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Fifoots Power Station, Newport - formerly Uskmouth Power Station and now owned by the AES Corporation - has been successfully brought back into operation. A key feature of this has been the refurbishment by TEi of the three original steam turbine condensers and the nine high pressure feedwater heaters.

TIGHT PROGRAMME

In winning this work, TEi was able to offer shorter overall programme times than its competitors by using state-of-the-art tube pulling and disposal equipment available through TEi’s exclusive licence agreement with Retubeco, the USA’s leading condenser and heat exchanger refurbishment company.

The condensers were re-tubed with 33,600, 1” dia, 18 gauge, 70/30 Cu/Ni tubes, air freighted from the USA due to the tight programme.

COLLABORATION

Close collaboration between TEi business units played a big part in the success of the project: at its Wakefield factory, TEi fabricated four new carbon steel water boxes, developing the design using the original cast iron water box drawings; TEi YIMPACT – specialists in explosive welding and heat exchanger inspection / repair – provided the hands-on retubing and expanding skills; and the entire project was co-ordinated and managed by the TEi regional office in Cardiff.

MAJOR WORK ON HP HEATERS

The nine HP heaters needed extensive refurbishment. The two highest pressure heaters on units 13 & 14 were completely retubed using tube-to-tubesheet explosive welding by TEi YIMPACT, thus guaranteeing the highest possible level of joint integrity.

The remaining seven heaters were all extensively refurbished with specialist weld repairs to tubesheets, flange machining, renewal of bolting materials (many to thread profiles no longer in common use) and full tube bundle pressure testing.

MAJOR WORK ON HP HEATERS

The nine HP heaters needed extensive refurbishment. The two highest pressure heaters on units 13 & 14 were completely retubed using tube-to-tubesheet explosive welding by TEi YIMPACT, thus guaranteeing the highest possible level of joint integrity.

The remaining seven heaters were all extensively refurbished with specialist weld repairs to tubesheets, flange machining, renewal of bolting materials (many to thread profiles no longer in common use) and full tube bundle pressure testing.

Download Fifoots & Kilroots PDF Case Study>

The success of Fifoots condenser retubing by TEi gave the owner, AES Kilroot, the confidence to contract with TEi for this challenging work.

LITTLE TIME TO DECIDE

Eddy current inspection of the condenser tubes carried out during a planned four-week outage on Kilroot’s No.2 unit showed that deterioration of the tubes had reached the point where a crucial decision had to be taken whether to plug further tubes, or carry out a full re-tube within the outage window.

WORKING CLOSELY WITH AES KILROOT

Close collaboration between TEi and AES Kilroot staff was a key feature in the project: station maintenance personnel removed two water boxes from one end of the condenser and a scaffolding access platform was erected by AES Kilroot ready for TEi to start work.

RAPID RESPONSE

Very shortly after contract award, TEi started work on site cutting the 11,300, 1” dia, 18 gauge aluminium brass tubes and setting up the Retubeco tube pulling gear capable of extracting and flattening tubes at up to 1.2m/s (240ft/min).

The flattened tubes are then ‘walked’ to a specially designed Retubeco cropping machine which cuts them into short lengths, collects them in a skip and enables them to be taken directly off site for disposal. The condition of the chopped tubes makes them highly
sought-after by the material reclamation industry.

WORKING ROUND-THE-CLOCK

TEi worked round the clock to extract all the tubes, clean and prepare the tube plates,
re-tube and roller expand the tubes into the inlet and outlet end tube plates.

Thirteen days after commencing work TEi delivered the condenser back to AES Kilroot, tested ready for service and ahead of the agreed re-tubing programme.

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THE PROBLEM

Heat Exchanger tubing can suffer from a wide variety of problems in service,

the nature of which is usually characteristic of the material and application.

Typical problems found include the following.

• Pitting corrosion

• Fretting at the baffle plates

• Impingement attack

• Mechanical damage

If these problems occur and remain undetected, they can often develop into leaks which more often than not result in an enforced shutdown. Such a scenario is usually very inconvenient and can often be quite costly.

THE SOLUTION

By carrying out appropriate tube inspection surveys on a periodic basis, e.g. annual shutdowns, it is possible to identify both internal and external defects in the tube wall before they lead to failure.

Having done so, tubes which are considered to be “at risk” can be plugged off or replaced before the unit is returned to service. In so doing, a much higher level of confidence in the reliability of the heat exchanger can be achieved and an unplanned shutdown avoided.

Yimpact Heat Exchanger Services offers a choice of three tube inspection systems to suit the tube materials normally used in the manufacture of heat exchangers.

Download Heat Exchanger Services PDF Brochure >

PAN AMERICAN IRIS ULTIMA INSPECTION

This ultrasonic tube inspection system can be used on both ferrous and non-ferrous materials.

• Inspects tubes from 9mm to 40mm internal diameter.

• Measures remaining wall thickness down to 0.5mm.

• Measures internal pitting down to 1.5mm dia.

• On screen wall thickness measurement.

• Results stored on IBM disks.

• Provides detailed information with regard to condition

and thickness of tubes, eliminates guess work and

percentage measurements.

EDDY CURRENT TUBE INSPECTION

Both single and dual frequency eddy current systems are available for the inspection of copper, copper alloy and other non-magnetic tubes used in a wide range of heat exchangers; from the smallest oil cooler to the largest Power Station main condenser.

Inspection probes are available for the most common tube sizes used in this type of plant, for example, 9mm to 38mm o.d.

The process which can detect both internal and external metal loss, is widely used in the following industries:

• Chemical

• Petro-Chemical

• Oil Refinery

• Power Generation

• Shipping

• Desalination

• Air Conditioning

Some of the typical problems which can be identified include:

• Internal/external corrosion

• Internal erosion

• Incondensable gas attack

• Vibration damage

• Steam erosion

DINSEARCH TUBE INSPECTION

The Dinsearch 1-00 series modular equipment is specifically designed for the in-situ inspection of carbon steel tubes in heat exchangers, gas coolers and boilers.

The system uses an established and proven electro-magnetic technique which will detect pitting, general corrosion, wear under baffle plates and thinning caused by erosion or corrosion; the defect most commonly occurring in steel tubular heat exchangers and boilers.

It will detect internal and external defects, but like other tube inspection techniques, will not necessarily detect leaks. With typical tube material, the equipment will resolve 1mm

diameter pits and 2% loss in wall thickness.

Inspection probes are available for tube sizes from 16mm to 75mm o.d. (5/8” to 3” o.d.) and for the normal range of wall thicknesses encountered in boilers and heat exchanger tubes.

HEAT EXCHANGER TUBESHEET /

SHELL THICKNESS MEASUREMENT

TEi Yimpact utilise Panametrics 36DL Plus Ultrasonic

thickness testing equipment to determine accurate

thickness measurements of the tubesheets/shell of

heat exchangers and general pipework.

OTHER SUPPORTING SERVICES

These services include:

• Individual pressure testing of tubes.

• Tube removal/replacement

• Supply / fit “dummy tubes”

• Supply / fit taper plugs, mechanical plugs, explosive plugs.

• Metallurgical Investigation

• D.P.I and M.P.I services