PEB Singapore PPE Mechanical flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Bending stress equation

For a beam in bending, stress at distance y from the neutral axis is σ = My/I, or σ = M/Z, where the section modulus Z = I/c.

Soderberg fatigue criterion

A conservative fatigue design rule stating σa/Se + σm/Sy = 1, where σa is alternating stress, σm mean stress, Se endurance limit and Sy yield strength.

Hoop stress thin cylinder

A thin-walled cylinder under internal pressure p has hoop stress pr/t and longitudinal stress pr/2t, so the hoop stress is twice the longitudinal stress.

Euler buckling load

Elastic critical load of a slender column, Pcr = π²EI/(KL)², with K = 0.5 fixed-fixed, 0.7 fixed-pinned, 1.0 pinned-pinned and 2.0 cantilever.

Fan affinity laws

At constant impeller diameter and air density, flow varies with speed N, pressure with N squared and shaft power with N cubed, so a 20% speed cut saves about 49% power.

Coefficient of performance

COP is useful cooling delivered divided by work input. For chillers, kW/RT equals 3.517 divided by COP, since one refrigeration ton is 3.517 kW.

Air changes per hour

ACH equals 3600 multiplied by volumetric airflow in cubic metres per second, divided by room volume in cubic metres, used for ventilation and plant-room design checks.

Sensible heat of air

Approximate sensible heat change of an air stream, Qs in watts ≈ 1.21 × volume flow in litres per second × temperature difference in kelvin, for standard air density.

Log mean temperature difference

LMTD = (ΔT1 − ΔT2)/ln(ΔT1/ΔT2), where ΔT1 and ΔT2 are the terminal temperature differences of a heat exchanger; a correction factor applies to multipass units.

Net positive suction head available

NPSHa = (Pa − Pv)/(ρg) + Hs − Hf, using absolute suction pressure, vapour pressure, static suction head and friction loss. Cavitation occurs when NPSHa is below the pump's NPSHr.

Hydrostatic test pressure

Pressure vessels are normally hydrostatically tested at 1.3 times the maximum allowable working pressure, adjusted by the ratio of allowable stress at test to design temperature.

Pump shaft power

Shaft power in kW = ρgQH/(1000η), where Q is flow in cubic metres per second, H total head in metres, ρ density and η pump efficiency.

Total float in CPM

Total float equals late start minus early start, or late finish minus early finish. Activities on the critical path have zero total float, so any delay there delays completion.

Cost performance index

CPI equals earned value divided by actual cost. A CPI below 1.0 means work is costing more than budgeted, and EAC is often forecast as BAC divided by CPI.

PERT expected duration

Expected duration te = (O + 4M + P)/6, weighting the most likely value four times; activity standard deviation is (P − O)/6, used for schedule confidence estimates.

Schedule variance

Schedule variance equals earned value minus planned value. A negative value indicates the project is behind schedule; SV is expressed in cost units, unlike the dimensionless SPI.

Public safety paramount duty

Under the Professional Engineers Act and the PEB code of conduct, an engineer's first obligation is public safety, health and welfare, overriding loyalty to client or employer.

Conflict of interest disclosure

An engineer must declare any financial or personal interest capable of biasing technical judgement, such as shares in a tendering contractor, and withdraw if it cannot be managed.

Competence limit in practice

An engineer should accept only work for which they hold current competence; where a task exceeds it they must engage a qualified specialist and remain accountable for coordination.

Confidentiality obligation

Client and employer information obtained during an engagement must not be disclosed without authority, and the duty survives the appointment, subject to legal or safety exceptions.

Professional Engineers Act

A Singapore statute administered by the Professional Engineers Board that governs registration, the practising certificate, disciplinary offences and use of the reserved title Professional Engineer.

Security of Payment adjudication

The Building and Construction Industry Security of Payment Act gives contractors a statutory right to progress payments and rapid adjudication, rendering 'pay when paid' clauses void.

Liquidated damages

A pre-agreed sum per day of delay that must be a genuine pre-estimate of the employer's loss; if it operates as a penalty it is unenforceable.

Design and build contract

A single contract under which the contractor is responsible for both design and construction, so the employer states performance requirements and the contractor carries design risk.

Hierarchy of controls

Ranked risk controls: elimination, substitution, engineering controls, administrative controls and PPE. Higher-ranked controls are more reliable because they do not depend on human behaviour.

Permit to work

A documented authorisation controlling high-risk tasks such as hot work, confined space entry or live electrical work, confirming isolations, gas tests and precautions before work starts.

ALARP principle

As Low As Reasonably Practicable: residual risk must be reduced until further measures are grossly disproportionate in cost, time or trouble to the benefit gained.

HAZOP guide words

A structured P&ID review applying words such as no, more, less, as well as, part of and reverse to process parameters to identify deviations, causes and consequences.

Net present value

NPV discounts all future project cash flows at the required rate of return and subtracts the initial investment; a positive NPV means the project adds value.

Simple payback period

Payback equals initial capital cost divided by annual net savings. It is quick to compute but ignores the time value of money and all cash flows after payback.

BCA Green Mark

Singapore's green building rating scheme, with levels from Certified through Gold, GoldPLUS, Platinum and Super Low Energy to Zero Energy, scoring energy, water and environmental performance.

Chiller plant efficiency

Expressed as kW of electrical input per refrigeration ton of cooling. About 0.65 kW/RT is typical good practice, while high-efficiency plants reach 0.5 kW/RT or better.