Results of airtightness test after flangetightening training

1. Introduction
We are a facility that conducts plant maintenance of
which there are not many within Nippon Express Co.,
Ltd., and working hard as the main contractor of daily
maintenance tasks and periodic repair work（SDMwork）to ensure the safety and stable operation inchemical plants.
In a chemical plant, there are many flange connections

Winter 2022

（hereinafter, abbreviated as“flange”）to connect themain parts of equipment（heat exchanger, reaction

Figure3

Inside view ⑵ of VALQUA Seal Training Center™

vessel, tanks, pumps, valves, etc.）and piping.

has been to eliminate leaking at airtightness tests.

Tasks to open and tighten flanges account for aHowever, on-site confirmation（such as hammering）

substantial proportion of daily maintenance tasks andafter implementation of work requires time and effort.

periodic repair work, and as a long-term issue, the goal

There have been many times that we inconvenienced
our clients because it took many days to successfully

No.42

pass the airtightness test.
In addition, since it is a chemical plant, it is necessary
to make the various operators aware about theimportance of flange tightening because some innerfluids may be harmful and there is a possibility of amajor disaster if there is a leak during plant operation.
When we were starting to investigate measures forFigure1 Outside view of the VALQUA Seal Training Center™（Nara）

improvement, we were introduced by Toyo Sangyo, Co.
Ltd. that VALQUA has training equipment. We visited
VALQUA’s Seal Training Center™（STC）in Nara andexperienced the training. Then, we considered theintroduction of this training equipment hoping that it
could be used to resolve our issues.
We handle a diverse range of gaskets, but we specified
the one that is used the most, No. GF300 to be
implemented.
This report is about the utilization status of“FlangeFigure23

Inside view ⑴ of VALQUA Seal Training Center™

tightening training”and its results.

Customer Solutions《Contribution》

2. U
 tilization of flange tightening training equipment（Settings for JIS10K 100A No.GF300）
2-1）Settings for evaluation criteriaFirstly, to utilize the flange tightening training
equipment, proficiency was ranked into 3 levels usingstars to clarify the proficiency judged by training
results.
“☆☆☆”Pass············· Can conduct flange tightening“☆☆”Level 2··········· C an conduct tightening under
the advice of a team leader
Target value 28.2kN“☆”Level 3················ Cannot conduct flange tightening

85% of the target value 24.0kN

Figure5 Tightening axial force distribution of sheet gasket（No.GF300）

Criteria for each rank were as follows:“☆☆☆”························· Torque value of bolts ① to ⑧ iswithin 90±5N·m, and no tendency2-2）Training method① Explanation of tightening methodof uneven tightening according

Explain the method of tightening in a diagonal

to the line graph.

pattern and increasing the torque in 3 steps.
② Explanation of evaluation criteria

between 90±5N·m and 90±10N·m,Explain 2-1, and explain why under 80N·m isand no tendency of unevenconsidered as a failure.

tightening according to the linegraph.

③ Training procedure
After each trainee acquires the sense of torque“☆”···································· Torque value of bolts ① to ⑧ isunder 80N·m or over 100N·m.

values using the torque-sensor training device（See photograph）, they are tested on the flangetightening training device（Photograph attached）
and when this is completed, the results are
printed out on the spot for evaluation.

Bolt axial force［kN］

Bolt
Bolt
Bolt
Bolt
Bolt
Bolt
Bolt
Bolt

Time［s］

Figure4 Sheet gasket（No.GF300）tightening axial force over time

Winter 2022“☆☆”······························· Torque value of bolts ① to ⑧ isFigure6Torque-sensor training device
4No.42

Results of airtightness test after flange tightening training

Figure7

Figure10

Scene from training（3）Figure11

Scene from training（4）Flange-tightening training device

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3. Results of flange-tightening training
3-1）Situation of the operators’skill level
Figure8

Scene from training（1）Table1Year

Training pass rate

successful
No. of trainees No. oftrainees

Pass rate

2017

568

224

39.5％

2018

559

240

43.0％

2019

562

264

47.0％

2020

557

267

48.0％

2021

563

284

50.5％

Five years have passed since we implemented flangetightening training. It started with a test format asshown in Table1, but in the beginning, rather thanFigure9
5

Scene from training（2）find operators that passed, we looked for those that

Customer Solutions《Contribution》

didn’t and restricted them from conducting flangetightening. This led to a significant drop in the number

4. Conclusionof leakage sites.

Further issues for the future would be that while thePrior to implementation, we asked operators to work

test for the training is conducted under good conditions

on flange tightening based on their years offor conducting tightening tasks regarding the site andexperience or an estimation based on how the flange

position, in the actual field, tightening tasks at such goodlooked, but being able to“visualize”with the training

conditions would be less than half the total. There is an

was one of the outcomes that were achieved

advantage that flange leaks at bad conditions stand out

immediately after implementing the training.

and places that require caution become clear, but toThis will continue to be part of the education program

reduce the number of leakage sites, we feel that it isbefore the start of periodic repair works.

necessary to create an environment similar to the actual
field for the training equipment and build up the skills of3-2）Transition in number of leakage sites atperiodic repair works

each operator.
In addition, we would like to focus on the status of theTable2 shows how the number of leakage sites atflanges（rusted, surface corrosion, distorted flanges, etc.）

periodic repair works changed from before training

and of the bolts and nuts（the screw of the bolt isimplementation until now.

rusted, etc.）and consult with the client to aim toTable2

No. of faulty
No. oftightening sites airtightness sites

Pass rate

improve the quality of our work and increase customer
satisfaction.
The target number of people receiving training is about

2017

8500

400

95.0％

2018

8500

400

95.0％

autumn periodic repair works, respectively. This

2019

8500

280

96.7％

requires more discussion on how to secure the days and

2020

8500

240

97.2％

times.

2021

8500

180

97.9％

300 each for the spring periodic repair works andIn closing, I would like to thank VALQUA, Ltd. for
manufacturing this equipment and conducting
maintenance every year, and offering us an opportunity
to report, along with the staff in connection with
distributor Toyo Sangyo Co., Ltd. We wish for continued
cooperation in solving issues in the future as well.

Shinya Kiriyama
Nippon Express Co. Ltd.
Shunan Branch, Heavy Machinery & Construction Section

6Winter 2022

Year

Transition of number of faulty airtightness sites

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