Quantcast STRENGTH AND LIFETIME

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TB 55-1900-232-10
The other classification societies have similar mark- ing requirements and grading systems as does ABS.
When towing a commercial ship, if it is intended to use the ship's anchor chain for a bridle or pendant, the chain
should be carefully inspected m accordance with the requirements of Section D-8. If the classification society
grade marking cannot be determined, the chain should be assumed to be Grade 1, which is roughly one-half as
strong as standard Navy chain.
Chain from unknown or non-marine sources, which is unmarked and which cannot otherwise be identified,
should not be used in towing
D-3 STRENGTH AND LIFETIME
Chain, properly used, should be the strongest and longest-lived element in the towing system. Because of its
construction and generally rugged configuration, chain is considerably stronger than wire or fiber rope of the
same nominal size
D-4 ELONGATION
The rugged, large-diameter, individual strength members of chain give it the least elongation, or stretch, under
load of any towline component This characteristic of chain is one of its prime reasons for being an element in
the towline system since working at chafing points, under constantly-changing tension, is minimized.
Additionally, the weight and flexibility of the chain promotes the towline catenary and mitigates the effects of
dynamic loading on the rest of the towing system.
D-5 MAINTENANCE AND CLEANING
As with other elements of the towline, chain must be properly maintained and cleaned. Perhaps the most
important element of chain maintenance is corrosion prevention. Corrosion leads to loss of chain strength
directly by reducing the diameter of the load- carrying rods that form the links. Further, for stud link chain,
corrosion can loosen the studs and eventually lead to their loss.
Corrosion prevention is best achieved by a fresh- water washdown of the chain after each use, coupled with
visual inspection for initial signs of corrosion During the required annual inspection, the chain should be
carefully cleaned, inspected and re- preserved as necessary; see NSTM 581 (Ref. 23).
Cleaning should be done by scaling, sand blasting or wire brushing Penetrating oil should not be used to loosen
the rust. After cleaning, a careful inspection should be made in accordance with Section D-8. All suspected
links should be checked by non- destructive test methods, careful measurement, sounding, etc.
Preservation after cleaning and any necessary repairs should be performed in accordance with Section D-8 and
with NSTM 631 (Ref. 4) For most chain, the use of TT-V-51 paint (asphalt varnish) or MIL-P- 24380 paint
(anchor chain gloss black solvent type paint) will be satisfactory
D-6 NEW CHAIN AND LINKS
New or re-issued chain or links that will be used as components of towline connections should be treated in the
same manner as new towing hawsers. The chain and links should be inspected and pertinent data entered in
the Towing Hawser Log. See Appendix F.
D-7 STOWING
No special stowing precautions are needed beyond attempts to prevent corrosion That is, try to avoid moisture,
salt, alkalines and acids. Oil and grease also should be avoided since they are difficult to remove and may
reduce the effectiveness of corrosion prevention coatings.
D-2


 


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