One seal material formulation cannot cope with all the different environments of the oil and gas industry.
by Eric Bucci (Trelleborg Sealing Solutions)
March 16, 2016

Seals are critical elements on offshore oil and gas facilities. Ensuring that seals are matched to their arduous and difficult sealing environments can extend their life and lower planned and unplanned maintenance, ultimately optimizing overall production costs. Selecting a supplier with a broad range of compliant materials has benefits in vendor reduction and processing performance.

Sealing Demands

One seal material formulation cannot cope with all the different environments of the oil and gas industry. Pressures and temperatures can be extreme. Some of the extreme media that must be handled include:

  • Hydrochloric, acetic and formic acids, which are used during acidizing and hydraulic fracturing operations
  • Aromatic hydrocarbons such as benzene, toluene and xylene
  • Alphatic hydrocarbons and carbon dioxide
  • Other chemicals to prevent corrosion of the piping, casing and associated equipment
  • Contact with these hazardous materials may cause swelling, the loss of critical sealing properties, or completely destroyed or dissolved seals. In addition to the severe chemicals, seal engineering must also consider the effects of drilling mud, which is highly abrasive. Drilling mud bases include diesel oils, mineral oils, esters or silicates. Downtime for planned or unplanned maintenance on an offshore platform or floating production storage and offloading unit is a significant cost for operators. The key to decreasing downtime and extending seal material life is to understand how seals react over time when exposed to severe operating conditions. Seal manufacturers are developing new compounds and technologies to meet evolving sealing requirements. Controls on these new formulations are necessary to ensure safety. This has led governing bodies to set standards that can provide the oil and gas industry with an unbiased, accurate way to assess performance.

    Sealing Standards

    Norsk Sokkels Konkuranseposisjon (NORSOK), standards developed by the Norwegian petroleum industry, is a popular governing body that serves the oil and gas industry, partially because it has been around since 2001. The NORSOK M-710 specification underlines the need for original equipment manufacturers (OEMs) to achieve higher levels of quality and compatibility for non-metallic seals. Certifications for NORSOK M-710 have three components. Annex A specifies procedures for conducting accelerated aging tests in an autoclave on constrained O-ring samples. Annex B comprises seal fluid compatibility recommendations. Annex C concentrates on the aging of thermoplastics and addresses explosive decompression resistance. Even though the rapid gas decompression resistance test regimes generated by reputable operators are highly regarded, the independent qualification of choice is NORSOK M-710, Annex B. NORSOK M-710 qualification of non-metallic sealing materials and manufacturers (Rev. 2, Oct. 2001) requires that individual seal materials be rigorously tested based on explosive decompression resistance. This is when gas or gas mixtures contact the elastomer surfaces and are absorbed under pressure. At high pressures, absorbed gas is compressed. When external pressure is reduced, the compressed gas rapidly expands within the elastomer, leading to cracking of the elastomer's body. These cracks propagate internally, which can cause void formations or cracks to appear on the elastomer surface, reducing seal integrity. The other tests conducted include sour and sweet gas aging, compression set tests and material property tests. The qualification has defined requirements for critical non-metallic (polymer) sealing, seat and backup materials for permanent use in subsea applications, including well completion; trees; control systems; wellheads; valves; and topside valves, such as those used in critical gas systems. Accreditation requirements are revised frequently. For example, the newer NORSOK standard certification encompasses all individual components within an assembly rather than the complete assembly. The American Petroleum Institute (API) maintains more than 500 documents that apply to many segments of the oil and gas industry—ranging from drill bits to environmental protection. API standards advocate proven engineering and operating practices and safe, interchangeable equipment and materials. The API recently converted Standard 10423 from the International Organization for Standardization, the governing body that relates to the certification of a completed oilfield piece of equipment, such as a gate valve. The entire gate valve is tested and approved by API, and the seals are part of the gate valve that receive certification. During the past two years, API has incorporated sealing system testing requirements to include fire tests for end connections; drilling well control systems; verification testing of wellhead surface safety valves and underwater safety valves for offshore services; specifications for sucker rods, polished rods, clamps and liners, couplings, sinker bars, stuffing boxes, pumping tees; and the isolation of potential flow zones during well construction. The National Association of Corrosion Engineers (NACE) is the standards-writing organization accredited by the American National Standards Institute (ANSI). ANSI recommends three categories of NACE standards: standard practices, material requirements and test methods. NACE uncovered multiple cases of failure caused by permanent compression sets of O-rings and cracked energizing springs. They deemed it necessary for seal suppliers to have specific certifications. The standards organization recently developed four test protocols to define elastomeric seal materials that help avoid damage during decompression in high pressure gas duty.

    Seal Suppliers

    Achieving compliance to all relevant standards is demanding, time consuming and expensive. This means that some suppliers lack the resources to undergo the required certification. However, a supplier that has a wide range of certified sealing materials and solutions is an asset to an operator. A reputable supplier should have a large selection of fully approved NORSOK M-710 materials in a range of types. An added bonus is material samples that have been pre-tested for temperatures and fluids to API and NACE standards by an independent third party.