Thickness reducing management system for pipes in pipe lines

A thickness reducing evaluation system for pipes in pipe lines made of either a carbon steel or a low alloy steel in a plant controlled under demineralized water, comprising:

• a pipe thickness measurement result data base unit which stores pipe thickness measurement results for respective measurement points performed during inspection of the pipe lines;
• a point pipe thickness reducing speed calculation unit which calculates a pipe thickness reducing speed through comparison of thickness measurement results at present inspection with thickness measurement results of the pipes in the pipe lines performed at previous inspection both of which are stored in the pipe thickness measurement result data base unit;
• a pipe thickness reducing speed model formula constructing unit which constructs a mathematical formula expressing pipe thickness reducing speed using at least one of the pipe line temperature, wetness of the fluid in the pipe lines and the fluid flow speed in the pipe lines which are determined at design stage as parameters and by making use of maximum values of the pipe thickness reducing speed calculated by the point pipe thickness reducing speed calculation unit;
• a maximum pipe thickness reducing speed calculation unit which calculates a maximum pipe thickness reducing speed at respective pipe thickness reducing measurement points in the pipe lines by making use of pipe line conditions in the pipe lines at the design stage based on the constructed pipe thickness reducing speed model formula.

A method of setting pipe thickness in pipe lines made of either a carbon steel or a low alloy steel in a plant controlled under demineralized water which takes into account of pipe thickness reducing due to erosion and corrosion in advance at the time of design stage thereof comprising the steps of:

• constructing a pipe thickness reducing speed model formula for a concerned pipe to be designed by classifying pipe thickness measurement data in a plant controlled under demineralized water and operated until now, when constructing the pipe thickness reducing speed model formula, the pipe thickness reducing speed data are classified depending on differences whether the pipe material is a carbon steel or a low alloy steel and whether the pipe inner fluid which was estimated in the design stage is a single phase of liquid or two phases of gas and liquid, in that the thus classified pipe thickness reducing speed data are formulated into model formulas in such a manner that in the case where the pipe inner fluid which was estimated at the design stage is a single phase of liquid and the pipe material is a carbon steel, the pipe line temperature and the fluid flow speed in the pipe line which were estimated in the design stage are used as the parameters, in the case where the pipe inner fluid which was estimated in the design stage is two phases of gas and liquid and the pipe material is a carbon steel, the pipe line temperature and the wetness of the fluid in the pipe lines which were estimated in the design stage are used as the parameters and in the case where the pipe material is a low alloy steel, only the pipe line temperature which was estimated in the design stage is used as the parameter, thereby, a group of pipe thickness reducing speed model formulas which take into account the pipe material and the inner fluid states are determined;
• determining whether the pipe line of the design object is a carbon steel or a low alloy steel as well as determining the pipe temperature, the pipe line inner fluid wetness and the pipe line inner fluid flow speed;
• selecting among the previously constructed group of the pipe thickness reducing speed model formulas a suitable pipe thickness reducing speed model formula which meets the determined pipe material and the inner fluid states;
• determining a pipe thickness reducing speed based on the selected pipe thickness reducing speed model formula by making use of the determined parameter values in the design state;
• calculating a minimum necessary pipe thickness which is required for the pipe based on information such as pressure of the inner fluid and diameter of the pipe representing design specifications;
• determining a design life time for the plant;
• after determining the design life time for the plant, preparing a diagram in which the pipe thickness is indicated along the ordinate and time is indicated along the abscissa;
• drawing from a point on the ordinate corresponding to the minimum necessary pipe thickness a minimum necessary pipe thickness line in parallel with the abscissa;
• further drawing from a point representing the design life time of the plant on the minimum necessary pipe thickness line a straight line raising leftward with a slope corresponding to the pipe thickness reducing speed;
• and
• determining the pipe thickness at the crossing point of the straight line with the slope of the pipe thickness reducing speed with the ordinate, namely at the time of zero representing the operation starting time of the plant as the design thickness.