7 replies to this topic

[dylant]

Hello,

Am trying to find the price of PVC pipe. I have been calling some vendors and they do not want to share the information.
Does anyone know or have the pricing information for PVC pipe?

Thanks,
Dylan

[mvancleave]

If all you need is smaller sizes (4-inch and below), try www.grainger.com. Your local hardware store can help with smaller sizes as well (possibly up to 6- or 8-inch). For anything bigger, that won't help.

It's too bad vendors won't give you quotes.

[dylant]

The problem is... I need a big size. I did my calculation and found out that I have to use 46 inch diameter PVC pipe.

If all you need is smaller sizes (4-inch and below), try www.grainger.com. Your local hardware store can help with smaller sizes as well (possibly up to 6- or 8-inch). For anything bigger, that won't help.

It's too bad vendors won't give you quotes.

[pleckner]

Please provide what we commonly call, "The Rest of the Story", i.e. some details of the system you are trying to design.

[dylant]

I am flowing sea water at a rate of 1.6 kgmole/hr, pressure = 35 psia, pressure drop 10 psia, temperature 12 Celcius. Am planning to use PVC pipe. I did the calculation and found out that I need a PVC pipe which has 46 inch of diameter. Since the pressure is not high, I bet schedule 40 is adequate.

However, since the pipe is so big, it needs to be customized. I am having trouble finding the price because I have not found any vendors who're willing to share information for such pipe or pipe with big diameters. Thus, I am wondering if somebody is familiar with the pricing of schedule 40 PVC pipe.


Thank you,
Dylan

Please provide what we commonly call, "The Rest of the Story", i.e. some details of the system you are trying to design.

[Art Montemayor]

Dylan:

As Phil infers, the rest of the story always turns out being the real important part of the scope of work.

If there are no typos and the terminology is correct, you have 1.6 kgmole of seawater flowing per hour. This translates to:

(1.6 kgmole water/hr) (2.2lb/kg) (18 lb/lbmole) (hr/60 min) (gal water/8.35 lb water) = 0.126 gallons seawater/min

I don’t think this is correct for a 46” ID pipe. There is either a huge typo or the terminology is not being applied correctly. I would expect something of the order of 20,000 gpm to 50,000 gpm as appropriate to a 46” ID pipe! Please tell us what the correct seawater flow rate really is.

If this thread involves a student problem that is merely academic instead of a real-life application (as I believe it is), then I think that that is more important as the rest of the story. I have frequently voiced my opinion on this Forum in the past that it seems ludicrous for engineering professors to insist that their engineering students do an “accurate” cost estimate of their assigned design problem. This type of exercise is, in my humble opinion, simply a waste of good student time that could be better spent in discussing and analyzing their solution to the problem and justifying the methodology to the profs. The cost or price of equipment and services is such a black art in the estimating field that it really serves no purpose to bring it up. All that is important, in my opinion, is a valid, safe, and thoroughly defended design that can be easily explained with engineering logic and calculations. The price of a piece of pipe depends on location, need, market situation, labor situation, politics, demand, and a host of other variables that few, if any professional cost estimators really understand. I cannot imagine a university professor being able to discern whether a pipe estimate is “accurate” or not. Hell, he is way out of his/her league and knows even less than I do about real, market prices. And that’s good! He/she have no business getting involved in something that is way out of their field - and totally out of their control and understanding. There are so many other more important engineering subjects to teach and so little time to do it in, that it is almost a crime to waste a student's attention on the subject of cost estimating at the university level. There are no such courses taught in universities because there are no profs that qualify to teach them.

Therefore, the best, logical way to assign a reasonable estimate to a PVC pipe would be to calculate the unit cost of a known piece of PVC pipe ($/lb) and apply that to the equivalent mass of the larger pipe --- plus a reasonable contingency for the added cost of it being much larger to fabricate and handle as well as for market demand being low.

