Removing Hard Scale and Rust from Cylinder Head Cavities?

<what is a way to remove hard scales and rust layeres from steel castings such as cylinder head cavaities.>

Pickling in something like phosphoric acid usually works. Phosphoric acid attacks the rust and scale leaving the underlying steel passivated with iron phosphate; one could paint onto the passivated surface once cleaned and dried.

<What other test could be carried out on used cylinder heads castings other than pressure test>

It depends on what is wanted to be tested. A dye pen will find cracks, for example. http://en.wikipedia.org/wiki/Dye_penetrant_inspection

ACIDS :
" RUST REMOVERS" DECAP 10 - 3440
This product contains muriatic acid for use in removing rust scales. - All properties are similar to DECAP 11, except in metal protection. DECAP 11 - 4386
Rust remover concentrate. Contains inhibited hydrochloric acid plus detergents and emulsifiers for fast penetration, suspension and elimination of residues. It is the most frequently used acid in chemical cleaning.
- Is effective for dissolving, either partially or completely, ferric oxide, magnetite, ferric phosphate, ferrous sulfide, calcium carbonate, hydroxyapatite and magnesium phosphate. In addition, it disintegrate masses of algae and microbiological slime sometimes found in water cooled heat exchangers and in compressor water jackets.
- Is appropriate for derusting carbon steel,
- Cleans, deoxidizes, in one operation, thus eliminating the need for rubbing and scrubbing. Fully inhibited to protect the base material without adversely affecting performance. Dissolves and removes grease, rust, corrosion, oils and other hard to clean deposits. DECAP 11 GEL - 3507
GELLED ACID - This clinging descaler is used as DECAP 11. FIDOX F - 4596
Organic acid formulated to prevent corrosive attack on boilers, condensers, piping or vessels, even where galvanized surfaces are involved. Highly recommended for cooling towers boilers and pressure washer equipment which utilizes stainless steel heads. FIDRO AMS - 3159
A POWDERED ACID SALT FOR REPLACEMENT OF LIQUID ACIDS - A dry acid salt which replaces most liquid acids. Since FIDRO AMS is a powder, it may be handled by unskilled personnel with no special equipment, thus reducing potential hazards associated with liquid acids. SAFER TO HANDLE. No special handling equipment required. No danger of spillage of liquid acids. No hazardous or corrosive fumes, either dry or when in solution.
SAFER TO EQUIPMENT. 3 times less corrosive than hydrochloric acid. Has been formulated to offer maximum protection to equipment during the de-scaling process. FIDRO AMS solutions are used as an acid dip on steel, cast iron, malleable iron, stainless steel, brass, admiralty brass, copper and zinc base die castings. In addition, FIDRO AMS is used as a pickel for removing oxide films, rust, heat treating and welding scale. Scale removal rate is increased at elevated temperatures. For descaling in the food-processing and bottling industries, heat-exchange equipment, autoclaves and humidifiers, condensers, boilers, water softeners, Humidifier, industrial washers, hard water scale and rust from air conditioning equipment, brewing equipment, etc. FIDOX CA 2 - 3056/1
The safe replacement for corrosive acids - Do not contain chlore ions - Act as medium pH (3.5) - This product is particularly useful for utily steam generators - A concentrated but mild organic acid formulation designed to replace harsh, dangerous hydrochloric and other mineral acids. Designed for removal of acid-soluble soils, such as rust and scale. Safe on stainless steel, aluminum, copper, ceramic, chrome, plastic. Food grade, can be used on food processing equipment, and in house applications such as flat iron. FIDOX CA - 3056
Similar to FIDOX CA 2, but contains hydrofluoric acid salt to be more active on hard to remove scales such as silicates and better action on magnetite and ferric oxides - Non food applications FIDOX DP 49 - 4483
Phosphoric acid based cleaner and rust remover and restorer - A phosphoric based rust remover and paint prep product recommended for ferrous and non-ferrous surfaces, removes light grease and rust in one operation; leaves a coating on steel which will accept paint; also treats aluminum prior to painting. - Colorless, practically odorless and non-fuming. FIDOX DP 300 - 3051
Cold Rust remover and cleaner for metal surfaces. FIDOX DP 300 is usable for ferrous metals and aluminum. It will clean light rust, grease and oil from metal surface, leaving a protective coating residue. FIDOX DP 300 act as special pretreatment for galvanized steel prior to painting. NON ACID RUST REMOVER FIDRO DNA - 3029
