CIP and SIP for seals

The acronyms may be short in the chemical processing, food and pharmaceutical industries, but they pose big sealing challenges. CIP (cleaning in place) uses chemicals lethal to the majority of elastomer seals, while SIP (sterilisation in place) employs superheated steam up to 140°C with an even greater deteriorating affect. In addition to this, for some applications, the seals must meet the strict requirements for FDA, Food and Drugs Administration, approval.

Working closely with major customers in the chemical industry, Trelleborg Sealing Solutions saw the trend for increasingly aggressive chemicals and processes. To extend seal life and reduce down time, Trelleborg tested existing materials and developed new compounds to cost-effectively meet performance requirements and approvals. The main conclusion of the research, the first of its kind within the industry, was that by matching the right sealing compound to a specific application, this could be achieved.

Specifying the right material when CIP and SIP is used is not a simple matter. In fact, test results proved that some elastomer types recommended in DIN 11864 and DIN 11851, applying to fittings for connections in process equipment usually subject to CIP and SIP, were unsuitable or not wholly suitable for sealing with these cleaning regimes. And FFKM, perfluoroelastomer, not given as a recommended material for sealing within the standards, was universally suitable even at elevated temperatures.

CIP chemicals

Automated CIP or SIP systems ensure safe and efficient processing, prevent toxic contamination of products and minimise re-contamination of the process. To achieve cleaning efficiency and effectiveness, a complex mixture of chemicals is required.

CIP cleaning media includes the following:

• Alkaline CIP mixtures based on sodium hydroxide and surfactants used to remove organic and fatty contamination, emulsions and gels;
• Acid CIP mixtures based on nitric acid and phosphoric acid or sulfuric acid used to remove inorganic sediments in tanks, tubes, fermentation or similar equipment;
• Alkaline CIP disinfecting mixtures based on sodium hypochlorite and active chlorine;
• Acid CIP disinfecting mixture based on per-acetic acid and hydrogen peroxide used on surfaces based on activated oxygen;
• Intensive disinfecting media based on hydrogen peroxide and surfactants added to alkaline CIP media to remove those residues requiring an oxidation stage.

These chemical media do not affect processing equipment manufactured from stainless steel but severe damage may be caused to elastomeric seals, especially in applications where thermal load and pressure are involved.

Seal materials must be chemically resistant to the product processed, CIP media used and also the harsh SIP sterilisation process using superheated steam. They need to withstand abrasion by any solids contained in the product and have a low level of extractables. Seal surfaces must be easy to clean and sterilise and, if required, the material should have FDA approval.

Standards applying to seals

Standards do not really help in deciding which materials to specify for seals. They only offer general information and refer just to groups of elastomeric materials and their compliance with FDA standard 21 CFR 177.2600. No specific characteristics are defined, such as vulcanising system or shore hardness, nor are indications given regarding chemical resistance to common CIP media or performance in steam sterilisation at temperatures up to 140°C.

The standards DIN 11864 and DIN 11851, covering fittings for the food, chemical and pharmaceutical industry on aseptic and stainless steel connections, recommend ethylene propylene diene rubber (EPDM), hydrogenated acrylonitrile butadiene rubber (HNBR), silicone rubber (VMQ) and fluoroelastomer (FKM) as materials for elastomeric seals used in sterilising technology. For some applications, these materials must also comply with the relevant FDA regulation under 21 CFR 177.2600.

However, the Trelleborg Sealing Solutions tests showed the following:

• Silicon rubber (VMQ) is not suitable for most CIP and SIP applications including alkaline media or under hot steam sterilisation conditions;
• Generally, HNBR is not suitable in any CIP media;
• The FDA-compliant FKM materials showed significant weaknesses in alkaline-based media as well as acidic media, including the per-acetic acid and hydrogen peroxide mix due to their polar nature;
• EPDM was established as an excellent sealing material for aseptic technology but some formulations are less suited to 'intensive' CIP additives;
• FFKM perfluoroelastomer showed most resistance in CIP media, especially at elevated temperatures. It is universally suitable for CIP applications and SIP sterilisation processes.

Performance in SIP sterilisation processes

After CIP cleaning, many process plants employ a sterilisation stage with steam, typically in the range 125 up to 140°C, and for this reason, the steam resistance of the elastomers used must always be considered.

The conclusions of Trelleborg Sealing Solutions on performance of elastomer materials in steam:

• At 125 up to 140°C FKM and HNBR are already beyond their performance limits;
• In the presence of atmospheric oxygen and steam, EPDM is resistant up to 150%deg;C whereas without oxygen, temperatures of up to 200°C are achievable;
• FFKM perfluoroelastomer offers the best temperature resistance with some grades capable of operating in temperatures up to 230°C;
• Steam temperatures are increasing up to and beyond 150°C. Under these operating conditions, EPDM may reach its natural limit and in these cases, perfluoroelastomer is the best material.

Selecting for chemical compatibility

The results of Trelleborg Sealing Solutions research demonstrate that it is not simple to select the optimum seal material for a CIP or SIP application. Even materials that may appear similar react differently in chemical media.