And that’s what I would hand in to my prof if it were me, explaining to him/her that it represents my best, honest, and logical engineering estimate – based on what it is intended to be used for. And if the prof doesn’t like that effort, then I am studying in a very, very, illogical engineering department and am not getting my money’s worth! And I would tell them so!

[dylant]

Interesting opinion, Art. And it is an interesting method you're suggesting. I never thought of calculating the price based on the weight. What I have on my mind was to collect some data of sched 40 PVC pipe of different diameters, make a graph, and use excel to generate an equation. Am tired of calling people and sending them email just asking how much things cost.

Anyway, it was HUGE typo. The seawater stream is 1.687e6 kgmole/hour.
Thanks for correcting.

-Dylan

[Art Montemayor]

Dylan:

I'm addressing the issue of cost estimating in this thread not only for your benefit, but for those other countless Chem E students who are wandering around, thinking that it should be addressed with unlimited amount of budgetted time and effort. After 47 years in this business - out in the trenches, and not in the university lecture halls - I can tell you with first-hand experience that NOBODY in his right mind expects a Chem E grad with less than 5 years of hands-on experience to turn in a credible, approximate, cost estimate on a real-life industrial application or project. It just doesn't make for common sense - or for good business practices. It's not that the young grads can't do it; they CAN, but with no less the same amount of experience and exposure than the Business Administration grads. Hell, the BA grads (& profs) will admit to the same thing themselves. It is ludicrous to think that cost esimating is simply a matter of dialing a few numbers or asking the right people and getting accurate costs for a project that won't be purchased for at least 9-12 months in the future.

It just makes for common sense to admit that one can't predict the cost of something like gasoline prices with accuracy - and it makes even less sense to make it a pre-requisite for an academic exercise that is only fiction. What difference does the accuracy of the cost prediction make for the engineering quality of the academic product? And who is going to prove otherwise that it is not "accurate"? I firmly believe that your Chem Eng profs should tire you out --- but in the process of instilling in you the practical, scientific, and engineering knowledge that you need in order to graduate with honors and capable of competing on a world-wide basis. That's the bottom line. Now that is worthwhile getting tired out for.

Cost estimating IS important - but for other reasons which you will soon learn when you graduate. Good business decisions are based on sound and dependable cost estimating. But you won't be called upon to make those sound and dependable decisions in your early years. That's when you will be busy amassing the experience and know-how of how to arrive at those sound decisions and those credible cost estimates. Right now, while you have not yet graduated, the important thing lies in knowing that good estimates are a formidable challenge in the future and that you should be aware that they are and what are just some of the tools that you can use to begin the process of cost estimating - and with what restraints and obstacles. In order to obtain accurate estimates you need business leverage: the ability to convince people that you have the money and the means to make a purchase from them in the time increment that you need. As you can well imagine, for that you need a formidable business position or an authoritative and credible job title. And that's only the beginning. Your company or business affiliates also need the same credentials. That, mainly, is the reason why a simple Chem E student can't just pick up a phone and obtain a credible, industrial-based cost estimate on equipment or services. It's that simple. Suppliers need a base from which to do business. They can't waste their time on those that have no intention of purchasing anything from them. They have other areas that they must cultivate in order to justify their existance and their business.

Unit cost estimating based on weight is not so far-fetched. It is just as logical a method as estimating heat exchanger costs by the $/ft² method. I personally have known many professional cost estimators that use it for estimating and budgetting the purchase of piping and process vessels - as well as structural steel. If you know the manufacturing process, you can make an accurate estimate based on the $/lb basis. I believe it is a viable and credible basis for a cost estimate if used intelligently and with good judgment.

I hope this helps explain what I previously gave you in a succinct and short response. The issue is important and it will not go away. I have known many Chem E students who tremble at the mention of having to make a cost estimate of an entire project. And these have been students who knew what they were doing and calculating. It shouldn't be that way at all. They should be told the truth and the practical, every-day challenge that awaits them in the industrial world. It's not complicated; it's just common sense. Engineering doesn't have to be Hell; it can be a lot of fun and personal enjoyment as well as a well-compensated career.