• Analysis of potential inconsistencies in the selection of prefabricated metal corrugated structures

    Methodology for analyzing potential nonconformities (meets the requirements of ISO 9001)

1. In order to determine the quality of the process and ways to improve it, it is not enough to simply regulate the process with evaluation indicators. It is necessary to investigate possible causes of process failures. To do this, an analysis of potential non — conformities is performed-the risk of disruption of the process (activity) is assessed and the criticality of potential failures is assessed in particular.
2. Organization of » analysis of potential nonconformities»
2.1 To investigate the process, the owner creates a «process analysis Group». Specialists from various fields of activity can be invited to the group for analysis. It is desirable to invite responsible executors of the process, as well as specialists of departments whose processes directly depend on the process in question. It is also desirable to have a group of specialists of various specialties (technologist, mechanic, supply engineer, economist, etc.).
2.2 After selecting the «analysis Group», the process owner prepares an order on the organization of» analysis of potential inconsistencies » signed by the process owner. If necessary, the involvement of a specialist should be coordinated with his / her Manager. The order specifies the purpose of the work, the time of work of specialists and assigns a person responsible for organizing the assessment.
3. The potential nonconformity analysis System takes into account the following types of nonconformity assessments:

     3.1 The probability of non-compliance (failure) is estimated according to table 1. the failure Rate can be estimated not only for the period between control checks.

Table 1

Probability of failure of the process (activity) Probability of failure of the process (activity) (P) Rank
Very high Rejection is almost inevitable 10
9
High In General, it is associated with previous processes that often fail. Repeated failures 8
7
Medium Moderate, generally associated with previous processes that had random failures, but not in greater proportion. Random rejections 6
5
4
Low Individual failures associated with similar processes. Relatively few bounce rates 3
2
Small Rejection is unlikely 1

3.2 the Degree of impact on the process goal is evaluated according to table 2.the degree of impact can also be evaluated for the impact of failure, not only for the period between control checks.

      

Table 2

The extent to which the failure affects the process goal (T) The test of significance of consequences of failure

(incongruities)

 Rank
Dangerous, without warning A very high significance rank when the type of potential failure causes a process mismatch without warning. 10
Dangerous, with a warning A very high significance rank, if the type of potential failure causes a discrepancy with the warning. It can be rejected if up to 80% of the product is detected. The consumer of the process is close to 80% likely to find a discrepancy and close to 60% likely to make a claim 9
Very significant A big violation of the process. The consumer of the process is close to 40 % likely to make a claim 8
Important Среднее нарушение процесса. Могут потребоваться дополнительные работы по устранению нарушения. Потребитель может выставить претензию с вероятностью до 30 %. Однако при определенных затратах несоответствие может быть исправлено 7
Moderate A slight violation of the process. The consumer can make a claim with a probability of up to 10 % of the product. 6
Weak A slight violation of the process. The process outputs can be used with the change of the process-user. The consumer is experiencing some dissatisfaction and it is unlikely that a claim will be made (up to 5 %) 5
Very weak A slight violation of the process. The discrepancy is noticed by most consumers, but it has little effect on the further course of the process 4
Minor A slight violation of the process. The correction of the subsequent processes will not require any significant effort. The discrepancy is noticed by the average consumer, but it does not lead to a violation of the subsequent process 3
Very insignificant A slight violation of the process. Without actual loss of quality of work. A violation can theoretically lead to a minor discrepancy that is automatically corrected in subsequent processes 2
Absent No consequences 1

      3.3 after ranking each potential process failure according to tables 1 and 2, a critical failure analysis table is compiled for the process. In the failures table, it is advisable to place the priority number of failure risk in descending order, equal to the product of the process failure ranks R=VхT (table 1 and table 2).

Resulting table:

Analysis of potential inconsistencies

on the device of the combined metal corrugated structure (SMGK)

(Example of calculating the risk level)

N пп Prefabricated metal corrugated structures offered by Viakon Technologies LLC (using special steels according to EN 10149-2).

Option I

 present in the construction market (using General construction steels).

