman07]

Sorry TugboatEng, I had to mentioned HTURKAK.