Details of Trelleborg Sealing Solutions tests

The following seal materials were tested:

• Two types of peroxide cross-linked ethylene propylene diene rubber (EPDM);
• Two types of fluoroelastomer (FKM), cross-linked with bisphenol;
• A hydrogenated acrylonitrile butadiene rubber (HNBR), cross-linked with peroxide;
• A FFKM isolast perfluoroelastomer, which conforms to FDA Guidelines 21 CFR 177.2400 (d) and 21 CFR 177.2600 (e, f).

After the test period the hardness (shore A) and percentage weight change were measured along with the most important parameter, volume change.

Because of the dead-space-free installation of seals in sterile technology, narrow limits are set on volume change of the sealing material.

Recommendations for use dependent on volume change:

• Less than 5% - material suitable for sealing;
• More than 5% but 10% or less - material can only be used for sealing with reservations;
• More than 10% - material not suitable for sealing.

Table of results:

CIP media*	EPDM 1 Peroxide cross linked Ethylene Propylene Diene Rubber	EPDM 2 Peroxide cross linked Ethylene Propylene Diene Rubber	FKM 1 Fluoroelastomer cross-linked with bisphenol
Alkaline CIP	Unsuitable	Strongly recommended	Unsuitable
Acidic CIP	Strongly recommended	Strongly recommended	Unsuitable
Disinfectant alkaline CIP	Strongly recommended	Strongly recommended	Recommended with reservations
Disinfectant acidic CIP	Unsuitable	Strongly recommended	Unsuitable
Disinfectant spray injection	Unsuitable	Unsuitable	Unsuitable

CIP media*	FKM 2 Fluoroelastomer cross-linked with bisphenol	HNBR Hydrogenated Acrylonitrile Butadiene Rubber cross-linked with peroxide	FFKM FFKM Isolast perfluoroelastomer, which conforms to FDA Guidelines 21 CFR 177.2400 (d) and 21 CFR 177.2600 (e, f)
Alkaline CIP	Unsuitable	Recommended with reservations	Strongly recommended
Acidic CIP	Unsuitable	Unsuitable	Strongly recommended
Disinfectant alkaline CIP	Strongly recommended	Unsuitable	Strongly recommended
Disinfectant acidic CIP	Unsuitable	Unsuitable	Strongly recommended
Disinfectant spray injection	Unsuitable	Unsuitable	Recommended

>Detail of test results by material and media:

CIP media*	EPDM 1	EPDM 2	FKM 1	FKM 2	HNBR	FFKM
Alkaline CIP	Not recommended. 8% shrinkage due to surfactants, which extracted constituents from the seal	Strongly recommended. Volume change minimal	Unsuitable. Destroyed by sodium hydroxide	Unsuitable. Destroyed by sodium hydroxide	With reserves 5% volume change but other results in alkali show limited performance	Strongly recommended. Best sealing material in this media on all three parameters practically unchanged
Acidic CIP	Strongly recommended. Practically no volume change	Strongly recommended. Practically no volume change	Unsuitable. Extreme volume increase	Unsuitable. Extreme volume increase	Unsuitable. Swelled by almost 100%	Strongly recommended. Practically no volume change
Disinfectant alkaline CIP	Strongly recommended. Minimal volume change	Strongly recommended. Minimal volume change	With reserves. Volume change of 6%	Strongly recommended. Minimal volume change	Unsuitable. Volume change significantly higher than other materials	Strongly recommended. Minimal volume change
Disinfectant acidic CIP	Unsuitable. 8% volume increase	Strongly recommended. Fully inert, the most cost-effective material for this media	Unsuitable. Volume change exceeded 65% probably due to absorption of acetic acid	Unsuitable. Volume change exceeded 65% probably due to absorption of acetic acid	Unsuitable. Significant volume change	Strongly recommended. Minimal volume change
Disinfectant spray injection	Unsuitable. Volume increase of 20% and surfaces became sooty	Unsuitable. Volume increase of 20% and surfaces became sooty	Unsuitable. Volume change of between 15 and 22%	Unsuitable. Volume change of between 15 and 22%	Unsuitable. High volume increase	Strongly recommended . Fully inert, the only sealing material suitable for this media

* The material test specimens were immersed in the following CIP media concentrations, at temperatures given for one week in accordance to DIN 53521:

• Alkaline CIP formulations based on caustic soda liquor and surfactants; concentration of 4%, temperature 80°C.
• Acidic CIP formulations based on nitric acid or sulphuric acid; concentration of 2%, temperature 80°C.
• Disinfectant alkaline CIP formulations based on sodium hypochlorite and active chlorine; concentration of 3%, temperature 80°C.
• Disinfectant acidic CIP formulation based on peracetic acid and hydrogen peroxide; concentration of 2%, temperature 80°C.
• Disinfectant spray injection media based on hydrogen peroxide with a concentration of 1%, temperature 80°C.
• Silicone rubber (VMQ) was not tested as initial experiments showed it not to be sufficiently resistant in alkaline media and under conditions of live steam sterilisation.
• EPDM 1 and 2 Peroxide cross linked Ethylene Propylene Diene Rubber
• FKM 1 and 2 Fluoroelastomer cross-linked with bisphenol
• HNBR Hydrogenated Acrylonitrile Butadiene Rubber cross-linked with peroxide
• FFKM FFKM Isolast perfluoroelastomer, which conforms to FDA Guidelines 21 CFR 177.2400 (d) and 21 CFR 177.2600 (e, f)