Seawater Pump 10

[PUMPDESIGNER]

I am being asked to replace the pumps on a four lane underground tunnel that is below sea level.
Project is overseas.
The pumps dewater the tunnel which appears to have moderate leakage from the ocean a few feet away, why I do not know.

The pumps in place fail constantly and they are tired of flying the manufacturer in to repair and replace them.

I have pumped seawater before, but not enough to know for sure how to obtain the maximum service life.

My first approach is to provide a multi-stage turbine, closed impellers, submersible motor, all 316 stainless. We do not have to pump solids, we can install self cleaning intake strainers.

The original equipment we are replacing is a rail type system for sewage, open impellers, cast iron body, bronze impellers.

We lift the water 40 feet, then move it 300 feet horizontally to the ocean to dump it.

Each pump will move 300 gpm @ 80 feet TDH.

Anyone with a firm opinion about the most reliable method possible?

PUMPDESIGNER

 

[sailoday28]

"We lift the water 40 feet, then move it 300 feet horizontally to the ocean to dump it." Please clarify
What is elevation of pump suction relative to the source level? What is elevation of final discharge relative pump discharge? ie, is the discharge at atmospheric pressure or submerged?

 

[jay165]

Pumpdesigner:

The problem of material selection has been discussed extensively under the "Saltwater Corrosion Engineering" forum. Suggest you do some searches to zero in on an answer. One thing I can tell you is that 316 is not acceptable in a saltwater environment.

 

[PUMPDESIGNER]

jay165 - I have heard before that 316 is not the best in seawater. I will follow your advice to check forums.
But quickly, I can get titanium pumps and motors, is that better?

sailoday28 - Pumps will be at the bottom of a sump in the water. Water then is pumped vertically 40 feet, then horizontally 300 feet with no fall or rise in that 300 feet.

Water is discharged at atmosphere or at high tide at most we would be 5 feet submerged.

This will help, I should have stated it in original post. System resistance including: 40 foot elevation, pipe and valves, is 76 feet @ 300 gpm.

PUMPDESIGNER

 

[sailoday28]

Is it possible that the 300 ft of piping is not flowing full and thereby decreasing system resistance? If so, depending on pump curve is NPSH met?

 

[PUMPDESIGNER]

I am sure of my system resistance statement 76 feet @ 300 gpm.
The required pump peformance is also correct, 300 gpm @ 80 feet.

PUMPDESIGNER

 

[Berko]

Hi Pump Designer,

Have you asked any pump manufacturers to offer advice on materials. After all, whichever one you choose for this application will have to give some form of warranty on the unit/s.

I am working on a similar application (but with Horiz. Split Case pumps) at the moment & we are looking at a pump with all wetted parts in Duplex SS.

I have no experience of Titanium pumps, but when working in the Nuclear Industry many years ago, all I can say is it is very expensive. For my own records, which pump manufacturer are you talking to who can offer Titanium pumps ??

Berko

 

[VER]

Pump designer, If water contains low dissolved oxygen < 1ppm, you may use nickel aluminum bronze material which is cheaper. However, if dissolved oxygen content is high, AISI 904L or Duplex SS must be used. These materials are widely used in Seawater Desalination plants with success. Goulds, Grundfos, and Flowserve are some of the pump manufacturers of submersible pumps that build pumps out of these materials.

 

[PUMPDESIGNER]

Berko and VER,
Thank you for your responses.
I can get affordable titanium from Grundfos.
I was already talking to Goulds, will talk to them more.
Was checking here because I have learned to be careful with manufacturers, they do not often put their top guys on the front line, the man I talked to in my office thought 316 stainless was good, but I had my doubts and check here first thankfully.

What is duplex stainless? Should I go over to the metallurgy guys to learn about that?

PUMPDESIGNER

 

[jay165]

You can also consider Super Duplex (25% Cr) and 90/10 CuNi as well. The major pump manufacturers should be able to help you.

 

[smckennz]

Hi Pumpdesigner
am a little surprised the existing pumps fail through corrosion; the combination is often used for seawater and normally lasts for quite a few years.
It may be advisable to check that the problem is in fact seawater corrosion and not something else. If the pH is high, titanium may be a disappointment.
I often use Grundfos for lighter duties; if you choose, be sure to check that the section thicknesses are adequate; they tend to use sheetmetal type construction which is unsuitable for long service duty. Also check motor efficiency which is often low in submersibles; especially borehole types. Somteimes is is better to go single stage dry motor if the sump arrangements permit.
My fave for seawater is still monel, although heaps of bronze impeller / CI casing seem to go forever.

Cheers

Steve

 

[PUMPDESIGNER]

smckennz - Thank you for your comments. I agree with most that you stated, specifically that Grundfos tends to be the cheap hydro-formed sheet stainless or titanium, and there are in fact many CI with Bronze impellers out there working.

I will investigate more to see what problems they are having. I do know for sure that their largest problem is seals failing and then the motors fill with water and destroy their motors. That means they must be using oil filled motors. I checked the controls and they are operating them alternately and every few days each pump works, so sitting there in the water is not the problem.

