Proper fabrication and regular inspection of chemical holding tanks can head off problems before they become serious. But those steps entail a cost that many companies often would rather put off. So far, only Delaware has adopted the ASME International Standard RTP-1, “Reinforced Thermoset Plastic (RTP) Corrosion Resistant Equipment.” Requiring companies to follow the standard would provide a measure of safety and reliability to some dangerous industries.
Sometimes it takes a tragedy to do the right thing. For instance, proper fabrication and regular inspection of chemical holding tanks can head off problems before they become serious. But those steps entail a cost that many companies often would rather put off.
The consequences of avoiding those costs were felt in the summer of 2001 at a Motiva refinery in Delaware City, Del. According to a government investigation, a worker had been repairing a catwalk above storage tanks when a spark ignited flammable vapors in one of the tanks.
The 415,000-gallon tank containing spent sulfuric acid—a mixture of sulfuric acid, water, and hydrocarbons—exploded, killing worker Jeffrey Davis and injuring several others. (Davis’s body was never found.)
In addition, more than a million gallons of sulfuric acid were released from the tank farm with approximately 100,000 gallons spilling into the Delaware River, creating a large fish kill. The investigation determined that the tank had holes in its roof and shell due to corrosion.
“This accident likely would have been averted by a stringent tank inspection and repair program,” said Rudolph Contreras, civil chief at U.S. Attorney’s Office for the District of Delaware.
“Although Motiva saved thousands of dollars in putting off the inspection of Tank 393,” Contreras continued, “it has now paid more than $58 million as a consequence of its actions. This fact alone should be a clear message to other companies that cutting corners on safety and the environment makes no economic sense.”
In the aftermath, rather than rely solely on corporate self-interest to protect worker safety, the state of Delaware imposed requirements on companies storing dangerous materials. The state extended these regulations beyond the steel tanks which ruptured in the Motiva accident to all tanks, regardless of their material. They looked not only to in-service inspection and repairs but also at such factors as the initial design, the material of construction, and testing of the fabricated vessel.
In 2004, Delaware adopted a law which included a regulation requiring all aboveground fiberglass-reinforced tanks of 1,100 gallons and greater intended for use in storing regulated materials to be designed, fabricated, inspected, tested, and stamped in accordance with ASME International Standard RTP-1, “Reinforced Thermoset Plastic (RTP) Corrosion Resistant Equipment.”
That was a great step forward, but since then no other state has adopted RTP-1. That’s unfortunate, as requiring companies to follow the standard would provide a measure of safety and reliability to some dangerous industries.
Three Parts of the Process
Fiberglass-reinforced plastic vessels have been around for more than 50 years and are found in a wide variety of services due to their ability to resist corrosion. They are used to ferment and store soy sauce, store gasoline, store and treat waste acids, clean the air coming out of coal fired power plants, store a wide range of chemicals, among other applications.
During the 1970s, as the use of FRP vessels for corrosive service increased, many specifications and standard methods were written to assist design engineers. The chemical plants where tanks were installed experienced an excessive number of failures, mostly related to construction. Because of these failures, several major chemical companies independently formed engineering groups that specialized in reinforced plastic equipment to develop internal specifications. Some companies experienced improvements in their failure rate; others did not. Parts of these specifications made it into the public domain, and tank manufacturers found themselves trying to make vessels that required adherence to conflicting specifications.
It was not long before it was decided that all companies involved would see more improvements and less confusion from a standardized method for the design of FRP tanks. In the late 1970s an ASME committee was formed to establish rules of safety governing the design, fabrication, and inspection of FRP vessels. On December 31, 1989, ASME RTP-1 was published as a national standard to assure quality and integrity of these vessels.
The document is designed to set the minimum safety standards for the design and fabrication of composite vessels, but RTP-1 is more than a standard specification: It is a process that encompasses design, fabrication, and inspection. Only by linking all three parts of the process can the purchaser have the verifiable assurance that the vessel was constructed as intended.
ASME RTP-1 used ASTM D3299, an ASTM standard first published in 1971, as a reference point. There are, however, several provisions in ASME RTP-1 that are not found in ASTM D3299. One of the most obvious and important differences is that an ASME RTP-1 accredited supplier has undertaken an extensive qualification program to be a stamp holder and be able to offer ASME-stamped vessels. This includes an approved quality assurance/quality-control (QA/QC) program, engineering, laminator certifications, demonstration laminates, demonstration vessels, and testing. In addition, ASME conducts “surprise” audits to ensure that the manufacturer is meeting the requirements of the standard.