PREVENTIVE & CURATIVE RUST REMOVER - Non acid - An excellent product for chemically cleaning boilers. - The mildly alkaline solution is much safer to handle than acids. - Deposits are almost completely dissolved, which minimizes subsequent manual clean-up, as there no precipitation during rinsing. - Removes copper from high pressure boilers - Very low corrosion rate. - FIDOX DA 20 - 3057
A highly alkaline chemical which is used to remove heavy rust deposits on parts - Does the work of acid pickles without danger of hydrogen embrittlement. No fumes and corrosion problems - It enable to operate at lowest cost and maximum efficiency. - Parts must be soaked in the hot solution. - Not corrosive for iron, rubber and plastics. - Do not use on aluminum alloys . MISCELLANEOUS FIRUST N - 3517
CHEMICAL RUSTPROOFING PRIMER AND RUST CONVERTER -
FIRUST N is a combination of carefully selected acids, and other compounds, that functions in a series of chemical reactions, as an all-in-one rust neutralizer, rust-proofer and paint primer. FIRUST N is not a rust-remover, FIRUST N converts the rust into a firmly bonded rust-proof layer, and is suitable as a primer for most types of finishes. The acids present first dissolve the rust then react with it to form water-insoluble compounds of iron. The reactions continue under the surface for up to 24/48 hours. This is why subsequent layers of paint must not be applied until after this delay. During the process, the surface of the metal changes in color. The end color varies from dark blue to black, mauve or dark reddish brown, according to the type of the metal (cast-iron, wrought-iron, mild steel., alloy-steel etc.,) and the nature and age of the rust. FIRUST N eliminates laborious preparation - Application is made directly over rusty surfaces. FIRUST N penetrates and neutralizes existing rust, and forms a protective barrier against corrosion. FIRUST N saves time and money - Restores corroded metal for longer life and reduced maintenance. FIRUST N is superior to a synthetic-resin-latex polymer primer containing rust converting modifiers because it do not left over the rust, but penetrate completely up to sound metal. USES For rust protection of iron or steel, whether it is already rusty. Must have a subsequent coating of any conventional paint after treatment. FIRUST N may be applied over damp surfaces. FIRUST N provides an ideal basecoat for epoxies, urethanes, chlorinated rubber, and enamel paints. Use FIRUST N on cars, boats, appliances, gutters, pipes, tools, fencing, machinery, water tanks, toys, barbecues, farm implements, valves, tankers, truck trailers, storage tanks, outdoor advertising sign supports/frames, decks, agricultural equipments, guard rails, conveyors, etc.- wherever rust is found. One liter covers up to 30 m2 of surface area. FIRUST 39 - 4236
RUST CONVERTER - Is similar in conception to FIRUST N, but it represent the latest rust prevention and coating technology for maximum corrosion protection for all iron and steel rusted surfaces. This modern scientific product will provide the absolute best protection against rust. LAST UPDATED : 29/6/2007

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If you're talking about gas engine cylinder heads, take them to a mechanic's machine shop. They will put them in a tank and "boil" them clean.

As for tests, you want to magna-flux the heads for cracks. Also, measure how much metal is left on the valve seats for grinding. Another test you can do is to measure how much wear has occurred in the valve guides. One more test - check the heads for flatness. This will let you know whether the heads are warped. If they are warped, you want to get them machined to flatten the surface once again.

If not cracked, metal still left on the seats, valve guides are not worn out, and the heads are "true" (flat), the seats can be ground and the heads can be put back into service.

The best way is to use grinding (if grit blasting is not possible) followed by power brushing and once you have got proper surface condition (without any laps, folds, crevices, i.e.) any suitable NDT such as but not limited to : DPI, MPI or UT may be performed. If you are looking for surface discontinuities go for DPI and MPI. If you are looking for internal discontinuities UT would be best.

Or an MRI if the heads are really mess up!

loose stuff can be taken off with ground walnut shell blasting in a power abrasive type of application with less risk of damage that sand blasting. You can also use fine steel beads which are less abrasive than sand/grit.

http://compomat.com/walnutshell2.asp

check their other grits too