Dear all
How can I put a "Slip Joint"(not bellows type) in CAESAR II?

Thanks in advance!

Hello Jeonggyu,

Actually, that topic is well covered in the Caesar II applications manual. Also, you will get many replies to give you more advice.

I will discuss "slip joints" of this type only here:

http://www.advancedthermal.net/slipjoints/slip_joints.htm

There is an associated topic that you should consider however. I copied this from a previous posting:

An associated topic for discussion might be the forces (of gland seal friction) that "build up" in "slip joints" before the friction is overcome by the increasing (with thermal expansion)axial force and they "pop" and, in "One great leap", compress to accommodate the pipe expansion. The compression of a slip joint is NOT a smooth and continuous movement. The expansion builds up the axial force until the force is greater than the friction in the seal, then they move enough to "exhaust" just enough force such that the force is again less than the resisting force of friction. The axial expansion force builds up again, forcing another sudden compression of the slip joint. The movements are abrupt and quite like an impact loading as the slip joint compresses on "heat-up"(and again as the joint is "pulled apart" on "cool-down"). It would be prudent to design the reacting anchors to be as robust as is practical in consideration of the alternating (heat-up, cool-down) axial forces (dynamic and static) that they must accommodate. We find broken anchors in many investigations of in-service steam piping systems that employ slip joints.

The seals in slip joints wear as a function of the heat and the number of thermal cycles that they experience. As they "loosen", the friction that resists the axial forces diminish. The joints (usually) have an adjustment that allows the seal to be "tightened" when it begins to leak due to wear (in-service surveillance is prudent). Tightening the seals again increases the friction and the associated resistance to compression/expansion movements.

The Caesar II applications manual does not mention these issues.

Regards, John.

Modeling is subject to what kind of slip-joint you are going to use, that is, will control only axial movement or both axial and lateral ?
Some slip joint for abrasive slurry and solid system should not be used for lateral movement. In this case, you can model as CNode with axial free and other five rigid DOF.
Typical Dresser Coupling for general service can absolve axial and lateral(max. 4 deg.) simultaneously. For this case, you can model as expansion bellows or two points CNode with axial and angular free.

Please do not forget controlling pressure thrust and put the guide support for this slip joint system. Also, gasket material is sensitive to solvent and temperature.
If you want to get more information, please contact to any stress engineers in Seoul; SKEC(Jaewon Chang), DIC(Byungkyu Ahn), LGE&C(Seongeun Lee), Samsung(Yongbae Kim).

Hi Gentlemen,

I digress a bit.....as someone who has never used a slip joint before I was intrigued by the I information I got from John Breen's response and his link, specially the part that deals seal leakage!! and the high performance (1000F/1000psig) of this item.
At these temperatures and pressures I would have thought that all joints would be welded joints i.e. no flanges due to safety reasons, never mind talk of joint leakage. I would have thought at such high temperatures the expansion would have to be absorbed by loops or expansion joints, even expansion joints at such high temperatures and pressures are undesirable for safety reasons, so prey enlighten me.
Can one use a slip joint in a petrochemical plant and satisfy the health and safety requirements? or more to the point where does one normally use
a slip joint?
I always thought that it is used in underground piping where low temperature and pressure and large movements are anticipated.
I look forward to your comments.

Regards
A

Aaron,
Many large US cities have miles of steam tunnels that are the routes of district heating steam piping systems. Large centrally located boiler houses produce the steam and it is sold to large office buildings, hospitals, and universities (just like electricity). The piping in the tunnels delivers the steam and returns the condensate to the boiler houses. There is no room for loops and so the thermal expansion of the piping is accommodate by slip joints. We go into the tunnels infrequently, so maintenance is sporadic at best. These tunnels are very hot and quite noisy when a steam line is heating up or cooling down because the slip joints make loud "bangs" when they are compressed or expanded. The resulting impact upon the anchors very often leaves them with broken welds. Sometimes the anchor bolts are pulled out of their concrete embedments. Yes, worn seals leak and sometimes it is so bad that the stem must be shut off to enter the tunnel for repair.

Regards, John.

Wow! I'm so grateful to you for all your comments and help. And Sun Wee, are you Korean?
I wish to contact guys which you've mentioned, but I am just a rookie in this field. Anyway thank you so much.

I vaguely recall using slip joints on a large bore (about 36”) flare line in a refinery many years ago. This is not common practice, however, but with the inherent difficulty of providing flexibility in large diameter sloping lines it would seem to make sense (assuming, of course, the joint is leak free).

for slip joints what will be the bending stifness values if it can rotate about 4 degrees in lateral direction

You'll have to ask the vendor for this sort of information.

Instead of slip joints I would look externally pressurized axial compensator. Talk to one of the "better" suppliers or look into main international supplier's pages. I have to warn that there are "short cut suppliers". If you model these into CAESAR be careful to get it right.

for slip joints what will be the bending stifness values if it can rotate about 4 degrees in lateral direction. If i have to assume a value what should be a good guess for 10" std pipe

John,

So when the district heating steam slip joint needs replacement, would it be with another similar ? Put another way, is a slip joint in that service considered current engineering practice in the USA, or to be avoided these days ?

I have seen new and upgraded systems installed in Europe, Rotterdam, Copenhagen, Oslo for instance and all used axial bellows.

Hi MoverZ,

We are still using them. Last year we put in 7 miles of new tunnels with steam and condensate return piping for the University of P********h (and their hospital systems) and the bid specification mandated slip joints of the type shown in the 9-8-05 reference above. At this point many owners are reluctant to change what they have done for years. Probably with the technology advances made in the last 20 years, bellows types (made to the EJMA Standard with the more predictable cycle life) would be a good choice but much of the time the "engineering" is done by the purchasing departments.

