Chemical Technology February 2015

Chemical Technology • February 2015

ust as stress can accelerate deterioration of metals

in a corrosive environment, operational stress moves

equipment and systems toward failure. Limiting stresses

within the operating environment maintains reliability.

The elements of the maintenance which are relevant are:

1. Protecting components from stress

2. Monitoring their condition, and

3. Undertaking component(s) replacement prior to the

failure threshold level caused by stress excesses.

The impact of maintenance costs over time spans which

can easily reach 25 years or more is finally much higher

than savings made on the investment side when purchasing

inappropriate valve technology, or when choosing solutions

not being ‘state of the art’ technology. The aim of this article

is to show, using the example of industrial

(butterfly) valves, how quality of components

is effectively influencing the cost efficiency

of industrial production plants.

Asageneralrulevalvescontribute1%–3 %

of the total investment costs of industrial pro-

duction plants. Therefore valves often suffer

from a certain lack of consideration, even

though, in the worst case scenario, one valve

failing can lead to a plant shut-down. Hence

it is important, from the beginning, to choose

the most suitable flow control technology.

This commences with the choice of the ad-

equate valve type, and the definition of the

appropriate valvematerials to be used. Once the valves have

been installed, and the plant put into service, operational

and maintenance costs start running. Quality aspects of the

valve have a considerable impact on operational cost, as, for

instance, on pumping capacity, power demand of actuators,

and energy efficiency of the entire plant.

Corrosion is one of the major threads in industrial pro-

cesses, having an important influence on cost aspects.

Therefore it is important to design the valves by using innova-

tivematerials and adapted solutions in order to prevent such

corrosion damages and thus additional costs.

The expectations for a production plant are evident:

safety to the employees and the environment, constantly

high product quality and plant as possible and operating and

maintenance costs as low as feasible.

Finally the dilemma often lies somewhere between

aspects of CAPEX and OPEX. As an example, when using

components with a low average material lifetime (AMLT),

savings on the CAPEX side can be made, but, on the other

hand, OPEX will be higher because they are replaced more

frequently. On the other hand, attempts to reduce specific

costs of maintenance or repair, most often end in higher

CAPEX. Consequently, using high end components and ad-

vanced technology will provide a safer operation of the plant,

higher production quality and a more favourable total cost

of operation (TCO).

One to three percent of the investments costs of an indus-

trial plant are caused by low and medium pressure valves,

while maintenance costs including replacement and repair

of such valves are estimated to be in the range of 4 – 7 %

of the OPEX.

Lifetime expectation of valves used in production pro-

cesses generally is in the range of 5–10 years, depending on

the quality of the valve, the working conditions, the frequency

of operation and quality of maintenance. A standard quality

valve is expected to provide ten years of trouble-free service in

these applications. Speciality valves can give reliable service

for time spans of 15 or more years. In extreme cases, valves

only last about two weeks, and quite often valves have to be

replaced after three to six months. In such cases it is mainly

corrosion, abrasion and scaling that are the cause of these

very short lifetimes. Themain effects are internal and external

leaking, with all the consequent effects.

When looking at butterfly valves, for example, various

aspects affect the lifetime expectation (AMLT). One of the

most important sources of valvemalfunctioning results from

the design and quality of the sealing elements. The lifespan

and reliability of elastomeric seated butterfly valves is largely

dependent on the valve liner which is the heart of the valve.

Careful evaluation of this seemingly simple element should

Big effect on small cause –

Valve technology under stress

Maintenance can be defined as the

degradation management of engineered

materials (equipment and systems) to

retain their performance within their

designed operating parameters.