Leak Sealing - Shared Learning Opportunity

What happened?

During a leak sealing operation on 19 November 2013 in Belgium on a 16" MOV (Motor Operated Valve) a steam explosion occurred resulting in the death of the technicians performing the work. (Not Furmanite Employees)
 What went wrong?  
The incident occurred in Unit 72 (Continuous Catalytic Reforming) of the Antwerp Refinery. The line contained Boiler Feed Water operating at 70Bar/1,015 Psi and 280°C/536°F. While the workers were repumping the clamp/enclosure that was installed on the Bonnet of the valve, (the two workers were employed by an external contractor) all bonnet bolts suddenly failed. The valve bonnet was launched 25m/75ft into the production unit.

Background/Additional Information
 The clamp/enclosure was installed in 2011. This was the 7th (seventh) re-pump on the clamp/enclosure.

There is always a risk that when injecting at high pressures and temperatures, some of the older style compound ingredients or breakdown products in them may have previously been acting in a negative way on the internal parts of the system or the bolts.

There is a possibility that boiler feed water has chemicals in it that could have been acting in a negative way on the valve parts or bolts as well.

Furmanite has a policy that after 3 {three} repump’s, engineering has to be made aware of this and the job has to be given extra attention to evaluate any possible factors that could be causing the requirement for it to be re pumped again and to consider if there are any extra safety factors that we must be made aware of, or actions that should be taken.

Investigation Results

Immediate Causes
Apart from the actual rupturing of the bonnet bolts, the exact cause of this is still unknown and under investigation.

How do we prevent it from happening again?

In all cases when attempting to seal high pressure and high temperature leaks, extreme caution must be used at all times.

No matter what the type of job is, review the area and the situation and ensure that if something were to happen, you are not in the path of destruction, and have two easily accessible routes of escape.

Before re-pumping anything, always check the structural integrity and the tightness of the bolts on the clamps/enclosures, restraints. If there is any doubt as to their integrity, then do not proceed, consult engineering with your findings, and continue with a more complete review of the job.

As stated before, after the third re-pump engineering must be made aware of the situation so that a complete review can be made to determine if there is a requirement to change the sealant being used, change the procedure being used and for any new safety precautions that must now be put in place.

In light of this incident on a boiler feed water line and the nature of potential failure mechanisms and affects, we are mandating a new requirement to all Technicians.

Until further notice ALL Boiler Feedwater leak-sealing activities WILL need to be assessed by the appropriate Engineering Team before ANY work takes place on that system, item or component.

Please note this is for your safety and the safety of your fellow colleagues. Engineering will endeavor to cause as little disruption to your planned activities as is reasonable, but not at the cost of safety.
What actions do I take?
All Furmanite Techs to be issued with this Safety Alert. (SDC Managers Globally)

All workshop supervisors / SDC Managers to ensure that leak sealing techs have access to a complete set of safety information on the compounds / substances that they use in their day-to-day operations and that their employees have been given suitable and sufficient information and instruction on their safe use. (SDC Managers Globally)

All Leak Sealing Procedures / risk assessments to be altered to reflect this safety alert. (Process Integrity Service Line Leadership)

All leak sealing class rooms training or CBT to include reference to the third repump rule and its requirements. (Global Engineering Manager)

Engineering Teams providing Chemchecks and or engineering reviews are to make techs aware of the potential problems associated with working on Boiler Feedwater (with its chemical additives) and the effect it may have on the internal valve parts and associated bolting. (Engineering dept. manager)

On site Machining - Welding, Stress Relief and NDT Case Study Steel Tube Mill Hydrotester

Overview

The 15,000 PSI Hydrostatic Tube and Pipe testing mill sealing surface heads, at a major manufacture of pipe and tube, had become cracked. The surface of the fill and purge head blocks in the hydrotester require a fine, indication-free finish on the sealing surfaces. The surfaces had become cracked to such an extent that, while the testing machine could still maintain a 15,000 PSI hydrostatic test pressure, excessive amounts of water were being wasted during the test process. The material of the head blocks, AISI 4340 Nickel - Chrome - Moly, requires specialized weld media and pre and post weld heat treatment procedures in order to prevent cracking. During the preliminary client interview Furmanite learned that the prior vendor's repair was completed using local torch preheat only, standard carbon steel compatible electrodes and without post weld stress relief. Furmanite advised the client to be prepared for indications of discontinuity deeper than expected due to the uncontrolled processes previously used which we expected to be revealed after the initial pre-machining process.

 

Solution & Implementation

 

PT check during Pre-Machining

Post Weld Machining

Heat Treatment

Furmanite offered an engineered six step controlled process as a solution, which was reviewed and accepted by the owner.

1. Step one:  An On-Site machining clean up cut utilizing a Furmanite manufactured Silk^® portable facing machine of the 22" diameter sealing surface of the heads commenced, with periodic PT until it was verified that all indications of discontinuity (cracks) were removed. The pre-machining excavation depth was roughly twice client expectations, due to the errant weld methods used previously-certain indications were deep enough to require hand grinding, to preserve as much parent metal as possible.
2. Step two:  The fill and purge head blocks were preheated and the temperature held.
3. Step three:  The critical 22" diameter sealing surfaces of the heads were welded with the proper low hydrogen electrodes, per weld procedure requirements. Sufficient material was applied raising the sealing surface higher than the OEM finish surface height.
4. Step four:  The facing machine was repositioned to the datum points and the overlay of weld was machined to a flatness tolerance 0.001" overall.
5. Step five:  The sealing surfaces were honed to create a surface finish of 32 RMS, which was required to satisfy the sealing criteria.
6. Step six:  The fill and purge head blocks were post weld stress relieved and then ambient air quenched.