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Pipe diameter change

Pipe diameter change

(OP)
Hi.
In inlet and outlet pipe nozzles we have diameter reduction or enlargement. Why?
For example picture of outlet nozzle of multistream heat exchanger have been attached. Why?


RE: Pipe diameter change

The pump discharge nozzle size is a function of the design of the pump.

The suction nozzle is generally sized one size larger than the discharge nozzle. Some exceptions are noted for specific types of other pumps such as solids-handling pumps where the suction nozzle size is made the same size as the discharge nozzle so that particles that enter the pump can also exit the pump. This assumes that the impeller design in that pump will also pass the same particle size.

The reducer on the inlet side of a pump ensures that the fluid velocity in the suction line is slowed sufficiently to provide a smooth flow of liquid with minimized friction losses in the piping to ensure as high as possible the NPSH available from the system.

The increaser on the discharge side of the pump is designed to increase the pipe diameter from the pump nozzle to reduce the fluid velocity in the discharge piping in order to reduce the total head the pump is required to pump against.

RE: Pipe diameter change

Hosein,
For anyone who is trained, experienced and familiar with process plant Piping it is quite normal and quite simple.
A The Vessel Nozzle and the joining Flanges (on the right) are one size maybe 18" NPS.
B The pipe (on the left) is another slightly larger size maybe 24" NPS.
C The Reducer (in the center) is how we join the two different sizes together.

Why are you questioning the Design?

Sometimes its possible to do all the right things and still get bad results

RE: Pipe diameter change

Inlet and exit nozzle sizes for vessels and heat exchangers are usually based on some approach to an upper limit on rho-v2. For shell and tube HX, see TEMA design books for inlet and exit nozzle size rho-v2 limits for various applications.

While in plant piping line sizes are based on generalised pressure drop limits or velocity limits(in most cases). Noise limits may also apply to continously operating high velocity flare lines.

RE: Pipe diameter change

Why are you asking, as pennpiper has already asked.
As to why, well this is what the pipe engineers specified.

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.)

RE: Pipe diameter change

(OP)
Quoted "While in plant piping line sizes are based on generalised pressure drop limits or velocity limits(in most cases). Noise limits may also apply to continously operating high velocity flare lines.".
I'm searching for this type of answer. I think there are lots of philosophy beyond this design.

RE: Pipe diameter change

Quite simple. Think about it. Nothing more than this. If you need a pump that has a capacity of 100 L/m, one that operates at 3600 rpm would be one half the size of a pump operating at 1800 rpm. One half the size usually means very much cheaper equipment and by using the smaller equipment, you can have a smaller plant. But faster velocity, high speed machines, pipe and equipment generally means higher pressure drops, bearing wear, lube oil consumpiton and the need for more maintenance. Design life usually is shorter as well.

The typical plant design problem: How to build a plant with the capacity I need as cheaply as possible that can operate for the longest design lifetime.

Solution:
If you can operate at a faster velocity, you can use smaller, usually cheaper, equipment. But pressure drop will be higher when the fluid has to travel through the small equipment and pipe size when moving at that faster velocity, so if you made all the pipe in the whole plant equally as small as the equipment, you wouldn't have enough pressure to get the fluid to the other side of the plant. The alternative to that is increasing the design pressure, which again would increase cost of designing equipment and pipe for the higher design pressure.

The optimum solution: How to design the lowest cost plant having the capacity I need depends on the cost of all the equipment and pipe. Equipment is very expensive and pipe is relatively cheap, so you can easily see that the best way to optimize the whole problem of designing a plant that uses expensive equipment and cheap pipe is to selecct the smallest, cheapest equipment, operating at the highest velocity and complement that by use of the largest pipes, operating at lower velocities and low pressure drops to keep total pressure loss across the plant to a minimum. That keeps the equipment costs low while larger diameter pipe, still having not so high pipe costs, give acceptable pressure losses.

Result: The plant is designed for required capacity, acceptably long design lifetime, runs at reasonable cost and has the smallest footprint. Optimized!

Technology is stealing American jobs. Stop visas for robots.

RE: Pipe diameter change

Not lots of philosophy, just correct engineering practice and knowledge applied to the design.

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.)

