Many power stations across the world historically use steam pipework in their plants. The pipes are mostly made from ½CrMoV steel. Although this type of steel is suited for the application, it has a tendency to age just like all other metals and is also susceptible to fatigue failure from the high pressures and extremely high operational temperatures.
Based on plant experience, it has been shown that the risk of CrMoV bend failure being catastrophic is greater than failures on welds and the pipes most susceptible to failure are the ones closest to the boilers which have to withstand temperatures of around 600 ˚C.
These steam pipe failures obviously have huge cost implications and more importantly major safety implications. A power plant shutdown due to any type of failure can result in millions of dollars in losses to the operating company and loss of trained personnel as well, not to mention the intangible losses to industries and homes depending on receiving power from these plants 24x7.
Strain measurement, metallurgical replication, dimensional measurements, hardness testing, and chemical testing are some of the current test methods used in power plants across the world, but do not have the ability to predict the remaining life of the pipes being tested or when to change these pipes.
Small scoop sampling and Impression creep testing is an viable alternative and is gaining global recognition because it supports finite analysis better than the traditional test methods and has more repeatability. The test results also are able to classify which pipes are in good condition and which are in critical condition.
The sampling for the test is done by a special machine developed specifically for this application. The machine samples a scoop from existing pipework without damaging it, and while the plant is operational. This is a offers an obvious benefit to maintenance staff who want to keep plant shutdowns to a minimum.
The Impression creep test or Indentation test is used to determine the level of material fatigue specifically used in the evaluation of in service power station steam pipes and pipe work fittings. The more worn and fatigued a metal the greater the indentation under an applied constant force defined as a compressive extension in mm.
This test has been refined and implemented for the UK Power generating company NPower (part of the EU RWE power generating group). Click
here to learn more about RWE and NPower, by Bristol University UK and Tinius Olsen.
Impression creep test equipment comprises of; data capture, graphing and load hold control software, a furnace, H25K-S compression testing machine, dual LVDT averaging extensometer 0.1µm resolution accuracy ± 0.5% of displayed value and alignment fitting.
To date (Feb, 2010) Tinius Olsen has supplied four systems;
- Nottingham University, UK who are commissioned to support NPower in metal fatigue analysis,
- Electric Power Research Institute (EPRI) - 2 machines in their North Carolina USA facility (EPRI are a US testing/engineering consultancy institute supporting US Power generators and ASTM re metal fatigue of steam power station pipe work), and
- Strathclyde University, Scotland who provide commercial testing to the Scottish power industry.
For information please contact -
Amit Mitbawkar
Team Leader - Industrial Materials Testing
SIGMA ENTERPRISES LLC
Engineering Products Division
PO Box - 96241,
Dubai, UAE
Tel - +971 4 8851828
Fax - +971 4 8851628
Mobile - +971 50 4450907
Email – amit_mitbawkar@sep.ae
Website - www.sigma-epd.com
) describes an object's tendency to shear (the deformation of shape at constant volume) when acted upon by opposing forces; it is defined as 
