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Introduction

A stress and surge analysis has been performed for the rewater

piping system of a LNG Plant, located in South America. The system

is constructed using Glassber Reinforced Epoxy (GRE) pipes. The

largest and most critical unbalanced forces were used to perform a

dynamic response analysis of the complete piping system.

Surge Analysis

The existing rewater plant contains two pump connections, a

fresh water and a seawater pump. During normal operation the

fresh water pump supplies the rewater, while the seawater pump

is used for backup in case of failure or when a large demand of

rewater is required.

A Transient ow analysis was performed using the software packa-

ge BOSuids®. BOSuids® is a commercially available package that

has been developed by DRG to perform transient ow analysis. The

pressure and ow distribution was calculated for steady state con-

ditions as well as for four critical transient scenarios. These scena-

rios include switching over from operating the fresh water pump

to the seawater pump, “the closing of all hydrants and monitors”,

simulatuously opening of the LNG sprinklers (largest ow); and -nally the tripping of both fresh and seawater pump subsequently.

These four scenarios were considered most important for the sys-

tem in terms of generating the highest and lowest pressures pos-

sible and the largest unbalanaced loads.

Stress and Surge Analysis

 Stress Analysis

The piping of the considered system is primarily buried and inclu-

des several connections to above ground re hydrants and corres-

ponding equipment. System routing and pipe properties used for

the analysis are based on data provided by the client.

The stresses are assessed conform ISO 14692, the standard for

GRE piping design. The software used to perform the stress analy-

sis is CAESAR II pipe stress software. This model incorporates the

unbalanced loads calculated using BOSuids® to perform the dyna-

mic stress analysis, relevant for fatigue.

“When performing a mechanical responseanalysis, it is highly importance to identifythe most critical scenario resulting in thelargest unbalanced loads”

Results

For given design conditions, several modications were advised

(with respect to the original design) to limit the static stresses

within the allowable envelopes, i.e. additional laminate reinforce-ments on top of the GRE wall thickness or application of exible

material. In addition to the static stress analysis, the unbalanced

loads were taken into account as a result of the pressure distribu-

tion of the transient ow in the system.

The maximum dynamic stresses were combined with the static

operational stresses and assessed against the ISO16492 long term

occasional envelope. It was found that none of the stresses were

greater than the occasional allowable.

More information on this subject? Contact us.

Fire Water System on a LNG Plant

Houtsingel 95

2719 EB Zoetermeer

The Netherlands

Reg nr. 27320315

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+31 79 361 5150

+31 79 361 5149

info@dynaow.com

www.dynaow.com

77Fiberglass