Estimating Cost of Sand Casting a Pump Casing 5

[MaintEngnr]

In the land of government contracting we are required to perform an independent cost estimate to compare to the customers quote. This becomes extremely difficult when it has to be done for a proprietary piece of equipment. In this case I have to develop an estimate for a 14 stage centrifugal pump casing and I don't have access to any fabrication drawings. Additionally, the only experience I have with castings was in a class in college. I have gathered some information online, but it is limited. Given it is a 14 stage pump, I would conclude that it would be a complex casting with many internal cavities for each volute and discharge from one stage to the next. The casing is split into an upper and lower half with a thick mating flange due to the 7300 feet of TDH across the pump. The lower case half has both the inlet and outlet flanges. It is just shy of 8 feet long and a little over 2 feet wide. The material is CA6NM (martensitic SS) and I was told it would likely be cast using the sand casting method. Are there any good resources out there that might help turn this into a more manageable task?

 

[EdStainless]

I used to make these, or at least similar ones.
We don't know what flow rating you have either.
Your only hope is to get other quotes and compare them.
The manufacturing costs are very complex.
You have cast bowls and impellers, and then all of these need to be machined.
You have inlet and outlets with flanges that may be cast or may be machined from bar.
There is also the shaft, and then bushings, and various hardware (clips and keys).

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P.E. Metallurgy, consulting work welcomed

 

[Artisi]

Put what ever price you think is a fair thing, if the bean-counters insist you go for pirate manufacture in lieu of OEM, let them suffer the consequences of not being able to find someone interested in making a guaranteed identical quality item as you can get from the OEM.
You will probably find it extremely difficult if not impossible to find anyone to even quote on its manufacture.

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.)

 

[TugboatEng]

Read the fine print. There must be exceptions. This must be an existing system you are repairing. Otherwise, you wouldn't need a specific pump. There are usually clauses that allow you to use the OEM for repair or replacement.

Otherwise, instead asking vendors to develop a new pump you need to do your due diligence and find an existing alternate pump that has similar performance.

 

[MaintEngnr]

We have two of these pumps in operation. We have a spare rotating assembly (shaft, impellers, etc.) that we keep in storage and use each time we rebuild one of our pumps to cut down on down time. The rotating assembly removed from the pump being rebuilt is then refurbished and put into storage as the spare. It was decided that we could further cut downtime if we just had a new case manufactured and then assembled as a spare pump with the spare rotating assembly and other spare parts that we have on hand. We already use the OEM for our pump rebuilds. As an alternative, I have tried to locate a used pump to rebuild. I was able to find several used pumps from the same OEM, but they are a high flow, low head variant (718 GPM, 4370 ft of head) whereas our pumps are a low flow, high head variant (375 GPM, 7300 ft of head). I spoke with a company (not the OEM) that rebuilds pumps and was told that modifying the case would be either prohibitively expensive, but most likely not feasible. I am pretty sure that unless a non-OEM could guarantee the same results as an OEM, then management would not be onboard with going with them.

 

[TenPenny]

There are replicator shops that can build new casings using 3d imaging and 3d pattern printing. What manufacturer is your existing unit? Can you take one of your units out of service to be measured? What part of the world are you located in? There are possibly several options to pursue depending on your specifics.

I know there is a shop owned by one of the big OEMs that has access to old pattern drawings and can 3d print new patterns, they can also use lasers to measure old casings to develop drawings to do the same.

 

[MaintEngnr]

I appreciate the input, unfortunately not a viable option for us. Back to the main question, which is regarding estimating the cost of the casting and the availability of resources to help get me develop a reasonable estimate.

 

[3DDave]

I don't see how you can estimate the cost. That will depend on the company that is doing the work and what facilities they have and vary with fluctuations in factory capacity/schedule and material availability/cost.

Company A might bid X and Company B might bid 10X. Look at your personal experience with castings of this size and complexity - if you don't have that experience what exactly can you use as an estimating basis?

It seems like this is intended to be a negotiation tool with an OEM that you think is charging too much for a spare case? Professionally, I don't see that as a good move. Unless you buy 20% of their output they might invite you to find another supplier.

 

[LittleInch]

OK, so reading this through it looks to me like you have a price from the OEM, but the bean counters from the government require you to provide an alternative quote.

Given that this is virtually impossible / verging on stealing the OEMs IP, my suggestion is that you simply write a short technical note stating most of the above, i.e. that no one else makes this complex, bespoke casting, there are no second hand ones available due to your specific requirement and you can't find anyone (list who you tried) to quote, plus this would be tantamount to patent / IP infringement given that the OEM is still in business and can provide you with a spare casting.

If possible find a casting shop and just ask them nicely / do you a favour to send you a short e-mail saying "No can Do" or quoting some extortionate amount as a budget cost. And / or that other company you quote just to get it in writing.



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

 

[MaintEngnr]

Thanks for the input. I'll figure something out!