A Review of Methods to Estimate Creep Damage in Low‐Alloy Steel Power Station Steam Pipes

Abstract

ABSTRACT:For large complex structures such as power stations, refineries and other processing plants, cost effective operation is essential. With power stations, failures of components without prior warning can have serious consequences for personnel on site and be extremely expensive in terms of both losses in generation revenue and repair costs. The ability to monitor and assess the evolution of damage is critical to maximising plant availability and to minimise the risk of failures that pose a threat to personnel safety. This paper relates to the methods used to estimate creep damage in service aged low alloy steel steam piping. Welds and the extrados of bends in steam pipes are a particular problem with regards to measuring for the onset and progression of creep failure. Existing techniques will be discussed with respect to traditional site based and laboratory testing and assessment. Emerging strain monitoring techniques will also be described and evaluated that include point-to-point measurement and twodimensional mapping of creep strain across the weld zone and other creep susceptible components of power-station steam piping.

A review of non-destructive techniques for the detection of creep damage in power plant steels

“…Laboratory tests have shown that the strain typically accumulated in Cr-Mo-V steel components over a 2-year period of plant operation can be measured with an error of less than 10% [128]. The silicon nitride targets are not affected by the formation of scale on the surface of the component, but they do tend to become dull with time after exposure to high temperatures, so that degradation of image quality is currently an issue [129].…”

“…Accurate strain measurements can be obtained in shortterm laboratory tests [132], whereas work is in progress to ensure that the inevitable degradation of the speckle pattern due to high temperatures and harsh in situ environmental conditions yields images of sufficiently high quality between maintenance intervals, at which time the strain map could be stored and the pattern re-applied [129,133]. It is postulated that this technique could be successfully employed for the early detection and assessment of creep damage across welds because highly localised increases of the strain rate in the HAZ would be easily recorded [129].…”

Recent Developments in Measuring Creep Strain in High Temperature Plant Components

“…Following the review work of Maharaj et al and Sposito et al , there have been some recent developments with respect to methods used to measure creep deformation. These include using magnetic field properties that measure Barkhausen noise or magnetic hysteresis, eddy currents that are disrupted by inhomogeneities and replicas where computer‐based image analysis has shown some promise .…”

Effective determination of cyclic-visco-plasticity material properties using an optimisation procedure and experimental data exhibiting scatter

“…Focusing on the future trends of power plant operation, these fluctuations will become more pronounced as operators attempt to generate in a highly strategic manner, maximising generation effectiveness [4]. Variations in loading or temperature present serious complications when analysing such components due to the cyclic hardening and/or softening behaviour of materials if the material works within the plastic range.…”