RE: Pipe diameter change

(OP)
BigInch (Petroleum), what are you talking about?

RE: Pipe diameter change

Plant design procedure. You ARE an engineer, right?
If you don't get that, you will never understand.
Do you think that equipment piping is smaller than plant piping because the fab shops can't buy bigger pipe??? No, there is an engineering design-cost optimization reason for it.

What part are you having trouble understanding?

Technology is stealing American jobs. Stop visas for robots.

RE: Pipe diameter change

For custom designed equipment, the engineer can make the nozzles whatever size they want. This doesn't mean it will be the size you want, right? For mass produced equipment, what you see is what you get. Then, there is equipment that is in between these two extremes. On a 13 inch impeller centrifugal pump we use, we can get either a 4" x 3" or 6" x 4". The choice is a matter of cost; the pump curves are nearly identical.

If the engineer can put a successful process together by wisely choosing the many pieces of equipment together, with their various sizes of nozzles, with pipe, valves, and fittings, then the engineer keeps his job/paycheck. If not, he doesn't. It is a highly personal optimization problem.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: Pipe diameter change

"You ARE an engineer, right?"

You may have identified the problem.

RE: Pipe diameter change

I think so too. Maybe he's a chemIST, as in not A chemical engineer.

Technology is stealing American jobs. Stop visas for robots.

RE: Pipe diameter change

In two phase flow, line sizes should also be based on avoiding undesirable slug flow regime throughout the entire turndown range. If not, you can have thermal duty failure in heat exchangers or excessive liquid loads in vessels for example.

Sometimes, a separator drum is used to split out the vapor and liquid phases in a 2 phase feed to a HX and act as a surge vessel also, and the 2 separated phases are directed to individual passes in a multistream HX for example. There are many cases reported of multistream HX thermal failure resulting from slug flow 2 phase streams fed directly to the HX w/o an intermediate V/L separator drum.

What is the problem with the configuration in the photo ? You have us all guessing.

RE: Pipe diameter change

Problem?
I don't think there is any problem. He just wants to know why the equip nozzles are smaller than the plant piping.

Technology is stealing American jobs. Stop visas for robots.

RE: Pipe diameter change

(OP)
Mr Biginch, I think you get me wrong!! If I'm being ungracious I apologize.

Not to brag, but I'm an engineer with descent eng-view. I know there's a reduction in pipe diameter, due to engineering consideration.

Quoted: "there is an engineering design-cost optimization reason for it."
I'm wondering what is that engineering design-cost optimization??

Look! I think we should consider lots of limitation:
1- corrosion limitation
2- pressure drop limitation.
3- Velocity limitation.
4- ...

Is there anybody show me how a desinger consider this limitation???

RE: Pipe diameter change

Well then put your engineering hat on.
The reasons you mention are the exact same that I told you above. Except for corrosion, which is unimportant in sizing considerations. Maybe you mean erosion, which might have an affect, if your fluid is heavy or dirty.

Technology is stealing American jobs. Stop visas for robots.

RE: Pipe diameter change

(OP)
Well, I don't think you mention that!!! anyway, I put my hat on long time ago, dear!!!

RE: Pipe diameter change

Thank You for your expression of gratitude.

Technology is stealing American jobs. Stop visas for robots.

RE: Pipe diameter change

For me the first thing I would be considering is the best pump selection (in terms of pump hydraulic efficiency)for the flow required and the minimum total head across the pump/s. I would run some quick head loss calcs. with the discharge pipe at the same diameter as the discharge flange and review the numbers, if head was considered excessive I would go up a pipe size and repeat the exercise until such times I was satisfied the power costs / pipe costs were at an acceptable levels to each other. By the pipe sizes shown it would appear this is a largish pump and every point of hydraulic efficiency lost could run you into mega bucks over the years of operation.
It's not rocket science, it comes down to straight economics.

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.)

RE: Pipe diameter change

BigInch, I wouldn't normally be so pedantic, but I'm stuck at work not getting paid "in case something comes up" right now, so I've got all the time in the world to mention that there are several corrosion mechanisms that are dependent on fluid shear, independent of erosive effects. So corrosion isn't totally independent of sizing considerations.

