118-print final-delayed coker high pressure cutting water...

MJ Moloney - ExxonMobil May-2012 coking.com 0a

Delayed Coker High Pressure Cutting Water Safety

This material is not to be reproduced without the permission of Exxon Mobil Corporation and coking.com.

Presented by Mitch Moloney of ExxonMobil Research & Engineering

[email protected]

@ coking.com Bahrain Conference November-2015

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High Pressure Cutting Water Safety

Topics:

November-2015 coking.com Bahrain

(3) Risk Scenarios

(4) Protective Facilities

(1) Quick Coke Cutting System Overview

(2) Industry Events and Near Misses

(5) Guide Rails

(6) Risk Analyses

(7) Layers of Protection

(8) Last look at Facilities

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High Pressure Cutting Water SafetyCoke Cutting Systen Overview:


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High Pressure Cutting Water SafetyCoke Cutting Systen Overview (cont’d):


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Industry Incident - 2nd Hand Reporting



DCU Background

Old 4-drum coker on 14-hr coking cycles

- Manual deheading and valve operations

- Old Coke Cutting System

- Did not use combination tool, instead they manually changed coke bits

- Cut coke through Crusher to a Sluiceway

⇒ They called the employees that cut their coke "Sluicers". They cut with two sluicers....One on top and one on the bottom of the drum.

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Industry Incident - 2nd Hand Reporting (cont’d)



The incident happened after midnight. Both heads were off.

� The pilot hole had been drilled with a 7” bit and the coke removal bit was installed.

� A first pass was made through the drum and the bottom sluicer reported to the top sluicer via radio that coke still remained in the drum, so a decision was made to cut the drum again.

� Communication between the sluicers was, most likely, not clear. The pressure to the nozzle was activated by the bottom sluicer while the nozzle was 3 - 4 feet above the top of the drum. The nozzle started to spin and 2300 psig water exited the 3/8" outlet cutting nozzles

� The water stream hit the top sluicer, who received severe lacerations to his abdominal area and was pronouced dead on arrival at the hospital.

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Industry Incident - 2nd Hand Reporting (cont’d)



⇒ The limit switches for the stem, which would have prevented activation of the high pressure nozzle, until it was safely inside the drum, were either bypassed or out of service.

⇒ The injured party was a long-time pipefitter that bid into the coker. He started as the bottom sluicer and worked there for 6 - 7 months, before advancing to the top sluicer position. He had worked the top sluicer position for 8 or 9 weeks before the accident.

⇒ It took about 3 - 4 hours to cut a drum. The sluicers did not work a "formal" work schedule (they don't have an 8, 10 or 12 hour shift), they report in for their drum, complete the drum and then they go home.

⇒ And were called back in to work every third drum.

⇒ Speculation was that the workers may have been in a hurry.

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Near Misses Have Occurred over the Decades



Older Cokers having less reliable facilities have a higher historical frequency=> Instruments that are prone to fouling, like pressure switches and

pneumatic solenoids, have lower availabilities

Cokers with less Operational Rigor will tend to normalize deviations => for example, technicians will live with safety instruments that fail

continually

Coke Cutters that disable the dead-man feature of the drill stem joy-stick create more risk=> The drill stem will leave the drum, if safety cutouts fail and the cutter

is not attentive, which is likely in this scenario

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Risk Scenario Analyses



There are 3 potential scenarios in play

(1) High pressure cutting water flows to a drill stem suspended above the top head of the correct drum (i.e., the drum to be cut)

(2) High pressure cutting water flows to a drill stem suspended above the top head on the sister drum or another drum pair

(3) Drill stem exits the top head while pressurized with cutting water� During normal cut� During Dome Cleanout

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Protective Devices Overview



May be relying on a manual cutting water block valve with Lock-Out, Tag-Out procedures

� This can be the original coker design

� Or, it can be due to replacing the MOV with a temporary manual gate valve

• In this case a management of change review is required. Sometimes these are referred to as a JSA (Job Safety Analysis) or JLA (Job Loss Analysis)

Manual Gate Valve with LOTO

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Manual TK Ball Valve with Limit Switch

Manual Ball Valve with Magnetic Proximity Switch

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Manual Orbit Valve with Limit Switch

Turns 90 degrees from Shut to Open

Prox Switch Types:

Top Worx GO Switch P/N: 73-14573F2

Micro Switch - Limit Switch P/N: 12CA2A-1A-8834

Proximity Rotary Limit Switch Model No: 44HD1

DISCLAIMER: EXXONMOBIL TAKES NO

RESPONSIBILITY FOR THE PERFORMANCE OF THESE

DEVICES

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Protective Devices Overview (cont’d)



MOV Position Switch conduit

Motor Operated Valve

Safety Critical Device (SCD) Plaque

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Pacific Cutting Water Block Valve

