MIL Standard Proposed Amendments

US MIL-I-17563C Test Ring Standard Changes Proposed by the IoIT

Because the US MIL Standard will not be further updated, it is proposed to promote it under the title of the IoIT standard in the future. It is not intended that the IoIT will 'own' the MIL standard, but that the new IoIT Standard will continue to work towards the goals of the MIL Standard.

Recommended Addition/Change To US MIL-I-Standard

  1. Test Ring - (Aluminium)

    A supply of Test Rings is now available from www.x-seal.co.uk. We understand that these rings are manufactured strictly to the US MIL 17563C in terms of size and density and performance. See US Mil Standard in the next section for further information.

    If you happen to have an alternative source for rings, be sure that you obtain rings with a porosity of 20% as per the US standard. We understand that there are rings available on the market with a porosity level of 10% and are easy to seal and therefore meaningless when it comes to quality control.

  2. Gas Chromatography Verification

    Gas chromatography
    Typical GCE sealant trace

    For the applicant to provide a representative sample of the sealant to be tested by GC/FD. This provides a footprint of the product that can be held on record on an approved website. The applicant's confidentiality is not breached as such information could easily be available in the public domain. See trace of original Ultraseal PC 504.

  3. Test Ring Preparation

    For the central laboratory to acquire its own test rings from the approved central source and carry out the impregnation with the applicant's sealant according to applicants publicly declared information. Test rings to meet the existing requirements of MIL standard – max 2 impregnations. If the rings fail the sealant is rejected.

  4. Sealant Peroxide Test

    Before commencement of the MIL Standard application for approval, sealant containing AZDN as the catalyst should be checked for the addition of peroxide catalyst. This is known to enhance poor sealant performance. However such mixing of catalysts is also known to cause pot life instability if used in a production environment. A simple test is available for detecting the presence of peroxide.

  5. Gas Chromatography Chemical Testing

    MIL 4.5.5.6 requires that sealed and pressure tight test rings are subject to Table 111 and shall remain pressure tight when tested to 50 psi. Such a test does not examine the possibility that there could be some migration of the sealant into the test media. This could take place even if the test ring remains sealed for the duration of the test. To be certain that such a condition does not exist, GC/FD examination of the test media for elements of the sealant should be carried out. To overlook such a potential situation could lead to problems in the field.

  6. Sealant Contamination

    Sealants can be in use for many years and expect to become contaminated. Well designed sealants are able to cope with reasonable levels of contamination and still perform satisfactorily. It is therefore recommended that the MIL Standard test procedure incorporates a contamination test containing a mixture of a regular aqueous wash solution at 5% by volume and mineral oil at 2%. Antioxidant in these products can have a significant effect on curability of sealants that have low catalyst content.

  7. Raw Material Contamination

    Sealants based on methacrylate monomers can sometimes contain traces of polymer as a result of an over reaction manufacturing process. All incoming raw materials for sealant formulation need to first be checked for polymer contamination. The presence of polymer can effect proper penetration of the porosity. This is a test that can be carried out in conclusion of – MIL Ref: 4.3.1.1 Pot Life Test.

  8. Quality Grading Of Sealants

    It should be possible to award points to the testing of a sealant. These points would be collated to provide a star rating **** for high quality and * for low quality. These gradings could be on view on the information web page for impregnants. The design authority would have access to this information and thus be able to make a distilled choice based on particular needs.

    As an example:

    1. Record whether a sealant requires one or two impregnations to seal the test ring.
    2. Record final sealant weight pick-up and sealability of the test ring.
    3. Record weight loss of sealant after 24 hrs at 150ºC
    4. Register rates of ring leakage, using the ring chart as noted throughout the test evaluation.
    5. Grade test performance of contaminated sealants.

    Again the availability of such information to the market place will encourage effective quality assurance at all levels. It will allow the original MIL test approval to relate to the actual application of the process.

Test Laboratory Responsibility (Recommended)

Conclusion

If an impregnation standard is to have any meaning it must relate to the actual application of the process in industry. The key to this must be the test ring. It is the one thing that draws the whole process together.

It is appreciated that there may be good reason why the existing US MIL Standard Ring is required to be manufactured from pure aluminium. However, from a commercial point of view it is more important for the ring to have regular conformity in its density and available porosity.

The use of a GC/FD trace allows traceability between the original MIL Approval and the product supplied to the process plant. It also allows the user of the sealant to ensure that the sealant is not compromised. If there is any doubt, the user should have access to the original sealant trace against which he can check the sealant's identity. Such a check could be carried out at the appointed test laboratory. A regular trace of the sealant might also provide an early indication of contamination.

Such available information can also be useful in the event of a dispute between supplier and user of sealant. It also provides a useful base on which to apply an international standard, one that can be adopted by most impregnation users for internal quality audit. Often sealants are purchased primarily on price, because it is the only visible means by which it can be commercially judged. At this point in time the US MIL-I-17563C is the only means of judging sealant quality, which if it remains ineffective in its present form could provide a poor image of the impregnation industry. We have a collective responsibility to approach the US Military and make our recommendations known and request that this standard be updated to a point that it becomes an accredited document with audit traceability that both supplier and user can refer to with confidence.

It is important to bear in mind that once the sealant has been decanted from its drum into the process chamber it is in a totally different world from that of a laboratory environment. The mere presence of metal has a considerable influence as to how the sealant behaves. Unlike paint that is mixed and used once, sealant may be in use indefinitely.