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christa.jpg (5628 bytes) Chemical Industry News Editor Christa Semko
Every two weeks, Christa will bring you the latest chemical industry news from around the world.  If you have a press release that you'd like to share with us, please mail it to us through our online contact form here.

Dateline: September 4, 2007

Technically Speaking

North America

Flexible Air Permits
The U.S. Environmental Protection Agency (EPA) is proposing changes to air quality permitting rules to encourage pollution prevention, provide increased flexibility, enable industrial facilities to make rapid changes, save resources for state permitting authorities and improve public information.  These proposed changes would affect both EPA’s operating permits and New Source Review (NSR) programs.  A flexible permit, typically with a five-year duration, would not provide approval for operational changes not within the scope of conditions considered at the time of the permit application and facilities would still be required to meet their requirements under the Clean Air Act.  The hope is that these changes will promote significant environmental and economic benefits while reducing the administrative workload for both permitting authorities and facilities.

New facility

PPG Industries has opened a new membrane cell unit for the production of chlorine and caustic soda at its chemical complex in Lake Charles, Louisiana.  The $100 million investment in new membrane cell production should yield about the same capacity as the previous technology did, but using 25% less electricity.  Converting to the membrane technology also helps the facility reduce maintenance and operating costs as well as strengthening its environmental performance.

In service

Enterprise Products Partners L.P. has installed its fourth propylene fractionator at the partnership’s Mont Belvieu, Texas complex.  The service of the new unit allows Enterprise to increase its production of polymer grade propylene (PGP) at the facility by 26% from 3.8 billion pounds/year (58,000 barrels/day) to approximately 4.8 billion pounds/year (73,000 barrels/day).  PGP is used in the production of plastic consumer products, pharmaceuticals, detergents and solvents.


Hercules Incorporated has purchased the specialty surfactants business of Dexter Chemical L.L.C., including the business related to Dexter’s product portfolio of phosphate ester surfactants sold under the Strodex and Dextrol trademarks.


Dow Chemical is permanently shutting down its Sarnia, Ontario latex operation this fall, leaving just one more unit to close before the entire site is decommissioned.  The plan is to have all of the site’s manufacturing cease by May 2009 with the closure of the propylene oxide derivatives plant.


Sherwin-Williams Co. has bought Columbia Paint & Coatings Co.  Columbia will become a subsidiary of Sherwin-Williams.  Columbia services the professional painting contractor, builder and do-it yourself markets through 41 company-owned stores in 11 states.  Sherwin-Williams is a manufacturer, developer, distributor and seller of coatings and related products to professional, industrial, commercial and retail customers via stores in all 50 states.

PET plant

Indorama Polymers plants to build a polyethylene terephthalate (PET) plant in Decatur, Alabama.  The $140 million facility, set to open in 2009, will add 430,000 metric tons/year capacity for the plastic to the growing U.S. market.  The biggest growth market for PET containers is bottled water.  The plant, to be called AlphaPet, will be located adjacent to a BP facility in Decatur that produces purified terephthalic acid, a key PET raw material.


Mossi & Ghisolfi Group will build an 800,000 metric ton polyethylene terephthalate (PET) facility somewhere in the U.S. while expanding existing facilities in West Virginia and Mexico. 


Ineos Oligomers has expanded its global production capacity for polyalphaolefins (PAO) by 10%.  The company currently has PAO manufacturing facilities in
LaPorte, Texas and Feluy, Belgium.  This additional capacity is part of a phased approach to ultimately add more than 50,000 metric tons/year of PAO production capacity by 2010.

New plant
Columbian Chemicals Co. has opened its new chemical plant in Camacari Pole, Brazil.  The $75 million facility has the production capability of 75,000 metric tons, which can be expanded as the market develops.  Columbian Chemicals produces carbon black – an engineered material that improves the strength, durability and overall performance of a range of products including tires and other mechanical rubber goods, as well as inks, paints, plastics and coatings.

DuPont has enhanced its global manufacturing network through a 20,000 tons/year expansion at its Ulsan, Korea compounding facility for nylon resins.  The expansion is in response to rapid demand growth for the company’s Zytel nylon resins in the region, particularly for automotive applications.


