Condition Assessment Audit of Steam Plants

A 3 to 4 day plant audit to evaluate the state of the main cycle components and piping, assess remaining life and fitness for service, and recommend inspection and life extension activities. This audit is typically the first step of plant-wide condition assessment and component life evaluation for the non-electrical systems. Utility and industrial steam plants and related equipment.

Note: The Water Chemistry and Corrosion Control Plant Audit can be performed during the same plant visit.

The objectives of the audit are:

Safety assurance of the mechanical equipment - main cycle components

Minimizing forced outages and maintenance costs

Operation at best achievable efficiency (heat rate)

Increasing equipment life leads to more frequent forced outages, higher maintenance costs, and safety problems. The cost of these problems can be up to $10,000 of lost electric production and $1 million a day of lost industrial production.

The main cycle components, condition of which deteriorates with time, include:

Boilers (waterwall tubes, superheater, reheater, headers)

High temperature piping

Heaters and other auxiliary equipment

The safety related damage mechanisms are:

Low Cycle Corrosion Fatigue (LCCF)

Thermal (low cycle) Fatigue

High Cycle Corrosion Fatigue (HCCF)

Stress Corrosion Cracking

Flow-Accelerated Corrosion

Technology exists to properly inspect equipment, determine the damage mechanisms and root cause, and repair or replace the damaged components.

The safety issues experienced in steam systems are shown in the table below:

Component	Damage Mechanism [1]	Major Influences [2]	Destructive Failures [3]	$ Impact [4]
Steam Piping	Creep	Welds, temperature, time	Y	10^7
	LCF, LCCF	Temperature changes
	Carbon steel graphitization	Temperature and time
Drums and Headers	LCF, LCCF, SCC	Temperature cycling, design, water chemistry	N	10^7
Boiler Tubes	LCCF (20 others)	Water chemistry, cycling, heat flux, etc.	N	10^5
Feedwater and Wet Steam Piping	FAC	Design, water chemistry	Y	10^7
	Cavitation	Design, operation	Y
	SCC	Residual stress, chemistry	N
	CF, LCCF	Weld quality, water chemistry, temperature changes	N
Deaerator, Flash Tank, Hot Water and Steam Vessels - Welds	CF, SCC	Design (water piston), residual welding stress, operation, water chemistry	Y	10^7
LP Turbine Rotors and Disks	SCC	Design stresses, temperaturen, high strength steel, steam chemistry	Y	10^7
LP Turbine Rotors and Disks	CF	Steam chemistry, design, vibration	N	10^7
LP Turbine Blades	CF SCC	Steam chemistry, design vibration, pitting, erosion, High strength steel	N	10^6
HP/IP Turbine Rotors	LCF	Cycling, inclusions, fatigue design	Y	10^7
Turbine	Destructive Overspeed	Steam chemistry (boiler carry-over) - sticking valves	Y	10^7 - 10^8
Turbine	Rubbing	Steam chemistry, deposits, thrust bearing wear, thermal expansion	Y	10^6

[1]	CF - Corrosion Fatigue LCF - Low Cycle Fatigue LCCF - Low Cycle Corrosion Fatigue SCC - Stress Corrosion Cracking FAC - Flow-Accelerated Corrosion
[2]	Age influences the degree of damage for all issues except the last two
[3]	At least one destructive failure during the last 30 years
[4]	Lost production and repairs per one event

Audit Description

Based on the industry experience and plant information gathered in advance and during the plant visit, critical components and their potential damage mechanisms are identified, existing inspection, maintenance, and operation practices are evaluated, and the needs for improvements and more detailed life evaluation and extension determined.

The audit is structured as follows:

1.	Information gathering - prior to visit
2.	Cycle and equipment design review - prior to visit
3.	Initial meeting - ~ 2 hours
4.	Review of plant experience - ~ 6 hours
5.	Review of operation, maintenance, NDT, water chemistry and corrosion control - ~ 2 days
6.	Preliminary Conclusions and Recommendations - provided before leaving the site
7.	Closing meeting: a joint review of the Preliminary Conclusions and Recommendations - ~ 2 hours
8.	Audit Report - ~ 6 weeks after plant visit