PRES 2 key terms

A measure of the residual lignin content of pulp after cooking, determined by permanganate consumption under controlled conditions; a lower value indicates more complete delignification and less bleaching chemical demand.

A single number that combines cooking temperature and time into one relative reaction-severity value, allowing cooks with different temperature profiles to be compared against a target degree of delignification.

The chemical removal of lignin from wood chips during pulping so that fibers separate; it proceeds through bulk, residual, and final phases, each with different selectivity and carbohydrate loss.

An alkaline pulping process using sodium hydroxide and sodium sulfide as the active cooking chemicals, producing strong pulp and a recoverable black liquor, and dominating chemical pulp production worldwide.

The clarified alkaline cooking solution of sodium hydroxide and sodium sulfide fed to the digester, characterized by its effective alkali, sulfidity, and residual chemical concentrations.

The spent cooking liquor leaving the digester, containing dissolved lignin and organic matter plus residual inorganic chemicals; it is concentrated and burned in the recovery boiler for chemical and energy recovery.

The percentage of the total alkali in white liquor present as sodium sulfide, expressed on an equivalent basis; it strongly influences delignification rate, pulp strength, and digester corrosion behavior.

The recausticizing step in which green liquor is treated with lime to convert sodium carbonate back into sodium hydroxide, regenerating white liquor for the digester.

The molten inorganic residue collected at the bottom of the recovery boiler, mainly sodium carbonate and sodium sulfide, which is dissolved in water to form green liquor for recausticizing.

A vertical pressure vessel in which chips and cooking liquor move continuously through impregnation, heating, cooking, and washing zones, with liquor extraction and circulation controlling the temperature and chemical profile.

A pressure vessel charged with chips and liquor, sealed, heated to cooking temperature, held for the required time, then blown or pumped to a blow tank before the next cycle begins.

The piping that carries cooked pulp and liquor from a digester to the blow tank; it experiences rapid pressure drops, flashing, and severe erosion where direction changes or fittings restrict flow.

One of the cylindrical ring sections welded together to form a digester shell; each course is designed for a specific pressure and temperature, and thickness transitions and weld details are critical to integrity.

The initial section of a continuous digester where chips are soaked in cooking liquor at lower temperature, allowing chemicals to penetrate before the main delignification reaction is accelerated by heating.

The mechanical separation of wood chips by thickness before cooking so that oversized and pin chips are rejected or reprocessed, improving liquor penetration uniformity and pulp quality.

A bleaching-stage process that uses oxygen and alkali under pressure to remove additional lignin from brownstock before final bleaching, reducing chlorine-based chemical demand and effluent load.

Cracking of austenitic stainless steels caused by the combined action of tensile stress and chloride-containing environments at elevated temperature; a key concern for pulp mill vessels and piping.

A family of stainless steels with a mixed austenitic-ferritic microstructure, offering high strength and good resistance to chloride stress corrosion cracking and pitting, commonly used in digesters and liquor handling.

Localized breakdown of a passive oxide film that creates small deep cavities, often initiated by chlorides or deposits; it can perforate equipment while overall metal loss remains low.

Accelerated metal loss where flowing or impinging fluid removes the protective surface film and fresh metal is exposed, common in blow lines, liquor nozzles, and pump casings.

Cracking of carbon and low-alloy steels exposed to concentrated sodium hydroxide at high temperature under tensile stress, relevant to causticizing and liquor-handling equipment.

Controlled heating of a welded assembly after welding to relieve residual stresses and reduce susceptibility to cracking; it is often required for thick-section carbon steel in corrosive service.

The widely used code for design, fabrication, inspection, and testing of pressure vessels; Division 1 gives design-by-rules requirements and Division 2 provides alternative design-by-analysis rules.

The highest internal or external pressure permitted at the design temperature for a pressure vessel or piping component, established by the governing code and design thickness calculation.

Extra wall thickness added to the code-required minimum thickness so that the component can tolerate expected metal loss over its intended service life before reaching the retirement thickness.

The code for process piping, covering design, materials, fabrication, examination, testing, and operation of piping in chemical plants and pulp mills, including requirements for severe cyclic and corrosive service.

A pressure test performed with water to verify strength and leak tightness of a vessel or piping system, typically at a specified multiple of design pressure with temperature and stress limits observed.

A written document describing the welding variables and steps qualified by a procedure qualification record, ensuring production welds meet the required mechanical and metallurgical properties.

An ultrasonic examination method that electronically steers and focuses beams from a multi-element probe, enabling rapid imaging of welds and detection of planar defects such as lack of fusion.

A passive monitoring technique that detects transient elastic waves released by growing cracks or active defects, often used during pressure tests to locate areas of concern in vessels.

A method that ranks equipment for inspection by combining the probability of failure with the consequence of failure, allowing inspection effort to be focused on the highest-risk items.

An automatic device that opens to discharge fluid when inlet pressure exceeds a set value, protecting vessels and piping from overpressure; sizing depends on the credible relief scenario and fluid properties.

A defined event that could cause overpressure, such as blocked outlet, fire exposure, or cooling failure, which is analyzed to determine the required relief rate and device capacity.

An independent control system of sensors, logic solvers, and final elements that brings a process to a safe state on demand, assigned a safety integrity level based on risk reduction needs.

An engineering evaluation of current wall thickness, material condition, and future corrosion rate to estimate how long a component can safely remain in service before repair or replacement.

A structured evaluation, often using fracture mechanics and code procedures, that determines whether equipment with known flaws or metal loss is suitable for continued operation under defined conditions.

Restoring a damaged sealing surface on a flange by machining or welding and remachining, followed by examination to ensure the joint will seal at design pressure without leakage.