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A spare part, spare, service part, repair part, or replacement part, is an interchangeable part that is kept in an inventory and used for the repair or
refurbishment Refurbishment may refer to: *Refurbishment (electronics) *Antiques restoration *Automotive restoration See also * Conservation and restoration of immovable cultural property *Reconstruction (architecture) *Remanufacturing *Renovation Ren ...
of defective equipment/units. Spare parts are an important feature of logistics engineering and
supply chain management In commerce, supply chain management (SCM) is the management of the flow of goods and services including all processes that transform raw materials into final products between businesses and locations. This can include the movement and st ...
, often comprising dedicated spare parts management systems. Spare parts are an outgrowth of the industrial development of interchangeable parts and
mass production Mass production, also known as flow production or continuous production, is the production of substantial amounts of standardized products in a constant flow, including and especially on assembly lines. Together with job production and ba ...
. In an industrial environment, spare parts are described in several manner to distinguish key features of various spare parts. The following describes spare part types and their typically functionality. 1. Capital parts are spare parts which, although acknowledged to have a long life or a small chance of
failure Failure is the state or condition of not meeting a desirable or intended objective, and may be viewed as the opposite of success. The criteria for failure depends on context, and may be relative to a particular observer or belief system. One ...
, would cause a long shutdown of equipment because it would take a long time to get a replacement for them. Capital parts are typically repaired or replaced during planned overhauls/scheduled inspections.  As description implies, these Capital Parts are typically expensive and are depreciated over time. Examples of capital parts include
pump A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they ...
s and motor sets used in industrial plants, or impeller or a rotor required for a pump or motor. This “spare” requirement would be determined by redundancy of equipment used in the industrial processes. 2. Consumables can be divided into two groups: * Operational consumables are typically consumed during operation and an example of these would be air filters, grease and lubricants, light bulbs, etc. (for a car, it would be washer fluid) * Inspection consumables are typically replaced during planned overhauls/scheduled inspections and an example of these would be fan belt, gaskets, lube oil, oil filters, etc. (for a car, it would be engine oil or transmission oil) 3. Inspection spares or outage spares typically refer to those spare parts used in conjunction with Capital Parts during planned overhauls/scheduled inspections and maybe reused but typically are not repairable and are discarded after removal from use if Inspection Spares are damaged. These Inspection Spares are sometimes mis-characterized as Capital spares (vs Capital Parts) and are also confounded with Inspection Consumables, which must be replaced at every inspection/outage.  (an example of inspection spares would be bearings and mechanical seals, large bolts and nuts.) 4. Operational spares typically refer to those spare parts that are used during operation of equipment and would not require planned overhauls/scheduled inspections to replace. In an industrial setting, operational spares would be gages, valves (solenoid, MOVs that are in redundancy), transmitters, I/O boards, small AC/DC power supplies, etc.) (for a car, it would windshield wiper)


Classification

In
logistics Logistics is generally the detailed organization and implementation of a complex operation. In a general business sense, logistics manages the flow of goods between the point of origin and the point of consumption to meet the requirements of ...
, spare parts can be broadly classified into two groups, repairables and
consumable Consumables (also known as consumable goods, non-durable goods, or soft goods) are goods that are intended to be consumed. People have, for example, always consumed food and water. Consumables are in contrast to durable goods. Disposable products ...
s. Economically, there is a tradeoff between the cost of
ordering Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
a replacement part and the cost of repairing a failed part. When the cost of repair becomes a significant percentage of the cost of replacement, it becomes economically favorable to simply order a replacement part. In such cases, the part is said to be "beyond economic repair" (BER), and the percentage associated with this threshold is known as the BER rate. Analysis of economic tradeoffs is formally evaluated using Level of Repair Analysis (LORA).


Repairable

Repairable parts are parts that are deemed worthy of repair, usually by virtue of economic consideration of their repair cost. Rather than bear the cost of completely replacing a finished product, repairables typically are designed to enable more affordable maintenance by being more modular. That allows components to be more easily removed, repaired, and replaced, enabling cheaper replacement. Spare parts that are needed to support condemnation of repairable parts are known as ''replenishment'' spares . A rotable pool is a pool of repairable spare parts inventory set aside to allow for multiple repairs to be accomplished simultaneously, which can be used to minimize stockout conditions for repairable items.