MOV Position Switch conduit

Electrical Power Supply

MOV

Motor Operated ValveView - 2

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Protective Devices Ovreview (cont’d)



Hand Wheel

MOV

Cutting Water Pressure

Flowserve Cutting Water Block Valve

Motor Operated Valve2001 Install

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Motor

Cutting Water Pressure

Motor OperatedTK Ball Valve


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Guide Rails and Position Switches – Site 1

Damage

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Run-to-Failure Event:

� Mechanical repairs were completed on the drill stem “signal-tree” with new wheels being installed on crosshead

� While performing function check of the wheels, it was noticed that at about the 180’ elevation, the ID of the drill stem guides was too wide allowing the guide wheels of the “signal-tree” to potentially dislodge from the holding rails again.

� While raising/ lowering of the drill stem, it was discovered there was approximately 30’-35’ of vertical guide rail that had excessive play and movement in the supports. It was later found that the welds on the vertical drill stem guide beams in numerous places were broken.

Guide Rails and Position Switches – Site 2

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Slide Valve Safety


Site-2 Damaged Guide Rails due to Weld Cracking

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Risk Scenario Analysis



Scenario Breakdown

� Set a standard time basis for evaluation of the event probability

� Typically an annual probability per coke drum pair is determined

� Presence of a position switch trip on the drill stem is taken as standard

1) Number of coke drum cycles per year

� Probability of Scenario Occurring – The Calculation:

Determine the following:

� There is general consensus in the industry safety community that the probability of a fatality should be less than 0.0001 (annual basis)

2) Probability of a worker in harm’s way

3) Probability that the drill stem rises to the trip point and would continue

4) Probability that protective device(s) is (are) inoperable or faulty

5) Probability that the worker is struck with water

Multiply these five factors together to yield an event probability.

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Protective Layers - Defined

Typically, at least two reliable independent layers of protection, with 90% availability, should be in place to ensure a low probability of high pressure cutting water being released outside the coke drum and injuring someone

DISCLAIMER

Detailed risk assessment is needed for each specific coker to properly define the needed layers of protection, their number and their availability

An alternative can be to provide a single layer of protectionwith 99% availability

The industry defines a Layer of Protection as a device or procedure that is in service, or used correctly, at least 90% of the time, which means it will

reduce the probability of a potential event by one order of magnitude, or a factor of 10

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If Instrumentation is used, it is a logic circuit connecting the Drill Stem Position Switches (guide rails / crosshead) and the Water Block Valve Position Switches to the Winch and/or Cutting Water Pump SD Switch(es)

What is a Protective Layer?

Limit Switches (guide rails and crosshead) � Magnetic Proximity Switch

Limit Switches on the Cutting Water Block Valve Position � Magnetic Switch on the manual valve, and/or� Position switches in the Motor Actuator

It can be Mechanical: The drill stem guide assembly can be designed to prevent the drill stem from leaving the coke drum, if secured in place. Or it can be an enclosure and guide that blocks the cutting water

It can be a Bit of Both: The Cow-Bell can be used, which is a device manually set in place, which enables operation of the coke cutting system AND activates an independent protective trip circuit

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Guide Assembly Protection

Figure-8 with Hydraulic Lift

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Drill Stem Guides (aka Bat Wings, Guide Plates, Media Lunas, etc)

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Guide Assembly Protection on Slide Valves

Z&J - BP Lingen Germany 2002 Delta Valve GV830

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Cow Bell

“Cow Bell” – Back-up Proximity Switch

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Dual, Manual Block Valve System



2” Low Flow Cutting Water Valve

Used for Boring

6” Main Cutting Water Valve

LOTO Tags and Chains

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Dual, Manual Block Valve System (cont’d)



2” Cutting Water ValveUsed for Boring

6” Main Cutting Water Valve

Nordstrom Dynamic Balance Valves with Hard Surfacing

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Drill Stem Limit Switches and Cutting Water Pressure Switch are used to trip the

Air to the Winch via a Solenoid

Winch Solenoid

Drill Stem Limit Switches

Cutting Water Pressure Permissive

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Safety Risks with this System



These Safety Components can fail in two ways:

� Trip solenoid jams due to foulant in air lines

� Pressure switch plugs with coke

So, daily checks of these instruments are needed to maintain reliability.

=> Otherwise you lose the one layer of protection.


A second layer of protection is needed to ensure a low probability the scenario takes place

=> Drill stem guide, locked in place

=> 2nd independent drill stem position indicator

=> Cow Bell

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Protective Facilities



Reinforced Cutting Shack Glass

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Protective Devices (cont’d)



Cutting Tool Positions

Cutting Tool Limit

Switches and Permissives in Use and

not in Bypass

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