Where We Go Wrong In Vessel Design

Dick Hawrelak

Presented to ES-317Y in 1999 at UWO

Introduction 30% of large property damage losses are

caused by failures in tanks, process drums and marine vessels.

Average Trended Loss was $40.5MM for tanks alone.

1984 U.S. National OSHA Record

6486 accidents. 516 injuries. 90 deaths.

OSHA Record Includes Power Boilers Water Boilers and Steel

Tanks Cast Iron Boilers Pressure Vessels (poorest

record)

Pressure Vessel Record 1310 / 6486 accidents 437 / 516 injuries 73 / 90 deaths

Press Vessel Components Shell Head Attachements Piping Safety Valves Misc

PV Failure Causes Operator error or poor maintenance

– 149 / 933 Faulty Design – 144 / 933 Corrosion or erosion – 132 / 933 Pressure control failure – 41 / 933 Other – 420 / 933

PV Failure Types Cracked – 403 / 1087 Other - 298 / 1087 Leakage – 163 / 1087 Rupture – 158 / 1087 Explosion – 22 / 1087 Collapsed Inward – 15 / 1087

Obtain Data & Analyze Search OSHA records On Internet -

Google Extract records Create Excel Database Sort and Filter data Analyze Data

Personal Experiences Based on 33 Years of Chemical

Plant Design at Dow.

Incomplete Mass Balances

Normal mass balance. Start-up, shut down or upset. Recycle conditions. Off-loading situations unplanned.

Residence or Hold-up Time

Inventory logistics not well defined. Flammable or toxic inventories too

high.

Containment

Dyke dimensions do not meet codes.

Drainage does not follow NFPA 15. Catastrophic failure overwhelms

dyke walls.

Materials Of Construction

Not suitable for corrosive fluid at high temperature.

Not suitable for low temperature excursions.

Quantum Explosion - 7 June 89

A-515-70 grade CS brittle failure of heat exchanger shell.

Start-up, inlet flange leak, isolated exchanger and depressured to flare.

30 minutes to failure. Two fatalities, seven serious burns, major damage to ethylene plant.

Nozzles

Level control nozzles in wrong location.

Nozzles too small creating impingement on far wall.

PSV nozzles not suitable for thrust.

Visit U.S. EPA CEPP Web Site

Chemical Emergency Preparedness and Prevention Office web site at www.epa.gov/ceppo/acc-his.html

Check Rupture Hazard of Pressure Vessels.

Check Catastrophic Failure of Storage Tanks.

Ammonia Storage Tank Modification Oil and Gas Journal, Dec 26, 1998 Pressure storage in spheres Removes bottom unloading lines. Converts to overhead siphon system. Excellent article on 4 process design

options.

Typical Pressure Vessel

KO Pot Design

Internals

Impingement details not well designed.

Pump-out sumps act as dirt trap. KO Pot internals not designed

properly.

Design Pressure

Design Pressure not suitable for upset conditions.

Reactive Chemicals P&IDs must be examined for

reactive chemical possibilities.

Low Pressure API Tanks

Very easy to bulge or suck-in resulting in loss of containment.

PSV, pad de-pad settings very close.

Floating roof explosion at Suncor in Sarnia. Roof hangs up on pump-out, air sucked into vapor phase, lightning ignites flammable vapor.

Breathing.

Pumping and temperature change breathing not allowed for in combination.

High breathing losses a cost and an environmental problem - Benzene tank.

Vapor Recovery Options Not well understood. See BLOSS program for design

options.

Flammable Storage Area

EO storage bunkers located 1 mile from ISBL.

3 independent means of checking quantity to prevent overfilling (dual LC, weigh scale & flow rate x time).

Refrigeration to prevent polymerization, chart temperature.

Dump contents to pond if runaway reaction takes place.

EO Storage

Toxic Storage

Possible Exam Questions What are three independent methods

for preventing overfilling of a storage vessel.

If a storage product can generate heat by polymerization at ambient temperatures, what safety measures should be considered?

What are the main problems with fixed roof, low pressure API type storage vessels?

Exam Questions Cont’d

What is one of the main problems with an API, floating roof storage tank in flammable service?

What are the safety measures that should be taken for a large chlorine storage sphere to prevent a toxic gas release?

Summary

This short list is indicative of some of the problems caused by poor engineering discipline in vessel design.

Recommend you obtain a copy of the Chemical Plant Design programs and follow the procedures built into the vessel design spreadsheets.