TCR Arabia - NDT and Material Testing Services in Saudi Arabia
NDT and Material Testing per ASTM API and NACE in Saudi Arabia
Remaining Life Assesment (RLA) of Boilers
TCR Arabia has a strong practice in accessing boilers for their condition and remaining life.

There are two RLA approaches viz., Level – II assessment and Level-III assessment.

A pragmatic approach is adopted by TCR Arabia in handling the cases of remaining life assessment. Efforts are put in to collect as much data as possible on the component / equipment history. Often brain storming sessions are conducted with the concerned people using the equipments including the outside experts who are familiar with the operational details. To collect opinions and ideas, which are evaluated vis-à-vis the testing and studies conducted at a latter stage.

CALCULATION BASED APPROACH

Calculation procedures are often employed to determine the expanded lives of components under creep, fatigue and creep fatigue conditions. From plant records, information on temperature and cycling history is gathered. By use of standard material properties and damage rules, the fractional life expended up to a given point in time can be estimated.

DESIGN APPROACH

Components which are operated bellow creep regime are generally designed on the basis of yield strength, tensile strength and fatigue strength with suitable safety factors. Under normal condition deformation and fracture is not time dependant. As long as the applied stresses do not exceed the design stresses these components should last indefinitely; but in practice various factors causes reduction in life.

The Remaining life assessment approach is derived as under:

1. Understanding the actual degradation mechanism
o FATIGUE
o THERMAL FATIGUE
o THERMO MECHANICAL FATIGUE
o THERMAL AGING
o CREEP
o EMBITTERMENT
o CORROSION

2. Visual examination

3. NDT involving In-situ Metallography, Ultrasonic Testing, Magnetic Particle Inspection, DP Test, Ferrite Measurement.

4. STRESS ANALYSIS - Stress analysis is carried out to know the strength of the material.

5. NON DESTRUCTIVE TESTING - NDT inspection data provide an good in-site to the component integrity.

6. LABORATORY TESTING - Laboratory testing of cut samples provide valuable information about the material soundness.

7. JUDGMENT OF FITNESS OF THE EQUIPMENT- Based on available data, a judgement of the fitness of the equipment is done.

8. SUGGESTIONS ON REPAIRING IF ANY - If required, repairing of the equipment is suggested, for life extension.

9. JUDGMENT OF REMAINING LIFE BASED ON ANALYSIS - Finally, the estimates for remaining life is carried out.

Often the physical properties are verified and not so common tests like Stress ruptures are conducted. Having ascertained the extent of degradation, judgment on the remaining life is made. In addition to this periodic inspection procedures are spelled out to monitor the health of the equipment during the course of operation. The results point out if any operational mistake, restriction in free movement by thermal expansion or any other damage mechanism prevailing is revealed and preventive maintenance approach can be formulated.

DEFINITIONS OF COMPONENT LIFE - When RLA is performed:

HISTORY BASED CRITERIA: 30 to 40 years have elapsed, Statistics of prior failures indicate impending failure, Frequency of repair renders continued operation uneconomical, Calculations indicate life exhaustion

PERFORMANCE BASED CRITERIA: Severe loss of efficiency indicating component degradation, Large crack manifested by leakage, severe vibration or other malfunction, Catastrophic burst

INSPECTION BASED CRITERIA: Dimensional changes have occurred, leading to distortions and changes in clearances, Inspection shows microscopic damage, Inspection shows crack initiation, Inspection shows large crack approaching critical size

CRITERIA BASED ON DESTRUCTIVE EVALUATION: Metallography or mechanical testing indicates life exhaustion

DATA REQUIREMENT FOR LIFE ASSESSMENT

Item

Level – II

Level – III

Feature

More detail

Most detail

Failure history

Plant records

Plant records

Dimensions

Measured or nominal

Measured

Condition

Inspection

Detailed inspection

Temperature and pressure

Operational or measured

Measured

Stresses

Simple calculation

Refined analysis

Material properties

Minimum

Actual material

Material samples required?

No

Yes


A detailed report along with evidences of damage of any and recommendations will be provided by estimation of RLA. Typically, at TCR Arabia we propose following line of approach to undertake the RLA of package boiler.

1. Visual Examination
2. Thickness Measurement of critical areas.
3. Ultrasonic test on critical joints
4. Collection of scales/ water from different sections and analysis in the laboratory.
5. In situ metallography on critical locations.
6. In situ hardness testing
7. Literature survey and experience of other in assessing the extent of judgments.

Correlation of all testing, process parameter history of operation would be undertake to assess remaining life of Boiler. Recommendations would be made to attain longer, reliable and safe operation of boiler. The final report would be submitted with results of testing, explanation of damages observed during testing and observation in document form.

Microstructures Reveal

Optical Micrograph

Optical micrograph of non-bluged zones tube wall side showing ferrite –pearlite structure with no internal defects

Normal Microstructure

Normal Microstructure ( good condition tube) which shows a typical ferritic pearlitic structure

Deteriorated Microstructure

Deteriorated Microstructure which shows the decomposition of the pearlitic colonies



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