Option II

 Note

The main goal is to obtain a design that meets the highest requirements for operational reliability and durability (at least 75 years)
  The potential mismatch between process Вероятность отказа процесса, В (от 1 до 10) Степень влияния отказа на цель процесса, Т (от 1 до 10) Приоритетное число риска, R=BxT (от 1 до 100) Вероятность отказа процесса, В (от 1 до 10) Степень влияния отказа на цель процесса, Т (от 1 до 10) Приоритетное число риска, R=BxT (от 1 до 100)
1. Non-compliance of the steel used for the production of corrugated elements with the required strength 1 10 10 1 10 10 In both cases, the steel manufacturer controls the production process and guarantees the minimum yield strength according to the declared SPECIFICATIONS.
2. Non-compliance of corrosion resistance of steel with the operating conditions of the structure 1 10 10 9 10 90 In the I version, alloyed and stainless steels meet the operating conditions, in the II-unalloyed steel is subject to corrosion and needs a protective layer
3. Non-compliance with the corrosion resistance of the «steel+zinc» system» 1 10 10 8 10 80 According to option I, special alloyed and stainless steels are produced with constant monitoring of the bucket sample in terms of compliance with the chemical composition (especially the content of silicon (Si), which prevents high-quality galvanization, the quality document guarantees its content of no more than 0.5%. For option II-the chemical composition in the TU is specified for reference (for example, Si from 0.5 to 0.8%), the steel manufacturer is not guaranteed, because during the smelting process at the metallurgical plant is not subject to control and, accordingly, can not be guaranteed to the consumer. According to the scope of application, TU steel is intended for General construction tasks (when it is necessary to guarantee only the strength characteristics — the minimum value of the yield strength). In practice, the amount of Si in steel batches may exceed 0.8%.
4. The poor quality of the zinc coating 1 10 10 7 10 70 In the I variant, the coating has a shiny appearance with a fine texture of at least 85 microns in thickness. The coating structure includes an outer layer of zinc.In the second version, the coating has a dark appearance with a rough texture. The «iron – zinc» alloy dominates the coating structure and often spreads to the coated surfaces and reduces the resistance during handling and operation. It requires additional coloring, otherwise, due to the porosity of the zinc layer, the aggressive environment is «delayed» in it, and an attempt to compensate for the shortcomings by increasing the zinc layer leads to the opposite (worse) effect.
5. Low quality of additional epoxy coating 1 5 5 2 5 10 A special coating compatible with the construction is required (taking into account the elastic properties of the steel)
6. Poor Assembly quality of corrugated elements in the structure 1 10 10 2 10 20 According to the I variant, the entire structure is reassembled at the factory before the galvanizing operation
7. The weakening of the joints connections during operation 1 10 10 3 10 30 Option I: using a high-strength bolted connection (with a conical cross-section); providing the Consumer with a design kit marked with each element, an easy-to-read Assembly drawing, a special set of tools and a torque wrench.
8. Exceeding the permissible deviations during Assembly (from the design dimensions) 1 10 10 3 10 30
9. Failure to meet installation deadlines when assembling structures 1 10 10 2 10 20
10. Increase in the cost of sandblasting and painting the structure over the entire service life 1 10 10 8 10 40 For option I: operating experience for 14 years has not revealed the need to allocate costs for maintenance and maintenance;

For option II: on highways, structures made of General construction steel require allocation of costs for current repairs and maintenance after the first autumn-winter period of operation.
  Total risk level of the design selection and installation process, ∑ 95 400  

 

Conclusion:

For the purpose of preventive actions to ensure the durability of the SMGC under construction, 1 variant is justified (using high-quality alloyed and stainless steels according to STB EN 10149-2), which has the lowest amount of risks (95 against 400), i.e. 4 times less risky, while attention should be paid to inconsistencies with the three highest risks (70 or more points), namely:

«p 2. The discrepancy of the corrosion resistance of steel operating conditions design» 90»
«p 3. The discrepancy of the corrosion resistance of the system «steel+zinc»» 80»
«p 4. Low quality of the zinc coating»
 70»