Replacement of Safety Valves

SCOPE:

The scope for this project is as follows:

Procurement:

* Supply and delivery to site 5 of Drum safety valves, two of superheater safety valves of the helical spring type, and the respective flange adaptors.

* The safety valves are to be supplied complete, and ready to be installed

* The safety valves are to be tested at the workshop before being delivered to site.

* The lift pressure and blowdown pressures to be preset at the workshop.

* Data books including all the test certificates and material certificates to be supplied with the valve.

* Data books are to contain (as a minimum) maintenance and operating manuals/instructions, and recommended spares list.

* Material certificates to be supplied in accordance to BS EN10204 with the "type 3.2" inspection certificates.

The procurement works excludes the following:

* Installation of the valve

* Setting of the lift and blowdown pressures on site

Labour/Fitment

* New valves will be installed during outages (MT, MGO & GO).

* The current elephant trunks of the Hopkinson's valves (serving as discharge pipes) will be removed and replaced with new pipe-work (single outlet pipework).

* Bending and re-routing of discharge pipe-work will be planned ahead of the outages.

* Discharge pipework will be supplied by the valve suppliers.

* The current flange installed on the Hopkinson's valves is not the standard flange adaptor flange will be fitted to accommodate the new standard flange on the spring loaded valve.

* Setting of the lift and blowdown pressures on site (floating).

Units 2 and 3 are running "out of normal", with operating pressures on the superheater outlets reduced to about 10.8 MPa. If pressures are increased above this valve, the valves will start chattering, which cause damage to the seat, hence loosing sealing capability of the valve (results in passing safety valves).

A plant walkdown conducted by Boiler Engineering, AIA, and GBE on 26/03/2009 revealed that unit 1-10 safety valves are defective/passing.

Unit 1 - 10 safety valves are not lagged (a requirement from NWS 1454 and the instruction manual of the safety valves - incident 03/149). This is believed to have exacerbated deterioration of torsion bars'