African Fusion August 2017

AFRICAN FUSION

August 2017

INDEX TO ADVERTISERS

Today’s technology

Afrox.......................................................25

Air Liquide South Africa..........................8

Air Products...........................................31

ESAB ......................................................18

Hydra-Arc Group...................................23

Lincoln Electric...................................OBC

Oerlikon............................................... IBC

SAIW.........................................................2

SANAS...................................................IFC

voestalpine UTP Maintenance.... OFC, 12

Welding Alloys SA..................................21

quipment and components such

as steam generators, pumps

and turbines that handle steam

and water in the steam cycle operate

in extremely harsh environments, be-

ing subjected to high pressure steam,

high temperatures and metal-to-metal

wear in seating areas. “These are the

main contributors of wear in steam and

water valves,” says Thermaspray spray

shop manager, Paul Young. “These

components require a variety of control,

safety and shut off systems and this is

where a lot of wear occurs,” he adds,

“Furthermore, the surfaces of valve seats

and spindles need to inhibit oxidation,

which can lead to adhesion damage at

high temperatures.

“Our thermal spray and PTA capa-

bilities enable us to refurbish and repair

a wide range of components used by

local power stations. These include fan

blade and steam side spindles, servo

motor and rack spindles, stator pump

bearing and accumulator housings, fan

blade shafts and liners, pump impellers,

nose tip liners, deflector rings, control

casings, sleeve and rotation plates,

sleeves and bushes as well as a range

of valves,” Young says.

Thermalsprayingprovidesincreased

resistance to high temperatures, oxida-

tion, traction, cavitation, chemicals and

corrosionaswell aswear resistance from

erosion, abrasion and friction.

Thermal spray coating and plasma-transferred arc (PTA)

claddingsolutions fromThermasprayprotectpowergeneration

components against corrosion and wear.

PTA clad hardfacing offers the ideal solution

for applications where severe impact and

corrosion are prevalent.

A schematic of the PTA weld cladding process.

PTA for the protection

of power components

Thermal spraying is considered a

‘cold method of welding’ where high

temperatures can be achieved in the

heated spray zone while the tempera-

ture of the part itself usually remains

under 100 °C. The process can restore

worn components to precise original

dimensions and extend component ser-

vice life – “and the subsequent increased

uptime and improved production trans-

late into significant cost savings for the

end-user,” notes Young.

PTA clad hardfacing offers the ideal

solution for applications where severe

impact and corrosion are prevalent.

Here, coatings that can withstand such

conditions by providing the necessary

protection to the substrate are required.

“This welding process is used to

producehigh-qualityweldhardfacingsof

Ni, Co and Fe alloys, as well as tungsten

carbide containing grades of the nickel

alloy,” continues Young. ”The PTA hard-

facings that are metallurgically bonded

to theparentmaterial, areable tohandle

impact, point and/or line loads that a

thermal spray coating cannot tolerate.”

The scope of work for various repairs

and refurbishments conducted by Ther-

maspray at eight power stations include:

Complete refurbishment of Semple

Valves, which involved stripping of the

valve, pre-machining, stress relief, ther-

mal spraying, PTA welding, NDT, final

machining, final grinding, and assem-

bly. Thermaspray also manufactured

rings and bushes for the Semple valve

from Mehanite material to the client’s

specification.

The refurbishment of valve spindles,

in partnership with a business partner,

included pre-grinding, thermal spray

coating, final grinding and NDT (DPI) on

thecoating.Therepairandrefurbishment

conducted on gland boxes demanded

pre-machining, thermal spray coating,

final machining and final grinding.

Refurbishment of valve seats in-

cluded pre-machining, PTA welding

with a cobalt alloy andmachining to the

required dimensions. The job included

PTA welding on new seats.

Pump refurbishment, which was

completed in conjunction with a busi-

ness partner, included machining,

grinding, thermal spray coating, and final

grinding. Electrical run-outs have also

been conducted on these shafts ensur-

ing the quality required. Thermaspray

also coated butterfly and ball valves to

increase wear and corrosion resistance.

Thermaspray, in a joint venturewith

Cape Town-based Surcotec, offers an

extensive portfolio of engineering and

thermal spray coating solutions to assist

OEM and end-user clients in reducing

costs and increasing production.

www.thermaspray.co.za