Back in 2015 I wrote about changing the “service” of a pressure vessel and all that should be considered in this change. Late last year my team and I ran across a very common error in “changing the service”, albeit the change was an actual change of location. Here’s what happened…

A facility got around to doing an NDE/NDT inspection on a 63-year-old pressure vessel. As one might consider, a vessel that is 63 and was going through its FIRST inspection may be an indication the facility does not have an effective pressure vessel management program and you’d be right. The vessel “failed” on a number of fronts and was no longer usable in the process that needed it. Caught completely off-guard, the facility was desperate to find a replacement vessel ASAP. Since a new vessel would take about 3-6 months to acquire, they searched sister facilities and the used pressure vessel market (and luckily we and the corporate engineering manager talked them out of this option!). But they soon discovered they already had an unused pressure vessel on site that would be “perfect” for the process.

The replacement tank would be a 17-year-old “propane tank”. Now as many of you know, there is not much difference between a Propane storage tank and an Anhydrous Ammonia storage tank. Both tanks had a MAWP of 250 psi and both had materials of construction that were acceptable to the process needs, but their similarities ended there.

This “change in service” involved taking a pressure vessel that was designed to be OUTSIDE and to ONLY see atmospheric heating (MAWT of 115F) and moving this vessel into a room that normally has an ambient temperature around 120F during summer months. This was a potentially serious design limitation for this vessel to be used in this room. However, the facility looked only at the Maximum Allowable Working Pressure (MAWP) aspect for the use of this vessel in the new service. Since the MAWP was the same as the vessel being replaced, they deemed this as a “replacement in kind” and no MOC review was required, which meant engineering, nor EHS, was not involved in this “change”.

A year later, the facility was going through their state’s pressure vessel inspection program and the company’s property insurer was the “inspector”. He notices that the vessel had been moved and began to ask questions about the new location and the new service. Of course, the insurer did not require a MOC, but they do require the vessel to be used and maintained per code. When the facility supervisor took him to the tank’s new location, the inspector immediately recognized the temperature inside the room was high. When asked what the temp was, the supervisor was unable to provide that data. They eventually obtained the room’s temp… 123F. It took the inspector all of about 30 seconds to recognize this vessel was being used outside its design limits. The inspector threatened to “red tag” the vessel, which meant the facility had to either take immediate action to correct the concern or remove the vessel from service. The facility chose to use a very large cooling unit to control the temp in the room WHILE THEY ORDERED THEIR NEW REPLACEMENT VESSEL.

The facility was not happy and felt the inspector was “way out of bounds with her assessment”. Comments like “this is industry practice”, “I have seen much worse issue pass”, etc. Bottom line, the inspector did her job and did it well! These pressure vessels have LIMITATIONS and these limitations are clearly posted on the nameplate; failing to recognize and operate the vessel within these limitations is not only DANGEROUS it is foolish!

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