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API 674 & API 675 ANALISI PULSAZIONI E REVIEW MECCANICO DELLE TUBAZIONI DEL SISTEMA

Background

Reciprocating pumps (including diaphragm pumps, plunger pumps, and other positive displacement pumps) are used in many applications, including petroleum production facilities and refineries. Interactions with connected pipelines and system parts must be taken into consideration as well as system optimization with correct sizing of pulsation dampeners.

A Pulsation Analysis and mechanical review of piping system is often necessary for new or existing reciprocating pumps systems to avoid typical problems such as:

excessive pressure pulsations and piping vibration;
pressure pulsation-induced cavitation;
undesired opening of PSVs due to pulsations;
fatigue failures to pipelines and components;

Scope

An acoustic analysis is recommended to optimize overall system design by investigating the interaction between the pump and pipeline with the following advantages:

– Reliable long-term operation: complying with defined limit values for pressure pulsation and extending the service life of the overall system;

– Increasing availability: Improving operating reliability and lowering maintenance costs

Pulsation dampeners design options:

Our experience as a dampener manufacturer and acoustic analysis engineering provide the best recommended options over our wide range of products for a safe pumping system operation. Focusing on existing or new pulsation dampeners installation performances.

If a preliminary piping layout is available as well as pump and liquid information, a preliminary computation of static suction head and pressure pulsations in the system, allow to select the correct pulsation dampener (size and type). Similarly at discharge static pressure is generally high and pulsations shall be lowered by suitable pulsation control to get acceptable piping vibrations and avoid pressure safety valve chattering.

Calculation methods:

Two level of efforts are available according to API 674 STANDARD: Approach 1 and Approach 2.

Both methods use a state-of-the-art numerical calculation method performed in Fox engineering department.

Design Approach 2

An acoustic system is modeled with detailed piping drawings, liquid properties and equipment information. Peak-to-Peak Pulsation Levels are calculated at the operating conditions and pump pressure steps are chosen to yield the highest expected pulsation amplitudes throughout the piping system. Pulsation amplitudes are then compared to the levels identified in API 674.

Pulsation-Induced Shaking Forces (Unbalanced Forces) are calculated to predict the maximum pulsation-induced shaking forces and unbalanced pressure acting on the critical elements of the piping system, such as pulsation control devices, pulsation control device internals, vessels, closed-end headers.

Piping Modifications are developed in the model if the pulsation analysis indicates that pulsation levels and/or shaking forces are excessive; modifications to the pulsation control devices and/or piping systems are made and the analysis continued until the system meets the guidelines defined in C.1.5 or other criteria as agreed upon by the Purchaser and Vendor.

A simple mechanical review shall be performed using span and vessel mechanical natural frequency calculations to avoid mechanical resonance. This review shall result in a table of various pipe sizes that indicates the maximum allowable span (based on the maximum pump operating speed) between piping supports as a function of pipe diameter, and the separation margin requirements of API 674.

Design Approach 1

This simplified analytical study includes the design of a pump pulsation suppression device using proprietary and/or empirical analytical techniques to meet the pulsation levels specified in API 674 This approach includes the study, good piping layout, good support/restraint principles, and adequate NPIP to design a pulsation solution.

Model is generated in accordance with a simple schematic diagram made available by the client. No extensive piping drawings are required. This method provides a good quantitative overview of the basic pressure pulsation behavior in the pipeline and pulsation dampener sizing.