Consumable

Parts that are not repairable are considered consumable parts. Consumable parts are usually scrapped, or "condemned", when they are found to have failed. Since no attempt at repair is made, for a fixed mean time between failures (MTBF), replacement rates for consumption of consumables are higher than an equivalent item treated as a repairable part. Therefore, consumables tend to be lower-cost items. Because consumables are lower cost and higher volume,
economies of scale In microeconomics, economies of scale are the cost advantages that enterprises obtain due to their scale of operation, and are typically measured by the amount of output produced per unit of time. A decrease in cost per unit of output enables ...
can be found by ordering in large lot sizes, a so-called economic order quantity.


Legislation

There is no UK or EU
legislation Legislation is the process or result of enrolling, enacting, or promulgating laws by a legislature, parliament, or analogous governing body. Before an item of legislation becomes law it may be known as a bill, and may be broadly referred to ...
which states that spare parts have to be available for any set period of time, but some
trade association A trade association, also known as an industry trade group, business association, sector association or industry body, is an organization founded and funded by businesses that operate in a specific industry. An industry trade association partic ...
s require their members to ensure products are not rendered useless because spare parts are not available. The 'six year rule' in the UK
Sale of Goods Act 1979 The Sale of Goods Act 1979c 54 is an Act of the Parliament of the United Kingdom which regulated English contract law and UK commercial law in respect of goods that are sold and bought. The Act consolidated the original Sale of Goods Act 1893 ...
relates to the time period for enforcing claims that goods where defective when sold, not to whether spare parts are available to repair them, and section 23(3) of the Consumer Rights Act 2015 states that a
consumer A consumer is a person or a group who intends to order, or uses purchased goods, products, or services primarily for personal, social, family, household and similar needs, who is not directly related to entrepreneurial or business activities. ...
cannot require a trader to repair or replace goods if "the repair or replacement is impossible", implying that if spare parts are no longer available the consumer's Right to Repair (or to have a spare part supplied) would be lost.Consumer Rights Act 2015
section 23(3)


Repair cycle

From the perspective of
logistics Logistics is generally the detailed organization and implementation of a complex operation. In a general business sense, logistics manages the flow of goods between the point of origin and the point of consumption to meet the requirements of ...
, a model of the life cycle of parts in a
supply chain In commerce, a supply chain is a network of facilities that procure raw materials, transform them into intermediate goods and then final products to customers through a distribution system. It refers to the network of organizations, people, activ ...
can be developed. This model, called the repair cycle, consists of functioning parts in use by equipment operators, and the entire sequence of suppliers or repair providers that replenish functional part inventories, either by production or repair, when they have failed. Ultimately, this sequence ends with the
manufacturer Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of secondary sector of the economy. The term may refer to ...
. This type of model allows demands on a supply system to ultimately be traced to their operational reliability, allowing for analysis of the dynamics of the supply system, in particular, spare parts.


Inventory management


Cannibalization

When stockout conditions occur, cannibalization can result. This is the practice of removing parts or subsystems necessary for repair from another similar device, rather than from
inventory Inventory (American English) or stock (British English) refers to the goods and materials that a business holds for the ultimate goal of resale, production or utilisation. Inventory management is a discipline primarily about specifying the sha ...
. The source system is usually crippled as a result, if only temporarily, in order to allow the recipient device to function properly again. As a result,
operational availability Operational availability in systems engineering is a measurement of how long a system has been available to use when compared with how long it should have been available to be used. Definition Operational availability is a management concept that ...
is impaired.


Commercial

Industrialization Industrialisation ( alternatively spelled industrialization) is the period of social and economic change that transforms a human group from an agrarian society into an industrial society. This involves an extensive re-organisation of an econo ...
has seen the widespread growth of commercial
manufacturing Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of secondary sector of the economy. The term may refer to ...
enterprises, such as the
automotive industry The automotive industry comprises a wide range of companies and organizations involved in the design, development, manufacturing, marketing, and selling of motor vehicles. It is one of the world's largest industries by revenue (from 16 % ...
, and later, the
computer industry A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations ( computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These progr ...
. The resulting complex systems have evolved modular support infrastructures, with the reliance on auto parts in the automotive industry, and replaceable computer modules known as field-replaceable units (FRUs).


