Heat Treatment Specific Requirements

When materials having different preheat requirements are welded together, it is recommended that the higher temperature is used. 

If welding is interrupted, the rate of cooling should be controlled or other means should be used to prevent detrimental effects in the piping. The preheat specified in the WPS should be applied before welding is resumed. 

For Cr-Mo steels, preheating in accordance with Appendix R of ASME Code Section VIII, and irrespective of wall thickness, should be carried out at the time of welding. This also applies to welding of nozzles, attachments, temporary brackets, and miscellaneous supports, temperatures should be checked and monitored. 

A preheating as above should also be performed for cai bon steel of large thickness (such as above 40 mm), for high-strength steel of medium thickness (such as above 25 mm). 

When the required preheat temperature is 144 °C or higher, the temperature should be maintained 

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For replacement gearing, the life obtained from the previous gearing should be evaluated. If satisfactory, replace with similar material. If longer life is required, selection of a heat-treatment specification yielding a higher hardness and, if necessary, a better material may provide the desired improvement. 

Furnaces. Titanium ustially is annealed or stress relieved in conventional furnaces constructed for annealing of steel. These furnaces are electric, gas fired, or oil fired, in order of decreasing popularity. The temperatxire-control equipment for these operations should have an accuracy of 5.5 °C ( 10 °F) and should be capable of controlling and recording the desired temperature within 14 °C ( 25 °F), except where tighter controls are required by the heat treatment specification in use. Some specifications require control of the aging temperature to 5.5°C( 10°F). 

Cladding and backing metals are purchased in the appropriately heat-treated condition because corrosion resistance is retained through bonding. It is customary to supply the composites in the as-bonded condition because hardening usually does not affect the engineering properties. Occasionally, a post-bonding heat treatment is used to achieve properties required for specific combinations. 

The specification requirements for electrode binder pitch, eg, high C/H ratio, high coking value, and high P-resin content, effectively ruled out pitches from gasworks or low temperature tars. The cmde tar is distilled to a medium-soft pitch residue and then hardened by heating for several hours at 385—400°C. This treatment increases the toluene-insoluble content and produces only a slight increase in the quinoline-insoluble (Ql) material, the latter by the formation of mesophase. 

Unlisted materials Unlisted materials which conform to a published specification and are of composition, heat treatment, and product form comparable with those of listed materials shall be subject to the same requirements as the listed materials. All other unlisted materials conforming to a published specification shall be qualified as required by the applicable item in col. B. ... 

In order to identify the production processes required to produce a particular product you need a production requirement in the form of product specifications which define the features and characteristics of the product that are to be achieved. By studying these specifications you will be able to identify the processes required to turn raw materials and bought-out components into a finished product. With manufactured products the processes may include machining, welding, fabrication, assembly, forming, plating, painting, heat treatment, etc. 

All aspects of the material s chemical, mechanical and physical properties which are included in the specification should be capable of measurement and certification. For critical duties all material supplied should be fully tested and certified by competent approved, independent test laboratories. All items of plant should be purchased with material certification. Additional certification is required in cases where the fabricator, in manufacturing an item of plant, used techniques such as welding or heat treatment which may affect the corrosion behavior of the construction materials. 

One piece from each lot of material in each specification and grade including heat treatment [Note (4)] unless Materials are qualified by the fabricator or erector as specified in sections B-l and B-2 above, in which case the requirements of section A-5 apply... 

The stress values for austenitic stainless steels in this Table may not be applicable if the material has been given a final heat treatment other than that required by the material specification or by reference to Note (25) or (26). 

An unlisted material shall conform to a published specification. Where composition, heat treatment, and product form are comparable to those of a listed material, requirements for the corresponding listed material shall be met. Other unlisted materials shall be qualified as required in the applicable section... 

Postweld heat treatment is neither required nor prohibited, but any heat treatment applied shall be as required in the material specification. 

Refractoriness. Refractoriness is determined by several methods. The pyrometric cone equivalent (PCE) test (ASTM C24) measures the softening temperature of refractory materials. Inclined trigonal pyramids (cones) are formed from finely ground materials, set on a base, and heated at a specific rate. The time and temperature (heat treatment) required to cause the cone to bend over and touch the base is compared to that for standard cones. 

Each type of dosimeter requires a specific procedure to ensure accurate and reproducible results, such as postirradiation heat treatment. Others need to be stabilized for a certain time (up to 24 h with some) before readings of absorbance are taken. The absorbance reading can be done by conventional spectrophotometry or other, more involved methods. 

Heat Treatment Conditions. Because of very finite process constraints In the food processing Industry, the heat treatment required for gel formation Is extremely critical when assessing the applicability of a given protein to a specific food formulation. For example, replacement of myosin (which has relatively low gel temperature requirement) In a hot dog formulation with a protein preparation requiring extremely high temperature for comparable gelation would not be desirable. 

While gelation temperature Is usually considered a characteristic property of a given protein system, the heating conditions required for gel formation may be Interrelated to all of the previously mentioned factors. It has been observed that WPG dispersions In 0.2 M NaCl will gel at 75 C while a temperature of 90 C Is required to gel WPG dispersions In distilled water (1). Heating time, at a specific temperature, required to form a protein gel structure Is generally considered to decrease with Increased protein concentration. Alteration of heat treatment conditions affects the gel s macroscopic and microscopic structural attributes. This has been dramatically shown by Tombs (A) with electromlcroscoplc evaluation of bovine serum albumin gels. 

The segment then undergoes suitable heat treatment to achieve the desired hardness. With the help of HIP technology it is possible to produce highly wear-resistant tool steels (primarily vanadium-alloyed) but also to combine abrasion- and corrosion-resistant properties as required (Cr-, Mo-, V-alloys). HIP technology (see Section 16.4.1) also allows to specifically create materials for different applications. 

Operation conditions. A specially designed oxygen mixer and the interlock system assure safe operation outside tbe flammability envelope. Simple design and high quality material specifications result in two to three year intervals between major turnarounds and on stream times as high as 98+% over one year. The heat of reaction is recovered as high-pressure steam (18+ barg), which can be used by other parts of tbe VCM process (e.g., pyrolysis). Wastewater does not contain suspended catalyst fines therefore, there is no need to settle them and then dispose as a hazardous waste. Copper levels in fixed-bed effluents are below 0.3 ppm thus, no treatment is required. 

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