Leaks are a huge problem for the oil industry. Even small leaks from pipes, valves, boilers, heat exchangers, etc., reduce efficiency and eat away at profits. Indonesias state-owned oil and gas company, PT Pertamina, suffered from leak problems in aging refinery and petrochemical complexes. This case history explores how this operating company solved its sealing problems.
Aging Asian downstream complex.
PT Pertamina was established in 1957. This national oil company (NOC) engages in both upstream and downstream activities. Upstream, PT Pertamina is active in oil, gas and geothermal exploration and production. For the downstream, this NOC refines, ships and markets transportation fuels, liquefied petroleum gas (LPG), liquefied natural gas (LNG), petrochemicals and lube oil. The company operates six refineries with a combined capacity of 1.046 million bbls. Two of the refineries are integrated with petrochemical plants that produce purified terephthalic acid (PTA) and paraxylene (PX). Five other complexes produce LPG, and there are two LNG plants with a combined 35,000 tpy incapacity.
Several of the refineries are older and predate Indonesias independence and the establishment of Pertamina. The Balikpapan refinery was established by Shell Transport and Trading in 1894. The original facility was destroyed during WWII, rebuilt in 1950 and expanded in 1983. The 2.5-km2 facility has two sub-units, which processes up to 260,000 bpd and produce fuelsaviation turbine fuel (AVTUR), aviation gas (AVGAS), kerosine, automotive diesel oil (ADO), industrial diesel oil (IDO), marine fuel oil (MFO) and special high-octane fuels along with LPG, paraffin, naphtha and low-sulfur waxy residue (LSWR). Balikpapan I has two refinery units producing naphtha, kerosine, gasoline and diesel and a high-vacuum unit producing paraffin-oil distillate. Balikpapan II opened in 1983, supplies AVTUR, AVGAS, kerosine, ADO, IDO, MFO and special high-octane fuels.
| Fig. 1. Balikpupan refinery had major leakage |
While the Balikpapan refinery has a rich history, aging seals can add up to major leakage issues. The spiral-wound seal designs in use at the refinery have been around about as long as the original Balikpapan refinery (1950s); unfortunately, these aging seals were not up to meeting modern demands.
The spiral wound gaskets would have a lifetime of about six to 12 months before they would start leaking, says David Hakim, a representative of PT Egamekinka Pratama, a firm in Jakarta that specializes in pump engineering, sealing devices and piping systems for the petroleum industry. Then they would have to use online sealinga frequent and expensive occurrence.
| Fig. 2. Evidence of leaks indicate failure of |
sealing gasket on this refinery unit.
Better sealing gasket.
Looking for ways to reduce maintenance and production costs caused by the leaks and environmental problems from spills, sealing consultants proposed replacing the spiral-wound gaskets with a combination of a live-loading system and steel-trap gaskets. The live-loading system consists of bolt-disk springs that maintain the desired pressure despite mechanical shock, pressure surges or thermal expansion and contraction. The steel-trap design maintains a seal on high-pressure, high-temperature lines, eliminating leaks and lowering maintenance costs.
This action would improve reliability of the seals and avoid replacing gaskets every six months or engaging in online repairs. The Balikpapan refinery could use this approach to achieve three or more years of leak-free operations.
| Fig. 3. Workers installing sealing gasket at |
Selecting the right sealing solution.
Choosing the right seal requires analyzing a combination of factors including the materials making up the joint to be sealed, operating temperature range, pressure class required and the processing characteristics such as pH of the materials that the seal is designed to keep in or out. One other factor to consider when looking at the temperature is whether it is constant, or if the equipment is frequently cycling thus causing flange bolts to loosen over time. For high-pressure applications in a refinery, maintenance crews have three basic options: spiral wound, camprofile (or kammprofile) or steel-trap seals.
Spiral-wound seals have been around for nearly a century and have justifiably earned a stable position in the maintenance marketplace. Consisting of alternate layers of a filler (typically graphite) and a metal (generally high carbon or stainless steel) wound in a spiral, they are more expensive than the sheet gaskets. But they do not need as high of bolt loading since some of the flange surface is in contact with the more compressible filler. While lower, the bolt load is still significant and can lead to warping and other problems associated with high bolt loads. In addition, unless handled with care, these gaskets can come apart during installation.
