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On-Site Plant Operations and Safety Auditing

On-site plant operations and safety auditing services compare actual operating practices to Rexarc, Customer, and/or Industry standards such as NFPA, EIGA, and/or other industry standards. This is a customized solution designed in accordance with Customer inputs. During this audit, Rexarc provides an objective third party review of the efficiency and safety practices employed by operators.

Scope of Audit

When providing this audit service, we thoroughly audit:

  1. Plant Operations
  2. Safety Procedures
  3. All Rexarc Equipment
Processes Audited

This service focuses on Rexarc Medium Pressure Plant Operations including:

  1. Start-up
  2. Cylinder Filling
  3. Equipment Checks
  4. Shutdown Processes

As a result of the audit, a report of findings is provided that highlights gaps in safety practices and procedures, recommendations for corrective actions, and equipment upgrade options to improve safety and/or efficiency in operations.

Why to have Rexarc Acetylene Plant Audit

As a part of Rexarc’s commitment to customer service, free audits are provided which focus on important safety issues and identifying efficiency opportunities. This review of a plant audit is specific to one location but the areas identified are common across the majority of audits that are completed. In this study, the areas identified are related to fittings used in the system, high pressure driers, and cylinder leads. The summary of the document includes solutions to each of the areas identified in the audit.

What Task are Performed in the Plant Auditing

During an audit, a qualified Rexarc representative reviews the equipment set being used in detail from the beginning of the acetylene cylinder filling process which is when the cylinders are weighed to check acetone levels to the end when they are weighed off of the scales to verify they were filled.

Prior to the review beginning, the Rexarc representative sits down with all who are interested at the customer site to review the process as well as gather any interests and concerns from the customer.From there, the representative is often accompanied through the plant by a plant operator. The plant review concludes and often a debriefing session occurs immediately after the audit for findings to be delivered. The debriefing session is often with the same individuals met with at the beginning of the visit.

During one of these visits, it was discovered that the company faced challenges with the pressure of fittings being used in the system, efficiency challenges with maintaining the high pressure driers after acetylene compression, and the opportunity to improve equipment and cylinder life through ammonia scrubber implementation. What follows are considerations and recommendations on how to best address the challenges at the site.

Pipe Fittings High Pressure Driers Ammonia Scrubbers
Acetylene can reach pressures of up to 50x higher than whatever its current pressure is, if
detonated. For example, if the gas is at 50 psi and detonates, it can reach pressures up to 2,500 psi.
Given this fact, all high pressure piping should be rated as such. Alternatives to carbon steel include
materials such as stainless steel and welded connections with working pressure ratings at or above
3,000 psi. For some applications and regulations, higher pressure ratings are required as well.
As an alternative to using calcium chloride, Acetylene gas can be dried using
different media and methods such as Silica Gel and other media, as well as Automated Regenerative
processes during which dried gas is cycled back through a drying chamber to dry the media in
preparation for the next drying cycle.
There are various methods of purifying acetylene. Alternatives include the
implementation of sulfuric acid towers, arsenic trichloride, and the use of an acetylene purifier and
purifying compounds such as Rexarc’s Monkey Dust to remove ammonia and other impurities. Other
methods include not utilizing an ammonia scrubber as designed by Rexarc but a vessel that is simply
filled with water to absorb the ammonia as the acetylene passes through and manually changing the
ammonia saturated water on timed intervals.


Proposed Solutions
Pipe Fittings High Pressure Driers Ammonia Scrubbers
High pressure fittings can be sourced locally. It is imperative that any individual who
works on the acetylene plant piping be trained in the chemical nature of the gas and the ratings required
as a result. Rexarc can also be a partner in piping expansions by providing piping kits which include
fittings and valves that are rated according to system and regulatory requirements. The benefits of
either solution are a safer working environment and regulatory compliance.
This plant has two compressors with combined capacity of approximately 5000
scfh (150 m3/hr). The high pressure driers being utilized have not been sized properly and are in poor
condition which requires increased labor to service on a more frequent basis than if the unit were sized
The system effects of ammonia are important to consider. When ammonia is
compressed, it turns into a thick, sticky, black tar-like compound which causes system constraints in
various areas. First is the piping itself. Over many years, pipe diameters will become smaller impacting
the flow of gas through them. It also makes cleaning of manifolds dirtier and more difficult during
preventive maintenance which is less efficient. The next item impacted are the charging manifold flame
arresters (Rexarc part number 3-01-0065). These become clogged from the ammonia which results in
decreased product life. The same impact occurs to the flame arresters located on the cylinder filling
leads (Rexarc part number 1-01-0318). Finally, cylinder life is impacted as this compound collects inside
the cylinders, the cylinder doesn’t accept as much acetone and ultimately acetylene. The life of the
cylinder can be shortened significantly as a result. Given the system benefits, ammonia scrubbers are


Pipe Fittings High Pressure Driers Ammonia Scrubbers
Training of personnel who perform maintenance on an acetylene plant is important to
safety. During training, required working pressures of the equipment is a critical item to verify is known
through assessments. The other recommendation is to review all existing piping within the system to
re-verify proper fittings are in use. It should be noted that during an audit, pipe thickness cannot be
verified so should a section of pipe be replaced, it is imperative that the proper schedule of piping be
The first recommendation is that the condition of high pressure driers be
reviewed for operational effectiveness. For maximum efficiency, each vessel is recommended to be
drained on an hourly basis. The second recommendation is to verify the flow rate of the high pressure
driers being used are at least as high as the capacity of the compressor. If either of the
recommendations are not able to be achieved, there are other challenges created within the system
such as this plant was experiencing. The final recommendation is to verify the vessels are in good
condition. This is a somewhat subjective statement but things to be aware of are corrosion to the
outside of the vessel. If the paint is ‘bubbling’, this is a sign that the unit needs additional maintenance
and potential replacement. With that, the recommended solution is that the plant purchase two sets of
calcium chloride driers, one properly sized for each unit. This will change the current practice of
draining an under-sized unit more often as well as will improve the safety of the units as those in place
are in poor condition.
Adding a purification component specifically designed to remove ammonia to
the system positively impacts the efficiency of preventive maintenance, service life of system
components, and helps with cylinder service life. Because of this, it is recommended that a review of
plant processing components be conducted and a plan for implementation be created if ammonia
scrubbers do not exist.


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