Exsam Questoin - Paper 2 Flashcards
Why are single pass welds inferior to multi pass welds with regards to mechanical properties? (4)
a.) They produce columnar grain structure with inferior properties, a multi pass weld will heat treat the weld below it with an increase in mechanical properties because the weld has an equiaxed grain structure.
What effect does a high carbon equivalent have in a welding environment? (4)
a.) The higher the CE (Carbon Equivalent), the hardenabillity, the greater the probability for a full martensitic structure and therefore greater susceptibility to HIC (Hydrogen Induced Cracking).
Explain the term t8/5 (3)
a.) Time taken to cool from 800°C to 500°C.
b.) It is the temperature / time cycle of an individual weld run and is the time taken during cooling for a weld run and its heat affected zone to pass through the temperature from 800°C to 500°C
Discuss the problems associated with the welding of quench and tempered steel an explain the steps that should be taken to ensure the satisfactory weld are produced?
When welding these type of steels hydrogen entrapment tends to be a problem that could result in cold cracking. Special precautions need to be taken during the complete weldment cycle. Firstly the correct handling procedures for the electrodes would apply, i.e. storage, transport and usage. They would need to be kept in a hold oven once the manufactures seal has been removed and once taken out of the holding oven placed into hot boxes for transit and usage. The lower strength electrodes (E7018; E7028) should be used with 4 hrs once removed form the storage oven, the higher strength electrodes (E11018; E12016) 30 minutes and the medium strength (E8018; E8016) 2 hrs. Cracked, wet or damaged electrodes should discarded or returned to the manufacturer. Damp or wet electrodes can be reheated and dried using correct drying procedures to remove any moister. In severe cases they should be discarded or returned to the manufacturer for drying. Preheat temperatures, as per the welding procedure must strictly be adhered to. Once the preheat temperature has been reached welding can proceed. Controlling the heat input by means of small stringer weld beads is considered good practice, preheat temperature is to be maintained throughout the complete welding cycle after which the weldment can be cooled according the welding procedure. Post weld heat treatment to prevent brittle fracture has by experience been has shown to be not required for these type of materials as reheat/intergranular cracking could occur. When stress relieving cannot be avoided a temperature about 28ºC lower than the tempering temperature is desirable.
under what conditions will corrosion occur
a.) Air. If it contains moisture.
b.) Water (fresh, distilled or salt water)
c.) Soils
d.) Rural, urban and industrial atmospheres.
e.) Food products.
Pneumatic testing is considered, under certain circumstances, to be parlicularly hazardous type of test. Explain why this is so and detail the circumstances under which a test of this nature is sometimes carried out in place of hydrostatic testing?
- when structure cannot carry liquid mass
- when vessel internal design do not allow hydro test
- where removal of liquid strays is impractical
- when approval is obtained from inspection authority and all relevant parties
- when a approved procedure is available with regards to safety precautions and procedure of testing
Define Stainless steel
Stainless steels as could be defined as those steels containing more than 10% chromium.
how is Stainless Properties achieved?
The “stainless” properties of stainless steel are achieved by the addition of a minimum of 10.5% chromium content ¹. The chromium forms a self-healing, passive oxide layer on the surface of the steel that protects it from corrosion and staining ¹ ². Other alloying elements such as nickel, molybdenum, and titanium can also be added to enhance the corrosion resistance and formability of stainless steel
List 4 main groups of S/s?
austenitic s/s
Martensitic s/s
Ferrittic S/s
Duplex S/s
Draw and label sketches of a tensile test specimen before and after testing showing essential differences in length and cross-sectional area?
explain way hardness tests carried out on welded fabrications
a.) To determine if the weld metal matches that of the parent metal and if a cross section of a joint is subjected to hardness tests, the relative values in the weld, the HAZ and parent metal can be investigated.
b.) High values in the HAZ will indicate a fast quench condition and may suggest the necessity of changes in the welding technique in order to increase the heat input and reduce the quenching effect and hardness.
c.) The result my demand a change in either parent metal or electrode.
Describe the purpose of
a welding procedure specification
procedure qualification record
list 4 essential for a WPS using the SMAW process as shown in asme section IX
- Base metal thickness qualified
- P Numbers qualified
- F Numbers qualified
- A Numbers qualified
- Weld deposit thickness qualified
Describe the essential features of a Quality control Plan and explain the benefits of using such a document for a welded fabrication
A set of policies, processes, procedures and work instructions required for the planning and execution of manufacturing activities, its purpose is for the manufacturer to meet customer needs, provider customer satisfaction, improve areas which need improvement thereby improving production, accelerate change and protect the manufacturers reputation.
List 6 essential variables in an asme IX wps using the gtaw process . Which if changed will require re qualification of the wps
Base metal thickness qualified
* P Numbers qualified
* F Numbers qualified
* A Numbers qualified
* Weld deposit thickness qualified
* Addition / deletion of filler metal
