Waste Incineration and Mechanical Stress Measurement

A dynamic measurement of mechanical stress can be made in numerous ways. One of the worst choices you can make is to measure dynamic stress inside a waster furnace, because: It gets hot – temperatures can get up to 900 C (1650F) inside a waste furnace. Molecule chains are shortened at high temperatures, as a fair portion of them turn into carbides (a.k.a. grinding powder) which fly about inside the furnace. A fair portion of what not is turned into carbide particles becomes highly acid. In some incinerators, explosion is used to remove soot. Particles group into lumps, which can from a great...

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Small Bore – a Low Cost Element that can become very costly

Piping vibration can be troublesome in itself. Small Bore Fittings (a.k.a. Appurtenences) can be worse and usually are the things that first fatigue and break on a piping system and thereby add system risk. There exists vibration fatigue risk criteria for piping vibration failure. These usually are expressed as vibration velocity for the simple reason that it is vibration velocity that is proportional to mechanical stress at resonance, i.e. at the a frequency where we expect vibration/stress to be the highest. Here is a small derivation as to why vibration velocity is proportional to...

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What is Angle- and Order- Analysis?

When analysing rotating machinery, one may use time or rotation as the reference. A time signal can be resampled from a fixed time resolution, dt, to a fixed angle resolution with the help of the tacho signal. This is what the tacho pulse looks like when resampled from the time domain to a fixed angle resolution (see Figure 1):   Figure 1. A tachometer signal resampled from the time domain to the angle domain. One revolution is one square pulse period. The machine is speeding up, as can be seen in the square pulse width being shortened in the time record. (Click figure to enlarge) When...

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DIY Encoder for RPM and Torsion Vibration Analysis

Torsion vibration can be difficult to detect in rotating machinery as vibration occurs in a rotating component or drive train. Torsion vibration may result in equipment damage as loads increase and machine internal timing is affected. This post is about optic sensors and the use of a Do It Yourself (DIY) encoder to detect torsion vibration. A tacho signal can consist of one or more pulses per revolution. It can be picked up using e.g. a rotary encoder placed at a free shaft end, magnetic or optic sensors for the purpose of torsion analysis. Torsion analysis can be made using other...

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Shock Waves from Non-linear Wave Steepening

Wave steepening is a non-linear wave propagation effect that arises for strong pulsation in bubbly liquids, e.g. as is the case for reciprocating pumps and water or oil based mud. Steepening form repetetive shocks and may adversely affect pump equipment and piping fatigue life. To understand this shock generating mechanism, we must first better understand what is implied by the phrase Pressure. There are three pressure components: Line Pressure  (LP) Kinetic Pressure (KP) Pulsation Line Pressure is the stationary part of the pressure, Kinetic Pressure is pressure that moves with the flow...

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Low Frequency Sound Transmission into Offshore Cabin

The strongest helicopter noise is found at frequencies below 100 Hz. Helicopter landing and take off at platforms can cause sleep disturbances. Offshore space is premium. Cabins therefore tend to be compact. Cabins are also module-built and installed side-by-side, which leads to complicated acoustic interrelation regarding flanking transmission paths. To further compound the issue, a platform is very stiff compared to an ordinary building on land. Many of the truths known in building acoustics, therefore, do not hold. At low frequency, stiffness is the governing factor for sound transmission...

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