somacast
Mechanical
- Aug 10, 2010
- 88
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,
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,
