×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

pipe failure
2

pipe failure

pipe failure

(OP)







Hello all, I have some equipment as shown in the pictures that have a pipe failure at the support attached.
This is a Vertical Recovery Tower 30" OD X 30' S/S operating at 50 PSI @ 100 F. According to the field foreman, the vessel started leaking 30 min after operation start.
my concerns about this failure were:
1.Transportation and erection procedure, but apparently all pipes are free from any erection load.
2.Material of origin, I checked the MTRs, and the material is according to SA-106,B Smls pipe.
3.Looking at the pictures, there appears to be pipe hanging off of the vessel connections and the pipe is supported by bricks, not concrete foundations. These foundations are probably not offering any support, vertically nor laterally. The pipe seems to be just resting on the bricks. I think it could be a vibration problem, because we cannot see where the pipes go. I suggest the customer should have poured concrete bases for the pipe supports, then secure the pipe with brackets and u-bolts. I think the customer’s pipe is not adequately supported and there must be some type of oscillating load. The failure look like fatigue, normally seen at a compressor station.

I have not be exposed to much to this kind of failures, I would appreciate if someone could guide me to figure out what could be the possible cause of this pipe fracture.
thanks a lot.

RE: pipe failure

Is there any temperature difference between the pipe that failed and the tower? The pipe is fixed both at the top and bottom, and there is little to no flexibility provided. If there were any differential thermal expansion between the pipe/column, this could lead to a failure.

RE: pipe failure

After review of the pictures, it would appear that the crack emanated from the toe of the structural attachment weld and is probably caused by mechanical fatigue. I would suspect you had localized bending forces acting on the column from the pipe support based on the crack orientation and location.

RE: pipe failure

This appears to be a case of VERY bad design done by really inexperienced people.

Management always seem to claim experts cost too much, but look at what amateurs did here. Now consider the cost for this repair plus the cost of lost production.

One expert would have seen this while in the early design stage and corrected it.

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

RE: pipe failure

Has this been hydro tested?

RE: pipe failure

I would go for the expansion stress and possibly other static forces hanging off that flange. Also from the photos it doesn't look like the tower has been bolted down??

The axial single attachment is very poor design and shows a lack of design knowledge about how to support and not stress pipe. At that diameter and length it could also start to vibrate from wind vortex.

classic stress concentration failure in my book. Just as well it leaked before it completely failed...

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

RE: pipe failure

In my opinion, poor welding and wrong procedure may have resulted in high residual stress and hence cracking.

RE: pipe failure

(OP)
good morning all, and thanks for your inputs...some answers to your questions and comments:
Marty007, there is not really a temperature difference or thermal expansion, the pipe has only one support at bottom close to the flange.
Metengr, I am agree with you as I mentioned it looks like due a fatigue, caused by pipe oscillation due to a lack support.
Spoonful, yes the vessels were hydro.
Littleinch, you are right, it looks like the tower is loose from the concrete slab, however I need to figure out if this is the operational configuration or if it was unbolted just because this unit is out of service. You bring a good point here "vibration from wind vortex"
Mechanical2014, I think the weld looks good, I don't know about the procedure or the weld quality, however the field foreman mentioned that point, maybe this is caused by overheat during the welding procedure.

I am agree with all of you guys in that the design is poor an inadequate, some of my solutions are:
1. As I mentioned pour concrete bases and anchoring the pipe with U-bolts.
2. Add a piece of plate as a repad to the support at the pipe side, this vessel is internally coated, so ideally I will add a pad at both sides to the pipe and to the vessel, but the customer do not want to affect the internal coat.
3. the customer suggest a solution as shown in the picture, which I think it would work, but really is important to understand what is causing this fail, because if this is for an extra load at the bottom, with this solution the load is going to transfer to the elbow or the vessel connection at top. in this pic you could see what I am proposing in (2)above a pad but at the pipe side.

With your experience guys what will be the best solution to fix those vessels, by the way I have 18 of 50 with the same issue.

RE: pipe failure

In the first few photographs by the OP...

That particular pipe support philosophy of welding pipe clips onto both the pipe and the vessel is inviting inevitable failure. To then support everything on sleepers below the first elbow at grade serves to accelerate the process towards the aforementioned inevitable failure.

RE: pipe failure

Sergio,

You need to do some sort of pipe stress analysis to determine what can and can't be done and use some proper pipe supports and hangers.

There is simply far too much stress concentration at the weld. At the very least this support needs to have a collar welded to the pipe with circumferential welds and then the support welded to that, NOT direct to the pipe.

in general anchoring things all over the place simply causes more problems - some flexibility and ability to move or expand is usually useful.

