Steam Cycle Water Chemistry Commissioning Guidelines

Description

Water and steam chemistry and corrosion control is often a neglected area during the storage, erection, and commissioning of the equipment when building new units. There are no industry-wide guidelines.

The lack of readiness of the related equipment, accumulation of corrosion products, and often the use of incorrect water treatment chemicals can lead to significant delays of commissioning and costly delays in transferring the steam cycle to the customer. One day of delay may cost as much as a quarter million dollars and delays of several weeks are not uncommon. In addition, bad water chemistry caused by condenser leaks, air inleakage, accumulation of corrosion products, and inappropriate chemicals may cause scale and deposits and permanent corrosion damage; particularly to the boiler or HRSGs and turbines.

Examples of Encountered Problems

• condenser leak leading to cycle contamination by seawater

• destructive overspeed of turbine due to high boiler carry-over and valves stuck open

• pitting and stress corrosion cracking of stainless steel feedwater heater tubes due to contamination during storage and erection

• pitting of turbine blades during storage, leading to their replacement

• improper operation - no training and guidelines

• system corrosion because water chemistry control was not functioning

The Commissioning Guidelines are Customized Based on Cycle Design and Type of Operation and can include:

1 Review of Cycle and Component Design

2 Preservation during Manufacture, Transport, Storage, Erection, and Layup

3 Water Chemistry Control and Management

4 Training of Operators and Chemists

5 Manuals

6 Inspections: Methods and Results

7 Pre-Operational Cleaning, Hydro Tests

8 Maintenance Procedures

9 Pre-steaming Checks - Boiler, Turbine, Condensate Polishing, Send-out Steam System, GT Injection

10 Performance Testing

10.1 Steam Purity/Carry-over

10.2 Boiler Hideout

10.3 Makeup/Water Storage

10.4 Condensate Polishing/Regeneration

10.5 Deaeration

10.6 Chemical Addition Equipment

10.7 Condenser: Leaks, Deaeration

10.8 Send-out Steam and Return Condensate

10.9 GT Injection System

10.10 Iron (and Cu) Transport

10.11 Sampling and Monitoring Equipment

10.12 System Corrosion

11 Cooling Water System

12 Chemical Discharges/Disposal

13 Chemical Laboratory

14 Commissioning Schedule

15 Safety Issues

16 Checklist - a list of tasks to be completed and signed off as a record for the transfer of the unit to the customer