PUMPDESIGNER

 

[smckennz]

Hi Pumpdesigner
not all filled motors use oil; some use distilled water.
They are shipped dry and occasionally users dont realise they have to fill them. Others fill them with tap water and experience insulation failures.
With the exception of Flygt and Grundfos, I have had a lot of trouble with wet motors. If a "trusted" brand is not suitable for the duty, my preference is dry (out of the water) motor pedestal type pump. then I only have to worry about the shaft guide bearings and servicing/lifting arrangements. some other members may be able to recommend other good brands of submersibles.

Cheers

Steve

 

[PUMPDESIGNER]

Thank you all for your comments.
Good comments too.

I have not the luxury of testing or observing their problems. But I think corrosion is not their problem based on their answers to my questions.

I think that perhaps the seals are failing on the existing pumps because they are allowing the pumps to operate too far out of their range, wide open in fact. That could cause high vibration that would tear up seals. I am guessing of course and at this point I will just have to play safe and do it all well, including putting flow orifices into the lines to force the pumps to operate within their range.


PUMPDESIGNER

 

[Artisi]

Hi Pumpdesigner
A bit more back ground to the failure / operation / pump make - model, how are they installed, how are they operated etc. would be nice.

I would initially be looking at an application problem rather than at a "pump" problem - because for 300 gpm at 80 ft - there are plenty of good quality contractor type pumps to do this job for ever and a day.

One of the problems I have found over the years in applications like this is poor control on the operating sequence with the pumps running constantly or for long periods with little flow thru them. If the pumped liqour contains a lot of fine solids - which is very likely in the application you are describing and if they are running for long periods without flow, you end up with a lot of abrasive material going round and round in the pump - it can be hell on seals and the wetted wear parts.
It could even be posible that they are running dry.




Naresuan University
Phitsanulok
Thailand

 

[PUMPDESIGNER]

Hello Artisi, God willing, perhaps we'll meet some day.
I guess I am in a continual bad mood lately. Facing tons of work on failed systems where the pumps sold to the customer are failing continually, often around once every 1-2 years. Customer gets worn out paying for this and then starts looking for help, finds us.

So many people claim to be experts, then they make a living off repairing what they sold to the customer in the first place. I am not a skeptic, and not a generalist condemning the industry, but just tired lately from the inundation of junky situations. In the morning when I feel better, I will probably be glad that we have this work, it is good work, and the people are more than willing to ante up the money, usually much more money than they gave to the orginal guys. In fact, I suppose I should enjoy the prestige and the higher prices we command. But I would just a little more often like to be there in the first place to get it right from the get go.

God Bless.



PUMPDESIGNER

 

[TZellers]

Don't overlook non-metallic, unless you like spending money. Seawater would be a slam-dunk. Can you use a vertical sump pump or do you need the VT? say like the VGRP from Flowserve or similar from Goulds. Multistage seems overkill for 80 feet. My 0.02.

 

[PUMPDESIGNER]

Thank you TZellers,
I was hoping someone would make specific recommendations.
We are really good at turbines, one stage would do this easy. We like turbines because they have no radial thrust at any flow rate, makes it easier to control properly and the pumps tolerate abuse better if the locals get to playing around with it. 10 years later they show up wanting more of the same because no other pump was able to withstand their use/abuse.

Anyway, I am very grateful for your recommendations. I will go to the flowserve site and have a looksy.

Do you have experience with the Flowserve pump you mentioned? Is it a Double Volute?

PUMPDESIGNER

 

[TZellers]

Yes, I do. I used to work for IDP, which is now Flowserve. To make matters confusing, the VGRP was originally designed by Ingersoll Rand, prior to their VJ with Dresser; but I digress.

The VGRP is nothing more than the standard ANSI non-metallic (GRP) wet-end mounted vertically and supported via non-metallic column. Therefore, parts interchangeability are decent. I can't recall if Goulds has one or not (vertical), but they certainly have the horizontal type (3196NM). The other big guy is Fybroc, with their Series 5500.

I can't recall which sizes have dual volutes. Usually, dual volutes come into play in the Group III sizes (13" and 15" nominal impeller sizes).

Options abound with pit covers and level controls, duplex or simplex arrangements and so forth. Just stay away from cantilevers and you'll be ok. IT doesn't sounds like a cantilever would work anyway based on the depths.

 

[KASTNER]

Hi

Im a german Pump Expert and in this job also responsible for the After Sales of Sea Water Pumps / Desalination Pumps. Because Sea water is not around the world the same sea water we do use today only the best one what we can get to manufacture the best product for the customer. The material 316L is according the standards fot sea water application suitable and in 80% you can use it (in cold water areas) without problems. In hot water areas and in slow flowing harbour areas is the best material god enough.

If you want to go a perfect way you should use a Duplex / Norichrom pump. To get more information about the special for the Desalination application designed pump, you should have a look the the homepage of (

http://www.KSB.com)

or contact the company KSB somewhere around the world and ask them about the pump "HGM-RO" (high pressure multistage pump - reverse osmose).

Regards from Germany
Jochen