Dear All,

What are the point to considered for Reciprocating compressor routing while doing static pipe stress analysis.
As per client instruction, we have to follow straight pipe b/w compressor suction side and scrubber bottle.

It depends on manufacturer. Some vendors advice to consider 10*OD at suction and discharge of the compressor and some others recommend lower straight run.

About stress analysis of the piping it should be pointed out that the route should be flexible enough for damping thermal displacements and decreasing nozzle compressor nozzle load. Generally nozzle load of reciprocating compressors are very lower than fixed equipment.
Besides supporting of the piping is the main concern.

Hi Shabeer,

While performing static pipe stress analysis it should be noted that the routing and supporting for the same goes to manufacturer or pulsation study specialist for the Pulsation and mechanical studies based on the design approaches listed in sec. 7.9.4.2 "Design approach" of API 618, 5th edition.
As per sec 7.9.4.2.3 & 4 : pre-study of the system, Acoustic Simulation,and Mechanical Review and Piping Restraint Analysis needs to be carried out by pulsation study specialist.

Also, the same is elaborated in Annex N of API 618, 5th edition.

Hence prior pipe routing, supporting and analysis becomes extremely critical as party performing above specialized studies can suggest major layout, supporting changes which can be very difficult to absorb at the later stage of the project. (later stage mentioned because, specialist analysis report & recommendation takes time and by that time most of the other nearby pipe routing gets freezed.)

So, some of the vital things that can be taken care of before submitting the documents for above mentioned analysis are:-

1) Flexibility should be added to the connected piping to minimize nozzle loads on the compressor as minimum as possible.
2) While adding flexibility to the piping, natural frequency of the system needs to be enhanced as maximum as possible. Guideline for same can be referred from sec 7.9.4.2.5.3.2 "Separation Margins" of API 618, 5th edition. ( I understand these guidelines are very stringent.. but again this is the beauty behind analysis of Recip compressor systems and hence frequency shall be as max as possible).
3) With the above two things done, one shall be prepared for some changes/modifications suggested after the pulsation vendor study. Hence adequate margin for the routing/supporting and nozzle loads shall be kept.

Dear Sirs,
In the most vibrating piping connecting to reciprocating compressors clamp type pipe support should be used. As I know know these clamps have rubber strip bonding inside it. I have some questions regarding this kind of clamps:
1- Do these kind of clamps keep a tight hold on the pipe? I mean does any preset load applies to the pipe? If yes, what is the value for preset load?
2- How can I specify thickness of the rubber?

Hi NRAM,

When Pulsation vendor/specialists performs the Pulsation and mechanical studies they come up with a defined unbalanced forces present in every leg of the piping system.

Depending upon the layout, supporting and some mechanical and process parameters some piping legs may have zero or small unbalanced forces in the piping leg and can be mitigated/balanced by considering frictional forces.
While in some of the piping legs, these unbalanced forces may be quiet high and needs special attention. For these cases, even though the piping leg is securely restrained, additional forces needs to be added into the leg to check the unbalanced forces(wherein clamps comes in picture).

These clamps (when securely tightened) introduces further normal force within the system and hence increasing the frictional force and thus together balancing out all the unbalanced forces in the leg.

So, as an answer to the first question: these clamps are specially designed to keep a tight hold on the pipe. For this, necessary preset loads or deflection(in case clamp is spring loaded) is provided by most of the pulsation vendors and the magnitude of it varies depending on the unbalanced force to be mitigated.

In response to the second question, i don't have much to say as the main purpose being achieving the required normal & friction force, rubber can efficiently do it to an extent but the question remains "For how much unbalanced force?"

Attached is a representation of spring loaded type clamp used for arresting vibration, just for reference.

Thank you very much Mr. Dinesh K.
Now some questions come up.
1- In some piping standard support detail there is a sketch like the attached picture. It doesn't mentioned preset load for spring or washer. I don't know what I should input to the software. Should I ask the vendor for preset load?
2- How can I model a support with preset load? Should I specify for example Y direction support with stiffness and external load by double click Forces/Moments?

When the pulsation analysis is done by the specialist, and given that the unbalanced forces are significant, they are suppose to and in a better position to provide the extent to which the system requires further loading.

For inputting in CAESAR II model, required force needs to be entered in the Forces/Moments section. Also, practically, at site the similar force needs to be imparted by providing the displacement to which the spring is to be compressed.

Are below load cases correct for this kind of clamps?

WW+HP+F1
W+D1+T1+P1+F1
W+P1+F1
W+D1+T1+P1+U1+F1

F1= clamp preset load
D1= nozzle quipment displacement
U1= uniform load due to occasional cases