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vibration evaluation of a pipeline in a system

vibration evaluation of a pipeline in a system

vibration evaluation of a pipeline in a system

(OP)
hello everyone,

Again, as part of my job every while I get an annoying task to fulfill, here I was asked to see if the report submitted by the contractor regarding high vibration in an axis at one support is acceptable.

Issue in few words: a reciprocating propane compressor was installed as part of an expansion at our facility, after installation, high vibrations in the piping was noticed, readings were high (I wasn't part of these steps), some were verbally reported as 50 mm/s , which way exceeds all limits of ISO 10816-8 of 28.5 at worst case, contractor stiffened the supports, by which he succeded in bringing down numbers (again, I wasn't with this project group :) ), except at one location, at which no matter what he did it remained at 23.5 mm/s.

looking at his submitted spectrum (attached), he submitted a report in which he claims that he simulated the stresses by CEASER and stresses doesn't exceed 18 MPA which is lower than that of ASME sec 8 div 2 figure 3-F.1M for this material of 48 Mpa … which he took uncorrected, and assumed its simply the endurance limit for this pipe.

well , while Iam not a vibrations expert, but I do have some questions please to understand things better:

1- Figure 3-F.1M is not corrected for temp? do we have to correct it as per table 3-F.1 ? if so what is E3 please here??

2- the temperature actually of this vibrating discharge line is going to be colder, in fact its a refrigeration compressor, so do I really have to correct the figure from the table?

3- looking at the spectrum at which the high vibration is occurring, can I use that along with the figure 3-F.1M to get the life in days etc, if I use the right frequency? there are 2 frequencies shown here, one is the CPM on x-axis, and the 6.1 Hz shown above, what is the 6.1 Hz above (right top side?)

4- he all of a sudden calculated an amplitude (A) at some page, A = ( V x 1.4) / (2 x pi x f) .. (where A is vibration amplitude mm. 0 peak , V rms velocity mm/s , f is dominant frequency of measured velocity Hz), and he used the V=23.5 which is the measured high velocity, and used hz=6 Hz from the spectrum attached, the value of A he got is 0.87 (written as 0.87 @ 1 mm. 0-peak), then he said he considered A=1 at CEASER calculations later which led to 18 Mpa figure.... is this correct?

5- is this satisfactory? I went through the entire 10816-8:2014 and through the related figure in ASME sec 8 div 2 .. the 18.5 theoretically means it is in the infinite region of the S-N curve, but is this enough ?

Sorry if the questions are too simple or too complicated :)

thank you in advance and regards,

RE: vibration evaluation of a pipeline in a system

3 - 369 rpm is the speed of the pump or motor, which is the same as 6.15 Hz in revs per second.
4 - no the frequency of interest is 3*6.15 Hz, hence A, the peak displacement amplitude, is 22.9*1.414/(2*pi*3*6.15). Luckily the mistake is conservative.

Cheers

Greg Locock


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RE: vibration evaluation of a pipeline in a system

(OP)
@GregLocock : thanks a lot , but regarding answer # 5 , may I get further explanation please ? what is the 3 actually? and how is peak displacement calculated ? I mean what is the 1.414 ? and what is the 3 ?

thanks alot

RE: vibration evaluation of a pipeline in a system

(OP)
@GregLocock : thanks again , well about my vibration book I wish if it helped, after all you need to give a useful opinion to your boss if he asked about it in a given report, a report of the weak type too, which doesn't help much in understanding it even :), I don't do vibration analysis everyday, not every year even , and if you don't you tend to forget between all other job requirements.

anyways I will wait for further help as I need to sum up what I have on it

RE: vibration evaluation of a pipeline in a system

(OP)
sorry again , gears of memory started to turn by reading more, isn't the rms 0.707 x amp ? and in this graph attached above it says amp= 22.91 ? sorry if the questions are too funny but things have evaporated over years (vibration book last seen in 2004) ..

also if I use figure A.1 from ISO 10816-1 to get the displacement, here which frequency at X-axis are they referring to ? RPM of the compressor 6.1 hz here ? or the CPM frequency at which this wave is happening which is 1121 cpm ??

I tried using the equation too from ISO 10816-1 eq A.4 to get the amplitude peak to peak which says si (displacement peak to peak in micrometers = (450 x Vi mm/s)/(fi Hz)… just to compare to the value from equation which they used in the report which is corrected here above too ….

any explanation would be appreciated, thanks in advance

RE: vibration evaluation of a pipeline in a system

(OP)
cool , thanks again very much

RE: vibration evaluation of a pipeline in a system

(OP)
as for other question .. if you have an answer or guidance please:

figure B.5 - overall vibration velocity limiting curve for the piping and dampers of a horizontal compressor of BS ISO 10816-8 ,, which frequency is the frequency on x-axis ? the frequency of the machine (RPM converted to Hz) which is 6.1 Hz here ? or is it the 1121.2 CPM (18.686 Hz) ? thanks again

I would have posted the figure from the ISO but I belive that is copy righted

RE: vibration evaluation of a pipeline in a system

Out of curiosity, what's you pipe size and SCH or I.D. and wall thickness? The Run length might be useful as well.

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