General Electric Co. completed the $11.6 billion sale of its plastics business to Saudi Basic Industries Corp.  Saudi Basic got GE’s $6.6 billion business including its Pittsfield, Massachusetts headquarters and 59 other facilities around the globe.  The money made from the sale will be used to buy back company stock.

Chemical plant

Royal Dutch Shell and Dow Chemical are in talks with the Iraqi government to rehabilitate and expand a chemical plant in southern Iraq for $2.1 billion.  The talks are surrounding the idea of either creating a joint venture or reaching a profit-sharing agreement.  There are signs that the talks may be concluded this year.

Technically Speaking

What is the difference between "Design Pressure" and "Maximum Allowable Working Pressure" (MAWP)?

It is not unusual for engineers to get confused with the terms "design pressure" and "Maximum Allowable Working Pressure" (MAWP). The two terms are not related mathematically; rather, they are related in a practical procedure that takes place during the actual fabrication of a pressure vessel.

Every Chemical Engineer - sooner or later - will have to deal with a pressure vessel fabrication or operation and it is sound and good advice that he/she should familiarize themselves with engineering terms employed and the logic of their application. In dealing with or specifying a pressure vessel, an engineer must resort to filling in or using a Vessel Specification Sheet that you should be familiar with and employ in the course of your work.

The "Design" pressure is that pressure that the engineer decides is the value of the pressure at which the vessel will normally operate (or which it must withstand under operating conditions). This value must include any normal excess pressure that can occur during the vessel's operation. This is a discretionary value that depends on the background and experience of the design engineer. Sometimes the design value can be 10% over the pressure calculated (as in a simulation) or as much as 25% more. Good engineering judgment is employed in arriving at this design figure.

Once the Specification Sheet is received by the vessel fabricator, mechanical fabrication design takes place in which alloys, fabrication techniques, available materials, and other factors are taken into consideration to generate a fabrication drawing. Although the design pressure given is employed to generate the required vessel physical characteristics, some practical factors - such as available materials, fabrication efficiency factors, and alloys employed - will result in a vessel that not only meets the required design pressure, but often EXCEEDS it. This is a fortunate and conservative procedure because it ensures that the vessel will meet pressure safety expectations. The Maximum Allowable Working Pressure (MAWP) is a result of back-calculating the ultimate resulting fabricated vessel and is the prime factor in setting the pressure at which the corresponding vessel Safety Relief Devices will be activated. I consider the MAWP the most important pressure value attached to a vessel and one that should be clearly understood and stamped on the vessel for all to clearly read. The MAWP will change with time (as will the related design value) due to wear, corrosion, and vessel fatigue. This is why it is so important to religiously keep and maintain current and accurate data sheets and calculations on all pressure vessels as they are inspected and repaired through the years of service.

When you have a need to set a PSV on a vessel and you don't have its MAWP figure, you can employ the "design" pressure value - as long as it can be proven that the vessel is in as good a physical condition as the day it was fabricated. Note that I'm going to lengths to define the physical condition of the vessel. We often neglect to mention that we are ASSUMING that the physical condition of the vessel doesn't change from the day it was fabricated. This can be dangerous assumptions that don't necessarily apply. A vessel can undergo corrosion and wear as well as other chemical attacks through its use and lifetime. Physical and meticulous inspections and reports are essential to ensure that the vessel can be safely applied to a process --- especially to a high-pressure application. And I consider any pressure over 50 psig as HIGH PRESSURE. When a vessel explodes, it isn't the pressure that kills you; it's the amount of shrapnel and steel pieces that are blown about that do the damage. And even 50 psig can cause a considerable amount of serious damage if allowed to trigger a vessel failure.

I have never come across the term "Maximum Operating Working Pressure" and can only presume it means the same thing as MAWP. People are forever changing the writing of terms in order to suit their own likes and dislikes. MAWP was first described and is still employed by ASME in the USA and is the term I have always used to define what I have described in the above.

Art Montemayor via Forums

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