Camprofile. Like spiral wound, camprofile gaskets use metal to support the softer sealing material. The camprofile gaskets, however, use a solid metal core surrounded by two layers of sealing material. The surface of the metal core has a series of concentric grooves to hold the sealing material in place. Camprofile gaskets can provide two significant advantages over spiral wound design. First, the metal support consists of a single piece rather than a thin wound layer, which can unravel. Second, the sealing material completely covers the surface of the metal ridges. Ideally, even when the seal is compressed, the metal ridges do not come in contact with the flange surfaces.
Unfortunately, real-world plant operating conditions are less than ideal, which brings up the limitations for this gasket-type design. The compressibility is limited to the thickness of the sealant layer as it passes over the highest point of the ridges, rather than the full thickness of the sealant. Any further compression must come from the elasticity of the metal. As a result, camprofile gaskets still require a higher clamping force than if the full thickness of the sealant can be compressed. In addition, since the metal backing is rigid, vibration or water hammer eventually leads to destruction of the soft graphite fibers. In severe services, this gasket design can cause the metal ridges themselves to break through and damage the flange surface.
Steel-traps seal design. To address these shortfalls, steel-trap gaskets incorporate technology originally developed for use on fighter aircraft. The seal base consists of a thin layer of convoluted stainless steel with a 0.015-in. graphite layer within the grooves on both sides. As a result, it is thinner and more flexible than either the spiral-wound or camprofile designs.
This design has several advantages over the older gaskets. Since the metal backing is a single piece, it doesnt come unwound like the spiral-wound gaskets. Most important, the flexible nature of the metal base means that the metal itself does not need to be compressed to achieve a seal. Instead, the metal acts like a spring, keeping the graphite tight against the flange. This greatly reduces the bolt load required, as well as the need for retorquing and warping of the flange. The flexibility also means that the gasket maintains its seal despite shocks or thermal cycling. Since this design is more pliable, the metal absorbs the energy of vibration and water hammer, thus preserving the service life of the gasket.
While the intricacies of seal design may be fascinating, what really matters most is not the type of seal used, but how the joint performs in operation. The object is not to have the most state-of-the-art gasket, but to ensure that failures do not result in costly shutdowns, environmental or safety hazards or add to maintenance costs. The bottom line is:
70 % of scheduled seal-replacement costs are labor related
One unplanned shutdown or a single leak far exceeds the few dollars spent on a seal.
| Fig. 4. Spiral-wound gaskets have several |
disadvantages since a real compression seal
is not possible.
Camprofile-type seals were installed at troublesome joints at the Balikpapan refinery in 2005. The first targets were two heat-exchanger nozzles. A self-locator gasket made of 316LSS with a graphite filler, along with flange-bolt disk springs, was selected.
A series of gasket replacements on other equipment began at the refining complex. In March 2006, an 8-in. self-locating gasket was installed on a converting valve from the power plants generator turbine and a 20-in. seal (also 304LSS) on a check valve. The converting valve seal was still working perfectly in May 2010. The check valve gasket was reinstalled in May 2008 and remains in good condition.
In 2007, a 24-in. seal was installed in the steam-line block valve and an 8-in. gasket was installed on a steam-line valve from the turbine generator. Another 24-in. steel-trap gasket was installed on turbine generator No. 5 in August 2008. All were 304LSS with graphite filler. These gaskets are still in operation and working well. In September 2010, additional gaskets were installed on a steam line and reboiler heat exchanger. Success of the gasket replacement solutions spread to other regional refiners, including Chevron Petroleum Indonesia, the countrys largest oil producer. HP
|The author |
John Paterson is president of Sealing Corp. of North Hollywood, California. The company manufactures a line of self-energized metal gaskets consisting of a corrugated metal carrier combined with different soft sealing inserts (e.g., flexible graphite, PTFE, mica or a combination thereof). These gaskets operate at high temperatures (200°C to 1,200°C) and high pressures (400 bar).