Piping Forces on Centrifugal Pump Connections

[JohnSr]

What are allowable (or reasonable) axial, transverse horizontal and vertical loads imposed by the connected piping on a horizontal centriifugal overhung back pull-out process pump? The pump in question is a Goulds 3196 XLT-X 4x6-17(15.5). It meets ANSI B73.1M and RESP 73H.

I know that API-610 specifies allowable loads for pumps that meet that Spec. and I believe they are a function of the nozzle size and the pump weight (among possibly other things). My pump is ANSI and I haven't been able to find similar information for it. Thanks for any help.

 

[checman]

John Goulds does have that information available. You need to contact the Goulds rep in your area or ask Goulds online. A good expansion joint with limiting rods may take up the load and keep the pump components in line and running smooth.

 

[JJPellin]

As a practical matter, the loads need to be very low in order to avoid negative implications on reliability. If you break the pipe flange loose, you should be able to slip in all the studs without applying any more force to the pipe that you can apply with your hands. (no chain-falls, come-alongs or jacks). If you place dial indicators across the coupling gap and tighten the flanges, the pump shaft should not move in any direction more than 0.002". For cold piping systems, this is very achievable. For hot systems, you have to rely on the piping designer to correctly model the system to account for thermal growth of the piping once it is in service. And this is a less exact science. We have had piping systems that passed this analysis, but then imposed such high forces in the hot condition that they cracked the pump support feel and destroyed the coupling. This may not provide the quantifiable numbers that you are looking for, but for the case of pipe strain, I feel that the numbers can lead to problems. The pipe forces that the pump company say are acceptable are probably excessive. The pipe forces that API or ANSI say are acceptable are probably excessive. And the pipe forces that a piping designer says are acceptable might be excessive if he is not very skilled at his craft.

 

[Zapster]

Not so sure expansion joints are such a good idea unless space constraints in the piping system will not allow sucifecint pipe flexibility. For example take an API 610 pump with a 6” end inlet. API 610 allows 700 lbf on the end nozzle "Fx" and 870 ft*lbf "My". For this hypnotically horizontal pump both distortion of the pump casing and misalignment of the pump and drive shaft were considered when the manufacturer designs their pump to API 610 specs. Looking at the code, the allowable pump shaft displacement ranges between is 0.005 to 0.007 inches in the Z direction when "My" is applied depending on grouting considerations. So far, seems ok per code.

Now assume an engineer is too lazy, cheep, or lacks the skill to do a flexibility analysis on the pipe system and just specifies an expansion joint. This might be fine if it is an atmospheric pressure system; however, lets say this is a booster pump and the system has an inlet pressure of 100 psig. Now there is a load on the pump housing (not the nozzle, but the back of the pump housing) that equals the effective area of the expansion joint time the pressure. This will be in the 4000 lbf range. Assume a 12” high pedestal supporting the pumps. Now you have 4000 ft*lbf on a pedestal supported pump that was designed for 870 ft*lbf moment + 700 ft*lbf from the axial load. Congratulations you have just created a problem by installing an expansion joint. No problem with thermal expansion though, now it is loading from pressure that is the problem.

In addition, now you need to install a rigid anchor that can handle the 4000 lbf load for the pipe side of the expansion joint. Also, you get to ensure the pump base mount is good for 4000 lbf in the axial direction plus the induced moment.

The point here is to show that to recommend an expansion joint, without sound engineering analysis, is a poor practice. In fact, you can create an additional expense for anchors, increase the loading on the pump, and shorten the life of the pump just because the engineering work was not done. Expansion joints on pumps should not be a first choice.

 

[Artisi]

the easy answer for the allowable piping loads on an ANSI pump is NONE.

Naresuan University
Phitsanulok
Thailand

 

[KernOily]

"the easy answer for the allowable piping loads on an ANSI pump is NONE."

... but this is not a reasonable answer. You need to get the allowable nozzle loads from Goulds. They have the data available. Then you use their formulas to calculate the resultant moments and forces and see if you are within their allowables. Use your pipe stress program to calculate the component applied forces and moments and plug those components into the Goulds formula.

There is a new proposed HI standard for allowable nozzle loads on ANSI B73 pumps but I think it is still a 'suggestion', at this point. You could get a copy from HI. You would have to ask Goulds if that XLT complies with the HI standard but I bet it doesn't because the standard is pretty new.

Expansion joint is the last resort. Pete

Thanks!
Pete

 

[checman]

JohnSr When I suggested an expansion joint may take up the load I was not suggesting you go to expansion joints are us to get one or order one from fly by night industries. Go to a company like Hyspan, they will ask for all the pertinent information and may even do the calculations for you if you send them a piping drawing. Expansion joints are an engineered product and have help me solve problems over the last 27 years. I have installed them on most all of the systems I have laid out without problems.

