mechanical seal for Ammonia Comressor

A mechanical seal is installed at ammonia compressor to seal ammonia gas from the compressor. The mechanical seal works on positive sealing principle.
The mechanical seal was dismantled on the basis of high consumption of seal oil. on dismantling the mechanical seal, the balance face of the mechanical seal was found damaged. therefore the balance face assembly had to be replaced. The new balance face repair kit included a balance face, springs and backup ring to act as seal below balance face. The backup rings were made of PTFE and were found loose on the retainer therefore new teflon backup rings had to be machined.
sizes were taken and backup rings were machine from the teflon bar but when the parting of the backup ring was carried out, due to heat produced from machining the teflon ring became loose again. New backup rings were therefore machined and the size was kept 2 mm less than desired value and when parted the teflon ring expanded to the required size. final dimensions

Outer Diameter                                  146.8 mm

Width                                                  1.8 mm

Thickness                                             1.5 mm

Low flow of axial piston pump

A pump supplying seal high pressure seal oil to a compressor with floating oil seals was disassembled for maintenance due to low flow problem. This is an axial piston pump with a barrel housing seven plungers. The barrel is surrounded by a bearing and housed in a casing. A splined shaft is responsible for the rotation of the barrel in the casing.

The seal oil bottle low level alarm sounded several times and the standby pump had to be taken in service. Whenever the standby pump was shutdown the low level alarm sounded which indicated low flow of seal oil pump. The pump was removed and taken to workshop for overhauling. On dismantling, it was observed that the clearance between the plungers and the housing had increased from 0.05 mm to 0.10 ~ 0.15 mm in all plungers.

In reciprocating pumps, minor changes in clearances can result in high effects to efficiency. The plungers and the barrel were replaced with new ones and pump was assembled. The pump was installed in the area and is now giving appropriate flow.

Modification of Pump Mechanical seal

We have a urea solution pump used for recovery of urea dust. Due to discontinuous and frequent start ups and shutdowns of the pump, the mechanical seal had a history of failures after every two to three months. The mechanical seal of the pump had to be attended every alternate month which caused lots of man hours and cost the company heavy consumption of inventory.
After some research it was decided to replace the existing mechanical seal with gland packing. This was done such that no machining of pump was required so as to revert back to the original design if necessary. The original seal design is shown below

The seal was modified with a spacer and a gland plate such that the gland plate was the size of the mechanical seal and a flushing line was provided for the packing. The modified seal arrangement is shown below

Barrel type compressor overhauling

This is an overhauling report of a barrel type compressor. This compressor was a part of a compressor train, consisting of three barrel type compressors, driven by a steam turbine.

The compressor was installed between two barrel type casings and the whole casing had to be lifted and shifted to workshop for overhauling. The compressor casing was overhauled preventively and to inspect the extent of damage at the thrust collar area. The thrust collar has a history of damaging the thrust collar inner diameter and the rotor.  Moreover, in previous overhauling damages were also observed on the key area. During last coupling and bearing inspection rusting was observed on thrust collar area.

 

 After casing shifting to workshop and opening of head flange the coupling were removed and the thrust collar was removed using the arrangement shown.

The damage on thrust collar was inspected and after extensive study it was decided to change the fit style of thrust collar on the rotor. Previously the thrust collar was clearance fit with a clearance of 0.02 mm. The result is as shown.

Fretting on thrust collar area

Sheared thrust collar key

The new thrust collar was machined with an interference of 0.05 mm and installed after heating on a new rotor. The rest of the overhauling was carried out in routine. Bearings and oil floating seals were replaced during the overhauling. During next overhauling the rotor and the thrust collar area was found in good condition.

Vibration peaks observed in turbine

Few days back intermittent vibration peaks were observed on a turbine at our plant. The turbine has a history of this kind of stuff going on it for a while. After the overhauling the turbine acts okay but after one or two years of continuous service the vibration peaks are observed. Previous overhauling reports revealed a history of burned oil deposits on the oil seal of the Governor end bearing.
After thorough research it was hypothesized that the peaks were due to the continuous development of burned oil deposits on the oil seal area. When the oil deposits' thickness equals the clearance available, the rubbing between of oil deposits with seal occurs and consequently the vibration increases and as the oil deposits are cleaned by the sharp labyrinths ends of the oil seals, the vibration disappears.

The burnt oil deposits can only be formed if heat (from the steam chest), air (from the vent of steam seals) and oil (from the bearing) are available at the oil seal area. 
To avoid the phenomenon of oil deposits phenomenon certain steps were taken:
- first of all an ejector was installed on the other end of the bearing to increase the amount of vacuum in the bearing housing so as to reduce the staying time of the oil in the oil seal.
- Secondly the oil seal was provided with a nitrogen insertion point so as to remove the availability of air
- Thirdly the oil seal oil drain holes were enlarged to remove any oil that may stay in the oil seal. this coupled with the ejector will ensure quick removal of oil from the oil seal.

The turbine was started and the peaks have not been observed for a while.

Welcome

Dear All,

I am a rotating equipment specialist currently working in petrochemical industry and I have created this blog to share some of the problems we encounter from time to time. I have been working at the current position for approximately three years now and I have got experience working will all sorts of rotating machinery. Most of the experiences I am going to share will be related to pumps, turbines, compressors and similar rotating equipment.


SHB