What does meeting RTP-1 entail? A vessel meeting ASME RTP-1 must have design calculations stamped by a professional engineer experienced in the design of RTP equipment. These calculations are based on actual physical testing of resin laminates. When the vessel will operate at an elevated temperature the physical testing will be conducted at the design temperature and require an analysis of multiple loading conditions. The design factor for sustained load events must be a minimum of 10 to 1 and 5 to 1 for transient loads.
“WITHOUT AN ASME STAMP, THERE IS NO ASSURANCE THE VESSEL WAS MADE ACCORDING TO THE DESIGN.”
A stamped ASME RTP-1 vessel also will have 50 psi-rated ANSI 150# drilled flanges—a factor of two greater than those allowed by ASTM D3299.
The maximum allowable working pressure for vessels covered by this standard is 15 psi as measured at the top of the vessel. ASME RTP-1 standard requires a hydrostatic test of the vessel prior to applying the stamp. If a vessel is designed for 2 psig or higher, ASME RTP-1 requires physical property tests for proof of design. These are usually conducted on manway cut outs from the finished vessel.
When an ASME RTP-1 vessel is delivered, it will have a full portfolio that contains the forms, calculations, and reports that cover the complete history of the vessel. It contains all of the information that went into the design, fabrication, and inspection of the vessel. It covers the complete history of the vessel fabrication—all of the information to assure the user that the vessel delivered meets the design criteria.
Since the standard was published in 1989 a revised edition has been published by ASME about every two years.
Those with a material interest in the document have the opportunity to comment and voice their views to the ASME RTP-1 Standard Committee, which meets twice a year. This consensus standard represents the best design, fabrication, and inspection technology for fiberglass-reinforced plastic vessels available today.
According to Design
According to Dale L. Keeler, a senior materials engineer at Dow Chemical, Dow has been involved with the development and continued support of RTP-1. Current Dow specifications leverage RTP-1 as a basis of internal requirements where it makes sense and supports safety and reliability. Other major companies, such as DowDuPont, Che-mours, Monsanto, Al-bermarle, and Southern Company, and Bayer, have also been involved in the development of the standard and continue their support. The internal specification of these large corporations often leverage RTP-1 as a basis of internal requirements where it makes sense and supports safety and reliability.
“We have a decision tree that our plants and project teams follow in our standards,” said Debra McCauley, an engineer specializing in plastics, elastomers and composites technology at Chemours. “If the vessel is considered critical service or has a design pressure equal or above what is specified in our standards, we require an ASME RTP-1 stamp. If the equipment has a complex shape or very high temperature, we may require a stamp as well.”
Some stakeholders have worried that the cost of an ASME RTP-1 stamped vessel would make them unprofitable, leading to the belief that a vessel designed and built according to ASME RTP-1—but not stamped—would still maintain all the attributes of a stamped tank except for the stamp itself, and at lower cost. Without an ASME stamp, however, there is no assurance the vessel was made according to the design. Without an accredited RTP-1-required QA/QC program, there may not be any material traceability, no assurance the vessel was produced with certified laminators, and no proof that required tests and inspections were conducted.
But even the supposed cost savings of foregoing the stamp is a bit of a myth. Most holders of ASME RTP-1 stamps have concluded that their additional costs to produce a stamped vessel are very small, and for some it has saved money.
When a vessel is constructed according to ASME RTP-1, the initial user’s requirements are spelled out in detail. These are chosen for specific reasons and if the different ones are used, the service life of the vessel may be reduced. Combined with the professional engineer’s review of the drawings, these explicit requirements minimize miscommunication between the fabricator and user.
In addition, implementation of the QA plan and the employment of qualified workers has shown that once-typical laminating defects and procedural errors can be eliminated. All told, these ASME RTP-1 features result in savings to the fabricator that more than make up for the cost of the program.
ASME RTP-1 is the only national standard that can assure a vessel owner that he has purchased a vessel that was constructed with the best available technology and that it has been inspected and tested to meet the design requirements.
Companies can, on their own initiative, indicate the importance that they put on safety within their facilities by opting for stamped RTP-1 vessels. It gives them the assurance that they have used the best available technology for design and fabrication of the vessel.
But the step that Delaware took by requiring the stamping of fiberglass reinforced plastic vessels could take these assurances further. It would ensure that workers would be protected by the best available technology, subject to regular inspection—and that no company could cut corners for a short-term profit at the expense of safety.