Regards checman

 

[KernOily]

Expansion joints are an engineered product only insofar as the product itself is concerned. A mis-applied expansion joint can cause WAY more problems that it can solve. I've seen it many a time. Proper application of expansion joints, especially the metal-bellows type, requires much experience and knowledge.

The joint manufacturer can not help you with application; they can only build a joint to your specs. They can't help you properly deal with and design around things like pressure thrust, pipe support issues, etc. As I said, an exp joint is always the LAST resort. There is usually a way to design it out of the system unless you are dealing with very high temperatures or equipment like steam turbines. Skilled piping designers and pipe stress engineers are the way around exp joints.

Thanks!
Pete

 

[Zapster]

checman, you have just made my point. You say that with few exceptions, you have called out expansion joints for pump connection. In addition, you have the salesman at Hyspan do your engineering for you.

Do you believe that the salesman at Hyspan is capable of pipe stress (flexure) analysis, and performs this service for their customers when they request it?
Do you think that the salesman at Hyspan is willing to accept the liability for designing pipe systems?
Do you think that the salesman at Hyspan is a licensed professional engineer willing to stamp the design he has made for you?
Do you think it is in the salesman’s financial interest to tell you that for most nozzle connections you do not need to use an expansion joint?

The answer to all of the above is NO!

Please tell me just what you think the salesman’s job is at Hyspan, to tell you that you are wasting money installing expansion joints on your pipe design. Or, that you have improperly designed the piping systems and to go back and do your engineering work? Or better yet, if the design is flawed, and if he knows how, he could redesign your piping system for you so you don’t need expansion joints. Now there is a salesman that will be on the bread line soon.

checkman, you must be involved in vibration/sound isolated systems or you are not engineering your pipe systems. This is common place with the HVAC folks because they don’t engineer their pipe systems. HVAC folks typically leave that to the plumbers and only specify the diameter of the line. Perhaps the only way to stay profitable in residential and commercial building design is to push off some of the design work on the installer/contractor.

Specifying expansions joints is no substitute for detailed engineering. Hyspan makes a high quality expansion joint and when I used to be involved in industrial piping, I would specify them where they were needed. This would be less than 5% of the time.

 

[checman]

You are right I normally count on the piping designer and stress engineer to get the piping close. I also fix ANSI pump problems created when engineers and owners try to save some money. There is no good reason to plan on loading an ANSI pump flange. I should have said that I redesigned piping systems. Most systems work if all of the piping and all supports are installed and adjusted correctly. This is much more difficult to do then you might think in the real world. All the equipment must also be on the same building footings and slab with no eceptions for the last support, as not to be effected by minor seasonal movements of a slab floor. No piping support can be attached to roof supports that flex with snow or heavy rain loads. In the northern part of the US most of the time one of the above criteria is not met and flange loading is the result. ANSI pumps do not handle flange loads well at all. Misalignment of key components is normally the result. Frame adaptors flex and gaskets compress to allow for this misalignment even under acceptable flange loads. API pumps are a different story they have tighter fits, frame adapters you can drive a truck over and spiral wound gaskets. I cannot even count the number of times I have taken a pump out and watched the flanges pop apart. I have watched as millwrights used pry-bars to align ANSI pumps and used winches and pry-bars to align flanges on API pumps. Have you been to your sites and ask if all the flanges lign up? If they dont is it the fitters fault?

 

[TBP]

checman - I too have witnessed attrocities with prybars etc. Much of the piping related misalignment problem can be solved by two things.

1/ Start the piping AT the pumps, and work away from them. Most intallations work TOWARD the pumps, and any misalignment of the piping occurs right at the pump connections - the absolute worst place.

2/ Properly trained steamfitters/pipefitters should be able to have the piping arrive pretty much dead-on. A huge number of plant management people think "Well, it's just pipe...ANYBODY can do it." If the guys are using prybars and come-alongs to make the last joint, then something is VERY wrong.

At the end of the day, this type of problem is a management issue. Who is allowing this situation to occur in the first place, and then to continue to exist?

 

[bingopin]

I have installed many (>200) ANSI pumps using the criteria mentioned by JJPellin with good results. Achieving .002" or less movement at the coupling when the pipe is bolted up can be challenging and many times requires the use of heat on the pipe, but it is almost always attainable. Our spec reqiures a field weld right at the pump on pipe 6" or larger.
Hot systems usually use an API pump and require careful modeling and analysis. These systems usually contain spring cans and/or spring hangers, which must be properly set and checked after system startup.
No way would I use expansion joints or flex hoses on anything other than water pumps unless the piping system just could not be designed otherwise. In my opinion, using these things will lead to an increased maintenance effort as well as increasing the chance for loss of containment. I have seen too many failed expansion joints in the past 30 years.