frischdampfeinstroemleitungen aus dem werkstoff 14mov63_en.ppt

2007/08/17 Siemens PGI / Duisburg / PG I14211 Technical Support

© Siemens AG 2007. Alle Rechte vorbehalten.

Piping material 14MoV63 in main steam admission lines of Siemens turbines



Damage and background-Main steam admission lines made of 14MoV63 in central-admission turbines (≥ 400°C)-Crack indications in the main steam admission line. Example: T5648, Sundsvall CHP -Cracks in main steam admission lines and inserts-Cracks in bends in the main steam admission line-Main steam admission lines made of 14MoV63-Repair welds in main steam admission lines made of 14MoV63VGB Guideline-VGB Guideline 509 L for material 14MoV63Siemens turbines affected -Overview of turbines affected in which material 14MoV63 was usedLong-term material behavior and inspection intervals- Service life versus long-term behavior of material 14MoV63Preventive actions-Substitute materials, condition monitoringMaterial inspections-Procedure for material inspections on admission lines made of 14MoV63-Schematic for non-destructive examination of pipe bends and welds-Procedure in the event of crack indications or damage to admission lines made of 14MoV63Safety philosophy-Conclusions

Contents



Damage and background



Main steam admission lines made of 14MoV63 in central-admission turbines ( ≥ 400°C )



Crack indications in the main steam admission lineExample: T5648, Sundsvall CHP

Risse

Technical Dataoperating hours: 150,000hmain steam : 530 ºCpressure: 130 bar



Cracks in main steam admission linesand main steam inserts

During the major inspection of the turbine, surface crack examinations were performed on the main steam admission lines and inserts for the HP cylinder (MS 130 bar / 530°C).A considerable number of cracks were found.



Cracks in bends in the main steam admission line

The areas showing the cracks were ground down until no indications were obtained. The cracks were between 3 and 12 mm deep. Due to the large number and the depth of the cracks, extended inspections were performed on the lines.



Main steam admission lines made of 14MoV63

In the course of our service activities we noticed that the admission lines and in some cases the steam inserts made of 14MoV63 in central-admission turbines commissioned between 1977 and 1983 may be susceptible to becoming brittle in the region of the bends and welds. Material studies have shown that there is a risk of relaxation-induced cracking and, in the fine-grained zone of weld seams, a risk of embrittlement due to creep.

At the time of their manufacture, the turbines were state of the art.



Repair welds in main steam admission lines made of 14MoV63

Piping material 14MoV63 is very difficult to weld and responds extremely sensitively to departures from the specified preheat and annealing temperatures. There is a risk of relaxation-induced cracking. What is more, the fine-grained zone of weld seams is susceptible to embrittlement due to creep. By today's standards, material 14MoV63 can be considered highly prone to damage. Because of its history, the material is essentially no longer used in applications subject to creep risk in Germany. However, it is still officially DIN-approved.



VGB Guideline



VGB Guideline 509 L for material 14MoV63

VGB Guideline 509 L "In-service inspection of piping systems in fossil-fired thermal power plants (second edition, 2002)" prescribes a first inspection of pipes made of material 14MoV63 after 70,000 operating hours.

The following is a quote from Section 4.3.1 of the Guideline on in-service inspections:

"Parts subject to a creep risk shall be inspected in accordance with TRD 508. Inspection of material 14 MoV63 shall commence not later than after 70,000 operating hours".



Siemens turbines affected



Overview of turbines affected in which material 14MoV63 was used

Turbine

number Plant Country HP type HP size IP type + size Series

5652 BANG PAKONG THA NG 90/81 N30-2 -4

5655 RENUSAGAR IND HNK 71/2,8 -4

5656 RENUSAGAR IND HNK 71/2,8 -4

5658 AL KHOBAR II 1 SAU NG 90/81 WK80/90 -4





5703 DHEKELIA "B" CYP HNK 71/3,2 -4

5704 DHEKELIA "B" CYP HNK 71/3,2 -4

5709 BANG PAKONG II THA NG 90/81 N30-2 -4



Long-term material behavior and inspection intervals



Service life versus long-term behavior of material 14MoV63

The harmonized procedure at Siemens (PG I, PG O) provides for reducing inspections intervals by 20%. The shortest inspection interval is limited to 20,000 operating hours. The following times must be observed to minimize potential risks:

Operating hours Hours to next inspection

70,000 56,000

126,000 45,000

171,000 36,000

207,000 29,000

236,000 23,000

259,000 20,000

279,000 20,000

299,000 20,000



Preventive actions



Substitute materials, condition assessment

The pipes should be replaced, if at all practicable. Material X10CrMoVNb9-1 (P91) should be used as a substitute. If the pipes are not replaced, condition assessment must be performed for the entire piping system. Only if the actual condition is known can a scope of inspection be defined and ordered for a specific turbine.

Executing department: (PG I14211, Technical Support in Duisburg).

Irrespective of the condition determined, these locations must be incorporated into the in-service inspection schedule and examined for changes at the agreed inspection intervals.



Material inspections



Procedure for material inspections onadmission lines made of 14MoV63

Surface crack examination requires the surfaces to be inspected to be free from rust, scale, deposits and other contaminations. Experience shows that the layers of scale that form in high-temperature zones can be effectively removed only by peening (vapor blasting using a water/sand mixture or dry peening agent).

All weld seams and pipe bends must be inspected 100%.

Inspection comprises the following:

-surface crack examination

-hardness test

-microstructure replicas

-plus section thickness and out-of-roundness measurements on bends



Schematic for non-destructive examination of pipe bends and welds



Procedure in the event of crack indications or damage to admission lines made of 14MoV63

If the inspections reveal adverse findings, the scope of inspection must be extended in consultation with an engineering and design calculation group in Duisburg (PG I14211, Technical Support and PG I14215, Turbomachinery Calculation). The inspection intervals given in the table must be adhered to. As a general rule, a further 10 locations should be inspected, which vary from inspection to inspection, so that after several in-service inspections an overall picture of the condition the piping has been obtained. A minimum scope of 10% of the most highly stressed locations plus 10 variable locations is required.

The largest possible scope should always be aimed for, in order to document the condition of the piping as accurately as possible. The inspections must be performed by Siemens personnel



Safety philosophy



Conclusions

Guideline 0-1136-7600-00 has been drawn up to establish a safety philosophy for how to deal with piping material 14MoV63 in Siemens turbines. A material inspection schedule must be drawn up by an engineering section (Siemens Duisburg, PG I14211, Technical Support) for each customer and each turbine. The installation schedule should specify which scope of inspection is to be performed after which interval. The actual condition of the piping must be determined by material testing and documented. Furthermore, the information documents already delivered to the customer must be archived.If, for any reason, permission for material inspections is not granted, Siemens must disclaim all liability concerning the safety of the main steam lines.

frischdampfeinstroemleitungen aus dem werkstoff 14mov63_en.ppt

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