I would remove that horrible welded support and replace it with a sliding one guided to prevent too much movement and then on the horizontal leg not support it until a few metres away to give the pipe somewhere to go both horizontally and vertical, basically an L shape. You might not think there is much of a temperature difference, but welding it locks in the temperature in the shop when it was welded. you might need to clamp another support round the main vessel about half way up to provide a guide to allow only vertical movement of the small diam pipe as this is a long flexible bit of spaghetti ad could easily vibrate or resonate due to wind or other vibration source.

given that the areas apparently floods easily, making the supports from concrete rather than a few bricks will help....

BTW that second photo is just about as bad as the first. You can see the movement of the pipe which can become locked up quite easily and will just wrench the support off the vessel or snap the U bolt. This is effectively an anchor point and not a sliding support and to brace it off a vessel.....

I don't know where this is or how the customer is getting away with it, but this is poor design. Make a better design.

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

RE: pipe failure

A detailed analysis of the stresses and moments generated is going to be really important to figure out how much will need to change to repeat it for the other sites, and the part of your first bit where you mentioned 'Supported by bricks' really made me shake my head.

The foundation is definitely the first part of any structure that should be considered, and this customer hasn't considered it at all.

That U-Bolt in the second picture looks like it's under a bit of strain already, more bad news for your customer I'd say.

Hopefully your customer learns some hard lessons here.

RE: pipe failure

(OP)
Snorgy and Littleinch, as I mentioned before, I am agree in that this design is really poor, by the way this is a non code vessel. Littleinch I didn't understand exactly when you say:
"this support needs to have a collar welded to the pipe with circumferential welds and then the support welded to that"
"replace it with a sliding one guided to prevent too much movement and then on the horizontal leg not support it until a few meters away to give the pipe somewhere to go both horizontally and vertical, basically an L shape."
" you might need to clamp another support round the main vessel about half way up to provide a guide to allow only vertical movement of the small diam pipe"

could you show me that graphically?
If this had been my design I would put more supports along the pipe, but as I told you those equipment are in service and we just need to submit a reparation procedure.

as always thanks a lot.

RE: pipe failure

(OP)
to clarify the picture showing the U bolt, this is not implemented yet as a repair procedure, the customer just come out with this idea as they did that type of brace for a firetube stack, we want to provide the better solution to be free of future issues and to provide a better design for future orders.

RE: pipe failure

The causes and remedies have already been thoroughly addressed, so I just want to add a moral to the story: there is no such thing as a non-load carrying weld.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

RE: pipe failure

Free engineering!

Ok here's a pretty crappy sketch, but I think it gets the principles across.

You do need to do some stress analysis though to make sure the top connection can handle the static weight. in most circumstances it is always best to allow the piping to move a little, but in a controlled manner rather than lock it all in with anchors and clamps

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

RE: pipe failure

(OP)
Littleinch, thanks and thanks a lot for your suggestions, I will perform a FEA to figure out what are the critical points, and from them I will suggest the better and most economical solution.

if someone else have another idea, please share with me.
thanks to all

RE: pipe failure

LittleInch,

Are those limit stops that you are showing at the end of the shoe in addition to the guide clips on the sides?

RE: pipe failure

Crap drawing. Guides onlY, no limit stops.

You should only need stress analysis not fea.

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

RE: pipe failure

Nothing wrong with limit stops, properly gapped. If gapped closely, my only suggestion then would have been one in-plane and one out-of-plane offset with a trunnion support on the downcomer somewhat below (reasonably close to) the top nozzle. That would ensure that the pipe hangs correctly without imparting a big moment on the nozzle; there would be some torsion though; probably not much if properly designed.

RE: pipe failure

Sergio76:
Look at your first photo, I suspect that the primary reason that pipe support is there is because that particular pipe, down to the flange, ships as part of that main vessel. It would break off at the upper elbow if it was just allowed to wag in the breeze during transit. Your later pictures show vertical pipes just as long and just a large/heavy, which do not seem to need that welded support plate. You say it was hydro. tested at the manuf’ers. plant, and leaked before the vessel really went into service. So, when and how did the leak and cracking likely happen? In your third photo the piping below the flange is much huskier/stiffer on the pipe that cracked, if that lower pipe exerts any force on the cracked pipe at the support. That is really a pretty feeble pipe support detail in its strength and welding, and it’s not too surprising that the pipe cracked the way it did. What are some of the loads, potential pipe movements, sizes, thicknesses, etc. around that pipe support? Show us a well proportioned sketch of those pipe details. Show us the orientation of the vessel and that pipe during transit.

RE: pipe failure

(OP)
Good morning All,
dhengr,the vessels were hydro as you stated, and they started leaking 30 min after they have been in service, apparently the transportation and erection procedure were good, but really I don't have much information about that, only a few pictures similar to the first one. The only information I have about the pipe is 3" Pipe Sch STD, SA-106,B, the plate support is 1/4" thk, I received a notification from the field foreman announcing that the 2" pipe failed as well at one clip support. Please see file for more details.

