Higher Reliability

Reliability is as important as Efficiency. Without good reliability, you cannot utilize the plant effectively. Reliability is one of MHI's major products.

Proven Structure for Flexible Operation.

Reliability of MHI boilers' structure is confirmed by long time DSS (daily start-stop) operation. Figures below show examples of design consideration for flexible operation.


Header Construction	Example of Analysis Model

Vertical Waterwall Furnace Configuration.

For supercritical sliding pressure operation once-through boilers, spiral tube wall furnace is generally adopted.
MHI has originally developed optimum furnace waterwall system using rifled tube.

Features

Simple Structure
- Easy manufacturing and construction
- Shorter installation period
- Less thermal stress for furnace water wall tube
Less pressure drop of furnace waterwall tube
- Less auxiliary power consumption for boiler feed water pump
- Uniform fluid temperature at fumace waterwall autlet
Less adhesion of slag on furnace waterwall

Only MHI has the successful operation records of supercritical sliding pressure once-through boilers with vertical tube waterwall furnace in the world.

Development of New Materials.

Higher steam conditions can be made still economical by adoption of new materials, which has higher allowable stress at high temperature.
MHI has been taking part in the development and verification of these new materials.
MHI is the most experienced and knowledgeable boiler manufacturer about new materials.

Effect of Material Selection
Main Steam Pipe (25.1MPa/604 deg.C)

SA335-P22 (2.25%Cr)	SA335-P91 (9%Cr)	ASME Code Case 2180 MITI SUS410J3 (12%Cr)

OD863.6 / t250 Weight (354%)	OD558.8 / t93 (100%)	OD508 / t68 (69%)

Remaining Life Estimation Technologies.

In order to maintain the reliability and to carry out preventive maintenance for aged boilers, it is necessary to establish the overall life evaluation technology. MHI has been developing such technology practically and systematically with NDE (Non Destructive Evaluation) and NDI (Non Destructive Inspection).

NDE Method for Creep Damage
Life consumption of high temperature pressure part by creep damage can evaluated by MLAS (Mitsubishi Life Assessment System). MLAS is a non-destructive creep damage detection and evaluation technology based on vast database of metallurgical analysis by electric resistance method.

NDE Method for Fatigue Damage
Life consumption of low cycle fatigue at attachment welding edges are assessed by analysis of micro-crack with MT (Magnetic particle test) Replica Method.

NDE Method for Fatigue, Corrosion Fatigue and Tube Thinning Damage
MHI has developed a NDI apparatus so called M-MAUS (Mitsubishi Multi-sensor
Automatic UT System) for fatigue and corrosion fatigue damage detection at furnace
wall. Also, UT equipment for tube wall thickness measurement and fatigue damage
inspection from tube inside has been developed.