Que5.8. What’s residual stress? Also write the causes and types of residual stress in welding. Answer Residual Stress It’s the stress which remain within a welded/ structure/ casting structure when no presence of external cargo thus they are tone balance within structure itself. Causes of Residual Stress in Welding Residual stresses in the welding arise due to 1. The discriminational heating of the plates by the weld heat source. 2. Thenon-uniform plastic distortion. 3. The cooling rate that accompanies welding processes. Types of Residual Stresses Mechanical Residual Stresses 1. It’s due to the original heating and rapid-fire cooling of the weld essence during the welding and after the welding independently. 2. Because of original heating essence expands and due to cooling it contracts. This process of original expansion and compression set up stresses in the workpiece. ii. Metallurgical Residual Stresses 1. This type of residual stress is developed during the phase metamorphosis which takes place while cooling from above the austenitizing temperature. iii. response Stresses 1. response stress is developed in a welding when the weldment is formerly attached to other portions of the structure. 2. Due to formerly being attached to other portion, thermal expansion and compression occurs to the weldment by the part of structure to which it is being welded, this results into response stresses. Que5.9. What are the styles used for measuring the stresses in weld structure? Explain any one of them. Answer Stress Measuring Method 1. colorful styles are used for the dimension of stress some of them are as follows Strain hand system, ii. Brittle fleece system, and iii. Photostress ways. 2. Stresses in welded joints are measured by strain relaxation ways in which the job is either crafted, sectioned or a hole is drilled. 3. The locked- in residual stresses get thereby released and affect the brittle fleece, photostress fleece or strain hand which in turn measures this effect and the relaxed residual stresses are calculated. Brittle Coat Method 1. This system makes use of a brittle coating also known as brittle lacquer or stress fleece which is principally a limed wood rosin K and dibutyl phthalate with carbon disulphide as a detergent. The brittle coating is commercially available. 2. An applicable coating for the being temperature and moisture conditions is named. 3. The job and the estimation strips are completely gutted and given an aluminiumpre-coating to give a bright background for easing the observation of the cracks. 4. Job and the estimation strips are scattered with brittle coating and permitted to dry for 15 to 24 hours. The fleece or lacquer becomes brittle on hardening. 5. At the place in the job where residual stress pattern and magnitude is to be determined, a hole of about 3 mm periphery is drilled. 6. The estimation strip is subordinated to biaxial tensile stresses and the point to cosign cracking is pronounced and the strain in the strain scale is read. 7. Residual stresses are calculated by comparing the results of the stress fleece on the job with those of a estimation strip. 8. Brittle fleece system gives quantitative results accurate to within ± 10 and can be used to descry static and dynamic strains in pressure or contraction. In this system, 1. Usual hand length is veritably small. 2. Approximate lowest measurable strain is 5 × 10 – 4 mm/ mm. 3. Approximate range of strains is0.05 to0.15. Que5.10. Describe the residual life assessment in detail. Answer 1. Residual life assessment is the time period during which the outfit shall retain the fitness for service characteristics. 2. Each welded structures have an anticipated service life. The factual service life may be more or less than estimated or anticipated service life. 3. To cover the extent of in- service downfalls, expansive and precious examination programs are generally accepted, in addition to routine examinations. 4. These examinations are more rigorous than the routine bones
and are necessary with a view to determine whether a material condition was service convinced or was since the structure was erected. 5. If a welded structure concerned is critical and its failure may beget hazard to life and health of the people living around. 6. A detailed examination of cracks( grounded on experience) and other damage observed in channels, pressure vessels and storehouse tanks are to be audited and on the base of experience of the examination done, following points in regard to examination ways need to be considered. Advanced ways should be used to descrysub-surface excrescencies, dimension, position, depth and number of cracks. ii. bettered or advanced ways should be suitable to 1. check the entire vessel outside and outdoors. 2. check during operation. 3. Examiner and measure excrescence on line. 4. Have sizing delicacy acceptable to identify the perimeters to critical excrescence size. Que5.11. What do you mean by deformation? bandy different types of welding deformation? Answer Distortion 1. deformation is the change in shape and difference between the positions of the two plates before welding and after welding. 2. There’s a good quantum of temperature difference at colorful points along the joint and therefore at any instant certain areas of base essence expand and others including weld blob contract. This marvels leads to deformation. Types of deformation Longitudinal loss 1. When a weld is deposited lengthwise on a light, narrow and impeccably flat strip of essence that’s neither clamped nor held in any way, the strip will tend to bow overhead in the direction of blob. This is due to the longitudinal compression of the weld essence as it cools. 2. Longitudinal compression is maximum along the weld centre line and diminishments towards the edges as shown inFig.5.11.1( i). 3. Longitudinal deformation depends upon the compression forces. ii. Stiffness of the section being welded. iii. Distance between the centroids of weld and section. ii. Transverse loss 1. When two plates being butt- welded together are neither too heavy nor held together, and are therefore free to move, they will be drawn closer together by the compression of the weld essence. This is called transverse compression. 2. Transverse compression exists each along the weld length and it depends upon the endless compression of rudiments in the weld zone as shown 3. The transverse compression can be averted by, Proper method welding. ii. Placing a wedge between the plates. iii. Separating the plates( before welding) to give allowance for compression. iv. adding the bow trip speed. iii. Angular loss 1. When two beveled plates are welded, it’s set up that the plates are pulled out of line with each other as shown inFig.5.11.1( iii). 2. Since the opening at the top of the single V groove is lesser than at the bottom, a lesser portion of the weld essence is deposited there, and therefore the delineation or pulling is topmost on that side of the joint. 3. Angular compression is related to the shape and size of the cooling weld essence zone and the stiffness of the remaining unfused part. 4. Double groove joints tend to minimize angular deformation because the compression goods of the two sides, i.e., top and bottom of the plate, get cancelled with each other. Que5.12. Explain in detail examination before welding, examination in between welding, examination after welding. Answer Inspection before Welding 1. Check out the welding joint drawing similar as confines, forbearance, process specificationetc. 2. Choose the suitable welding process by easy system. 3. Set the welding parameters similar as current, voltage, frequence, oppositionetc. 4. elect the disfigurement free material as per specification. 5. Selection of proper size, proper flux carpeted electrode as per specification BIS specification). 6. elect the Jig and institution of proper size as per welding joint complexity. 7. Proper arrangement of welding common cooling and ventilation as well as bank. Inspection in Between the Welding It’s the alternate stage of examination and it involves 1. Welding groove( Edge medication) should as per specification. 2. method welds should be of acceptable size, length and pitch, 3. system of welding similar type that minimal deformation should be in welding joint. 4. Welding position, fit up gap should be as per welding procedure. 5. Slag on the welding joint should be duly removed from each pass in multipass bow welds. Inspection after or Completion of Welding 1. Find out of determine parcels and weld quality of a weld object. 2. Find out felicity of weldment with the help of Destructive testing, and ii. Non destructive testing.