RE: pipe failure

(OP)
Dhengr, have you seen this type of crack on similar applications with this kind of supports? The suggestion stated by Littleinch is appropriate to fix this issue, my only concern is the cost of this repair, since as I mentioned before, those are a non code vessels and the customer is cheap on those, for that reason the customer suggest the U-bolt solution as shown in the picture. if you have seen this before could you share how they addressed a repair solution?

Littleinch finally is our responsibility to fix the failure and make sure the vessel work properly, no matter what will be the cost, and your input looks like a really good solution to avoid future problems.

thanks again.

RE: pipe failure

There actually is some logic that goes into that kind of detail. And for a lot of low-stress/low-load applications, it will work fine.
I assume the failure mode is differential movement from temperature changes, but that could vary some.
Note that the small-diameter pipe is stiffer with a radial load than a larger pipe would be. So using either a larger pipe or shorter clip (shorter in the vertical direction) would reduce the problem. Turning the flat bar sideways would allow more flexibility. In either case, you're assuming that the stiffness of the pipe and ell are adequate to support the pipe, and just need a standoff at that point.
The main motivations for using that style are corrosion resistance and simplicity, with the corrosion resistance being more critical if the support is submerged.

RE: pipe failure

Sergio76:
I’ve seen that kind of crack, on that type of weld detail, on a number of different structures, over the years. That is just an awful weld detail however you cut it, and it will often crack right where it did, under a variety of loading conditions. The stresses at/in that weld toe have the potential of being very high (almost infinite), triaxial stresses; and any imperfection in the weld in that region, which is pretty likely, just amplifies the potential problem. You don’t seem to know what loads or pipe movement you are trying to support/control/restrain, so how are you going to design a fix for the problem? Once the tower is in place, are you trying to prevent too much load on the upper elbows and flanges? You gotta explain to the customer that he went cheap on the first go-round and he can see what he got. You also said he’s got a bunch of these vessels to amortize this engineering effort over. The others will likely need the fix too. Your first photo shows that they weren’t lifting on that 3" pipe, but how can you say the shipping and start of lifting went fine if you can’t answer my questions? I’ll bet most of the damage happened during shipping, a 3" pipe spanning 20-30' will sure bend and vibrate in transit, potentially starting a crack at the toe of that weld. That pipe should be blocked and strapped to the vessel for transit. Maybe with something as simple as a 6"x6" wood block, shaped to fit each part and strapped to the vessel and the pipe. Then, add to the potential transit stressing the operating stresses in the pipe, which will be predominantly tension in the pipe, maybe some bending or axial loading from the pipes below, and the crack would grow and fail, like your picture shows. You also need to know what loads the rest of the piping is applying, to start to make a reasonable analysis. If you do less, you may be quick and cheap, but you are doing a disservice to the client. And, you have to explain this to him, if he really wants a proper fix. I’m really pretty sick and tired of a lot of the quick and dirty, git er done, engineering we see these days. They don’t spend the money or the time to do it right the first time, and then think the fix should be quick and cheap because they think they’ve already paid for it once, even though it didn’t work from the start. Still, if you don’t know the loads and pipe movements, I don’t know how you are really going to provide a good fix. And, if the owner doesn’t want to pay for this effort he’s going to get the same crap he got, on-the-cheap, in the first place.

RE: pipe failure

(OP)
Hello all, after some weeks figuring out about the cause of this failure, it was determined that excess vibration during transportation started this failure, then when the equipment was in operation the additional loads acting on the pipe increase until it fail. I discovered as well that welding quality is poor ( as I mentioned, those are a non code vessels), in order to avoid future problems, we are going to redesign the clip support and our first step is run a stress analysis. the loads I am considering are:
W= pipe weight in direction -Y (assuming Y as vertical axe)
Qz= Wind load in both directions X and Z
P= load at bottom of the flange due to the connection with pipe on field in -Y

is there any other load I may concern, are the constrain points OK?
Wind load happen one at a time, I think Qx is the worse case, is that correct?
is correct also apply the Wind load at the pipe COG?

thanks a lot for your inputs.

RE: pipe failure

Hi Sergio76

I realise I'm late to the party but I'd like to ask a couple of questions:-
1/ how was excess vibration determined during transportation?
2/ What NDT was done on the welds? Because its a non coded vessel it doesn't automatically mean poor welding. For the
future design how will you ensure the welds are good.
3/ What are the additional operating loads you mention? I ask because you need them for the redesign.

I'm not disagreeing that the support could be a lot better designed however I'm not convinced that the failure mode as been correctly identified.
Looking at the photographs there is the joint that failed but it seems to me that there is another joint on the same pipe with exactly the same detail and yet no mention of this as been made, also if excessive vibration set the failure underway what tests have been done to verify there are no cracks in the other joint?
Finally when I look at the failed joint, the crack runs at 90 degrees to the longitudinal direction of the pipe which suggests to me that stresses in the longitudinal direction of the pipe are responsible which may well be caused by differential thermal expansion of the pipe or even during weld cooling in manufacture.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources