This case study presents a critical review of the pulsation and vibration analysis carried out by a third-party supplier, focusing on the Q8 Terminal compressor station. The analysis, conducted in accordance with API 618 Design Approach 3, aimed to assess the dynamic response of the compressor and associated piping systems. The review evaluates the scope, methodology, input data, results, and overall efficacy of the study, while identifying gaps and providing recommendations for future work. All findings and insights in this case study are strictly derived from the reviewed project documentation.
Scope of Analysis
The pulsation and vibration analysis covered all piping between the compressor and the cooler, with the modeled geometry extending from several pipe segments upstream of the first stage separator to segments downstream of the third stage cooler within the auxiliary block. The initial study included nine operating cases, varying compressor speed, suction/discharge pressures, head end suction valve unloading, and clearance volumes. An updated study expanded this to twelve cases, reflecting increased suction pressure and the deactivation of one of the three first-stage cylinders.
Geometry starts upstream of 1st stage separator (picture taken from original report):
Geometry ends downstream of 3th stage in the auxiliary block. (picture taken from original report):
Despite this comprehensive range of scenarios, the critical limitation identified was the omission of the compressor’s actual current operating condition. Specifically, the configuration in which all head end valves are unloaded at both the first and second stages was not included among the analyzed cases. This gap undermines the relevance of the analysis to the compressor’s present-day operation.
Additionally, while the study reported the inclusion of forced mechanical response analysis for segments exhibiting high shaking forces, the documentation lacked sufficient detail to confirm the full extent of this analysis. Visual evidence suggested the focus was primarily on the Pulsation Suppression Devices (PSDs) and separators, with ambiguity regarding the inclusion of other piping sections.
The project scope did not include static stress or thermal flexibility analysis, which, while not a requirement of API 618 pulsation analysis, is often critical for a thorough understanding of system integrity under operational loads.
Methodological Review
Despite this comprehensive range of scenarios, the critical limitation identified was the omission of the compressor’s actual current operating condition. Specifically, the configuration in which all head end valves are unloaded at both the first and second stages was not included among the analyzed cases. This gap undermines the relevance of the analysis to the compressor’s present-day operation.
Additionally, while the study reported the inclusion of forced mechanical response analysis for segments exhibiting high shaking forces, the documentation lacked sufficient detail to confirm the full extent of this analysis. Visual evidence suggested the focus was primarily on the Pulsation Suppression Devices (PSDs) and separators, with ambiguity regarding the inclusion of other piping sections.
The project scope did not include static stress or thermal flexibility analysis, which, while not a requirement of API 618 pulsation analysis, is often critical for a thorough understanding of system integrity under operational loads.
Review of the model input and results
The available reports provided limited transparency into the specific model inputs, such as detailed geometry, pipe diameters, and vessel configurations. Only general visual representations were available for verification.
Input data comprised twelve acoustical load cases in the latest report, reflecting a range of speeds, pressures, and valve configurations. Although graphs suggested further speed variation was considered in shaking force calculations—a good practice given the compressor’s variable speed—this was not explicitly documented.
Crucially, none of the analyzed cases represented the compressor’s current operating condition. This omission calls into question the applicability of the study’s findings for present-day operations.
The results section in both reports was notably sparse. The initial report offered only pass/fail tables for various criteria; the updated report included four shaking force graphs but lacked sufficient detail for comprehensive review. Relative vibration and stress data were presented as frequency response graphs, which, while useful for overview, did not specify component locations, impeding meaningful assessment.
There was no evidence that either the full system was analyzed for forced mechanical response, or that non-resonant shaking force allowables and mechanical separation (API 618 step 3a) were verified for all piping. The likely scenario, based on available figures, is that forced mechanical response was assessed only for the PSDs, separators, and intermediate piping—not the entire system.
Key Findings and Technical Conclusions
The review identified several critical issues:
- The actual compressor operating condition with all head end valves unloaded was not included in the pulsation analysis, limiting the study’s relevance.
- The geometric scope was restricted, omitting upstream piping to the slug catcher and downstream piping to the discharge scrubber.
- Input data and results were insufficiently detailed to permit verification of compliance with API 618 across the full system.
- It is probable that only a subset of the system—mainly PSDs and separators—was analyzed for forced mechanical response.
- The practice of installing supports during hot operation was deemed atypical and not beneficial, except for marginal cases involving rod run-out.
While the supplier’s use of conservative dynamic stress limits and advanced modeling techniques aligned with good engineering practice, the lack of comprehensive documentation and case coverage means mechanical conformance to API 618 could not be verified.
Recommendations
Based on the findings, the following actions are recommended to ensure a robust and compliant pulsation and vibration analysis:
- Update the API 618 pulsation and vibration analysis to include all piping from the upstream slug catcher to the downstream discharge scrubber, capturing the full system geometry.
- Explicitly analyze the current compressor operating condition with all head end suction valves unloaded at both the first and second stages.
- Conduct a static stress and thermal flexibility analysis, or confirm that such an analysis has been performed by another qualified party.
- Enhance the level of detail in input and results documentation to facilitate independent verification of system compliance and adequacy of recommendations.
Addressing these recommendations will help ensure the system’s dynamic and static integrity under all relevant operational scenarios and provide a clear record of compliance with industry standards.
Next Steps
The reviewed pulsation analysis provided a solid foundation but left significant gaps in system coverage, operating case representation, and documentation depth. For future analyses, comprehensive scenario coverage, transparent methodology, and detailed reporting are imperative for ensuring both technical rigor and regulatory compliance at the Q8 Terminal compressor station. Furthermore, this analysis has been further improved by Dynaflow where a
- Site visit has been performed
- Stress assessment analysis was conductedÂ
- API618 DA3 was conducted