Military

Military operations are significantly affected by
logistics Logistics is generally the detailed organization and implementation of a complex operation. In a general business sense, logistics manages the flow of goods between the point of origin and the point of consumption to meet the requirements of ...
operations. The system availability, also known as mission capable rate, of weapon systems and the ability to effect the repair of damaged equipment are significant contributors to the success of military operations. Systems that are in a mission-incapable (MICAP) status due lack of spare parts are said to be "awaiting parts" (AWP), also known as not mission capable due to supply (NMCS). Because of this sensitivity to logistics, militaries have sought to make their
logistics Logistics is generally the detailed organization and implementation of a complex operation. In a general business sense, logistics manages the flow of goods between the point of origin and the point of consumption to meet the requirements of ...
operations as effective as possible, focusing effort on
operations research Operations research ( en-GB, operational research) (U.S. Air Force Specialty Code: Operations Analysis), often shortened to the initialism OR, is a discipline that deals with the development and application of analytical methods to improve decis ...
and optimal maintenance. Maintenance has been simplified by the introduction of interchangeable
modules Broadly speaking, modularity is the degree to which a system's components may be separated and recombined, often with the benefit of flexibility and variety in use. The concept of modularity is used primarily to reduce complexity by breaking a s ...
known as
line-replaceable unit A line-replaceable unit (LRU), lower line-replaceable unit (LLRU), line-replaceable component (LRC), or line-replaceable item (LRI) is a modular component of an airplane, ship or spacecraft (or any other manufactured device) that is designed to ...
s (LRUs). LRUs make it possible to quickly replace an unserviceable (failed) part with a serviceable (working) replacement. This makes it relatively straightforward to repair complex military hardware, at the expense of having a ready supply of spare parts. The cost of having serviceable parts available in inventory can be tremendous, as items that are prone to failure may be demanded frequently from inventory, requiring significant inventory levels to avoid depletion. For military programs, the cost of spare inventory can be a significant portion of acquisition cost. In recent years, the
United States Department of Defense The United States Department of Defense (DoD, USDOD or DOD) is an executive branch department of the federal government charged with coordinating and supervising all agencies and functions of the government directly related to national sec ...
(DoD) has advocated the use of performance-based logistics (PBL) contracts to manage costs for support of weapon systems.


See also

*
Buffer stock scheme A buffer stock scheme (commonly implemented as intervention storage, the "ever-normal granary") is an attempt to use commodity storage for the purposes of stabilising prices in an entire economy or an individual (commodity) market. Specificall ...
* Carrier onboard delivery * Complete knock down * Demand chain *
Flight spare Flight or flying is the process by which an object moves through a space without contacting any planetary surface, either within an atmosphere (i.e. air flight or aviation) or through the vacuum of outer space (i.e. spaceflight). This can be a ...
*
Logistics support analysis Logistics Support Analysis (LSA) is a structured approach to increase efficiency of maintenance and reduces the cost of providing support by preplanning all aspects of Integrated Logistics Support. A successful LSA will define those support req ...
* Military surplus *
Overstock Overstock, excessive stock, excess2sell, B-stock, or excess inventory, is the result of poor management of stock demand or of material flow in process management. Excessive stock is also associated with loss of revenue owing to additional capit ...
* Reorder point * Safety stock *
Service life A product's service life is its period of use in service. Several related terms describe more precisely a product's life, from the point of manufacture, storage, and distribution, and eventual use. Service life has been defined as "a product's ...
(lifespan) * Spare tire *
Underway replenishment Replenishment at sea (RAS) ( North Atlantic Treaty Organization/Commonwealth of Nations) or underway replenishment (UNREP) ( U.S. Navy) is a method of transferring fuel, munitions, and stores from one ship to another while under way. First devel ...
*
Warranty In contract law, a warranty is a promise which is not a condition of the contract or an innominate term: (1) it is a term "not going to the root of the contract",Hogg M. (2011). ''Promises and Contract Law: Comparative Perspectives''p. 48 Cambri ...
*
War Reserve Stock A war reserve stock (WRS), also known as pre-positioned stocks, is a collection of warfighting material held in reserve in pre-positioned storage to be used if needed in wartime. They may be located strategically depending on where it is believe ...


References

{{Authority control Systems engineering Costs Inventory