ULTRASONIC TESTING PART 2

DEAD ZONE :- THE TRANSDUCER IS NOT READY TO RECIEVE  SIGNALS FROM NEAR SURFACE FLAWS AS IT IS STILL VIBRATING DUE TO INITIAL PULSE.

The dead zone can be verified with an International Institute of Welding (IIW) calibration block. With the time base calibrated to 50 mm, and the transducer on position , the extent of the dead zone can be inferred to be either less than or greater than 5 mm.

Fresnel Zone (Near Field) The sound beam radiated close to the transducer consists of a tapering near field or Fresnel zone beginning at the crystal surface, followed by a spreading far field or Fraunhofer zone. 

Fraunhofer Zone (Far Field) Beyond the near field is the Fraunhofer zone . Here the beam diverges and is referred to as beam spread. Through the far field the sound behaves similar to a beam of light, in that the sound pressure disperses according to the Inverse Square Law (i.e., the intensity is inversely proportional to the square of the distance) and travels in straight lines.

FORMULA FOR CALCULATING NEAR FIELD:-

                                  N= D^2/4lambda (λ)

                                              N= NEAR FIELD

                                              D= DIAMETER 

                                              LAMBDA:- WAVELENGTHS

DIVERGENCE ANGLE CAN BE CALCULATED BY FOLLOWING FORMULA

Φ = DIVERGENCE ANGLE= sin -1(1.22LAMBDA/D)

                                                        ULTRA SONIC TESTING

                                                     PART 1

 ULTRA- SUPER

SONIC- CONNECTED WITH WAVES

1=INFRASONIC SOUND RANGE < 20 Hz (Hertz)

2=ULTRASONIC SOUND RANGE >20 KHz

3=SONIC SOUND RANGE 20Hz- 20 KHz 

                                                    WAVE PROPAGATION

1- LONGITUDINAL WAVES

           ---particles movement is in the direction of waves.

           ---can travel both in liquids and solids.

2- SHEAR WAVES/TRANSVERSE WAVES

          ----particle movement is perpendicular to the direction of                         wave.

          ----only travel in liquids.

3- SURFACE WAVES

         ---- combined motion of longitudinal & shear waves.

4- PLATE WAVES/LAMB WAVES

         ----similar to surface waves

         ----only for thin plates(few wavelength in thickness)

  

Why preheat is done? 

FIRST UNDERSTAND WHAT IS PREHEAT:-

Preheat is the application of heat to a joint immediately prior to welding and

is usually applied by either a gas torch or induction system.

NOW:-

one of the main

reasons is to assist in removing hydrogen from the weld.

HOW PREHEAT TEMPERATURES ARE CALCULATED

Preheat temperatures for steel structures and pipe work are calculated by

taking into account the carbon equivalent (CEV) and thickness of the

material and the arc energy or heat input (kJ/mm) of the welding process.

REFER STANDARDS BS EN 1011 FOR PREHEAT TEMPERATURES.

***In general, thicker materials require higher preheat temperatures.

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                                                                              HVAC

FIBROUS GLASS INSULATED HVAC DUCT SYSTEMS

and how they provide .

1. • Quiet, efficient air delivery
2. • Improved indoor environmental quality
3. • Cost-effective energy conservation
4. • Enhanced occupant comfort

FIBROUS GLASS INSULATED HVAC DUCT SYSTEMS

Introduction

Fibrous glass has been used as thermal and acoustical

insulation in forced air heating, ventilating, and air

conditioning systems ever since these systems became

widely available following World War II. Today, fibrous

glass duct systems, duct liners, duct wraps, and

commercial insulation boards contribute to indoor

environmental quality (IEQ) and occupant comfort in

residential, commercial, industrial, and public buildings of

all kinds. These include homes, apartments, schools,

hotels, motels, medical facilities, theaters, shopping

centers, office and government buildings, factories, and

many other types of structures where occupant comfort

and indoor environmental quality are important criteria.

                  Fibrous glass insulation is used in air duct systems for four basic reasons

                                1 Temperature control - Delivery of heated or cooled air at
                                  comfort levels suited to building occupancy requirements.

                       2 Acoustical control - Absorption of noise generated by
                         central air handling equipment and movement of air
                         through the ducts, as well as “cross-talk” carried by ducts
                         from one space to another.

                3• Condensation control – Prevents condensation in or on
                ducts when installed R-value recommendations are
                 followed, reducing the likelihood of moisture damage to
                     ceilings and other interior finishes.
                 4• Energy conservation - Reduction of HVAC system
                 operating costs by controlling heat loss or gain through air
                   duct walls, helping systems run more efficiently

WELDING INSPECTION

1 General

Welding Inspectors are employed to assist with the quality control (QC)

activities that are necessary to ensure that welded items will meet specified

requirements and be fit for their application.

For employers to have confidence in their work, Welding Inspectors need to

have the ability to understand/interpret the various QC procedures and also

have sound knowledge of welding technology.

Visual inspection is one of the non–destructive examination (NDE)

disciplines and for some applications may be the only form.

 

Guidance and basic requirements for visual inspection are given by:

BS EN 970 (Non–destructive Examination of Fusion Welds – Visual

Examination)

2 Basic Requirements for Visual Inspection

(to BS EN 970)

BS EN 970 provides the following:

• Requirements for welding inspection personnel.

• Recommendations about conditions suitable for visual examination.

• The use of gauges/inspection aids that may be needed/helpful for

inspection.

• Guidance about information that may need to be included in the

inspection records.

• Guidance about when inspection may be required during the stages of

fabrication.

3 Welding Inspection Personnel

Before starting work on a particular contract, BS 970 states that Welding
Inspectors should:
• Be familiar with relevant standards*, rules and specifications for the
fabrication work that is to be undertaken
• Be informed about the welding procedure(s) to be used
• Have good vision – in accordance with EN 473 and should be checked
every 12 months
(* standards may be National or Client)
BS EN 970 does not give or make any recommendation about a formal
qualification for visual inspection of welds. However, it has become industry
practice for inspectors to have practical experience of welding inspection
together with a recognized qualification in Welding Inspection – such as a
CSWIP Qualification.

4 Conditions for Visual Inspection

Illumination

BS EN 970 states that the minimum illumination shall be 350 lux but

recommends a minimum of 500 lux*.

* normal shop or office lighting

Access

Access to the surface, for direct inspection, should enable the eye to be:

• Within 600mm of the surface being inspected

• In a position to give a viewing angle of not less than 30°