Naphthenic acid corrosion, flow accelerated corrosion (speaking of a very specific phenomenon in BFW systems) and ammonium bisulfide corrosion are the ones that spring to mind immediately.

RE: Pipe diameter change

NBrink, I wouldn't argue with you at all. Thanks for telling me about that. Makes sense. Other than I just didn't plain know about it, I didn't mention it because I wanted to keep the explanation of the classic pipe size trade-off problem limited as simple as possible. As it is, it seems that the OP didn't understand too much of my simplified explanation anyway.

Technology is stealing American jobs. Stop visas for robots.

RE: Pipe diameter change

I would place my bets on the process designer having a velocity and pressure drop in mind that means a larger pipe than the 'standard' of the HEX supplier.

A piping designer should be concerned about what the larger piping is doing the smaller HEX nozzle. The larger pipe is stiffer and will put high loads on the smaller nozzle. Often we will specify larger nozzles that the connecting pipe just to keep the nozzle loads under control.

RE: Pipe diameter change

There are also velocity limits related to corrosion for copper nickel lines in seawater service. Upper velocity limits also apply for water wet non CRA hydrocarbon gas lines where corrosion inhibitors are being injected continously.

RE: Pipe diameter change

KevenNZ,
You mention a very interesting point about the pipe loads. Larger pipe is stiffer and will put high loads on the nozzle. That mMakes sense.
Larger pipe catches more wind and weighs more, so wind and gravity, and even dynamic loads would be higher for moving pipe (on a ship for example). That started me thinking about thermal loads. When large pipe and small pipe are operating at equal temperatures, stressses will be more or less equal, but the larger pipe will place greater loads on attached equipment and supports.

While as logical as that is, I would say that, due to the design sequence as it passes through process and then into piping and then pipe stress flexibility engineering. It is somehwat isolated, as there is little opportunity for feedback from piping to process. Process is acustomed to telling us the pipe size and how big the equipment should be, because they've done the velocity, power, and cost optimization study already. So that's ususally the end of the discussion and as a consequance, the environmental and thermal loads are not often included in the pipe diameter - equipment size optimization practices. I will say the same for corrosion and erosion as well. The piping and corrosion engineers may come to mutual agreement on increasing pipe size, but that decision is not normally (in my experience) isn't part of the pipe diameter - equipment sizing optimization. About the most that would ever happen as a result of increasing pipe diameters for corrosion or erosion, or load limiting purposes on a typical petrochem project would be reanalysis of overall pressure drop and adjusting the pipe purchase budget. Pipe diameters would be increased and anchors would be added to make the piping enginer happy and possible further affects on equipment size would not be considered.

At least it's that way for pipeline, refinery and chemical plant design where heavier pipe weight and larger gravity, dynamic and thermal loads are more or less easily and cheaply accommodated. The practice is different, if the pipes were going into an airplane, SpaceLab, or the starship Enterprise, or in ocean going ships and offshore platforms, where accommodating high weights, loads and large piping and equipment volumes can all be relatively costly, or dangerous, to have onboard.

While there could be a number of other factors that may affect the pipe diameter -equipment size optimization, I have to stick with the idea that the two most important factors are the relatively low cost of large pipe, to keep operating pressure to a minimum vs the higher cost of buying larger equipment that must operate at high pressure. The resulting optimized objective then becomes purchasing equipment as small as possible for the given capacity and lowest possible operating pressure. To put it in terms of what the OP might understand. Nobody is going to spend millions extra on buying larger, heavier equipment just so the nozzles can match the pipe diameter. (... no matter how nice it would be to get rid of those eccentric reducers that nobody seems to remember which way to orient the flat sides.)


Technology is stealing American jobs. Stop visas for robots.

RE: Pipe diameter change

Subtle BI smile

RE: Pipe diameter change

Did I go too far down that dirt road?

For one, nobody has ever changed my pipe size because of any corrosion concern. That was why I never thought of it before. And I have changed pipe configuration before because of thermal stress, but I don't recall ever changing diameter, or even wall thickness. I know that offshore platforms conduct weight reduction studies, but usually they have more of an affect on establishing maximum process, methods and capacity rather than on things as specific as pipe size, is there weight and room available for dehy, or will we pipeline with two phase flow to the next platform?

Technology is stealing American jobs. Stop visas for robots.

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