Stress analysis
Why stress analysis?
Stress analysis is carried out for all lines covered in critical line list. This is to ensure flexibility of lines operating at elevated Temperatures and also to ensure that load on equipment Nozzles is within remissible limits due to expansion of piping. Stress sketches are prepared in isometric form on STD stress sheet showing location of all supports.
Stress analysis ensures
1. Integrity of pipe & piping components against pressure and dead weight.
2. Flexibility of pipe from thermal expansion.
3. Safety of nozzles to the connected critical equipments
4. Proper supporting against dead weight, thermal expansion & occasional loads like & earthquake
5. Proper selection and specification of special supports like spring hangers and expansion joints.
Stress analysis is carried out for
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Stress critical lines
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Elevated temperature lines
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80 NB & above > 260 deg c.
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150 NB & above> 120 deg c
Jacketed lines
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Equipment critical lines
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Lines connected to rotating machinery - pump (API 610), turbine (NEMA - SM23) reciprocating compressor
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Fired heater (API 560), air cooler(API 661), reformer vessels with brittle linings
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Analysis to ensure the nozzle loads within stipulated maximum
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Specified by codes /equipments vendors.
Support critical lines
Two phase flow lines very thick & very thin lines. That is, lines having dia to wall thickness ratio in the range 10 < D/T > 90 relief critical lines. Relief valve discharge lines flare header, liquid blow down lines downstream of bursting disc.
How Stress Analysis is carried out?
Stress analysis is carried out using software like “CAEPIPE” output data is tabulated on stress sketch. A typical stress sketch giving input and output data is enclosed nozzle loadings on equipments is transmitted to vessel /mechanical group for approval if it exceeds permissible limit.
Statutory approvals
Various statutory bodies:
1) Chief inspector of factories
2) Chief inspector of boilers
3) Chief controller of explosives
A) Petroleum act & rules ( for storage tanks)
B) Gas cylinder & static & mobile pressure vessel rules
4) Oil industry safety directorate
5) Tariff advisory committee
6) Pollution control board
7) Local bodies ( Municipal / District authority, port authority, Aviation authority, highway authority etc.
8) electrical inspection
9) town planning authority.