BTW, I didn't know that "slip joints" could be deflected laterally.

I am surprised we have not heard from CraigB on this one as he has spent more time underground than a coal miner. Maybe he would rather forget?

Regards, John.

I am talking about dresse couplings

John

I have studiously avoided this post after your extremely thorough response to the initial question. But you are right - I have personally been through most of the steam tunnels in P********h. Mostly, when the slip joints fail, the repairs can be accomplished by replacing the packing in the joint. Actually, I remember those trips fondly - not for the environment or the view, but for the fact that in those days I was strong and flexible enough to scramble around down there and not have to spend days recovering. Those were the days!

I suspect the reluctance of owners to replace slip joints with bellows comes from two sources.

1. They are comfortable with the performance of the slip joints.

2. They are concerned with catastrophic failure of a bellows at high loads. Slip joints, although they leak a lot, have virtually no chance of a catastrophic failure.

Finally, a few paragraphs for ramanathan:

You are continually posting a question here that no competent stress engineer would think of replying to. And if, by some chance, somebody posts a number, are you going to use it in your model? How in hell do you plan on citing the source?

Grow up! A part of becoming a competent stress engineer is developing the ability to research issues like this in a professional manner. In this case, as Richard Ay has already stated, you need to contact a representative of the manufacturer of the coupling you propose to use, and get a response directly from him that you can use in a model and cite in your report.

Anything less than that is simply negligence. If you reported to me, and used a number in a stress analysis that you got off an internet discussion forum, I'd fire you. Got it?

craig
thankyou for the information I am doing some testing work of slip joint modeling that is the reason i asked for a guess value this is not for any project.

ramanathan,

Check the Hyspan Barco website for a number of flexible joint options,

www.hyspan.com

The Barco ball joints could allow more rotation than a slip-joint, if that is required. The O**o State University Powerhouse has a pair of 10" Barco ball joints in a configuration similar to a tied universal assembly. This accomodates the steam piping differential movements between the 200 psi steam main header and the tunnel entry point for steam service line to their fieldhouse. Ball joint operating forces are affected by friction and lubrication, like the slip joint operation.

The limited space inside a tunnel means the piping linear expansion is taken in the Dresser type slip joints, and the corners are relatively fixed in position. The above ground steam lines are usually arranged so that there is clearance at corners for the expansion to bend the piping, loops or flexible joints. The choice to use slip joint, ball joint, bellows joint, or expansion loop, will depend on expansion, fluid service, reliability, cost, loads, and available space constraints, among others.

Hi Richard,

I see that you too are an explorer of tunnels!!! O**o State's steam tunnel network is legend.

http://www.infiltration.org/underosu/tunnels.html

BTW, did you watch the O**o State F*****a basketball game? I was rooting for the Buckeyes but sadly it was not to be.

Regards, John.

John,

The pictures and information of the utility tunnels are definitely educational for pipers that are used to the wide open spaces of refineries and process plants. We were fortunate that we did not need to go back too far into the tunnels - just needed to verify which way the piping was expected to move. The recently completed project replaced four boilers and auxilaries. The old boilers were 40-50 years old. Parts of the building date back almost 100 years with riveted structural beams, riveted vessels, and some TG units old enough to be in the Smithsonian museum. Some portions of the utility tunnels must be the same age.

The Florida schools do have some advantages when recruiting athletes for the nice warm climate there. The Buckeyes have a long tradition to help them keep competitive in big sports. I heard that the income from just four football games provides funding for all the athletic programs there.

Their university hospital receives steam from the powerhouse, and due to its importance factor, there were seismic design requirements added for the project. New piping has seismic restraints, while existing piping got grandfathered in. Did project piping for Univeristy of P********h require a similar consideration for seismic restraints ( not knowing the zone)? It would seem that the piping in utility tunnels would be sufficiently restrained for seismic type loads, without added struts or bracing.

Regards,
Richard Yee

Hello again Richard,

We did the seismic analyses for the University of P********h tunnel piping and as you stated the systems were very much guided into the slip joints so the stresses calculated in the seismic analyses were low (I think that most RFP's now routinly ask for seismic analyses to IBC). We allowed a little more freedom for the pipe to move at the "free" elbows. Many of the elbows were restrained and the expansion was "pushed" away from them and into the joints. "Lessons learned" compelled the design of stout reinforced concrete anchors and restraints.

I was drawn into a legal case (not one of my favorite pursuits) involving one of the replacement boilers that you mentioned. It was one of those cases where the "project management company" was not always represented on-site, the original design was not "constructible" and the mechanical contractor ended up making the "design drawings" of the system that was actually built (but never properly analyzed). The owner stepped in and fired everybody. Needless to say, the seismic analyses were never done and none of the piping for the project was in the steam tunnels. I had the opportunity to spend some time in the power house and as you said it was a fascinating place.

Regards, John

P********h = pukesburgh ????

Hello All,

My esteemed colleague, Herr Luf (a Cleveland native) has yet again thrown the gauntlet (will he never learn).

http://cgi.ebay.com/Only-Sign-Life-Cleve...3QQcmdZViewItem

Now you have seen the T-shirt. A picture of a road sign: PITTSBURGH, 142 MILES. Underneath, the words: THE ONLY SIGN OF LIFE IN CLEVELAND.

Pittsburgh and Cleveland residents squabble like kid cousins at a family picnic, trading insults and maintaining legendary "turnpike rivalries", especially (but not exclusively) in football. Actually I know many nice people from Cleveland. Cleveland is a nice place to be from.

Ha! And he thought I would respond negatively. I guess I showed him.

Regards, John

well I'll see you your ebay url and raise you another ebay url.....

http://cgi.ebay.com/Pittsburgh-Sucks-Cle...VQQcmdZViewItem

Happy Easter John